Overview of tools and materials for making an ankle cup.
I put a pencil mark on the sleeve at 1mm from the edge as a guide for determining how far into the tube I wanted to cut the groove.
The ball cutter head is 6mm so if you align the mark with the edge of the tube, then the center of the groove ends up at 4mm from the edge. With original CG ankle cups this distance is 3.5mm.
Use a bootfoot without sleeve and make sure the sole is firmly screwed against the feet. The other bootfoot can remain on the leg, but it is better to remove the bootsleeve and any clothing that covers the ankle cup.
Before cutting, decide how far up the tube the groove should be:
If the groove is closer to the edge of the tube the ankle ball will fit more loose but the range of motion of the ankle joint will be greater, if the groove is further away from the edge the ball will fit more tightly (and the cup will hold its shape better so it will remain tight for longer !) but the ankle joint can not bend as much.
Cut the groove by gently rolling the rotating head along the inside of the tube, two or three complete turns should be enough.
After cutting the inside groove use the cutter head to chamfer the inner edge of the tube.
- to relieve the strain when inserting the oversized ankle ball and
- as a guide for popping out the ankle stem in a tilting motion.
You can use either the small (2.3mm) cutter head or a small round file to make the cut-out, make sure the cut-out has a smooth round shape without sharp angles.
If the ball won't go in, use the large cutter head to chamfer the edge of the cup a little more and test fit again.
If the ball fits too tight or doesn't 'pop' into the groove, slightly widen the inside groove and test fit again.
If the ball fits loose, cut the edge of the tube just beyond the inside groove and start over.
This distance determines the length of the newly made cup, so measure from the sole of the foot on the new cup and mark the right distance on the tube.
If you are making a pair of ankle cups, mark the first one 13mm from the edge and determine the height of the second one as described above.
Remove the bootfoot from the tube and cut the cup off the tube at the mark.
Use either a saw, a tube cutter or a knife to cut the tube. If you use a knife do not try to force the knife straight through, but make the tube roll by moving the knife back and forth along the marked line whilst applying moderate pressure. This way of cutting is both more accurate and much more safe.
Insert the peg into the top of the ankle cup and make two pencil marks, one at the edge of the cup and one 12mm above the edge of the cup.
After marking the peg, pull the peg out of the ankle cup again.
Cut the peg from the rod at the upper mark.
The tape should protect this part of the peg from getting sanded down.
Measure the width of the peg, it should be about 4.8mm wide. The width should be sanded down to 4.0mm. Sand the first side down until the total width is 4.4mm, then sand the opposite side down until the total width is 4.0mm. Sand each side right up to the masking tape, but try to create a slight taper: a total width of about 4.2mm near the masking tape helps to fit the ankle firmly to the leg.
Repeat the above for the remaining sides.
Apply water to the file and the surface while sanding to avoid airborne plastic dust.
Use a thin square file to file the locking groove in each side.
Using a sharp knife, cut the tip to a pointy taper: 3.0mm wide at the tip to 4.0mm wide at 4.0mm from the tip.
Save the snips of plastic cut from the tip, these are useful for filling the gaps between the square rod and the inside of the tube later on.
Use the nail file to clean up any sharp edges, etc.
If inserting the peg into the leg takes too much force, then it needs some more sanding, look closely at the gaps between the peg and the hole in the leg to see which side is too wide. Sand this side some more and test fit again.
Remove the peg from the leg and fit it to the newly made cup (which still has the bootfoot fitted), the lower edge of the locking groove in the peg should be exactly 6mm above the top of the cup.
Pop the bootfoot out of the new ankle cup.
Use the snips of plastic that resulted from cutting the pointy tip to fill the gaps between the peg and the curved inside of the tube. This adds more surface for the glue and increases capilary action to draw the glue into the gaps.
Glue the mounting peg into the cup using Plastruct Plastic Weld glue or a similar type of glue that melts plastic. Note that most types of Superglue (Cyanoacrylate) are not suitable because these types of glue can not withstand shear stresses.
Apply the glue sparingly and from the top of the ankle cup only to avoid damaging the inside of the cup.
Let the glue cure for at least a day, after that the ankle cup is ready for use.
comparison of new and original v1.5 ankle cup
CG v1.5 ankle cup dimensions.
White tube (Plastruct TB12 Butyrate): 13mm tall (9.5mm diameter) centerline inner groove at about 3.5mm from the lower edge.
Gray peg (Plastruct ST06 ABS): 18mm tall (6mm inside the white tube, 12mm outside; 4.0mm wide, 4.0mm deep) 2.0mm wide locking groove at 6.0mm from the edge of the tube, top 3.0mm chamfered. The locking groove is cut in all four sides of the peg.
The new cup is slightly smaller (0.5mm) in diameter than the original cup, this allows for fitting some thin styrene tubing around it which is useful for painting as most types of paint won't adhere well to this type of plastic.
If you do want to paint the cup itself, model enamel paints work best.
I also made a separate ankle cup that I used for reference when making ankle cups and for test-fitting ankle balls.