A111D2 71527=1 NBS

PUBLICATIONS

NBSIR 87-3664

Study of Die Polishing for United

States Mint Phase III

Karl Ousterhout

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Manufacturing Engineering

Automated Production Technology Division

Gaithersburg, MD 20899

October 1987

Final Report

Prepared for: QC- DEPARTMENT OF COMMERCE

1 qq

ial Bureau of Standards

J

irsburg MD 20899

87-3664

1987

C.2

Research Information Center

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1 lo* oration. Centej^ a . . * - *arciru of blandards

Gaithersburg, Maryland 20899

NBSIR 87-3664

STUDY OF DIE POLISHING FOR UNITED

STATES MINT PHASE III

Karl Ousterhout

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Manufacturing Engineering

Automated Production Technology Division

Gaithersburg, MD 20899

October 1987

Final Report

Prepared for: U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
- . . . , < * . ' : • ' H

%*y‘' : ’ IU •*<)! ; * •
Study of Die Polishing for

United States Mint

Phase III

Karl Ousterhout

Mechanical Engineer

Automated Production Technology Division

National Bureau of Standards

I . Statement of Problem

This research was undertaken to determine the feasibility of automating the

polishing process of proof dies at the United States Mint, The dies polished

during this research endeavor were the obverse Kennedy half-dollar dies, While

most of the techniques used in this study are new, some of the techniques

developed by Sidney Weiser (Phase 1 December 16, 1985 and Phase 2 December 3,

1986) were incorporated into the polishing procedure.

The main goals of this research are:

1. Develop a method of mechanically polishing proof dies which results in a quality level equal to or better than that now achieved by current

manual methods.

2. Develop the optimum production rate that can be achieved in mechanically

polishing proof dies.

3. Utilize a machine tool with at least 4 axes of motion.

4. Exercise initiative and ingenuity in the use of conventional and

computer technologies, and develop through experimentation the best

polishing compounds and materials, tooling, tool paths, speeds, masking

techniques or other methods of protecting areas not to be polished.

II. Introduction

The techniques developed during Phase I and Phase II proved that it is possible to

automate the proof die polishing process. A three-axis vertical milling machine

was used to develop and test these techniques. The die was mounted on the table

of the machine, which provided two orthogonal translations in the horizontal

plane. The column of the machine provided the vertical axis of motion. With this

machine, the concentric tool paths were programmed using two linear axes of the

table, while the table was stepped vertically from one concentric path to another

in order to follow the die surface profile in the vertical plane. As a result of

this type of tool motion, the pattern of concentric tool paths was visible on the

surface of the die. To eliminate this visible tool pattern, three finish passes

with a randomized star pattern were introduced into the polishing procedure in

Phase II. Although this method was successful in removing the tool marks, it

unnecessarily increased the turn-around time for each die. A better approach

would be to avoid creating these marks in the first place. Providing a rotary

axis for the die to be rotated while the polishing tool was moving radially in and

out and following the surface profile vertically proved to be a solution to this

problem. In addition, this configuration results in simpler NC programming and

faster execution.

Another problem observed during the earlier phases of the research involved

overpolishing of some parts of the die due to the compliance of the polishing

tool. To decrease the compliance of the tool requires better control of the tool

orientation with respect to the die surface. The ideal situation is to position

i
the polishing tool surface tangent to the die surface continuously during the

operation. This permits the polishing tool to cover the surface area with less

deflection and pressure. But this technique requires an additional programmable

rotary axis of the polishing machine. Since such a machine is unavailable, a four-axis vertical milling machine (FP4NC) was used in the current phase of the

research. In addition to two linear motions in the horizontal plane and a

vertical motion, this machine has a programmable rotary table with a vertical axis

of rotation. Furthermore, the spindle of this machine can be indexed manually to

give the tool an inclination over the part surface. This feature of the vertical

milling machine proved useful in testing the idea of keeping the tool tangent to

the die surface. Various tool angles were tested to check the influence of tool

orientation on the polishing quality.

