[tejanoiniowa]

This is my 1st post so please be patient I am having flatness issues. I have 6" diameter stainless steel blank discs. They are about .25" thick. My finish thickness is .19". So that leaves me about .03" per side to face off. I have to maintain .0005" flatness and a 32 finish. I made a fixture plate to bolt them on to and the part is flat until I unbolt the part (bolts are screwed in from the back side of the fixture plate). I even tried to torque the part down but no luck. I also tried some aluminum pie jaws with the chuck pressure turned down pretty low (100 psi). I think any lower the part might fly out. I am having the same issue with the pie jaws. I'm using a test indicator and I zeroed it out on the edge(0 degree side) and ran it from the edge to the center of the part it went from 0 to -.002 then I ran it from the center to the opposite side(180 degree side) and it went from -.002 to 0. Then when I measure the 90 degrees to 270 degree side I'll get something like .002 on the outside to -.002 in the center to .004 in the opposite side. So I know when if bolt or chuck on the part it distorts the part.
I could get them lapped but I have to keep the cost down! Any tips or ideas would be much appreciated.

[zero_divide]

Facemillin thin materials is no joke.
Don't clamp them down.
Hold them down with least amount is side pressure as you can.

Make sure you have support underneath.
Use Very Very sharp insert with minimal radius....
When clamping down set up an indicator to see whether part moved on you.

Also very important: make sure you don't distort pieces when clamping them.
Don't even tap them with a mallet. Make sure there is no stress before machining.
After each rough pass do a cleanup as your part moves as you remove material.

When all fails send them out for grinding.
Half a thou is very hard to keep in this case.

[tejanoiniowa]

@Zero_divide thanl you for the reply. I will try that.