Another Surface Finish Question

[skmetal7]

x2 mill cnc'd
new 1/4" solid carbide em .002" finish pass DOC (.01" rough DOC)
4600 rpm (max rpm) 10 IPM (on final pass)
6061-t6 aluminum

and i get this surface finish.... pics (one pic is right after the final pass, 2nd is after light sanding)

my mill is trammed. i cant feel any "humps" between passes. am i running too slow? Ive used wd-40 as a cutting fluid. my sfm is ~300 so i guess its lower than recommended for al. but would that give me these circles?

[SpeedsCustom]

Those are some light cuts your taking and your still getting that? Up your IPM and try something other then wd-40.


-Jason

[skmetal7]

yea i like to do many quick passes for roughing, then take a slow finish pass. maybe the aluminum is galling because its rubbing, that's all i can think of

[MRM RCModels]

Originally Posted by skmetal7 x2 mill cnc'd new 1/4" solid carbide em .002" finish pass DOC (.01" rough DOC) 4600 rpm (max rpm) 10 IPM (on final pass) 6061-t6 aluminum and i get this surface finish.... pics (one pic is right after the final pass, 2nd is after light sanding) my mill is trammed. i cant feel any "humps" between passes. am i running too slow? Ive used wd-40 as a cutting fluid. my sfm is ~300 so i guess its lower than recommended for al. but would that give me these circles?

You're cutting to slow. For face milling you want the cutting tool to be at least 1.5 times the size of the part. Try increasing the size of the cutter, and make multiple (lighter) cuts at faster speeds. I use a 2in face mill feeding at 20 IPM with four 0.0005in passes. Get an extremely smooth finish. Even with 20% overlap.

[bertmiller]

to me it looks like there is something wrong with your table.
try to loosen or tighten it.

[BobWarfield]

For a 2 flute, your feedrate is what my feed/speed calculator recommends. Go twice as fast with a 4 flute or 20 IPM. That kind of job you can use a 4 flute, BTW, and it's helpful.

Looks to me like things are bouncing. There are periodicities in the pattern. It's almost like something creates a dwell or change in feedrate every so often.

Check your gibbs and make sure they are tight on all axes.

Are you running ballscrews? Check the preload.

There may be enough play in your spindle bearings, quill, or z-gibbs for the cutter to bounce up and down slightly.

Cheers,

BW

[fretsman]

Originally Posted by bertmiller to me it looks like there is something wrong with your table. try to loosen or tighten it.

Agreed, either the x or y axis table or screw has "hump" in it or something to that extent. Looks like it's "bouncing".

Maybe put an indicator on your headstock and run it across the table (both ways X and Y directions) to see if you can see any errors.

Dave

EDIT: looks like Bob beat me by a minute - lol!

[sansbury]

I got results like this on my X2 when the spindle was not tightened up enough. Is there any kind of grinding or rattling noise when the spindle is running? If you're not cutting all you should hear is the motor. I'm assuming based on the RPM that you are running a belt drive.

[Regnar]

Have you tried facing the parts in the other direction. If you are going using the x axis try the y axis next time. This will rule out if its the Head or the particular axis. Along with all the other suggestions you should also check that lead screw to make sure it is parrel to the table. If it is canted it will lift up on the table every time you make one full revolution, also if you have problems when you tighten down the gibs this might be your solution.

[Teyber12]

I don't have a x2 but this screams TRAM to me... anyone else?

[SScnc]

Well I'll stick my .02 cents in here also. I think if it were tram it would be more consistent but as Bob W pointed out it's not exactly. I think it's the Z gib not tight and the spindle head is "bouncing".

I'm curious to find out what skmetal7 finds out.

[philbur]

I vote for lack of spindle bearing preload.

Phil