The techniques developed during Phase I and Phase II which were incorporated into

the polishing procedure are:

1. The same type of rotating compliant tool holder was used for roughing.

2. Oak veneer was used for the roughing tool.

3. Hard felt plugs were used for final polishing.

Also, the same data points were initially used; however, upon inspection it was

determined that the original tool paths did not follow paths of constant height on

the die surface. Consequently, the polishing tool would not be in intimate

contact with the die at all times. To insure that the polishing tool would be in

contact with the die at all times, the die surface was traced with a dial

indicator and appropriate tool offsets were added to the original data resulting

in the tool path program shown in Appendix A. The addition of this data allowed

the polishing tool to follow the exact contour of the die surface.

2
The 23 obverse side Kennedy 50 half-dollar dies which were delivered to The

National Bureau of Standards are listed below.

Serial Number

#8609327

#8609328

#8609329

#8609330

#8609331

#8609332

#S609334

#8692249

#8692250

#S692251

#S692253

#8692254

#8692255

#8692256

#8692257

#8692258

#8692259

#8692127

#8692128

#8692130

#8692131

#8692133

All of the dies listed above were polished except for die #S692133„ The 12-

micron, 3 -micron, and 1 -micron diamond polishing compounds and the hard felt

polishing tools were supplied by the U.S. Mint and are identical to the materials

used in the manual polishing process performed by the U.S. Mint.

III. Technical Approach

As mentioned previously, a four axis-Deckel milling machine^- was used to polish

the dies. Since four axes of motion were used (instead of three), a new technique

was developed to polish the dies. The spindle was fixed to the desired angle and

the die was rotated (A axis) while simultaneously moving the tool in both the

radial (X axis) and the vertical direction (Z axis) . Since the milling machine is

not capable of attaining high spindle speeds, a Precise Products Corporation —7332

high-speed grinding tool was mounted directly to the quill of the vertical mill.

This grinder has a variable power source which allows spindle speed to be adjusted

between the range of 3,000 and 45,000 rpm.

1^Certain commercial equipment, instruments, or materials are identified in

this paper in order to adequately specify the experimental procedure. Such

identification does not imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the materials or equipment

identified are necessarily the best available for the purpose.

3
The compliant roughing tool holder was fashioned by cementing a 3/4- inch diameter

neoprene rubber pad, Durometer 40, to the bottom of a steel mandrel (see Figure 1,

page 5). The actual roughing tool was made from a 3/4-inch diameter, 0.020 inch

thick piece of pressure sensitive oak veneer. To insure that all the roughing

tools used were similar, both the neoprene rubber pad and the oak veneer were cut

by a die. The polishing tool supplied by the U.S. Mint was made by cementing a 3/4-inch diameter plug of hard felt to a steel mandrel (see Figure 2, page 5).

Because a new polishing tool readily absorbs both the diamond compound and the

lubricating oil, four consecutive dies were polished with the same polishing tool

before changing the polishing tool.

As mentioned previously, the original data points (with the addition of vertical

displacements) were used for the polishing process. Ten consecutive passes were

used to polish the face of the die. Also, after the initial setup phase, it was

determined that the random star pattern developed in Phase II was not needed.

Therefore, on the average, a single roughing or finishing pass was completed in

four minutes (see individual data sheets for specific times) . This results in a total polishing time of 12 minutes - a 50% improvement over the polishing time

achieved in Phase II.

The tool height was initially set by bringing the tool into contact with a piece

of 0.004- inch thick clean paper which was inserted between the tool and the die.

The force needed to pull the paper out was set with a small spring scale. The

tool was then lowered the thickness of the paper plus an additional preload (see

individual data sheets for specific information)

.

The following pages contain the initial conditions, polishing technique, and the

results of the polishing procedure.

4
Figure 1

ROUGHING TOOL

Figure 2

POLISHING TOOL

5
TEST # 1

SERIAL # S609327

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in

both the radial direction (X axis) and in the vertical direction (Z

axis) to generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

ToolsFirst roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing - 3/4-inch diameter X 1/2-inch long hard felt plug.

Preload

First roughing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 4.5 Oz

.

0.006 inches.

pullout

Second roughing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

.

0.006 inches.

pullout

Polishing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper , 1 . 5 Oz

.

