micro boring 440c = finish problems

[Fala_Man]

I am turning 440c parts that have a .08 +/-.002 bore that is .2161 +/-.0004 deep. There is a .031 hole thru at the bottom of the bore.

The finish call out is 16 or better on the bottom bore face. I know 440c sucks and 440f is a great option, only 440f isn't readily available in 5/16 diam.

Currently I am turning these parts on a miyano turning center with Blazer coolant. Using Internal Tool .05x.22 boring bar at 2500rpm .0003ipm.

It is has always been an issue and the problem is intermittent...here in lies the other issue with finish and that it will run smoothly for awhile(200-1000 pcs then just not get finish anymore. Even first cut with a new tool.

Any idea's to get finish would be greatly appreciated.


Thanx

[Big Daddy]

Try and richin up the Blazer to at least 16% mix minumun first of all. While your doing that make sure that thing is really warmed up! But there are a couple of tricks you can do to the tool. I've faced that delemma on Miyano's. I put on my old man glasses (pull down magnifiers) and very carefully using an very smooth Arkansas hard stone starting from the heal of the tool stone upwards applying a very tiny radius. maybe all of about .0003 max and thats on a new or just re-ground tool. I do this with the tool out of the machine and in my hand. Then re-load and make small test cuts (.005 deep max) on the face of a blank round make sure you have no tit left. none... zip. not even a hint of a tit! It sounds like you nailed the rpm & ipm so I don't think thats your problem. Then the other thing is how deep is your finish pass,,, too deep,,, crappy finish,,, too shallow,,, too fast tool wear.. then crappy finish. And you'll get the same effect with too many spring passes too. I like to work stuff like that with a .002 or .003 finish pass max. You'll get too much chip build up in your bore with anything bigger then that. Even .003 might be too much. Then there is only one trick left but I dont think you'll need to use it. but keep that miyano warmed up and the room at 68* or as close as possible. They really dont like temp changes at all in close tolerance work. I think you'll find if the temp changes,, they change. I hope this helps good luck.