Help with turned spline

[Dgriff]

Im new to this forum, but have been with the emastercam forum for some time. I recently changed jobs and have been given a task of acheiving a 4 to 6 micron finish off of the machine. I am not having success at all to this point. I am in the process of systematically eliminating all variables one at a time both with the software (Mastercam V9.1) and the machine. Here are my parameters: Running a Haas SL20-APL Belt Drive. Trying to machine a parabolic spline and acheive a high surface quality (no second op polishing, just thin film coating after machining). Current insert is an uncoated solid carbide w/ .015 nose radius. Finish pass is .002 material removal at all imaginable feeds and speeds. I guess my question is what tools/parameters does Mastercam have bulit in to ensure that my posted code is optimal and all other issues are machine related. Should I convert the spline to arcs or leave the code linear and make changes in the machine parameters. Please bear in mind that I have VERY minimal lathe experience. I have been a Mastercam mill guy for 5 years, but not lathe experience until two weeks ago. Any advice at all would be greatly appreciated. I have officially hit the the freaking wall.

[HuFlungDung]

What kind of material are you machining?

Is this an optical surface? What kind of surface quality can you achieve when facing a flat? There might be some vibration issues with the machine to analyze and solve.

I think you should go with interpolated arcs, as you will get smoother transitions.

[Dgriff]

We have machined both 6061 and 7075 aluminum with better results in the 7075. Yes I am machining an optical suface and trying to avoid second op polishing if possible. I would consider polishing in the spindle if I can acheive the optical surface with not too much added cycle time. I agree with you that there may be some machine issues to resolve. I just want to make sure I am producing the best possible code to eliminate one of the variables. I am looking into the slab that the machine is sitting on right now. We may rip up the floor and put in a 36in slab for this particular machine. My other question is, is there a drawing tool in Mastercam to create a true parabolic spline? Right now I am creating the geometry in Solid works and transfering to Mastercam.

[HuFlungDung]

Most likely you should research diamond turning tools for aluminum. I believe this is what "they" are using
I wonder what the proclaimed spindle runout of your lathe would be and whether it is perfectly adjusted to achieve it? Surface roughness is partly due to tool scallop, but if the spindle is floating a bit on the bearings, it is going to be next to impossible to hit your requirement.

Someone who knows will have to tell you if Mastercam has a parabola drawing function, I don't know.

I would likely find a formula somewhere, plot a few accurate points and draw a spline through them. I don't really know how close the interpolated curve (made of arcs) will be, but that is most likely all that your cnc can cut anyways.

[cadcam]

are you useing the setting in the finish for Micro_in to set for this finish.
are you filtering the Spline path?

As for splines we have Parametric and Nurbs for Spline control. these should work fine.
Are you programming from the Solid or are you creating a slice for your profile or again are you taking the 3d wire and Squashing it?