1100M Spontaneous Chatter

[johnnydoejr]

I've read all the existing chatter posts, but haven't seen any quite like what I'm experiencing with my Tormach 1100M machine. I get horrible harmonic squealing from the machine in X, Y, or compound movements. No reasonable manipulation of feed rates, DOC, WOC, RPM, etc. will do away with it. However, the first few cuts of a run are usually fine and then the chatter develops out of nowhere despite the cut parameters remaining the same. This typically seems to coincide with a directional change. Once it's started, it continues indefinitely.

The thing is that if I remove the tool from the spindle and then re-seat it, I can usually go back to perfect cuts for a short period before the chatter starts again. And I want to be clear, it's not a case of harmonic vibration building progressively from the start of a cut. It's good one minute, and then in an instant the squealing starts.

For troubleshooting I just got done with the following test cuts in 6061 aluminum:

X-axis linear profile pass with a .375 3FL .020R ZrN end mill at 5100RPM, 30in/min, .5" DOC, .075" WOC
I made 3 passes flawlessly, then made 2 passes in the y-axis with the same parameters without issue. On the third Y-pass the moment the mill enters the cut I get horrendous chatter, and at that point any further cuts in any direction will chatter terribly...even if I try a less aggressive cut. I removed the tool from the spindle, checked that the ER20 collet or end mill holder set screw were still tight (I ran this multiple times with different style tool holders), then reinserted the tool. Then I was able to get several more good passes before the chatter redeveloped.

It leads me to believe that the problem is in the spindle/collet, or the tool holder to spindle interface. It seems like the tool/holder is moving in the spindle under load, but I'm just speculating (there's no visible pullout from the spindle going on). I've tried several spindle collets and tool holders without change. Checking runout on the spindle I.D. shows well within tolerance...just a few tenths. Checking runout on the inside of an ER20 holder returns about .001.

I dialed in runout at the cutter flutes before these test cuts and after the chatter started I checked it again. Certainly seemed like the tool had moved. I'm torquing the tool holders to spec and wouldn't expect such consistent behavior across many tool holders if they were the source.

FYI, I've adjusted the gibs with no impact. Additionally, you may say that my cut parameters above are nearing rigidity limits of the Tormach but I see the same results with MUCH less aggressive cuts as well.

Any ideas? Any help would be appreciated.
Thanks.

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[popspipes]

I have had something similar, it turned out to be the endmill, switched to another of a different brand and the chatter went away.
An ever so slight bit of pullout will cause this too, the flange of the holder needs to be seated well against the spindle nose.
Using the shortest endmill possible for the job helps as well.
My main endmill is .250, it causes the least of problems, smaller is good as well, the larger ones are more "finicy"
The Z jibsk have a bearing on this as well.
once chatter is introduced its hard to get rid of it, kind of a self sustaining thing.
I made mainly stainless parts and fittings on my lathe and Bridgeport, a few years of that gives plenty of experience with chatter ha!
I have an 1100 s3 so its a similar size machine.

[AUSTINMACHINING]

Are you using a power draw bar or tightening the R8 collet manually. ?. You could test with a solid R8 set screw tool holder to see if its a tool retention problem. Also pre-load on the spindle bearings would be worth checking.

[johnnydoejr]

I should mention that this machine is used by multiple individuals, I'm just the one trying to run down a solution. We all see the same symptoms and it's been going on since we received the machine (i.e. it didn't develop out of a machine that was running smoothly). Since none of us are professional machinists we initially assumed that this problem was user error (in feeds/speeds, etc.) and so we weren't actively troubleshooting from the perspective of a potential problem with the machine itself. Because of this, we've had the machine for a quite a while and in that time have tried every combination of variables we can think of to isolate the cause. Stub tooling, set screw holders, different diameters, tool manufacturers, coatings, tool geometry, etc. It's all the same result.

We have a power draw bar but I will do some cuts after manually tightening the collet to eliminate it as a source. Spindle preload was next on my list. During the chatter the surface finish suffers everywhere, but the bottom of the cut (at the face of the end mill) is especially bad. Maybe that's an indication of axial movement? I just have no reference for whether that's typical of chatter that isn't attributable to axial movement also, because again, I'm not an experienced machinist.

Thanks for the help. Open to other suggestions of things to check as well.

[CL_MotoTech]

I'm not on a Tormach, but I experienced similar issues when my spindle bearings were under torqued. Absolutely nasty results, inconsistent, and confusing at best.

[AUSTINMACHINING]

One of these would at least help rule out tool holding.


What is your work holding setup ?.

I should mention that this machine is used by multiple individuals, I'm just the one trying to run down a solution. We all see the same symptoms and it's been going on since we received the machine (i.e. it didn't develop out of a machine that was running smoothly). Since none of us are professional machinists we initially assumed that this problem was user error (in feeds/speeds, etc.) and so we weren't actively troubleshooting from the perspective of a potential problem with the machine itself. Because of this, we've had the machine for a quite a while and in that time have tried every combination of variables we can think of to isolate the cause. Stub tooling, set screw holders, different diameters, tool manufacturers, coatings, tool geometry, etc. It's all the same result.

