Hex Stock = not holding diameter tol's?

[PoiToi]

Hi all, I have a citizen L20 (V) that's somewhat new to our shop and I am haivng a funky issue rear it's head the last few days.

I am running 1/4" hex leadloy stock and it doesn't want to hold the half thou total tolerance on one of the diameters. I am confused, because the roundness on *every* part is within .0002", but one part to the next the diameter will vary (sometimes), to almost a thou and a half.

I've tried slowing down the spindle speed, and the feed, to no avail.
anyone have any insight on what could be causing this??
thanks!!

[glenthemann]

Well, you mention 1/4" hex, the first thing I was gonna say was guide bushing tightness but since you say its completely round, then I am guessing that this diameter you speak of is one of the smaller ones? How is the roundness, or I should say the concentricity of this diameter compared to the others?

Are you using righthand or lefthand tooling to cut said diameter? Sounds to me like the material is pushing away from the cutter. If feeds and speeds havnt helped then maybe you should look at the tooling youre using? If its not razor sharp that could be a reason why, then again I dont know the job or what the part looks like so Im really just guessing here. Forgive me if I seem like I am just going over what you probably already tried, this would just be my next route of investigation.

Glen

[hacdlux]

two suggestions:
check the center height of the tool,

if you enough land in your gb rough/finish see if it eliminates the deflection

i just had a part where i had to rough and finish in .500 segments for 7 inches of part in order to get surface finish down to my stds

good luck