You don't say what diameter that endmill is, but you are running WAY to light a chip load, which would explain chatter. At 5000 RPM, and that DOC, you should be running up around 70 IPM.Originally Posted by HLF Ordnance
Regards,
Ray L.
If the ER collet and the tool-holder tapers do not match within what is a quite tight tolerance then I would think that chatter is a very probable outcome. Generally we are talking about cheap collets, made to a price not a quality. We spend countless hours complaining about the low quality of Chinese imports and then we turn around and expect our beautifully, shiny $9 dollar a piece ER collets to be tip top.
Phil
Is this just another bore war with a sample of just one example? I wonder if the OP really wanted a real solution or just wanted to get a kommando title on this thread.
MY bad... It was a 3/8 em.
I did try using the recommended F and S from G wizard but I have had issues with collet pull out in the past and I usually start a 1.5 hour op and then go do something else (ATC BABY!!!). The 3/8 em only mills a small corner (half open pocket) and then its done (~45 seconds).
I am going to try to buy a higher quality collet and try it out. Never thought about that!
HLF
Ahh, that could be it. Are you by chance milling a corner with the same radius as your tool? You can get chatter doing that because you are going to generate a lot of side load as it makes the turn and the direction of deflection changes. If the corner radius is .1875, I would try dropping to a .25 end mill (radius .125) and let the machine work the turn rather than relying on the shape of the tool.
This is also confusing, the ER holder is no longer than the weldon type holder as far as I recall.
Phil
BUMP
The weldon holder is .8" shorter than then ER20 holders.This is also confusing, the ER holder is no longer than the weldon type holder as far as I recall.
Phil
As I've mentioned before, I can run weldon held tools about 40% faster than tools in the ER20 collets. There simply is no comparison between the two when efficient production is the goal. Especially given that the weldon holder fits into tighter locations and allows greater flexibility in jig design.
I generally can get shorter stickout in the weldon holder due to the same reason, so it's comparing apples to oranges mostly. I use the collet holders for detail work and finish passes, but for roughing it's 100% weldon holders.
EDIT: It's also easier to get coolant in on the weldon holders when doing deep slots because the huge nut doesn't block you out.
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.
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
A poet knows no boundary yet he is bound to the boundaries of ones own mind !! ........
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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
Try G-Wizard Machinist's Calculator for free:
http://www.cnccookbook.com/CCGWizard.html
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.
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