Workpiece holddown device

A workpiece holddown apparatus is shown that includes a post, removably securable to a variety of work tables and benches by a bolt extending through a hole or slot in the work table or bench and received in a threaded bore in one end of the post. An arm assembly consisting of a tubular sleeve is radially disposed on the post for 360.degree. rotational and axial sliding movement thereon, and includes an arm radially extending from and attached to the tubular sleeve at an upward angle taken from a perpendicular of the axis of the post, the arm terminating with an internally threaded bushing in which is threaded a screw having an axis parallel to the post. The screw includes a handle portion and foot portion, the foot portion adapted to contact and press against a workpiece as the screw is tightened. In addition to the clamping force exerted on the workpiece by the screw, the threaded bushing holding the screw, and consequently the attached arm, is moved upwardly as tightening occurs, which creates a moment about the sleeve on the post. The sleeve, having a slight clearance between its inner surface and the post, is axially offset by the upward movement of the arm thus providing a binding action on the post. The workpiece is thus securely held between the work table or bench and the foot portion, in a variety of variable positions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to devices for holding objects or workpiece 
and, more particularly, to a holddown device having 360.degree. swivable 
maneuverability for moveable attachment to various tools and tables 
2. Description of the Prior Art 
During cutting, drilling, and performing other machine tool operations upon 
a workpiece, it is vital that the workpiece being acted upon is securely 
held in place, whether the workpiece is on a drill press, a mill table, a 
welding table, a workbench, or otherwise. Should the workpiece move or 
slip while the operator is performing an operation on the workpiece, the 
unsteady workpiece can spin, break, splinter, or be propelled away from 
the work table 
Various devices have heretofore been devised for retaining variously-shaped 
workpieces on work surfaces during machining operations, including 
parallel clamps, C-clamps, angle plates, jackscrews, step blocks, 
V-blocks, flat straps, U-straps, gooseneck straps, and specialty clamps 
designed to work with particular tools. These devices, however, are 
tolerably effective in holding the workpiece since in most instances two 
or more of them must be cooperatively utilized in order to securely retain 
the workpiece. It is cumbersome and timeconsuming to set up the workpiece 
holding apparatus for possibly only one operation thereby adding to the 
labor cost and the possibility of problems due to the interaction of the 
various pieces. 
One prior art clamping device is shown in a tool catalogue from Woodcraft 
of P.0. Box 1686, Parkersburg, W. Va., and consists of a notched shank or 
post that rests in a table-mounted collar having matched ridges within the 
collar to prevent slipping of the post. A non-moveable 
transversely-extending arm is formed at the top of the post distal the 
table surface, the arm having on its extended end, a pivoting second arm. 
The second arm has a pivoting foot portion for holding against the 
workpiece and an internally threaded bushing on the other end 
accommodating a threaded screw that angles against and tightens on the 
distal end of the post throwing the post off the perpendicular so it binds 
to the collar 
Several problems associated with this type of prior art clamping device are 
its manner of adjustability, its ease of adjustability, and its 
adjustability with respect to the workpiece. First, the height of the post 
is adjustable only in discrete steps defined by the notches in the post 
and the associated rings in the collar. Second, if the height of the post 
is adjusted, the second arm must pivot about its axis either upwards or 
downwards changing the location on the workpiece that the foot contacts. 
In order to remedy this, the location or orientation of the workpiece must 
be changed in order for the foot to contact the same location Third, the 
second arm has only a limited range of motion defined by the pivot and the 
practical length of the threaded screw in being able to contact the post. 
Another prior art clamping device is shown in U.S. Pat. No. 
3,575,373--Reinhardt et al. entitled "Holddown Device." There, a flat arm 
extends essentially perpendicular to and is movable on a central post. 
Extending from the distal end of the arm, relative to the post, is a 
spring-biased holding pad for contacting the surface of the piece to be 
held down The arm is canted on the post by the pressure of the biasing 
spring 
This prior art clamping device is disadvantageous in that it cannot clamp 
down on a workpiece with enough force to prevent the workpiece from 
moving, especially when the workpiece needs to be drilled, milled, or 
otherwise, and is particularly designed to be used in conjunction with a 
plurality of the same devices for holding gas meters, or the like, during 
transportation. 
