I have a Doosan/Daewoo MX 2500LT mill/turn machine. It has a FANUC 18i-TB controller, 12 tool lower turret, 40 tool Capto ATC upper milling turret with Y/B-axis.

This particular machine does not have two spindles, rather it has a tailstock. I have read all of the manuals several times looking for some direction on what pressure to set the tailstock. I am hoping that I can get some good information from here.

Our product is a carbide insert cutting tool for woodworking equipment. They range in diameter from 3" - 10" and from 6" long - 70" long. With such a wide range of stock, it is obvious that tailstock pressures would need to be adjusted. I use a 3-jaw chuck and a facedriver depending on the part size. Riten makes a good tool and they supplied me some generic tailstock forces based on driving diameter, depth of cut, and feed. I also spoke with their engineering dept and they do have some formulas for calculating how much tailstock pressure is necessary. Unless you are taking a simple cut, the cutting forces of the tool can become very complex, expecially when you add a C/Y/B axis interpolation.


I found that I tried to replicate how I would set a manual tailstock on an engine lathe. I would increase the tailstock pressure until I felt the center adequately grip the workpiece, ie couldn't spin it anymore. For the most part this works. The trouble I have been having is some pretty fierce chatter on my final pass to size. I rough the profile with a 433 insert to .24 larger diameter. I then switch to a DNMG 433 insert and take 4 .03 DOC finish passes to adjust size, etc. The first three work fine everytime, the last one chatters every time. I haven't been able to see any relationship to the diameter, so it could happen with a 4" diameter or a 1" diameter.

With the programming, feed, speed, DOC all the same between the cuts, why would it chatter on the last? My guess is that I have too much/too little tailstock pressure for that particular part.

Anyone have any good suggestions for me??

Thanks!

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So the last 4 passes are exactly the same program except .03 deeper on each pass. What is the smallest diameter? Try running a test piece and take the smallest diameter and move it up .5 or even 1" and try running it. It may jest be that the part is flexing from tool pressure. Also if your tailstock pressure is to high then. You can actually collapse the part.

I think your chatter is coming from to large of a nose radius to finish, try a cnmg 4305 which should be about .0075 nose radius. I think you need to also slow your speed down on the finish cut. Leave about .01 total to finish.

The pressure should be high enough to support the work piece. If you can rotate the part and the live center rotates then that's high enough. The chuck does all the clamping.

I agree on the tool nose radius. Depending on the material being turned a lighter pass for finish as well as a smaller nose radius should solve your problem. If you need any type of radius on the workpiece you can always use tool nose compensation with the smaller tool nose radius.
Good luck!