0.002 inches.

pullout

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

= 2 degrees

=4.2 minutes per cycle.

= 12.6 minutes

Results

First roughing

Second roughing

Polishing

- General appearance very good. One low spot visible

on the back of head. Concentric plane pattern

visible. Scratches visible with 2X magnification.

- Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"R" of "LIBERTY"

.

- Faint scratches still visible with 2X magnification.

Three low spots evident- (1) behind head, (2) between

"I" and "B" of "LIBERTY", and (3) by "IN GOD".

6
TEST # 2

SERIAL # S609328

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

ToolsFirst roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing - 3/4-inch diameter X 1/2-inch long hard felt plug.

Preload: First roughing - Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.004 inches.

Second roughing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Polishing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.004 inches.

Spindle speed = 17,500 rpm

Head angle = 2 degrees

Time = 4.2 minutes per cycle.

Total time = 12.6 minutes

Results

First roughing - Concentric plane pattern visible. Scratches visible

with 2X magnification. Missed areas on top of head

should have used 0.006 inch preload.

Second roughing - Concentric plane pattern barely visible. Scratches

still evident with 2X magnification.

Polishing - Faint scratches still visible with 2X magnification.

Missed many spots due to lack of preload on first

roughing pass , Increase in spindle speed did not

adversely affect the die surface finish.

7
S609329

TEST # 3

SERIAL #

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools: First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Preload

Polishing

First roughing

Second roughing

Polishing

- 3/4-inch diameter X 1/2-inch long hard felt plug.

- Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

- Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

- Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.004 inches.

Spindle speed = 17,500 rpm

Head angle = 2 degrees

Time = 4.2 minutes per cycle

Total time = 12.6 minutes.

Note: Program corrected for over polishing of hair line.

Results: First roughing

Second roughing

Polishing

Very good finish. Lost one hair by "R" of "LIBERTY"

Concentric plane pattern visible. Scratches visible

with 2X magnification.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"R" of "LIBERTY".

Faint scratches still visible with 2X magnification.

Low spots evident between "I" and "B" of "LIBERTY"

and "IN GOD".
TEST # 4

SERIAL # S609330

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel In the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools: First roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad

Durometer 40.

Polishing 3/4- inch diameter X 1/2 -Inch long hard felt plug

Preload: First roughing

Second roughing

Polishing

Contact

force

Contact

force

Contact

force

with 0.004 -inch thick

Additional preload of

with 0.004- inch thick

Additional preload of

with 0.004- inch thick

Additional preload of

paper

4.5 Ozpullout

0.006 inches

paper

,

1.5 Oz

pullout

0.006 Inches

paper

,

1.5 Oz. pullout

0.004 inches

Spindle speed

Head angle

Time

Total time

= 17 , 500 rpm = 3 degrees

=4.2 minutes per cycle.

= 12.6 minutes.

Results

First roughing - General appearance very good. Over polished at "R"

of "LIBERTY". Concentric plane pattern visible. Scratches visible with

2X magnification.

Second roughing - Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"R" of "LIBERTY"

Polishing - Faint scratches still visible with 2X magnification.

The only bad areas that remain are by "IN GOD" and

"R" of "LIBERTY"

9
TEST # 5

SERIAL # S609331

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

ToolsFirst roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing - 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 4.5 Oz

.

0.006 inches.

pullout

Second roughing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

.

0.006 inches.

pullout

Polishing - Contact

force

.

with 0.004 -inch thick

Additional preload of

paper , 1 . 5 Oz

.

0.004 inches.

pullout

Spindle speed

Head angle

Time

Total time

= 17 , 500 rpm

= 3 degrees

= 4.46 minutes per cycle.

= 13.38 minutes.

Results: First roughing

Second roughing

Polishing

Best roughing to date. Concentric plane pattern

visible. Scratches visible with 2X magnification.

Did not over polish hair line.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"R" of "LIBERTY".

Hair line much better than before - only lost one

hair by "R" of "LIBERTY". Over polished "s" mint

mark. Orange peel by "IN GOD".