In addition, holddown devices of the prior art are limited in their range 
of movement due to their mounting location or physical constraints such 
that orientation of the workpiece is confined to the range of movement of 
the holddown device. Further, most devices of the prior art cannot 
accommodate workpieces having vastly different thicknesses. Also, with 
prior art devices that purportedly allow vertical and/or horizontal 
clamping, either the devices cannot accommodate both or they are not 
reliable enough to securely hold the workpiece Further, transportability 
and adaptability of the prior art holddown devices to various machines and 
tables is extremely limited and in most instances the prior art devices 
are confined to the location in which they are originally installed. 
It is thus an object of the present invention to overcome the shortcomings 
of the prior art and provide a simple, yet effective workpiece holddown 
that is also extremely versatile and readily transplantable. 
SUMMARY OF THE INVENTION 
The present invention provides a workpiece holddown device that securely 
holds a workpiece under a screw mechanism by a double binding action of 
the screw mechanism and an arm assembly and post mechanism, and is adapted 
to be removably mountable on any work surface. A sleeve surrounding the 
post and slidable thereon, is disposed at one end of the arm assembly, and 
includes a minute clearance between the post and the inner surface of the 
sleeve for frictional binding during clamping and axial slidability on the 
post in an infinite number of positions. Upward force exerted at one end 
of the arm assembly by the screw mechanism during clamping of the 
workpiece creates a moment about the arm assembly which frictionally binds 
the sleeve to the post as the arm assembly is upwardly angle as a result 
of the exerted force. 
In a preferred embodiment, the present invention provides an easily 
transplantable workpiece holddown device including a post secured to a 
work table or bench, an arm assembly rotatably and axially displaceable at 
one end upon the post, and a screw portion disposed on the other end of 
the arm assembly for tightening down upon a workpiece. The arm assembly 
includes an arm with a sleeve on one end for movement on the post, and a 
threaded bushing on the other end for receiving the screw mechanism. 
A workpiece holddown device for retaining a workpiece onto a work surface, 
the holddown device comprising a post including mounting means for 
removably securing the post to the work surface, an arm assembly extending 
from the post perpendicular to an axis of said post, the arm assembly 
being rotatable and axially slidable about the post, and screw means 
disposed on the arm assembly distal the post for clampingly holding the 
workpiece against the work surface, the screw means creating a moment 
about the arm assembly to bind the arm assembly to the post when the screw 
means is tightened on the workpiece. 
In one form, the arm assembly includes a cylindrical sleeve surrounding the 
post, an arm attached at one end to the cylindrical sleeve and extending 
therefrom at an angle, preferably not more than 45.degree. from a line 
perpendicular to the axis of the post, and an internally threaded 
cylindrical bushing attached to the other end of the arm that threadedly 
receives a screw assembly having a handle at one end and a foot at the 
other end that holds the workpiece against the work surface, the screw 
assembly turns within the bushing independently of the axial and radial 
movement of the arm assembly on the post. 
Binding of the workpiece against the work surface is accomplished by the 
downward force of the screw assembly clamping against the workpiece and 
work surface. In addition, the bushing and sleeve are respectively bound 
against the screw portion and post by a shifting of their axes relative to 
the screw portion and post in opposite directions resulting from the force 
of the screw portion clamping against the workpiece. 
It is an advantage of the present invention that it can accommodate 
workpieces of various extreme dimensions by having an axially slidable arm 
on a post providing infinite variations of clamping positions. 
Another advantage of the present invention is that it is easily 
transplantable to a variety of tools and tool environments. 
It is yet another advantage of the present invention that it can 
accommodate and is easily adaptable to a wide range of shapes and sizes of 
workpieces to be clampingly held, and requires very little effort in 
setting up. 
It is further an advantage of the present invention that it is easily 
adaptable to be utilized in horizontal and vertical orientations.

