[double a-ron]

Well, I was roughing out 2" od 4140ht at 500 sfm, .02 ipr and .15 radial D.O.C. and by the time I was done with the 4th pass the stock had been pushed back about .125". I am using bored jaws, G50 at 2500 rpm, and 350 psi of chuck pressure on a tl-15. Anyone think going to hardened serrated jaws would stop this? Anyone used them? They're not cheap. I thought I'd ask before I bought them.

[txcncman]

Use a stop in the spindle or step jaws. Serrated jaws might help. Another consideration is actual contact area. If you turn up the pressure too much, you cause misalignment of the jaw surfaces, thus less contact area.

[Geof]

As mentioned your jaws may be splaying at that pressure so you are not getting good contact. Did you bore the jaws with a jaw ring at the same pressure you are using now.

If the jaws are a good fit you may be able to get similar metal removal rates by taking the rpm down to something like 2000 and increasing the feed to 0.25 ipr. The lower rpm will reduce the centrifugal force that is reducing the grip.

Or you may have to get a cenytrifugally compensated chuck. ($$$$$$$).

[double a-ron]

I'd be all over stepped jaws as I have plenty of brand new soft jaws here, but I'd like to bar feed the stock. US shop tools has hard jaws for $300. Anyone used them? Seems too cheap. The jaws were bored with a ring at about 275 psi and .005" under size and look like they are making good contact with the bar. I still have some juice left in the spindle and I'd like to get closer to what iscar publishes the insert can handle: WNMX 452, 700 sfm, .276 doc, .03 ipr. I know 20hp wont get me all the way there, but I'm only at about 110%. I'd like to see that at about 160.

[txcncman]

What kind of material stick out are you talking about? With 2" thick jaws, step bored to 1.75" deep, and 2" diameter bar stock, I would confidently run 8"-10" sticking out.

[gizmo_454]

I'd be all over stepped jaws as I have plenty of brand new soft jaws here, but I'd like to bar feed the stock. US shop tools has hard jaws for $300. Anyone used them? Seems too cheap. The jaws were bored with a ring at about 275 psi and .005" under size and look like they are making good contact with the bar. I still have some juice left in the spindle and I'd like to get closer to what iscar publishes the insert can handle: WNMX 452, 700 sfm, .276 doc, .03 ipr. I know 20hp wont get me all the way there, but I'm only at about 110%. I'd like to see that at about 160.

There are many things limiting you in your fight for feed, speed, and depth of cut you are trying to achieve. Let us take a look at some of them.

1) The infamous "chuck". In your TL-15, I would seriously consider a collet setup. They have better grip and are not prone to the centrifugal force issues that chucks have when running at speed.

2) Bar whip. If you have any slop in your spindle liner ID to the bar OD, the bar will not run "true" at speed and can act as a 4-5 foot lever pushing on your clamping device. With the steel bar you are running, there is a lot of weight swinging around out there. If the bar weighs 45-50 pounds static, what happens when you put it 0.1" off center and wind it up to 2500 RPM? That will be a boat load of force trying to pry your chuck open.

3) Lots of axial force with only one thing to hold it...the chuck. With the DOC you are taking, and the feed you are trying to achieve is putting lots of pressure straight down the long axis of the bar with nothing to support it. try taking your 2" bar of steel and hold it vertically using only one hand to hold it off the ground. Now have someone stand on the top end of the bar. Assuming your arm was supported so it could not move vertically, where is the bar going to go? Now put the bar on the ground and hold it with the same hand with the same volunteer standing on the bar again. Now where is it going? No where.

4) Rotational force. Let us take the example above and add to it that I am going to attach a 1 foot bar to the side of it and twist while the guy is standing on the bar you are trying to hold.

In our SL-10, in 1144 steel, with a 0.1" DOC and 0.006-0.007" IPR, the 1-3/8" round bar will move back. Granted, the machine is no where near as big or powerful as your TL-15. But we are running a collet chuck since we do lots of bar work.

To make a long story short, step back a little bit and take in the big picture. There is more going on there than just a chuck jaw issue. If it were me, I would back the feed down and keep the load on the spindle at or below 100%. It will likely help the issue you are having, and prolong the life of the machine. Just my $0.02.

Good luck!

Mike :cheers:

[KenFoulks]

+1 on the collet chuck

Do you grease your chuck every 6 months? If not, chuck pressure may be lower than desired.

Hard jaws should help. There are fine and coarse serrations and one of them may help more than the other based on your stock finish. I use hard jaws for a lot of my testing, but I always have a hard stop.

[Edster]

If your using a standard kitagawa chuck they recommend greasing it every 8 hour shift!

I bought a set of hard jaws from USST for my SL-10 but they had a lot of runout and I ended up returning them. I'd look at better brands.

[double a-ron]

Somehow I knew those jaws were going to be off. The price is too good to be true. H and R gets almost twice what usst is charging, might check them out.