Methods to eliminate chatter on long thin piece

[pmurdock]

Ok. in my experience I've run upon the following methods to help eliminate chatter on long thin pieces. I have a Haas SL-30 and trying to suss out a better way. I am using a tailstock on 304 stainless steel cutting it down to 3/8" diameter - with 9" overhang. Getting heaps of chatter.

1) Steady Rest - unfortunately didn't buy the machine with this so not a cheap way to go.

2) Cut it SUPER slow when I get down to the final diameters on the finishing cut. I had success with 0.001 ipr and 400 rpm. But it took FOREVER to cut.

3) Step cut - cut 1" down to final size and then move on to the next 1" section. I will try this in the next few days to see how effective this is.

4) a BOX TOOL - I have searched high and low for vendors who supply such a tool. Does anyone have experience with a box tool on a VDI-40 turret lathe? From what I have read it can work just as well as if there was a steady rest there - the question is do they make this tool for CNC lathes? My normal supplies of exsys and parlec don't seem to carry anything like this.



I've been looking at pursuing option #4, but haven't had any luck finding a tool yet. any ideas?


cheers,
Paul

[Geof]

Have you tried Spindle Speed Variation; look it up in your Haas lathe manual.

[mrainey]

A few possibilities for ideas:

http://www.cuttingtoolengineering.co...eativeturn.pdf

www.boyar-schultzsmt.com

http://www.cnczone.com/vb...light=box+tool

[pmurdock]

thanks to all for the tips. Just an update to the thread.

I enabled SSV (spind speed variation) 50 RPM spread over 3 seconds - and it does indeed help reduce the chatter. However it's still there..

I tried step cutting and that did eliminate chatter altogethr but as mentioned in previous thread one has to cut it just right in order to avoid uneven surface features. ie I can see small cutting marks at the 1" intervals. I'll need to play around with this a bit more to see about cleaning up those cutting marks.


My next step is to try a positive rake cutting angle. I've been using all negative rake tools and this is stainless 304 - so perhaps deflection, chatter, and cutting forces which should be all reduced using a positive rake cutting angle will help?


cheers!
Paul

[williams480]

If the part shape allows, you can start at the chuck and work towards the tailstock.

This can reduce the harmonics coming from the thin workiece, once chatter starts it's hard to eliminate.

They key is to not let it get started, as the tool will pick up the chatter left by the previous pass.

Good Luck.

[billcain]

You don't say what the starting Diameter here is.

I have done some 17-4 Tubbing cutting from .625 to .375. I Used a Neg/Pos insert (A Negative holder with a Kenemetal insert which changes it to Positive). Best cut came from doing 1 Pass. I remember the settings being somewhere around 400 SF at about .008-.012 FPR. This feed and insert combination broke the chips and worked great. The biggest problem I had after that was makiung sure the Coolant got to the Tool.

[HuFlungDung]

You might try an Iscar cut-grip style tool. These work very well, IMO, on 304 stainless. They can be had with what amounts to positive rake chipbreaker geometry, and they roll the chip into an easy to handle long coil, that is smooth to handle.

The finish cut should be in the neighbourhood of .050 DOC with this tool, barely scraping the work will not pan out. Ideally, figure out how to program a toolpath that will cut the part in one pass, if that is all the material that you have to remove. This toolpath could involve curvature that counteracts the flex of the part to produce a straight cylinder. It may take a couple of tries at it to come up with a suitable toolpath.

Turning the piece from larger diameter stock in one pass gives you the advantage of the rigidity of the original stock diameter.

The Cut-grip tool allows for an aggressive feedrate yet gives an excellent surface finish because of the scraping action of the insert. But it takes a good firm feed pressure to tilt the insert and make it work as planned, hence the light cuts are out on a flimsy part.

The aggressive feedrate helps fight chatter because the tool tip is buried well below the surface of the previous cut.

I cannot swear that this will work as well for 9" long parts, but works good for 6" length, going from .350 to .234" diameter Nothing else could match the performance of the Cutgrip in this application.