Corresponding reference characters indicate corresponding parts throughout 
the several views. The exemplifications set out herein illustrate a 
preferred embodiment of the invention, in one form thereof, and such 
exemplifications are not to be construed as limiting the scope of the 
invention in any manner. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, there is shown a preferred embodiment of a workpiece 
holddown device 10. Workpiece holddown device 10 includes a post 12, an 
arm assembly 14, and a screw assembly 16 secured or fastened to a work 
table 18, such as a drill press, mill table, work bench, or the like. In 
the preferred embodiment, the entire workpiece holddown device is 
fabricated from steel to provide a heavy and solid tool that can withstand 
repeated torque and pressure loads. Although steel is preferred due to its 
strength and relative low cost, other materials can be utilized in 
fabricating the workpiece holddown device, e.g. other metals, alloys of 
metals, and composites, that offer the same or superior material strength 
and torque load requirements. 
Referring to FIG. 2, there is shown post 12 as it is secured to table 18. 
In an exemplary embodiment, post 12 was constructed having an overall 
length of 6 inches, and an outer diameter of 1.06 inches, although the 
length of post 12 is quite variable depending on the desired location and 
use of the holddown device, while the outer diameter of post 12 is 
variable only to the extent that post 12 can be securely seated upon table 
18 without movement off the vertical axis and still accommodate a bolt of 
sufficient size to handle the torque and stress. Table 18 includes a slot 
34 through which a conventional bolt 22 having a conventional bolt head 24 
extends from the underside 19 of table 18. Between bolt head 24 and table 
18 is a washer 26 and a rectangular plate 28 both of which serve to 
vertically stabilize bolt 22 and post 12, and distribute the clamping 
force from bolt head 24 against the underside 19 of table 18. Post 12 has 
on one end a tapped or threaded bore 30 that threadedly receives bolt 22 
such that post 12 screws down upon bolt 22, or alternatively bolt 22 
screws into bore 30, with sufficient clamping force until end 32 of post 
12 contacts the top 33 of table 18. Thus, post 12 is firmly secured to, 
but easily removable from, table 18. 
Referring again to FIG. 1, post 12 is preferably mounted in a slot like 
those found on drill press tables in order for the holddown assembly 10 to 
accommodate a wider range of movement as assembly 10 is moved along a path 
indicated by arrow R. Although a slot is preferable, a slot of sufficient 
diameter to accommodate the bolt could also be used. Thus, a workpiece 20 
may be held at different positions along its length by adjusting either 
workpiece 20 or, alternatively, easily adjusting the holddown post 
position. Radially disposed on and surrounding post 12 is a sleeve 36 
having a longitudinal length of 1.25 inches, although any suitable length 
can be utilized. Sleeve 36 is freely slidable on post 12 in an axial 
direction indicated by arrow X and is also freely rotatable 360.degree. 
about post 12 in a direction indicated by arrow Y. Sleeve 36 has a 
clearance 39 (see FIG. 2) from the outer surface 37 of post 12 to the 
inside surface 38 of sleeve 36 of approximately 0.002 inches. Although the 
clearance between outer surface 37 and inside surface 38 can be greater or 
smaller than 0.002 inches, it has been found that 0.002 inches is an 
optimal value. If there is less clearance, sleeve 36 will not be able to 
be easily moved either axially or circumferentially and be frictionally 
bound thereon. If there is more clearance, sleeve 36 will not frictionally 
bind to post 12, thus requiring more pressure to be exerted against sleeve 
36 to bind sleeve 36 against post 12. Consequently, if there is too much 
clearance between outer surface 37 and inner surface 38 there would be no 
binding regardless of the force exerted by screw assembly 16. 
Attached to sleeve 36 by welding or other suitable means, is a radially 
extending arm 40 having a height of 1 inch or an approximate height 
corresponding to the axial length of sleeve 36, and an approximate 
thickness of 1/2 inch although all dimensions are contemplated as 
modifiable. Arm 40 is preferably 3-5 inches in length depending on the 
desired application, although a 7 inch arm could be used for all 
applications, but greater or smaller lengths may be utilized depending on 
the workpiece being held or the application. Also, the longer the arm, the 
greater the pressure exerted upon post 12 during clamping of a workpiece. 
Arm 40 is attached to sleeve 36 at an angle, designated O, that is shown 
in FIG. 1 as measured from a line perpendicular to the centermost axis of 
sleeve 36. In FIG. 1, angle 0 is approximately 20.degree.. Although the 
degree of arm angle is not critical, arm 40 should be attached to sleeve 
36 such that there is at least a nominal upward arm angle 0 as taken from 
a line perpendicular to the centermost axis of sleeve 36. Preferably, 
angle O would be less than 45.degree. from the perpendicular. An arm could 
be attached to the sleeve at an exact perpendicular to the post axis but 
this would limit its overall maneuverability. 
