Machine parts expander hold down

A workpiece fastening device usable on a machine tool fixture, comprising an elongated tubular body having knurling along the outside of the top end of the body, a taper on the inside thereof, and a plurality of slots extending longitudinally about half the length of the body. A lock washer with a yieldable portion is welded to the bottom end of the body to allow a workpiece to be pulled flush against a fixture. The tubular body is slip-fitted into a through-bore in the workpiece until the lock washer rests upon the fixture, and a bolt having a head taper matching the taper in the tubular body is then inserted through the body and is threadably received in the fixture. Upon tightening of the bolt, the top of the body expands causing the knurling to grippingly engage the bore in the workpiece. After the body is completely wedged in the bore, further tightening of the bolt causes the lock washer to be distorted slightly thereby allowing the workpiece to be pulled flush against the fixture.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improved hold down device for fastening 
a workpiece to the surface of a machine tool fixture plate. More 
particularly, the invention relates to a device that converts a straight 
through bored hole in the workpiece to temporarily act as a counterbored 
hole for bolting the workpiece to be machined to the work supporting 
surface with the head of the hold down bolt recessed. 
2. Description of the Prior Art 
The method used to attach workpieces to be machined to a work support 
surface when the heads of the hold down bolts had to be recessed was to 
counterbore each hole, and often both sides of each hole, when the 
workpiece was to be worked on both sides. For accuracy, the workpiece must 
be precisely positioned for both counterboring operations. Thus, the 
set-up and machining time before actual machining of the workpiece was 
significant. Particularly, when the workpiece was quite bulky and/or 
heavy, accidents during turn-over of the workpiece may have caused loss of 
workpieces due to the requirement for multiple handling. The present 
invention eliminates the counterboring operation for hold down bolts 
thereby reducing set-up time and increasing productivity. 
3. Statement of the Prior Art 
The following patent is cited as the most pertinent prior art of which the 
applicant is aware: 
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U.S. PAT. NO. NAME DATE 
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2,403,330 D. C. Benton 
2 July l942 
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U.S. Pat. No. 2,403,330 to D. C. Benton on "Blind Fastening Bolt and Nut" 
relates to a bolt, sleeve and nut combination used to attach two plate 
members together. In operation, the sleeve and nut are placed upon the 
bolt. Then the assembled bolt unit is inserted through an inline bore 
extended through a top and bottom plate. After insertion, the head of the 
bolt rests on the top surface of the top plate and a taper provided on a 
sleeve extends through the bottom surface of the bottom plate. The nut is 
provided with a tapered portion conforming to the taper on the sleeve, and 
the tapered part of the nut is provided with a plurality of slots dividing 
the tapered end of the nut into sections which spread as the nut is 
tightened, thereby engaging the bottom surface of bottom plate and drawing 
the two plates together in a mating relationship. 
The only relevance between the above cited patent and the present invention 
is that each uses a sleeve having a taper located on one end. However, the 
taper on the sleeve used by Benton is used to spread the serrations 
located on the nut thereby allowing the nut to pull two parts together 
while the taper in the sleeve of the present invention provides a means 
for locking the sleeve in a first part and at the same time provides a 
shoulder for a bolt head to work against in pulling a second part into a 
mating relationship with the first part. 
BRIEF SUMMARY OF THE INVENTION 
This invention affords an efficient and cost saving means for attaching 
workpieces to be machined to the table of a machine tool when the bolt 
heads must be recessed to enable access to the workpiece for machining 
thereof. Non-counterbored holes formed in the workpiece are converted into 
counterbored holes thereby saving the machine time required to counterbore 
each tie-down hole in a given workpiece, turn over the workpiece, align 
same, and counterbore the other side thereof. The improvement in a 
reusable fastener comprises a tubular body portion having a knurled outer 
top portion and an inwardly tapered inner portion. Longitudinal slots are 
cut into the top of the body, extending approximately half the length of 
the body, and providing bifurcations around the top half of the body. A 
split ring or spring washer is spot welded to the bottom end of the 
tubular body with a portion thereof yieldably extending below the body for 
engagement on the work support surface prior to final seating of the 
tubular body in the bore. A bolt having a taper on the underside of its 
head complimentary to the taper in the body portion operates to spread the 
bifurcations of the body as it is tightened in place. 
In use, the tubular body portion of the present invention is slip-fitted 
into an in-line bore, formed through the workpiece to be machined. The 
split ring spring, on the bottom end of the tubular body portion rests 
upon the machine bed or fixture designed to hold the workpiece during its 
machining operations. Aligned in the table or fixture is a hole threaded 
to receive a mating bolt. The bolt, having a taper on the underside of its 
head that matches the taper provided in the top portion of the tubular 
body, is then inserted through the tubular body and is threadably received 
in the machine table or fixture. Upon tightening of the bolt, the 
bifurations located around the top portion of the tubular body are 
expanded causing the knurling on the outside of the bifurcation to 
grippingly engage the bore provided in the workpiece. After the tubular 
body is partially wedged into the bore provided in the workpiece, further 
tightening of the bolt causes the workpiece to be pulled down to bring the 
bottom surface thereof into a flush mating relationship with the machine 
bed or fixture. During pull down, the split ring located on the bottom of 
the tubular body, and resting in contact with the machine bed or fixture, 
is urged into the bore provided in the workpiece. The split ring acts as a 
positive stop during the insertion of the tubular body into the bore, but 
is yieldable and assures the gripping action of the bifurcations are 
effective upon pull down of the workpiece into intimate contact with the 
machine bed. Thus, the workpiece may be machined to a high accuracy taking 
advantage of the highly planar machine bed. After the workpiece is 
machined, the bolt is removed from the machine bed or fixture, the tubular 
body portion can then be pushed out of the bored hole and reused. 