10
S609332

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

TEST # 6

SERIAL #

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools

First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing - Contact

force

with 0.004- inch thick

Additional preload of

paper, 4.5 Oz

0.006 inches.

pullout

Second roughing - Contact

force

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

0.006 inches.

pullout

Polishing - Contact

force

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

0 . 004 inches

pullout

Spindle speed

Head angle

Time

Total time

= 17 , 500 rpm

= 4 degrees

= 4.2 minutes per cycle.

= 12.6 minutes.

Note: Program changed to skip head for first seven passes.

Results: First roughing

Second roughing

Polishing

General appearance very good. Tool not polishing up

close enough to head before lifting up . Tool also

coming down late - leaving unpolished portions.

Concentric plane pattern visible. Scratches visible

with 2X magnification.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Slight over

polishing of "R" of "LIBERTY" although not as bad as

before

Problem areas are before head and behind head where

tool lifts up early and comes down late. Over

polished "s" mint mark.

11
S609333

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

TEST # 7

SERIAL ??

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools : First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250- inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 4.5 Oz . 0.006 inches.

pullout

Second roughing - Contact

force

.

with 0 . 004- inch 9 thick

Additional preload of

paper, 1.5 Oz

.

0.006 inches.

pullout

Polishing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

.

0.004 inches.

pullout

Spindle speed

Head angle

Time

Total time

= 17 , 500 rpm

= 4 degrees

= 4.2 minutes per cycle.

= 12.6 minutes.

NoteProgram changed to allow tool to come closer to head before lifting up and

to come down earlier.

Results: First roughing

Second roughing

Polishing

General appearance worse than before. Orange peel

evident in many spots. Concentric plane pattern

visible. Scratches visible with 2X magnification.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Orange peel

still visible.

Faint scratches still visible with 2X magnification.

Three low spots evident - (1) between "R" and "T" of

"LIBERTY", (2) between "I" and "B" of "LIBERTY", and

(3) by "IN GOD".

12
TEST # 8

SERIAL # S609334

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel In the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools

First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

Second roughing Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

Polishing Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.004 inches.

Spindle speed

Head angle

Time

Total time

= 17,500 rpm

= 4 degrees

= 4.2 minutes per cycle.

= 12.6 minutes.

Note: Program changed again to dip tool into low spots.

Results: First roughing

Second roughing

Polishing

General appearance very good. No low spots visible

anywhere. Concentric plane pattern visible.

Scratches visible with 2X magnification.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Hair line looks

very good.

Over polished "s" mint mark. Along back of head

polishing is not complete and does not extend up to

head

13
TEST # 9

SERIAL # S692249

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

ToolsFirst roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250- inch thick neoprene rubber pad,

Durometer 40.

Second roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

Second roughing Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Polishing - Contact

force

.

with 0.004- inch thick paper, 1.5 Oz

.

Additional preload of 0.004 inches.

pullout

Spindle speed

Head angle

Time

Total time

= 17 , 500 rpm

= 2 degrees

= 4.2 minutes per cycle.

= 12.6 minutes

.

Results

First roughing - Still missing one spot in back of head. Concentric

circles are less noticeable than before. Low spot

are visible by "L" of "LIBERTY", "1" of "1987", and

behind neck.

Second roughing - Concentric plane pattern has disappeared. Small

spots on top of head are being missed by polishing

tool

.

Polishing - Three low spots evident - (1) between "T" and "Y" of

"LIBERTY", (2) between "I" and "B" of "LIBERTY", and

(3) by "IN GOD". Over polished "s" mint mark.

14
TEST # 10 Part: Obverse side Kennedy 50 cent die

SERIAL # S692250 Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing

Pattern

Ten concentric passes around the surface of the die.

Tool travel In the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250- inch thick neoprene rubber pad,

Durometer 40.

Polishing - 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing - Contact

force

with 0.004- inch thick

Additional preload of

paper, 4.5 Oz

0.006 inches.

pullout

Second roughing - Contact

force

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

0.006 inches.

pullout

Polishing - Contact

force

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

0.004 inches

pullout

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

— 2 degrees

= 4.2 minutes per cycle.

= 12.6 minutes.

15
Figure 3

CUP ROUGHING TOOL

0.375 Dia.

0.750 Dia.

Compliant neoprene rubber'

cemented to steel arbor

with contact cement.