Attached to the other end of arm 40, by welding or otherwise, is an 
internally threaded bushing 42 drilled and tapped for 3/4-10, although 
other sizes and thread spacing can be utilized. Bushing 42 is attached to 
arm 40 in an orientation such that its axis is parallel to the axis of 
sleeve 36. Bushing 42 is of approximately the same axial length as sleeve 
36 but has a smaller inner and outer diameter, however the diameters of 
bushing 42 are variable. Threadedly received in bushing 42 is a screw 
portion 44 having on one end a foot 46 which contacts the workpiece at a 
location 48 between foot 46 and table top 33. Screw portion 44 is 
approximately 4.63 inches long with a 3/4 inch diameter having 3/4-10 
threads, although these dimensions are modifiable. On the other end of 
screw portion 44 is a cap 50 formed integral with screw portion 44 through 
which is received a cylindrical handle 52 movable in a transverse 
direction Z, relative to screw portion 44 and cap 50. Handle 52 terminates 
on either end with cylindrical end pieces 54a and 54b formed integral with 
handle 52 allowing the operator to easily turn screw portion 44. Screw 
portion 44 thus turns within bushing 42 as handle 52 is turned. Turning 
handle 52 in a particular direction turns screw portion 44 in a likewise 
direction. 
Screw assembly 16 exerts an upward force upon arm assembly 14 when screw 
assembly 16 is tightened upon workpiece 20 by a screw action of threaded 
bushing 42 as foot 46 contacts workpiece 20 and is securing or holding 
workpiece 20. Threaded bushing 42 will continue to move on the screw 
portion 44 as screw assembly 16 is tightened. When an upward force is 
exerted by screw assembly 16 on one end of arm assembly 14, a moment 
exists about arm assembly 14 that causes sleeve 36 to axially tilt or 
shift about post 12, the amount of shifting being determined by clearance 
39. Thus, sleeve 36 is frictionally bound or locked upon post 12 by the 
moment created by the upward force of the clamping action so that arm 
assembly 14 locks itself at any desired position. 
The securing of post 12 would normally be as shown in FIG. 2, as table 18 
could be any supporting surface such as a plate, a workbench, or 
otherwise. There are, however, additional mounting surfaces which may not 
be configured so as to be able to secure post 12 in the conventional 
manner. Referring now to FIG. 3, there is shown an alternative embodiment 
regarding the mounting or securing of post 48. FIG. 3 shows a sectional 
view of a typical mill table 56 in which there is typically an elongated 
channel 58 having a rectangular cross-section defined between a lower 
table portion 60 and an upper table portion 62. Upper table portion 62 has 
an elongated bore 64 that longitudinally communicates with channel 58. 
Disposed in channel 58 is a conventional T-nut 66 having a bolt 68 
threaded therethrough. T-nuts with bolts are typically used to secure 
parts to devices that have channels, such as mill tables, and are 
generally of a standard size. Bolt 68 is generally a large bolt, larger 
than bolt 22 of FIG. 2, and is received in a threaded bore 70 in one end 
of post 48. Because bolt 68 is a large diameter bolt, it is preferable to 
include a ring-like collar 72 radially surrounding post 48 for extra 
vertical support and stability of post 48 since there would be less end 
post material to contact the table surface in this embodiment. Collar 72 
includes a bore 74 through which bolt 68 extends to be threadedly received 
into threaded bore 70 of post 48. Post 48 is shown resting on a bottom 
surface 76 of collar 72 which contributes to the stability of post 48. 
On the other end of post 48, still referring to FIG. 3, are two 
diametrically opposed notches or flats 78a and 78b forming radially inward 
steps. Notches 78a, 78b are to be utilized by a suitable wrench in order 
to tighten post 48 onto bolt 68 since it is not possible to tighten bolt 
68 by the T-nut being disposed in channel 58. Alternatively, any type of 
configuration can be utilized in place of notches 78a and 78b that can 
accommodate a tool for tightening post 48 onto the table surface. 
