What kind of chuck pressure do you use in this instance????

[gixxergary]

Im bar pulling a 24 inch long, 1 3/8 diameter piece of 1018 in my Haas Sl-20. 3 inches of stock, sticking out of the 3 jaw chuck. The chuck is well greased and free. Im currently running 325 psi on the chuck, but Im still getting tons of vibration. Ive tried faster, slower, heavier and lighter feeds, but I cant get this thing to stop. The thing is, I tried shortening the bar inside the draw tube, down to 12 inches, thinking it was just too much out back, but I still get the same issue.

Do you folks have ANY insight on this. Ive been dealing with this on certain jobs for way too long now. The hydraulics show a max pressure rating of 600 psi, but I cant imagine having to run it over 300, or am I way off base with my thinking. Can these machines handle 400 to 500, or is that just a bandaid for something else.

Thanks in advance for your help!!
Gary

[Technical Ted]

What's the actual size (OD) of the bar & ID of the tube?

[Geof]

It is probably a Kitagawa chuck; find the specs on maximum drawbar force and I think you will find you can go well above 325 psi.

Don't increase rpm; that so-called fictional force...centrifugal force, seems quite real to a rapidly spinning chuck. Try boosting your feeds an SL30 has plenty of rigidity; also look up Spindle Speed Variation in your manual because this can help when all else fails.

You might also check your chuck jaws; are you using the hard jaws or custome bored soft jaws? Bored to size soft jaws can be much better for controlling vibration.

[tobyaxis]

You can also make a sleeve or spindle liner to absorb some of that vibration. It will also provide more stability.

If at all possible can you use a False Center?? If you can, use a Bell Type Center Drill preferably the largest one you have and use the Tail Stock.

[gixxergary]

Good Morning,
The bar stock is 1.375, finishing at 1.340 with a bull nose radii on the end. We are parting these off at 3/16 thick. Its an 8" Kitagawa chuck with 2 inch thru hole. This particular process, is making 8 pcs per 3 inch pull. No room to add a center on this one. (its an SL-20). I am using the hard serrated jaws.
Where can I find the maximum clamping force for this Kitagawa? Ive searched google, and came up empty. I will try making some steel soft jaws this morning, to see if that fixes the problem. I need to be able to crank this thing up, we have a large production order, and it had to be quoted low to get it in house, so we need to make some fast cycle times.
In your opinion, with this circumstance, where would your speeds and feeds be, for a simple g72 facing and part off be?? Thanks again for your responses!!

Gary

[MikeOD]

Have you considered going back to a soft jaw (much better choice in my opinion)? Have you used a 0.001" shim to verify that your current chuck jaws are actually contacting the part over their entire length? You usually need to bore soft jaws with a taper to make that happen...and you NEEEEEED to support the back end of the bar with a spindle liner. I've never had much production success with hard jaws...not worth the investment.

[Geof]

We make an identical part; 1-3/8" leaded drilled 3/8" and parted of at 0.20". I will look at the program on Monday but I think we are running around 1000rpm for the parting and 0.005" per rev.

Definitely go to the custom size soft jaws, I am surprised you are getting chatter with a hydraulic chuck because ours is an HL1 with the spring closed chuck.

[gixxergary]

I made lots of progress today. I ditched the hard jaws, and bored out some aluminum soft ones. ( no steel ones in stock to use). I upped the pressure to 375, and cut my cycle time, just about in half. Im sure if I get some steel soft jaws, that should secure it even further.
To be honest, Ive been machining for 20 years, and have owned my own machine shop since 96, and I never once, thought, that bored aluminum jaws would hold better than the hard ones. As said in one of the replies, I checked the clamp marks from the hard jaws, on the work piece, and yes, they are NOT clamping equally, and not even close to holding a part round.
The next step, I need to pick up a better parting tool. Im using a Manchester dogbone type groove/cutoff/turning tool. Its great for small parts with a back side chamfer or radius, but I cant seem to get the chips to break, they just spool up. Any suggestions on an excellent cut off tool?? Its time to invest in one. Prefferably, one with replacement anvils, so when it goes, the holder stays intact.
I wanted to say thanks, for all the quick replies!! Its been a long week, and I finished it up on a high note, instead of the usual problems to come back to on Monday.

Gary

[Geof]

Originally Posted by gixxergary .... Any suggestions on an excellent cut off tool?? Its time to invest in one. Prefferably, one with replacement anvils, so when it goes, the holder stays intact.... Gary

We use Iscar Heligrip I think it is. they don't have replaceable anvils and I am not sure this would protect the holder if the insert died during a part off. We find when this happens we finish up with a parting blade that has a bar-shaped notch in it.

This doesn't happen very often because we have a tool count alarm and change the inserts but occasionally we get caught out when a batch of material is slightly harder or in some way different and kills the insert faster.

[MikeOD]

Well I'm glad to hear we're beginning to find the issue...I really strongly suggest getting some 0.001" shim stock to verify your contact with the jaws after you're boring them...I usually bore a taper into the jaws around 0.001" per 1.0" (but that can vary a bit from chuck to chuck and also with wider or thinner jaws...and jaws with the back side relieved for tool clearance will then need more taper sometimes due to deflection during clamping)...and I agree that you should get steel soft jaws. The aluminum ones are probably ok...but they won't last long. I also advocate using boring rings or a spider to bore the jaws...with a kitagawa or like style chuck where the jaws are serrated on the bottom, it's very common to bore them with the chuck clamped on nothing, then move them 1 step in on the serrations...this is ok for a lot of work, but when concentricity tolerances go up, using a boring ring or a spider and using them in the same position they were bored in usually helps that a lot.

Parting in a pecking cycle to clear the chip can help the tool survive a lot longer...you need to learn the tool wear on the insert on your parting tool and change it before it breaks...due to the nature of the blade being buried in the material with the insert, they tend to always get damaged if the insert breaks in a cut...but inserts are CHEAP and it's worth replacing them a few parts before you've gotten every last cut out of them to avoid replacing the blade.

Have you setup some kind of a spindle liner to support the back end of the part while it's in behind the chuck? Doesn't need to be anything fancy, just some PVC plastic that fits in the draw tube, and has a little bit of clearance for the raw material to slide through smoothly.