Oak veneer

polishing pad.

Cup designed to hold

rubber more firmly.

0.200

0.093

16
TEST # 11

SERIAL # S692251

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyper lube oil

Tools : First roughing - 3/4-inch diameter pressure sensitive oak veneer

adhered to 0,250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0,250 -inch thick neoprene rubber pad,

Durometer 40,

Polishing 3/4-inch diameter X 1/2-inch long hard felt plug.

Preload: First roughing - Contact

force

with 0.004- inch thick

Additional preload of

paper, 4.5 Oz

0.006 inches

pullout

Second roughing - Contact

force

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

0 . 006 inches

pullout

Polishing - Contact

force

with 0.004- inch thick

Additional preload of

paper , 1 , 5 Oz

0.004 inches.

pullout

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

= 2 degrees

= 4.2 minutes per cycle.

= 12.6 minutes.

Note: Tool holder sides were shortened 0.050 inches to allow rubber to flex

more .

Results: First roughing

Second roughing

Polishing

General appearance getting better. One low spot

visible on the back of head. Concentric plane

pattern visible. Scratches visible with 2X

magnification. Corrected program for back of head.

Tool is still overheating.

Concentric plane pattern still visible. Scratches

still evident with 2X magnification. Still missing

back of head.

Faint scratches still visible with 2X magnification.

Low spots which are visible are (1) behind head, (2)

"IN GOD". Over polished outside edge of date - 1987

and "T" of "TRUST".

17
S692253

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

TEST # 12

SERIAL #

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

ToolsFirst roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing 3/4- inch diameter X 1/2- inch long hard felt plug.

PreloadFirst roughing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 4.5 Oz

.

0.004 Inches.

pullout

Second roughing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

.

0.004 inches.

pullout

Polishing - Contact

force

.

with 0.004- inch thick

Additional preload of

paper, 1.5 Oz

.

0.002 inches.

pullout

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

= 2 degrees

= 4.2 minutes per cycle.

= 12.6 minutes.

Results: First roughing

Second roughing

Polishing

General appearance very good. One low spot visible

on the back of head. Concentric plane pattern

visible. Scratches visible with 2X magnification.

Tool is still overheating.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"s" mint mark, "8" of "1987", and "T" of "TRUST".

Faint scratches still visible with 2X magnification.

Polished through "s" mint mark, "8" of "1987", and

"T" of "TRUST" . Hair line starting to lose

sharpness

.

18
TEST # 13

SERIAL # S692254

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools

First roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250- inch thick neoprene rubber pad,

Durometer 40.

Second roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250- inch thick neoprene rubber pad,

Durometer 40.

Polishing 3/4- inch diameter X 1/2 -inch long hard felt plug

Preload: First roughing

° Second roughing

Polishing

Contact with 0 004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.004 inches.

Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.004 inches.

Spindle speed

Head angle

Time

Total time

= 15 , 000 rpm

= 2 degrees

= 3.6 minutes per cycle.

= 10.8 minutes

Results: First roughing

Second roughing

Polishing

General appearance is better. Over polishing "8" of

"1987". Concentric plane pattern visible. Scratches

visible with 2X magnification. Tool is still

overheating

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"s" mint mark, "T" of "TRUST", "8" and "9" of "1987”.

Faint scratches still visible with 2X magnification.

Three low spots evident - (1) behind head, (2)

between "I" and "B" of "LIBERTY", and (3) between "R"

and "T" of "LIBERTY" . Polished through outer edge of

"1987"

19
TEST # 14 Part: Obverse side Kennedy 50 cent die

SERIAL # S692255 Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

ToolsFirst roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing - 3/4 diameter X 1/2 -inch long hard felt plug.

PreloadFirst polishing - Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.004 inches.

Second polishing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Polishing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

= 2 degrees

= 3.6 minutes per cycle.

= 10.8 minutes.

Results

First roughing - General appearance very good. over polished "8" of

"1987". Concentric plane pattern visible. Scratches

visible with 2X magnification. Tool is still

overheating

.

Second roughing - Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"T" of "TRUST", "8" and "9" of "1987".

