Aluminum Finish on an X3

[pzzamakr1980]

Sieg X3
Modified Spindle 6000rpm
17/64 3 Flute GW Schultz Aluminum Specific Carbide Endmill
Flood Coolant, Green Mist Coolant in High Concentration
.1 DOC, 50% Stepover at Most, .005 Finish Pass, 25ipm
Import ER20 Collet and Tormach Collet Holder
Bolted To Fixture Plate- Fixture Plate Held In Vise
.0005 Total Measured Runout/Vibration

The issue that I am having is this, I am getting a poor surface finish on any cut I make. Be it a pocket or a contour. The coolant is doing a pretty darn good job of keeping the cutting area clean. The poor finish looks like fine lines that run vertically on the sides of the pocket or contour, its a very slight scalloping. It occurs on all sides of the pocket and the sides of the contour, regardless of direction, so I dont believe it is caused by head misalignment.

Is this caused by the runout/vibration. I say runout/vibration because just turning the spindle by hand, there is no detectable runout according to my .0005 Last Word Indicator. At 6000rpm, the needle will swing a tiny bit, so that is why I say runout/vibration.

Any suggestions. Thx

[mc_n_g]

.005 might be a little light. I would try to leave a little more say .02 to .03 for the final at least. You also don't say if you are climb milling or not. This will have a big difference on the finish. How new is the finishing end mill? Is it a dedicated finishing mill and not the one you used for roughing? Is it a long end mill? This will tend to vibrate or skip if long and light light cuts. Is this finish with all end mills or just this one? What type of aluminum? Why the odd size of end mill? Is this a resharp?
There are a lot of factors which can play into this.

[widgitmaster]

It sounds like a rigidity problem!
Try putting as large a diameter pin in the spindle as you can, and let it stick out as long as at can. Then place an indicator up close to the spindle nose, and set it to zero. Then with your hand try to move or bend the pin! This will show any looseness in the machine, and help you adjust / tighten it up!
Also, a cheap or reground end mill can also produce a similar finish, as not all flutes are sharpened equally or concentric.

Hope this helps!
Widgit

[pzzamakr1980]

Okay, I bumped up the finishing pass to .015. Climb Milling. Its the same endmill I use for roughing. Its a general purpose aluminum cutter. The endmills LOC is .75. Its chucked up to just above the flutes. Finish with all end mills. I noticed the same problem when I was cutting with a 2flute 1/2in held in a end mill holder. 6061-T6. Odd size because they had em cheap, and they were brand new, but just odd size so didnt sell. The finish was the same on the first hole as on the last.

Sadly, I dont believe there is any way I can tighten up the spindle, which is the only place I would think would move with this light a cut. There is a discussion going on about making the x3's column more rigid, but I havent attempted it yet, and with this cut being so light I don't think it would be a factor.

Should I increase the finishing pass feedrate. There is the option for it under mastercam for pocketing, but not for contouring.

[Pressfit]

Sieg X3

"At 6000rpm, the needle will swing a tiny bit, so that is why I say runout/vibration."

Any suggestions. Thx

Please remind me to never loan you my tools.

[widgitmaster]

Increasing the feed rate increases the roughness or resolution between the high & low spots, try increasing RPM and decreasing feed just for a .01 pass. It's like cutting a thread, the more TPI the finer the surface!

Also, end play in screw or bearings can give a chatter like finish.

Widgit

[pzzamakr1980]

Hardy har har. I guess if I was doing something wrong with my tools, I would probably be breaking the little 1/16 bits I use. If you dont have something constructive to offer, dont say anything at all. I'm just kidding... I actually thought the remark was kinda funny. Only kinda though....

But seriously, when the Indicator moves between the the hash marks .0005 what else do you call it besides runout.

Thank you Widgit, I will give that a try. Thats what I thought you were supposed to do for a finish pass, but someone else had told me that you should increase the feed rate, which I thought was contrary to common sense, so I ignored him. In all fairness, I probably just misunderstood him in the first place since he does this stuff for a living.

[Pressfit]

Sorry, but I couldnt resist. Only someone that really does it for a living would truly appreciate the tool thing. I didnt think you were actually bearing the indicator on a rotating spindle though it sounded like it.

Anyway, the others have told you correct. It could be anything but likely a rigidity problem. Perform a test...go to a large end mill, say.750 dia or something like that and make cuts. If the same thing exists then its either the spindle or the holder. Then try a solid endmill holder with the 3/4". If still a problem then you can probably conclude its the spindle.

[pzzamakr1980]

Oh, I didnt even get that part. I didnt understand why you were giving me crap until you mentioned holding the indicator in the spindle. LOL. Now I understand, and its even funnier. I just went back and read my original post and yeah, it does sound like I was holding the indicator in the spindle.

Okay, I have used a 1/2in with a solid end mill holder and I got the same finish. I was only taking .005 on the finishing pass, so I will increase the finishing pass material and see if that helps. I'm thinking that it is the spindle, either because of vibration or runout.

Right now the spindle is driven by a gear, which I've heard can contribute to poor finish. Is this the case? I intended to replace that with a belt drive at the spindle to lessen gear noise anyways, and this might be another good reason to do so.

Also, I was looking at Vibrafree's website, and was curious if the mirror finish they are getting on their parts is typical of good cnc machine's only, or if the benchtop variety is able to make as nice a finish.

[Pressfit]

Oh heck yes. A tight toothed belt and pulley system is going to be better than a gear drive first of all. With gears, you have to have a small amount of backlash for lubrication between the teeth. Which is going to bounce back and forth as the cutter goes from load, to no load. It gets REALLY bad when you are using a radius-endmill because the flutes are pretty much vertical with the centerline of the cutter (no helix).

[pzzamakr1980]

Okay awesome, then I will do that this week while I wait for replacement metal to come in. Thank you Press.

Also, I was wondering if anybody has a good example of how a slot finish or pocket finish is supposed to look. I know Eric's work is always shiney and beautiful, but I was curious if its the same on the slots/contours as it is on the face milling. Is this the case Eric, or are the finishes as smooth as they look?

[fpworks]

I noticed you are using a G.W. Schultz endmill, which we use from time to time. By chance is that a GWA series? If so, how much use does it have and have you ever used it for cutting anything other than aluminum?