The folks at Wilson Combat were kind enough to share the specs on cutting frame tangs to fit their grip safety with me and I wanted to post the information for others to use. Wilson makes a hardened steel fixture used for modifying the frame tangs by hand but I wanted to make a fixture that would allow me to cut the frame tangs using a rotary table on the milling machine. For those of you interested in doing the same thing, here are the details.
Many grip safeties require that the frame tangs be cut to a .250 or .220 radius with the thumb safety hole as the center of that circle. The Wilson thumb safety uses a compound radius with respect to the thumb safety hole. That means that the radius distance changes at different points on the arc. This makes cutting the frame on a machine a challenging job if you use the thumb safety pin as the center of the arc.
The good news is that the Wilson grip safety does use a radius with a constant length, it's just that the thumb safety pin is not the center. That center is located .031 down and .016 forward of the thumb safety pin center and the radius is .223:
Wilson grip safety frame tangs referencing the thumb safety hole:
Radius = .223
.031 down
.016 forward from the center of the thumb safety pin
I posted a drawing here:
Spec file
I just received this information yesterday and haven't built a fixture yet but here is what I plan to do:
Put a rotary table on mill and center it under the quill. Attach a plate to the rotary table, move the entire mil table the distances listed above, drill a 5/32 hole in the plate to reference the thumb safety pin hole and then drill and tap a couple of holes to use for clamping the pistol frame to the plate.
To use the fixture, the rotary table is set up on the mill centered under the quill and the frame is clamped to the plate on the rotary table using the offset hole for the thumb safety to locate it.
I use a similar method to cut frames for .250 and .220 radius grip safeties but the thumb safety hole is centered on the rotary table since they have a constant radius.
To get a good close fit without a gap between the frame and the thumb safety, the frame tangs are left slightly oversized and final fitting is done by hand but cutting them on the mill reduces the amount of fitting necessary. The same method is probably necessary to fit a Wilson grip safety too.
I will post updates as soon as my next project requiring a Wilson grip safety comes up.
Many thanks go to Wilson Combat for providing this information!
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