Polishing - Faint orange peel visible with 2X magnification.

Over polished front of neck.

20
TEST # 15 Part: Obverse side Kennedy 50 cent die

SERIAL # S692256 Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools : First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing - 3/4 diameter X 1/2 -inch long hard felt plug.

Preload: First roughing - Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.004 inches.

Second roughing - Contact with 0.004= inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Polishing - Contact with 0.004= inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

= 2 degrees

= 3.6 minutes per cycle. = 10.8 minutes.

Note: Reduced tool holder cup length to .100 inches.

Results: First roughing

Second roughing

Polishing

General appearance better. Numbers and letters look

much better although "8" of "1987" seems to be on the

thin side. Scratches visible with 2X magnification.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Numerals and

letters look much better, however low spot behind

head has reappeared.

Faint scratches still visible with 2X magnification.

Two low spots evident - (1) behind head and (2)

between "I" and "B" of "LIBERTY".

21
Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

TEST # 16

SERIAL # S692257

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing

Pattern:

Ten concentric passes around the surface of the die.

Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools First roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.004 inches.

Second roughing Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload 0.006 inches.

Polishing Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload 0.004 inches.

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

= 2 degrees

= 3.6 minutes per cycle. = 10.8 minutes.

Note: Reduce tool cup holder length to .050 inches.

Results: First roughing - General appearance very good. Appears that tool is

lifting too early. Scratches visible with 2X

magnification

.

Second roughing - Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"R" of "LIBERTY"

.

Polishing - Pit marks visible over most of the die. This is

probably due to lack of preload on initial roughing

pass .

22
TEST # 17

SERIAL # S692258

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction =* 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40,

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Tools

Preload:

Polishing

First roughing

Second roughing

Polishing

3/4 diameter X 1/2 -inch long hard felt plug.

Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.004 inches.

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

= 2 degrees

= 3.6 minutes per cycle

= 10.8 minutes.

Results: First roughing

Second roughing

Polishing

General appearance very good. Faint orange peel

visible from tip of nose to top of head. Concentric

plane pattern visible. Scratches visible with 2X

magnification.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. slight orange

peel at top of head.

Faint scratches and orange peel still visible with 2X

magnification

23
TEST # 18 Part: Obverse side Kennedy 50 cent die

SERIAL # S692259 Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

Tools: First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing

Preload: First roughing

- 3/4 diameter X 1/2 -inch long hard felt plug.

- Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

Second roughing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Polishing Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.004 inches.

Spindle speed

Head angle

Time

Total time

= 15,000 rpm

= 2 degrees

= 3.6 minutes per cycle.

= 10.8 minutes.

Note: Program compensated for errors at top of head.

Results: First roughing - General appearance much better than before. Last

pass may be leaving a ring around the die.

Concentric plane pattern visible. Scratches visible

with 2X magnification.

Second roughing - Concentric plane pattern has disappeared. Tiny pit

marks up by the top of head - otherwise fine.

Polishing - Faint pit marks up by the top of the head still

visible with 2X magnification. Ring around die due

to last pass.

24
TEST # 19 Part: Obverse side Kennedy 50 cent die

SERIAL # S692127 Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves In both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Tools

First roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0,250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing

Second roughing

Polishing

Contact with 0,004- inch thick

force. Additional preload of

Contact with 0.004- inch thick

force. Additional preload of

Contact with 0.004- inch thick

force. Additional preload of

paper, 4.5 Oz

0.006 inches.

pullout

paper, 1.5 Oz

0,006 inches.

pullout

paper, 1.5 Oz

0.004 inches.

pullout

Spindle speed

Head angle

Time

Total time

= 17,500 rpm

= 2 degrees

= 3.6 minutes per cycle.

= 10,8 minutes.

Results: First roughing - General appearance better than before. Polishing

tool coming down too early at back of head and over

polishing "R" of "LIBERTY". Concentric plane pattern

visible. Scratches visible with 2X magnification.

Second roughing - Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification. Over polished

"R" of "LIBERTY".

Polishing - Faint orange peel between "I" and "B" of "LIBERTY".

Polished through "s" mint mark.

