[Bird_E]

Hello all,
I have completed my conversion of my X3 desktop mill to CNC and all is working great except for some surface finish issues. When ever I mill a profile of part the surface finish on the side wall leaves chatter marks. I have tried diffrent speeds and feeds and cutters, climb or conventional milling, but no luck. I believe the problem is vibration in the head. I believe 90% of the vibration is comming from the belt that connects to the motor. If I tighten the belt up it gets alot worse, if I loosen it, it does get better to a point. Does anyone know what I can do to reduce the vibration/ improve surface finish?

Also, does this sound reasonable: 1/8 4 flute cutter, 2000rpm (that is my max), .050 depth of cut only taking .010 of the side wall running at 10ipm.

THanks!
Bob

[cncadmin]

I have the same problem I attributed it to the machine not being heavy enough. But you got me thinking now, I'm in the process of looking for a better motor. I wonder if a V-belt would run smoother?

[ViperTX]

So, 2 potential causes...no coolant and vibration from multiple sources. If tightening the belt causes problems...it could be problems with the bearings and problems with the belt...you can eliminate the belt by moving to the....darn forgot their name....I think poly V belts. You could also look at doing a roughing cut and then a finish cut.

[anoel]

Backlash in the gears in the head maybe? Z Gib Tight? (I know on my micro-mill I'll get hellish amounts of chatter in the head or the table if the gibs aren't pretty darned snug.)

[cncadmin]

I use coolant and still get chatter, I did loosen the backlash in the spindle bearing a bit, but once they get hot they should lock up tighter? The gear may have to much play in them, might be worth getting hardened gears? I will take the extra effor and lap my gibs, that will allow tighen up them.

[Bird_E]

Yes,
I have tried with and without coolant and get the same result. The gears do have some backlash, that may explain why I tend to get a little better finish when the load on the spindle is higher and more consistent.
I also tried to tighten up the spindle bearing a little, but then they get too hot, so I backed them off.
I also installed a bushing on the drawbar so that when I tighten it up it doesn't tighten off center.
It didn't help that much. But it makes me feel better!
Bob

[ViperTX]

anyone measured the runout?

[Bird_E]

My runout seems to be .0005 -.001
Bob

[JFettig]

I personally dont like v-belts, I converted mine from v-belts to GT2 metric timing belts and its very quiet and works very well.

If in aluminum, 4fl end mill taking .0005" chip load at 2000rpm you should be running at 4IPM.

Are you climb milling or conventional milling? if you have non loaded screws, you should not climb mill.

Jon

[Bird_E]

The motor belt is a timming belt and not a V-belt.
I am running preloaded ball screws, the results are the same wether I'm climb milling or conventional milling
Bob

[JFettig]

leave the timing belt, tha shouldnt be the problem.

what kind of end mill is it your cutting with? carbide or hss? what material?

The feeds I gave you are for aluminum. your running about a .0015" chip load which is outrageous if taking a regular cut.

Jon

[Bird_E]

Running 4 flute carbide, 7075 AL. I'm only taking a .010 finish cut, with a z step of .050.
Bob

[Kookaburra]

I had a similar issue on mine. When I checked in to it I found that the pitch on the motor pulley did not quite match the timing belt. As there were not any numbers on the belt I decided to just get two new pulleys and poly belt that I knew were a pitch match. Another thing I found when I pulled it off was that the large pulley shaft was rubbing on the inside of the clearance slot on the motor adjustment plate, I opened up the slot to ensure that when I tensioned the belt there was no way it could rub any more.

Hope you get it sorted.

[steveg]

Bird have you tried either a 2 or 3 flute cutter you "might"
be getting a bit of built-up or clogging of aluminum in the
flutes of your endmill, also are you just touching the side of the cutter or the end as well?