Turning 4130 steel?

[Pontiff51]

Hello all. My problem is turning a tube 35" long, .812 ID with a .077 wall thickness. I worked with the machine seller over 6 weeks to finally get it running without chatter. The machine is a brand new Daewoo 2500 dual turret. I'm using a steady rest, hydraulic and self centering. RPM is 1350 Feed is .0085 IPR and depth of cut is .060 roughing and .015 finish. The finish is pretty good but I can't get the chips to break during roughing or finish cut. I get 8 to 12 inch long chips that are like springs. I have thousands of parts to mfg. and I know it's only a matter of time before the steady rest tangles one up. I am machining these parts on a hardened arbor. When I ship a few hundred parts to my customer I'll be able to shave some time off these parts (right now 19min) by doing some R+D with inserts and speeds and feeds. If anyone has machined 4130 before and has any ideas how to break a chip, I hope you'll post your ideas. Thanks.

[WOLOG]

Change your roughing insert to a positive geometry rather than a negative geometry. Negative inserts are not good for thin walled parts due to push off and such. Play around with your feeds and speeds to get a tight little chip. I cut 4140 HT all day long but you have to push hard to get a chip. The positive insert will shear the material rather than rub it raw which leads to stringy shavings. How do you like the 2500? Is it the TL or the TT? I am thinking about buying a TL2500.

[HuFlungDung]

If you are still in an experimenting mood, I'd recommend that you try the Iscar cutgrip tooling. In my experience, it does not necessarily break the chip, however, they can roll the chip into a nice smooth, tight coil about 3/16 to 1/4" diameter, and the coil may break when about 6" long.

Do the cut in one pass. The Iscar cutgrip is capable of excellent finish at a feedrate of .01 but be aware that setting of the tool is critical to prevent chatter. The cutgrip insert leans ever so slightly away from the cut direction due to the force of cutting, and this creates the insert clearance. So the tool must be set so that this tipping of the insert does not cause it to hog in along the broad nose. Only the corner does the cutting.

I used to turn .350 dia 304 stainless tubing down to .245 OD, leaving a .005" wall thickness with these inserts, one pass only. I also used a mandrel inside the tube for support. Turned length was 5.5", and cnc made it possible to program a gentle arc to counteract the flex of the part, as I had no steady nor follower for this process. I turned several hundred of these, finally I got smart and had tubing custom made for the application

[Pontiff51]

thanks guys, i'm going to check out iscar's tooling this week. my customer is our uncle sam, he ain't changin' nuten'. i'm using a TL it's pretty good. hydraulics on demand is nice and quiet.

[rhundl]

I would use a #1 radius tool for chatter problems. 4130 is a little more gummy than 4140, I would probably try a .008-.01ipr feedrate. Also I would try to keep the two cuts equal depth to maintain a chipload on the tool. At .015 finish, I would assume that it wouldnt break a chip very well at all. As far as rpm I would try around 400-600 sfpm. This is where I would start but might end up right where you are. Hope this helps