25
S692128

Part: Obverse side Kennedy 50 cent die

Performed by: Karl Ousterhout

TEST # 20

SERIAL #

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

ToolsFirst roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing - 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing - Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

Second roughing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Polishing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.004 inches.

Spindle speed

Head angle

Time

Total time

= 17,500 rpm = 2 degrees

= 3.6 minutes per cycle. = 10.8 minutes

.

Note: Program changed to compensate for top of head and mint mark.

Results

First roughing - General appearance very good. Concentric plane

pattern visible. Scratches visible with 2X

magnification

.

Second roughing - Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification.

Polishing - Finish looks very good. Polished through "s" mint

mark.

26
TEST # 21 Part: Obverse side Kennedy 50 cent die

SERIAL # S692130 Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C„N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches

Lubricant

Tools

Hyprez - Hyperlube oil

Preload:

First roughing 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing

First roughing

Second roughing

Polishing

3/4- inch diameter X 1/2 -inch long hard felt plug.

Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 Inches.

Contact with 0.004- Inch thick paper, 1.5 Oz. pullout

force. Additional preload of 0.004 inches.

Spindle speed

Head angle

Time

Total time

= 17 , 500 rpm

= 2 degrees

= 3.6 minutes per cycle.

= 10.8 minutes

Note : Program changed to compensate for "s" mint mark.

Results

First roughing

Second roughing

Polishing

Excellent final finish. Best finish to date.

Concentric plane pattern visible. Scratches visible

with 2X magnification.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification.

Slight over polishing of "s" mint mark. Otherwise

the die is probably acceptable.

27
TEST # 22 Part: Obverse side Kennedy 50 cent die

SERIAL # S692131 Performed by: Karl Ousterhout

Method: Part mounted to rotary table of C.N.C. milling machine. Part rotates

about the Z axis (A axis rotation) while the polishing tool moves in both

the radial direction (X axis) and in the vertical direction (Z axis) to

generate the tool path.

Polishing: Ten concentric passes around the surface of the die.

Pattern: Tool travel in the vertical direction = 0.011 inches.

Lubricant: Hyprez - Hyperlube oil

ToolsFirst roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Second roughing - 3/4- inch diameter pressure sensitive oak veneer

adhered to 0.250 -inch thick neoprene rubber pad,

Durometer 40.

Polishing - 3/4- inch diameter X 1/2 -inch long hard felt plug.

Preload: First roughing - Contact with 0.004- inch thick paper, 4.5 Oz . pullout

force. Additional preload of 0.006 inches.

Second roughing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.006 inches.

Polishing - Contact with 0.004- inch thick paper, 1.5 Oz . pullout

force. Additional preload of 0.004 inches.

Spindle speed

Head angle

Time

Total time

= 17,500 rpm = 2 degrees

= 3.6 minutes per cycle.

= 10.8 minutes.

Note: Program changed to compensate for "s" mint mark.

ResultsFirst roughing

Second roughing

Polishing

Appearance very good. Scratches visible with 2X

magnification.

Concentric plane pattern has disappeared. Scratches

still evident with 2X magnification.

Slight over polishing of "s" mint mark. Otherwise

die looks very good.

28
IV. Conclusion and Recommendations

The die polishing techniques developed by this research prove that automated die

polishing is feasible. However, there are currently too many variables which

change from die to die for the die polishing process to be fully automated. During

the course of the research the following variables were noted to change on a frequent basis:

(1) Die height

(2) Die base diameter

(3) Die surface profile

The die height and base diameter changed from die to die while the surface profile

did not change much (if any) for dies with consecutive serial numbers (i.e., in the

same batch) . Noticeable changes were noted when dies with different serial numbers

were polished one after the other. Even though the surface profile changes were on

the order of 0.0002 - 0.0005 inches, these minute changes seriously affect the

polishing process. The main reason for this is the lack of any kind of feedback to

monitor the die- tool interface during the polishing operation.

The parameters which produced the best results during the polishing process were:

(1) Polishing tool angle of 2 degrees.

(2) Spindle speed of 17,500 rpm.

(3) Cycle time of 3.6 minutes. This corresponds to a feed rate of 5

inches per minute.

