If the TTS is so awesome, why do I get horrible chatter with a 3/8 end mill?

[beanbag]

OK, here are some of the 3/8 end mills that have chattered when using the TTS ER20 holder:
CGS ZrN 2 flute high helix carbide
Niagra 3 flute TiCN high helix .09 corner radius carbide
Deboer 3 Flute TiCN .03 corner radius, regular helix carbide
Detroit Tool 2 flute uncoated carbide, regular helix

material is aluminum.

RPM's have varied from 2k to 5k, feeds from 10 ips to 40+ ips
I checked runout one time and it was fine.

I have tried multiple tool holders.
DOC usually does not exceed .375 and WOC usually does not exceed .17.

One very specific example of chatter is 4k rpm on the DEboer end mill with .09 DOC .125 WOC, 20 ips. Dropping the rpm sometimes helped, increasing the feed did not. In fact, due to one "accident", I went up to about 40 ips, and it squealed very loudly and caused the TTS holder to slightly pull out of the R8 and scrapped a part. All at .09 DOC.

I guess you have to crank down on the drawbar REALLY tight with this setup, because if it pulls out just a little bit, you suddenly lose a whole bunch of rigidity and are now barely holding on with 1" worth of shank. (Which I think was too little in the first place)

I don't remember ever getting chatter to go away by increasing the feed.

Anyway, I think a lot of the time with me, the chatter indicates too much material removal for the amount of tool stiffness. If I find a setting that does not chatter, increasing both the RPM and feed proportionately can now cause chatter, which means it is not simply a matter of chip load per tooth.

For now, when I need to do a lot of material removal, I use a plain R8 collet.

[dertsap]

OK, here are some of the 3/8 end mills that have chattered when using the TTS ER20 holder:
CGS ZrN 2 flute high helix carbide

material is aluminum.

RPM's have varied from 2k to 5k, feeds from 10 ips to 40+ ips
I checked runout one time and it was fine.

Anyway, I think a lot of the time with me, the chatter indicates too much material removal for the amount of tool stiffness. If I find a setting that does not chatter, increasing both the RPM and feed proportionately can now cause chatter, which means it is not simply a matter of chip load per tooth.
.

The CGS high helix should do that cut like it was nothing so too much material for the tool isn't the issue , too much material for the machine is more likely . Sometimes conventional milling will solve the problem and CGS does recommend that any cuts below 1 1/2 dia be cut conventional , I know that your cuts aren't to that depth but my point is that its worth trying on a less than rigid machine . .005 chipload/tooth and 8000 rpm is the start point for those end mills , since yours will only run at 4000 then you should be running at max and I'd start at .006 chipload , if the chatter persists then youve got other problems , be it the machine or your machining approach

[BobWarfield]

Could be a lot of things going on here. Just a few thoughts:

- When you switch to an R8 collet instead of TTS the chatter goes away. But, not only did you go from TTS to R8, you may have also gone to a different R8 than the one you used with TTS. Is that the case? If so, I wonder if that R8 is okay? Might be worth getting another in the same size to try.

- You are certainly extending the stick out, which could lead to more deflection and hence chatter. But, I wonder about that. You could use G-Wizard to figure the deflection of an endmill whose stickout is the length from the end of the R8 collet to the end of the TTS holder, and whose diameter is the minimum diameter of that TTS holder. Assume HSS. If the stickout is way under 0.001", say 0.0005" or less, that's not too terrible. Your problem is likely elsewhere.

- Does the chatter happen a lot, or only under "certain circumstances"? If it's the latter, tell us more about the circumstances. They may be particularly chatter prone (e.g. endmill same radius as minimum radius cut as was already mentioned).

- Pullout has been mentioned. Be sure your tooling is clean and not oily. Good info on that in Tormach's white paper on collets. More in this CNC Cookbook article:

Getting the Best Performance from ER Collet Chucks « CNCCookbook

- Consider that if you look hard enough, you can always induce chatter. Maybe you're just at that spot. Chatter is a resonance phenomenon. Your machine and tooling has a particularly frequency that equates to spindle speed and number of flutes for a particular combination where it will be most likely to chatter. Apply enough force via feedrate and it will always chatter there. Probably more than you wanted to know about chatter here:

CNC Milling Chatter and Stable Milling Speeds

That's part of our feeds and speeds tutorial.

- One more thought. If you start to decide it is unusually easy to get your machine to chatter, I would start wondering about the bearings and their preload.

Lastly, I don't ever recall hearing before this thread, that too little chipload will cause chatter and I can't see why that would be the case. Too little chipload will cause rubbing which will prematurely wear the tool out, but a chipload of 0.001" on an endmill is enough that this would not be the case. Some inserts designed for really coarse work can have a problem there, but not a standard EM.

Cheers,

BW

[beanbag]

Dertsap,

I saw on the CGS web page that if the length of cut EXCEED 1.5 diameter, is when you should go conventional. Does that mean I should use a conventional cut if I do a profile finish pass?

Bob,

That is an excellent guide on your web page. I also suspect that too little chip load is not a problem since otherwise I would have problems with my finishing passes. I suspect that the problem is with the TTS junction, and not that the end mill or ER collet is bending too much.

One potential problem is that the junction seems especially prone to pullout, because the collar is already trying to pull the 3/4 shank out. In fact, even with a somewhat firm crank on the drawbar, even a 3 flute 1/4" endmill at 5k rpm, .27 DOC, .08 WOC 22ips can pull out the TTS holder. Because there is coolant splashing everywhere, there could be a little on the shank. I still think the 3/4" shank is too short as well.