We have a power draw bar but I will do some cuts after manually tightening the collet to eliminate it as a source. Spindle preload was next on my list. During the chatter the surface finish suffers everywhere, but the bottom of the cut (at the face of the end mill) is especially bad. Maybe that's an indication of axial movement? I just have no reference for whether that's typical of chatter that isn't attributable to axial movement also, because again, I'm not an experienced machinist.

Thanks for the help. Open to other suggestions of things to check as well.

[johnnydoejr]

YES! I pulled the spindle to look at bearing preload. I re-seated the upper bearings and tightened the preload nut back down. The manual says to tighten it approximately 5 degrees after it seats against the preload washer. Doing so definitely made it tighter than it was when I removed it.

After reassembly I notice a significant improvement in performance. I still get some chatter, but it's more mild and only occurs on the more aggressive cuts now. I think this is going to be the source of the problem.

I'd like to increase preload slightly more to see if I can reduce the chatter further. The manual makes it sound like the upper limit of preload is governed only by temperature in the spindle, but it doesn't suggest where to take readings. I ran the machine for almost 2 hours after the adjustment while producing a part and I took temperature readings of every exposed surface on the spindle along the way to include up inside the spindle bore (was probably indicating off the collet I.D.). I never saw readings above 90 degrees Fahrenheit, but none of the exposed surfaces really indicate what temperature the internal components are experiencing.

Do I need to do some disassembly to indicate off the top of the upper bearings? Or is the temperature limit (155 degrees in the manual) intended to be read at the spindle nose? If so, I have a lot of room to go tighter.

Thanks for the help guys. Before this adjustment the test part I ran would have eaten all my tools. It was very satisfying to get productive work out of the machine.

[popspipes]

Glad you found the problem!
My spindle is on its eighth year, I use the machine quite often but not a production environment, the temp never runs over about 20 degrees above ambient, 5140 rpm for over an hours time.

[mountaindew]

Glad you found the problem!
My spindle is on its eighth year, I use the machine quite often but not a production environment, the temp never runs over about 20 degrees above ambient, 5140 rpm for over an hours time.

My 6 year old spindle gets pretty warm after running for an hour. Doesn't get any hotter but still double shop temp easy. I probably run some way to aggressive drilling ops in the past doing tests or parts and maybe stressed spindle a little. Might look into rebuilding or replacing it this year.

[jwatte]

Double temp, be it Farenheit or Celsius, doesn't sound too scary by itself. What I've learned I have to worry about is the tipping point where the parts expand enough that they generate sufficient additional friction to generate even more heat expansion in a death spiral that ends up breaking down the lubrication and then you're toast.

If it's double-temp on the outside casing, then perhaps the bearings are a lot hotter on the inside? Might be worth checking out with a thermocouple or other easily inserted thermometer right after you finish a cut.

[mountaindew]

Double temp, be it Farenheit or Celsius, doesn't sound too scary by itself. What I've learned I have to worry about is the tipping point where the parts expand enough that they generate sufficient additional friction to generate even more heat expansion in a death spiral that ends up breaking down the lubrication and then you're toast.

If it's double-temp on the outside casing, then perhaps the bearings are a lot hotter on the inside? Might be worth checking out with a thermocouple or other easily inserted thermometer right after you finish a cut.

Not as hot as z axis motor but still 170 deg +. Not to worried about it short term. It has been this way for couple years but something fir me to keep in mind. I try to keep my mill clean, lubed, adjusted and maintained like the very expensive accurate tool it is to me. I just replaced the r8 tts collet, applied anti sieze, Replaced the Belview washer stack and adjusted pdb to max psi. After doing this I was amazed how much smoother everything works after simple maintenance like this. Makes me think I should do more.
I do see people that just run em hard and put em up wet. That's ok also! Mostly depends on what you do and how you work and the results you want short and long term.
For me safe, drama free works best.
Anyway good reason to pick up a tool to check this and keep an eye on

[popspipes]

My spindle temperature has always been just a bit above ambient since new, I check the tool shanks when the tool is removed, I think its a bit more accurate than the outside of the spindle housing but not the bearing itself so who knows? I have had problems with chinese grease in other bearings, so a bit tongue in cheek on this but the machine is 8 years old the first of Feburary. I did make a slinger early on to keep the coolant from splashing up into the lower bearings as there is no seal on the bottom of the spindle. (series 3 1100)
This does happen as I discovered after the machine sat for a week, the spindle was stuck, it did free up easily, this was the reason for the slinger (I was using water based coolant at that time).

I for one am glad there is a bit of activity on this forum!!

[jwatte]

> 170

Whoah! You have it 85F degrees in your workshop? :-) I was more thinking 130F heat ...
170F probably still doesn't cook the grease, but I wouldn't want to get it any hotter!
if it's calcium grease, 170F is actually the upper temperature limit, but chances are it's lithium, which can go to 300F.
(I wonder if they document which grease they do use in the bearings?)

[mountaindew]

> 170

Whoah! You have it 85F degrees in your workshop? :-) I was more thinking 130F heat ...
170F probably still doesn't cook the grease, but I wouldn't want to get it any hotter!
if it's calcium grease, 170F is actually the upper temperature limit, but chances are it's lithium, which can go to 300F.
(I wonder if they document which grease they do use in the bearings?)

Manual recommends a bearing preload with a resulting max operating temperature of 155 deg. I looked at this in the past and decided I was running at specs. But I think I better check it more carefully now.