Cy Girl - Cutting down ZC ankle cups

ZC offers spare ankle cups with its Eve figures, these won't fit Cool Girls without modification but can be useful anyway.
One problem is that the spare ankles are 20mm tall, CG ankles are 15mm tall and so are the regular ZC ankles. 20mm ankles don't look right on CG or ZC girls, so it would be nice to cut the ankles down.
However, cutting the ZC ankles down looks easier than it actually is for two reasons, the first one being that the material is very tough, the second one is that you're likely to run into air pockets inside the plastic which will ruin the strength of the shortened ankle.

Tools and materials needed:

Further useful tools:

preparing the ankle for cutting
Mark a line at 5mm from the top of the cylindrical part of the ankle, you can use a pencil or cut a 5mm wide strip of masking tape and wrap that around the top of the ankle.
If you have a variable speed power tool, wrap some masking tape around the ankle peg, then fit the peg of the ankle into the chuck.
applying saw blade to ankle
Using the saw blade and running the power tool at its lowest speed, cut a groove about 2mm (0.08in) deep around the ankle.
If you don't have a power tool, just cut the groove along the line, rotating the ankle by small steps.
cutting down a ZC ankle step 3
Remove the ankle from the power tool, remove the masking tape and use the saw blade to make cuts along the sides of the peg.
Carefully saw exactly down to the depth of the groove.
cutting down a ZC ankle step 4
Ankle cup with saw cuts down to the groove, side view and top view (right).
cutting down a ZC ankle step 5
Using the saw, deepen the groove until it reaches the sides of the peg.
Remove but do not discard the pieces on the top sides of the ankle.
cut down ZC ankle with air pocket exposed
Uhoh: an air pocket ! I ran into this one before I cut down all four sides of the top and already cut open one side to expose the entire pocket.
Carefully inspect the newly exposed area for air pockets by holding the ankle against a bright light source.
If you see any translucent areas, cut open one side and refer to the Repairing air pockets section below.
Otherwise, using a sharp knife, trim the newly exposed sides of the peg to the exact same size as the peg, cut 5mm off the top of the peg and round off the top.
Using the knife or the nail file, make the top of the cup smooth so the gap between the cup and the leg is small and even.
Then your shortened ZC ankle is ready.

Repairing air pockets

Tools and materials needed:

reinforceing a ZC ankle
On the left, a look inside a ZC ankle peg, note the small hole. Below the ankle is a length of threaded rod already cut to size.
On the right a ZC ankle with the threaded rod partly screwed in, the slot in the tip of the wire is just visible.
Fixing an air pocket requires two steps:

First the air pocket needs to be filled with plastic then the ankle needs to be reinforced with a piece of threaded rod.
Cut one side of the air pocket open. Cut some leftover pieces of plastic that were cut off the ankle before into small slices about as tall as the air pocket. Apply some glue to a each piece and insert it into the air pocket, align the piece lengthwise in the ankle peg. Stuff as many of these pieces into the air pocket as possible. Apply some more glue and let the ankle cure for at least a week.
reinforcing ZC ankle, diagram
Measurements for reinforcing a ZC ankle cup.
The brown circle represents the air pocket, the orange dome represents the inside of the cup with the hole in the center.
After the glue has cured the ankle can be reinforced with a piece of threaded rod.
First measure the distance from top of the air pocket to the lower rim of the ankle cup, adding 5mm (0.2in) to this number gives D the minimum depth to drill (measured from the rim of the ankle cup). Fit the drill into the pin vise and mark distance D from the tip of the drill with some masking tape.
Subtracting 14.2mm (0.56in, the depth of the cup) from D gives L the length the piece threaded rod needs to have.
If you look into the cup you can see a small hole in the top of the cup, place the tip of the drill bit in this hole and carefully drill straight through the top of the ankle and into the peg until you've reached depth D.
threaded rod with slot
Piece of threaded rod with slot cut in righthand tip.
The nut is only used for restoring the thread after cutting and can be removed after running it along the thread from tip to tip.
Cut a piece of threaded rod, slightly chamfer one end and cut a small slot into the tip on the other end. Insert the chamfered end into the hole inside the ankle, insert the blade of the screwdriver into the slot in the wire and gently screw the wire into the hole, it should not stick out of the small hole that was originally in the cup.
reinforced ZC ankles
On the left, a look inside a ZC ankle peg with the threaded rod screwed completely in.
On the right a reinforced ZC ankle with the peg modified for CG v2 legs, the scar where the air pocket was filled with bits of plastic is just visible.
Now the ankle is strong enough to be used on Cool Girl legs.
Due to the large forces required I would recommend against trying to fit a repaired ankle to a ZC leg.

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