Using the information above, the U.S. Mint could partially automate the die

polishing process by following the procedure described in the following paragraph.

Set up the polishing machine and polish a large batch of dies with 12 micron

diamond compound. After the individual dies have been polished they should be

inspected for minor defects. And, if any are found, they should be polished out by

hand. Continuing in this manner, the dies x^ould return to the machine to be

polished with a 3-micron diamond compound. And, after inspection and touch-up,

return to the machine for polishing with a 1 -micron diamond compound. Any

remaining defects could be polished out by hand.

This simple but effective die polishing procedure would greatly increase the

productivity of the U.S. Mint. For full automation of the die polishing process an

additional phase of the die polishing research should seriously be considered to

alleviate some of the problems encountered during the present research.

The next phase of this research should use a machine with at least two rotary and

two linear axes. The present study demonstrates that tilting the polishing tool

improved the overall performance. With an additional rotary axis, the amount of

tilting can be programmed for the tool to be tangent continuously over the surface

profile of the die.

29
To compensate for the three variables mentioned earlier, the following two methods

should be explored:

(1) Force Feedback: This method would use real-time control techniques to

enable the polishing tool to exert constant pressure on the die surface.

By using this method, subtle changes in die height and surface profile

would be compensated for automatically. No measurements of the die

surface would be necessary.

(2) Surface mapping: This technique would involve three dimensional

scanning of the die surface. First, scan the die surface with a suitable

scanning device such as ultra- sound. Second, change the data obtained

from the scanning process into appropriate numerical values. Third,

transform the numerical values into a code compatible with the die

polishing machine tool controller. Fourth, load the transformed code into

the die polishing machine controller.

Regardless of the method employed, the polishing operation should be completed with

a final inspection to ensure the surface quality is acceptable. This can be

accomplished using an ultrasound sensor. By replacing the polishing tool with this

sensor and running the same NC program on the machine tool, it is possible to scan

the entire die surface following the same tool path. During the scanning, a control computer stores the locations of the rough spots. After the scanning, the

sensor is replaced by the polishing tool again, and based on the sensory

information gathered, the control computer directs the tool to repolish the bad

spots. This type of deterministic control system with in-process gaging would

significantly decrease the incidence of producing unacceptable dies.

30
NBS-114A (REV. 2-80 V. U.S. DEPT. OF COMM.

>

4.

BIBLIOGRAPHIC DATA

SHEET ( See instructions)

TITLE AND SUBTITLE

1. PUBLICATION OR 2. Performing Organ. Report No.

REPORT NO.

N —HBlS T R 8 7 3 6 6 4

3. Publication Date

Study of Die Polishing for United States Mint

Phase III

5. AUTHOR(S)

Karl Ousterhout

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s) 7. Contract/Grant No.

national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

see Block 6

10.

SUPPLEMENTARY NOTES

J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of mo.st significant in formation . Jf document includes a si gn i fi cant

bi bi iography or literature survey, mention it here) This research was undertaKeh to determine the

feasibility of automating the polishing process of proof dies at the United States Mint.

The dies polished during this research endeavor were the obverse Kennedy half-dollar

dies. While most of the techniques used in this study are new, some of the techniques

developed by Sidney Weiser (Phase I December 16, 1985 and Phase II December 3, 1986)

were incorporated into the polishing procedure. The main goals of this research are:

1. Develop a method of mecahnically polishing proof dies which results in a quality

level equal to or better than that now achieved by current manual methods.

2. Develop the optimum production rate that can be achieved in mechanically polishing

proof dies.

3. Utilize a machine tool with at least 4 axes of motion.

4. Exercise initiative and ingenuity in the use of conventional and computer

technologies, and develop through experimentation the best polishing compounds and

and materials, tooling, tool paths, speeds, masking techniques or other methods of

protecting areas not to be polished.

12. KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key

dies, polishing, polishing compounds, polishing proof

words by semi colon s)

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

X'^XJnl imited

For Official Distribution. Do Not Release to NTIS 34

; Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402. 15. Price

T Order From National Technical Information Service (NTIS), Springfield, VA. 22161

$11.95

USCOMM-DC 6043-P80