[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?

[CROSSHATCH]

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]

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]

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

[skmetal7]

the weird thing is, I only get that finish with the 3 flute uncoated carbide endmill. ive tried facing with a larger hss endmill and the finish is better. but i was just wondering if i could get a better finish with this endmill if i ever do a pocket and this is the largest endmill i can use

and yeah i have to take apart my mill and readjust everything, what are good maintenance hours? oh and i have no gibs on my z axis, i use linear rails on the column.

one more thing, since you can remove the spindle from the dovetail part that attaches to the column, how do you square it up when you reattach it to the spindle? i have trammed my z axis, BUT when i move the z up and down, i can see the needle move on my dial indicator a few thousandths over about 2 in. in the x direction. (you cant get at the bolts to adjust it when its on the column)

[Wood Chuck 59]

There are 4 main places to start with. My first impression is thet your machine itself is not ridged enough. with a light duty machine, a light finish cut may not keep enough pressure on the part to prevent chatter. The next thing to look for is the spindle. If you have an indicator, set it up & check for side to side, & up & down movement. the spindle may allow too much movement for a good finish. The most important things I suspect is that your cutter is not truely sharp. Get a good magnifying glass (5 - 10 X) and look at the cutting edge. It should only make contact on the corner The center needs relief. It also needs relief in the back of the cut, so that it isn't dragging along once it has made its cut. Using the magnifying glass, look for a shiny flat spot on the bottom corner. Cutting speeds & feeds are crucial to a good finish. high RPM's & low feedrate = good surface finish, as long as everything else is good. HSS is probably better than carbide for aluminum. A good cutting fluid is also important.WD-40 is not a cutting fluid.
Chuck

[sansbury]

the weird thing is, I only get that finish with the 3 flute uncoated carbide endmill. ive tried facing with a larger hss endmill and the finish is better. but i was just wondering if i could get a better finish with this endmill if i ever do a pocket and this is the largest endmill i can use

Have you tried an HSS or Cobalt mill the same diameter? Carbide tends to like a heavier cut which doesn't always work the way you want on these little machines. I avoid it on my X2 for that reason.

Also, some machines and some tooling combos just don't get along well. Whether it just happens to hit a certain harmonic frequency or what, who knows, but the results speak for themselves. Sort of like people who say WD-40 isn't a cutting fluid--I have full flood with soluble oil which works great but for a quick job WD is often more than enough.

[tikka308]

I'd second what sansbury suggested - try HSS. Although it's not as strong as carbide, it actually has a sharper edge, which is better for aluminum.

[HawkJET]

You can see in the photo after sanding, there are consistant cutter marks about 80% the cutter diameter. You say that it is a 1/4" cutter so the cutter marks are about .2" apart. This is the pitch of most ball screws and could indicate a need to tighten the gibs in the x axis. If there is any runout in the leadscrew, and the gibs are too loose, the leadscrew can be lifting the table once each revolution.

An explanation as to why it is worse with this cutter could be that smaller cutters will plunge easier and contrary to the previous post, carbide E/Ms are sharper than HSS (because they are harder and sharpened with a diamond grinder so have a better surface finish).