Need help boring zirconium

[cncprogrammer]

I am trying to stabilize the finish bore in a medical part we machine. I have a very tight tolerance and seem to hit it by chance with little repeatability. I am machining an I.D. that is tapered (12/14 morse taper) I have 2 minutes of tolerance on the included angle which translates into about .00018" per side at .700" length. I am using a practically brand new lathe that performs well. We routinely machine the same taper, but with 5 minutes of tolerance, in cobalt chrome. I am running against an air gauge and a CMM, which btw coincide with one another. Any ideas? Thanks in advance.

 

[jbel]

Can you give more info on inserts used, coolant or air blow off, speeds and feeds used, etc....

 

[Don039]

The first and most important question you need to answer is "Are ytou sure this isn't a gage R&R problem?" What is your gage R&R?".

With such a tight tolerance, both geometry (roundness and trueness of taper) have a great effect on the ability to hold tolerance. Keep in mind that the geometry odf the hole ideally should not exceed 10% of the tolerance. With such a tight tolerance you should have readings taken with a circular geometry measurement machine to get an idea of what several parts look like.

Also, if you can measure the diameter at one or two levels, you should check to see that the diameter variation is within a reasonable tolerance. 10% or less if possible.

The old fshioned way to do this is to compare the tpare against a master by "bluing" it. For the bluing, you do not use layout blue, but Prussian Blue from a paint store wiped very thin and consistently on the plug and then the plug is applied to toe internal taper.

What resolution (finest increment) does your air gage have? If you want a 10% R&R, your gage needs to seaolve between 2 & 3% of the tolerance. (This has to do with "the way the "numbers work".