An object of the present invention is to provide a reusable device which 
allows a non-counterbored hole to perform the functions of a counterbored 
hole. 
Another object of the present invention is to provide a hold down assembly 
with a spring attached to a body portion to enable the assembly to pull a 
workpiece into intimate engagement with a machine bed. 
Although the characteristic features of the present invention are 
particularly pointed out in the appended claims, the device and method 
employed will be better understood by reference to the following 
description taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention in a workpiece hold down or fastener device relates 
to a fastener device comprising a body portion working cooperatively with 
a bolt in pulling two parts together where one part is provided with a 
bore extending therethrough and another part is provided with a mating 
threaded hole. 
Referring now to FIG. 1, in a preferred embodiment, a fastening device 10 
is shown as a two part assembly which includes a tubular body 11 having a 
top or second inserted portion 12 and a bottom or first inserted end 14. 
The top portion 12 of the tubular body 11 is provided on its exterior with 
a knurled surface 13 and on its interior with a taper 15, which merges 
into the inner diameter of the tubular body 11. In the top portion 12 of 
the tubular body 11 are formed a plurality of slots 16 extending 
longitudinally approximately half the length of the tubular body 11, and 
thereby providing a plurality of bifurcated portions 17. Each bifurcated 
portion is covered exteriorly with knurling 13 and interiorly is 
configured with the inward taper 15. 
The first inserted or bottom end 14 of the tubular body 11 is provided with 
a resilient, split ring 20, preferably in the form of a lock washer, spot 
welded to the bottom end 14 of the tubular body 11. The free portion of 
the split ring, substantially diametrically opposed from the welded area, 
is displaced longitudinally from the tubular body portion when not 
stressed, but is yieldable, and movable into contact with the body 
portion. The split ring 20 has an outer diameter less than the inner 
diameter of the bore 28 and an inner diameter greater than the outer 
diameter of the bolt 25. The bolt 25 of the clamping device 10 is provided 
with a taper 26 on the underside of the bolt head 27 that complements the 
inward taper 15 provided in the top portion 12 of the tubular body 11. 
Referring now to FIG. 2, a typical usage for the present invention 10 is to 
attach a workpiece to a support table or fixture of a machine tool. The 
method used is substantially as set forth below. 
The tubular body 11 is slipped into an in-line through bore 28 provided in 
a workpiece 29. The body is seated at a depth such that the resilient ring 
20, fixed to the first inserted end 14 of the tubular body 11, contacts a 
top surface 30 of a fixture plate 31, also having formed therein a tapped 
hole 32. The bolt 25 is then inserted through the tubular body 11 and the 
split ring 20, and is threadably received in the tapped hole 32 in the 
fixture plate 31. 
Upon tightening of the bolt 25, the threaded engagement with the tapped 
hole 32 in the work support cause the bolt 25 to be pulled into the 
workpiece. After the bolt is recessed slightly below the surface of the 
workpiece to be machined, cause the taper 26 under the bolt head 27 
engages the taper 15 of the tubular body 11 to expand the bifurcations 17 
causing the knurling 13 on each bifurcation to grippingly engage the 
internal wall of bore 28 provided through the workpiece 29. FIG. 2 
illustrates the position which the various parts occupy upon initial 
assembly of the fastening device in the procedure for attaching the 
workpiece 29 to the fixture 31. 
After the tubular body 11 is completely wedged into the the bore 28, 
further tightening of the bolt 25 causes the tubular body to pull the 
workpiece 29 and the fixture 31 into a firm and intimate mating 
relationship thereby closing any gap 35 existing therebetween. While the 
gap 35 is being closed, the longitudinally displaceable portion of the 
split ring resilient, means 20 is urged into and recessed in bore 28, 
compressed against the surface 30 of the fixture. Further, tightening of 
bolt 25 causes the workpiece to be pulled against the fixture thereby 
completely closing the gap 35 as the tubular body 11 presses against the 
split ring 2a, and the latter presses against the work support surface. 
Thus, the workpiece is brought into intimate engagement with the fixture 
plate surface permitting highly accurate machining of the workpiece. 
After machining, the workpiece 29 is released from one work support surface 
30 by removing bolt 29 from the tubular body 11. Upon partial withdrawal 
of the bolt, the split ring 20 lifts the workpiece from the work support 
surface 30, Also, the bifurcations of the tubular body withdraw from the 
bore 28 of the workpiece permitting removal of the tubular body from the 
workpiece. Hereafter, the fastener 10 is reusable in attaching another 
workpiece for machining. 
The invention has been described as to the structural features of its 
preferred embodiment.