Post 48, as shown in FIG. 3, also includes threaded bore 80 in the 
non-attached end of post 48 which would be used to secure post 48 to a 
device utilizing the simple mounting structure as shown in FIG. 2 with the 
smaller diameter bolt. Threaded bore 80 is optionally included in post 48 
as shown in the embodiment of FIG. 3, but for greater versatility, bore 80 
is included so that one may mount post 48 on more surfaces and tools. 
Referring now to FIG. 4, there is shown an alternative embodiment of the 
workpiece holddown assembly designated 90. Post 92 is secured to the work 
surface or table 94 through slot 96 in the same ways as shown in FIGS. 2 
and 3, and described herein. However, instead of having only one arm 
assembly about post 92, there are attached two arm assemblies 98 and 99 
both having a sleeve 100 and 101, an arm 102 and 103, and a threaded 
bushing 104 and 105. Each arm assembly is as described hereinabove 
although arms 102 and 103 may be of different lengths rather than having 
the same length in order to provide more user flexibility. Likewise, each 
threaded bushing 104 and 105 have a screw assembly 106 and 107 each having 
a screw portion 108 and 109, an end cap 110 and 111, a handle 112 and 113 
terminating in cylindrical end pieces 114a, 114b and 115a, 115b, and feet 
116 and 117 that contact workpiece 118. 
Thus, it is possible to locate two (2) or more arm assemblies on the same 
post, where the arms can be the same or different lengths depending on the 
particular application or workpiece orientation. Thus, it is contemplated 
that one post can accommodate a plurality of arms up to a workable 
maximum. 
In operation, and referring to FIG. 1, workpiece holddown device 10 
functions as hereinbelow described. Workpiece 20 is situated upon the work 
surface, table, or otherwise while arm assembly 14 is rotated so that foot 
46 of screw assembly 16 is over the location on workpiece 20 that is to be 
clamped. Adjustment of screw assembly 16 such that foot 46 is over 
workpiece 20 is accomplished by sliding arm assembly 14 on post 12 and/or 
turning screw portion 16. Alternatively, if post 12 is mounted in a slot 
(e.g. slot 34) post 12 may be moved, however, this is generally not 
necessary due to the great range of movement already afforded by the 
present invention. Arm assembly 14 is thus rotated and slidably raised or 
lowered while screw portion 16 is turned to adjust workpiece holddown 10 
such that foot 46 is over clamping position 48. Once arm assembly 14 is 
correctly positioned over clamping position 48, screw portion 16 is 
tightened down upon the workpiece. The tightening of screw portion 16 
provides very secure clamping of the workpiece between foot 46 and table 
surface 33. This tightening also creates an upward force causing threaded 
bushing 42 to upwardly rise on screw portion 44 thereby creating a moment 
about sleeve 36. This moment causes sleeve 36 to be axially offset in a 
clockwise direction relative to the axis of post 12, thus binding itself 
upon post 12. This upward tension of screw assembly 16 further causes 
bushing 42 to be axially offset in a counterclockwise direction relative 
to the axis of screw portion 44 thereby binding itself upon screw portion 
44, preventing screw portion 44, and screw assembly 16, from 
counterrotating and loosening the binding or clamping force being exerted 
upon the workpiece. Thus, there is a double binding action of the arm 
assembly 14 preventing arm assembly 14 from radially or axially shifting 
during clamping in addition to the screw portion 44 securing the workpiece 
upon the table. 
The procedure is similarly performed when there are multiple arm assemblies 
upon one post, as shown in FIG. 4, or there are multiple workpiece 
holddown devices being employed. 
The dimensions and materials of workpiece holddown 10 are not absolute, and 
deviations from them are contemplated and expected. The dimensions herein 
specified were utilized in the exemplary construction of the present 
workpiece holddown device, and do not necessarily represent absolute 
construction preference. 
While this invention has been described as having a preferred design, the 
present invention can be further modified within the spirit and scope of 
this disclosure. This application is therefore intended to cover any 
variations, uses, or adaptations of the invention using its general 
principles. Further, this application is intended to cover such departures 
from the present disclosure as come within known or customary practice in 
the art to which this invention pertains and which fall within the limits 
of the appended claims.