I did see Tormach's guide on drawbar torque. That study seems like something I would do, and this fact worries me, because I am not an engineer. A REAL company with engineers like Bridgeport or Haas would not recommend some novel micky mouse solution like putting lapping compound on your end mills.

Anyway, this is MHO on the TTS system for now. If I have some free time I can go and measure various aspects of it.

[SCzEngrgGroup]

"In fact, even with a somewhat firm crank on the drawbar, even a 3 flute 1/4" endmill at 5k rpm, .27 DOC, .08 WOC 22ips can pull out the TTS holder." - You are doing something VERY wrong then! I use TTS holders almost exclusively, and I have NEVER once had one pull out on me. I routinely run 1/2" endmills, doing 1/2" deep slotting at 15-20IPM. I also run carbide three-flutes, 0.250" deep, up to 70IPM, also slotting, and have NEVER had one pull out. Proper drawbar torque is at least 25ft-lbs, NOT a "somewhat firm crank". You NEED to tighten the drawbar better.

Regards,
Ray L.

[Scott_M]

What size wrench are you using on the drawbar ? As in, length of handle ? If you are using the little 6" long wrench that came with the machine then I agree that the drawbar is not tight enough. If you have a torque wrench it would be interesting to find out how much torque you are getting with a firm crank. Tighten as usual then loosen with the torque wrench to find out what you have been using.
I also have never had a TTS pull out and I have done some pretty serious cuts.

I also think you may have misread the use of the lapping compound. You would put it on the shank of the TTS not the endmill and only if all other reasonable means failed.

Scott

[dertsap]

Dertsap,

I saw on the CGS web page that if the length of cut EXCEED 1.5 diameter, is when you should go conventional. Does that mean I should use a conventional cut if I do a profile finish pass?

.

sorry i wasn't thinking and when i said "below" i meant deeper .
generally even if your running deeper than 1.5 dia its not really necessary on a finish pass. But if there is chatter then it very well could be the cure to run conventional no matter the depth
I use the CGS 55 degree on a daily basis and rarely hear them chirp unless they are being pushed hard and when i say hard i mean hard , so i find it highly unlikely that your problem would be a tool issue .

is the chatter happening on the finish passes or just on the rough pass , also are you plunging the end mill to depth in the material or are you leading in , ramping to depth ?


.

[beanbag]

I need to check with a torque wrench, but "somewhat firm crank" for me means about 20 something ft lbs, and "really leaning into it" means about 35+. I have not had a pullout when "really leaning into it", and it fixes the chatter a small fraction of the time.

I never get chatter on a finish pass, and usually I aim for about 30% tool width when roughing. Sometimes I have to stick the end mill into a corner (higher engagement angle) and that increases the chance of chatter. (obviously)

[beanbag]

I think the ER20 TTS holder is more prone to pullout than the weldon type because it is longer. Pullout happens not from the static axial force, but from the endmill wobbling back and forth at the spindle rpm (from the point of view of the spindle). Since the ER20 holder is longer, the wobble force is greater.

[Don Clement]

I did see Tormach's guide on drawbar torque. That study seems like something I would do, and this fact worries me, because I am not an engineer. A REAL company with engineers like Bridgeport or Haas would not recommend some novel micky mouse solution like putting lapping compound on your end mills.

Anonymous and not an engineer. Who is REAL here?

[beanbag]

Of the two Tormachs I use, the more chattery one, which I call Chatter McChatterton, seems to have really long ER20 holders. They measure 2.5" from TTS collar to the tip.

[Don Clement]

When you are anonymous, you can post anything about anything. Who’s going to believe you? However the thread title gets repeated and it's déjà vu all over again.

[beanbag]

Thank you for your helpful and insightful comments.

[dertsap]

this may be as obvious as the tool plunge question i asked but have you tried to swap holders and document the difference of how each machine performs

[beanbag]

this may be as obvious as the tool plunge question i asked but have you tried to swap holders and document the difference of how each machine performs

As I mentioned a while ago, I swapped between different holders, but that is only within the set that comes with each machine.
I kind of came to the realization yesterday that the set that comes with the more chattery machine looks longer than the set that comes with the less chattery machine. I'll have to measure the length on the other machine to see if they are the same. No, I can't take the collets on one machine and bring them to the other. What does your ER holder measure out to?

Edit: I see I didn't fully answer your question last time, but this chatter is happening during the "regular" part of the cut. I'm not complaining about lead-in chatter only.

[dertsap]

No, I can't take the collets on one machine and bring them to the other. What does your ER holder measure out to?

.

I don't have a tormach so i can't answer that question , I work with much larger machines .
So you can't take a holder from one machine and swap it with another ?

[dertsap]

I just looked at the tooling for the tormach and hadn't realized before now that they are not tapered holders which has thrown out any of my thoughts of buying one in the near future . Anyhow length can definitely be a contributing factor with a design like that

[TXFred]

So you can't take a holder from one machine and swap it with another ?

From earlier discussion with beanbag in another thread, I learned that he doesn't have a Tormach of his own. He has two friends who let him use their machines. But if he started walking out the door with their tool holders, he'd probably lose privileges.

Frederic

[Peter Neill]

As I mentioned a while ago, I swapped between different holders, but that is only within the set that comes with each machine.
I kind of came to the realization yesterday that the set that comes with the more chattery machine looks longer than the set that comes with the less chattery machine. I'll have to measure the length on the other machine to see if they are the same. No, I can't take the collets on one machine and bring them to the other. What does your ER holder measure out to?

Quite possibly they are different, I've noticed (just from the interweb rather than 1st hand experience), that they have changed the geometry of the TTS holders since the ATC was introduced.
You can see the difference below,both are 5/16" holders.

[David Bord]

Gib tightness can impact chatter as well correct?

David