Mechanical Device Fabrication (Original Solid PVC).
The University of North Carolina version of Dr. Rick Gracely's DNIC Thumb Nail Pressure device was mostly made of standard pluming supplies:
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The split washers are made of the ends of electrical wire spools sold by Digi-Key under the part number C2015X-100 (where X is the color code: R for Red, etc.).
A- In a short piece of 2x4, bore a 1" in diameter , 1/2" deep hole by means of a 1" "Spade" / "Flat" drill bit (Figure 1). Do not drill through the 2x4, the small hole in the middle will serve as an alignment guide for the drill bit when cutting the washer.
B- Cut the spool as shown in figure 2.
C- The 1" hole is slightly too big for the spool, it helps to wrap about 3 turns of electrical tape around the spool to get a tighter fit (Figure 3).
D- Align the 2x4 hole with a 1/8" drill bit as shown in figure 4, and fasten in position to the drill press table.
E- The washer itself is cut with a 1"1/2 (38 mm) rotary saw blade. The plastic of these spools has a very low thermal resistance. Drill very slowly in short bursts. If needed, stop cutting and clean off the melted plastic (Figure 5).
F- Saw off the remaining piece of spool shank, and file down washer until smooth (Figure 6).
G- Place the newly cut plastic washer between the washers of a cheap rotary sander hardware. This does a fairly good job at centering the washer on the shaft (Figure 7).
H- Place in the drill press and file the washer until it fits snugly inside the PVC tee (Figure 8). Then cut a slit in the washer so it can be threaded onto the syringe thumb end (Figure 9).
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The "Whole" washer is made from a 1/8" thick, 1.5"x 1' bar of natural acetal that is actually almost 1 5/8" wide.
A- The center hole is bored with 11/16" Spade (or Flat) drill bit, the outside rim is cut by means of a 1"1/2 (38 mm) rotary saw blade. Because the length of the spade bit is so much longer than the rotary saw blade, and our drill-press down travel is limited, we had to cut the spade bit stem to approximately match the length of the rotary saw blade, in order to keep the bit to work alignment when changing bit.
B- The bar is placed in a wise firmly anchored to the drill-press table. A piece of wood is placed under the bar and the drill bit is aligned with the underside opening in the wise to avoid drilling into the vise.
C- Carefully align the bit with the center of the acetal bar.
D-Start with the 11/16" spade bit and drill half way through the bar.
E- Swap with the 1 1/2 " rotary saw bit, and again drill half way through the bar.
F- Go back to the 11/16" spade bit and finish the center hole.
G- Then finish the outer rim with the 1 1/2" rotary saw bit.
H- File the outer rim of the whole washer in the same way as it was done above for the split washer (Figures 7 & 8)
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PVC Cap Hole:
The cap is made from a standard 1" PVC pipe cap of type 40 PVC.
Making a holding bracket and template to center the hole.
The bracket is made of two short pieces of 2x4 fastened together and a square metal plate (around 2.5"x 2.5")
A- Screw the square metal plate to one of the 2x4 pieces.
B- Drill a 1/8" hole in the middle of the plate, into the 2x4 piece to mark the center.
C- Remove the metal plate, and with a 1 5/8" Forstner drill bit, bore a 1 3/4" deep hole using the 1/8"center marked in the previous step.
D- Grind a rim approximately 1/2"high and 1/2 mm deep into the top of the hole for the cap to fit inside the hole more easily.
E- Because the cap fits tightly inside the hole, a means of removal must be provided, such as drilling an extra 1/2" or larger hole into the bottom of the main hole going all the way through the 2 pieces of 2x4.
Drilling the hole in the cap.
A- Place the PVC cap into the hole and screw on the template metal plate.
B- Drill a 1/8" hole through the center hole in the template all the way through the PVC cap.
C- Remove the template.
D- Drill the cap hole with the 11/16" spade drill bit.
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PVC Cap Mounting:
The cap and the tee are fastened together with a piece of 1" PVC pipe approximately 2" long. The pipe is cemented to the cap with PVC cement and screwed to the tee with three screws set 120░ apart around the circumference. The template for the holes is made of a hose clamp such as the Murray type-F No.28 (2 1/4 -1 5/16).
A- The Tee outside diameter is 1 5/8" thus the holes should be 2ÁR/3 = 1.70" apart. The three holes are drilled with a #31 bit, 1.70" (43mm) apart, 8mm from one edge as shown below.
B- The clamp must be shorten to 8 1/4" (about 1 3/4" shorter than original) so that the end will not interfere with the drilling of the pilot holes.
C- Insert the syringe with the two washers into the tee as well as a piece of 1" pipe and squeeze tightly together. Place the hose clamp around the tee and tighten aligning the first hole (nearer the screw) with the tee mold line (this is if several identical units are to be made).
D- Drill the three holes with the same bit used to drill the holes into the clamp (#31) being careful not to drill through the syringe if it is not to be discarded.
E- Mark all around the pipe, where the pipe enters the tee with a pencil. Remove the clamp and take apart this temporary assembly.
F- Enlarge the holes in the tee with a 1/4" bit.
G- Enlarge the holes in the pipe, with a #8 bit, and tap with a 1/4-20 pipe tap.
H- Insert the 1" pipe into the cap, squeeze tightly (in a vise if needed), and mark, with a pencil, where the pipe enters the cap.
I- Measure the length of pipe needed inside the cap, measure this length from the previous mark and cut the pipe.
J- Cement the cap to the pipe, squeezing tightly (in a vise if needed), until the cap almost reaches the pencil mark.
K- It is recommended to engrave a mark on the pipe to indicate where to align the cap-tube combo with the tee when assembling them together.
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2005 May 10