# Cutting Cir Clip grooves in Pistons



## JPL (Jan 12, 2019)

Hi all...

Looking for the method you use to cut the groove in the wrist pin area in a piston for the cir clips. I have avoided this in many of my designs but I now need to do it. The groove will be approximately .02" wide , .02" deep, inside a .177" dia hole.

Tnx in advance.


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## cheepo45 (Jan 12, 2019)

Make a mandrel to hold your piston by the pin hole in your lathe.
Leave enough room to cut the groove.
Make or purchase a .020 wide internal groove tool that will fit in the pin hole.
 Scott


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## tornitore45 (Jan 14, 2019)

Making the tool
Take a piece of drill rod 
Turn down a diameter equal to the wrist pin minus 0.030
Offset 0.020 and turn eccentric 0.050 wide and starting 0.020 from the end, keep turning until you are cutting on the opposite side
Remove one half of the machined section 0.010 below the center.
Harden, no temper needed for such a small cutter to be used in alum

What you have is a 1/2 moon seen from the front, there is a hanging beak 0.020 axially long and o.o40 radially.
The small (-0.030) diameter will provide the back clearance and the milling below the center will result in a front rake.

It will take you less to make the cutter than it took me to describe it.


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