Can someone post pix of a tac-one body?

[Nobody]

This is a Tac body.

You cleaned a tac-one body, not reshape it.

[luke]

I had my machinist try to mill out the left side of a tac body to match the right side (to use a reverse valve). Even with a fine bit on high speed taking super light passes, the body cracked along the line in the top. The material there is just super thin. So we ended up just cutting off the entire back of the body.

Live and learn. Don't try to shape tac bodies.

I'll rephrase for Nobody.

I have successfully machined the area around the valve assembly on the left side without damaging the body. I'm not sure what your machinist did, but it actually sounds like he used a large 2 flute endmill which could cause the damage you suggest. I use a 1/2" 3 flute carbide end mill to machine that area.

[bowcycle]

I use a 1/2" 3 flute carbide end mill to machine that area.

Did you mill off the Weaver rails first?
I asked him to leave the rails intact. I think the problem was going between the different thicknesses of material.

[luke]

I doubt that wouldn't matter. I won't pretend to know for sure what he did, but if I were to wager a guess I would say he likely used a large 3/4" or 1" end mill and when he made the initial it grabbed the part and broke it. The tail end is very flimsy and is a tricky cut. Unfortunately sometimes this happens when customizing parts. There's always a risk of destroying parts and on occasion stuff gets ate up before you learn the nuisances of modifying a part. Sometimes you dont know what to expect until you do it, that just goes with the territory.