Machining 300M and actually breaking chips?

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choprboy
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Machining 300M and actually breaking chips?

Post by choprboy »

Anybody have any tips for machining 300M (4340 vacuum arc remelt)? I picked up a bunch of bars of surplus, have had no problems running 4140, but the 4340 is giving me continuous long hot chips that birdnest badly. Comes off real hot, turns purple, sharp and nasty.

Playing with all different feeds and speed. The best I have been able to do is about 180 sfm, ~.035 doc, ~.009 feed with a 432 WNMG, makes tight curls about 1-1/2" to 2" long that snap and fly across the room. Lower feed/speeds produce long strings, I think it wants even more feed, but my 3HP lathe is bogging down. Trying to run slow with a large feed/depth produced a poor finish and harsh cutting action.
earlgo
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Re: Machining 300M and actually breaking chips?

Post by earlgo »

I haven't tried it but have often wondered if affixing a taller chip-breaker to the top of the tool would prevent this. I don't imagine it would need to be too much taller, just enough to intercept the chip as it comes off the cutting edge.
Occasionally this happens on my little 1/3 hp Atlas and some of the curly chips have snagged me hurtfully.
Just a thought.
--earlgo
Edit: I don't use 300M but this happens with 4140 pht in my case.
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Magicniner
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Re: Machining 300M and actually breaking chips?

Post by Magicniner »

earlgo wrote:I haven't tried it but have often wondered if affixing a taller chip-breaker to the top of the tool would prevent this.
I have some inserted tooling that has exactly that, the chip breakers have a 45 degree slope to deflect the chips, they came in a separate box to the inserts.

- Nick
LIALLEGHENY
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Re: Machining 300M and actually breaking chips?

Post by LIALLEGHENY »

Unfortunately you are correct....you need more HP on your lathe. You need to be pretty aggressive with 4340. it does not cut well at slow speeds. Higher speeds and feeds are needed. Strings means your not moving fast enough. What diameter material are you starting out with?

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rudd
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Re: Machining 300M and actually breaking chips?

Post by rudd »

If all else fails, interrupt the feed occasionally.
choprboy
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Re: Machining 300M and actually breaking chips?

Post by choprboy »

Yeah, just seems like it needs to be more aggressive, but don't have the power. I'm running about 475rpm between about 1-1/2" and 2", step down to 300rpm above 2+". Double checked, .035-.040 doc with a 0.0102 feed rate. Thinking about trying a 431 insert, or maybe getting one of those holders that takes a TNMG/TNMM insert with the deep chip breaker along one edge.

Surprisingly, once I got a good rhythm, it did plunge and part off pretty good, .125" HSS cutoff blade at 70-100rpm to ~.6" depth.
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BadDog
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Re: Machining 300M and actually breaking chips?

Post by BadDog »

I had a slug of what was supposed to be 4140 (said so on the bin) about 4" x 6", but it wasn't like any 4140 I had ever turned. I think the final consensus (here?) was that it was 4340 pre-hard. It was way worse than the worst stainless at razor sharp endless ribbons. My problem was I was not being aggressive enough. I had to really crank up both depth and feed, pushing it pretty hard. Finally the chips got big/thick/hot enough that they broke off in tight round curly-cues about 6" long that made a thunk-ring as they bounced about blue hot and smoking. Once I got after it hard enough, it machined beautifully. Embarrassed to say, but those chips were kinda cool and surprisingly substantial in the hand (like holding a hand full of heavy razor blades), so I actually kept a few... :oops:

I had to turn down a small section to get within parting depth, but at a bit under 3", it parted just fine with a Sandvik carbide parting blade.

But that's on a 7.5 hp 4500 lb lathe. I would hate to cut that stuff on a more modest sized machine. My old Rockwell 11 would never have been able to break those chips. The part was an adapter hub for a Cummins 12V 6BT conversion I was helping a friend with. He wanted to run a Houghten(sp?) electric medium duty fan clutch, but no combination of parts he could find would make it fit with his fan/intercooler location limitations. So I made him a (from memory) 1.5" spacer hub held onto the Cummins hub with 6 bolts, and a 30x1 (or was it 1.5?) left-hand metric thread on one end for the electric clutch. One of the more memorable parts I've made, mainly sticking in my memory because the material was so difficult to machine. It's good to have a lathe with easy metric capability...
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choprboy
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Re: Machining 300M and actually breaking chips?

Post by choprboy »

Yeah, I'm on a 3HP 1300lb 13x40 lathe... so I just don't have the power. Tried a few more things. Running geared down, slow and deep, doesn't work, poor cutting action and sticking in the material. Tried a HSS with a sharp edge an deep groove, still won't break and can't turn fast enough to get a decent cut without burning the tool.

Got a TNMM with a deep groove from Grizzly, not thrilled with it (already broke 2 corners), but finally managed to get curly-Qs at 200-300FPM with 0.010 feed and 0.040-0.060 depth of cut. Running about 2.5HP according to the current draw on the VFD. Still coming off real hot and quickly turning blue, then fading to reddish-brown and purple. The chips are almost like poorly tempered spring steel and even the small chips ring when they hit the floor. I suspect they might more readily break with flood coolant, but I don't currently run with that.
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Harold_V
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Re: Machining 300M and actually breaking chips?

Post by Harold_V »

If you chose to use HSS, you'd have to change the way you're thinking. For one, slow it down. As you've already discovered, it won't tolerate excessive surface speed, but the surprise for you will be you can move as much metal.

Depth of cut is critical if you hope to break chips. Shallow cuts like you're taking tend to be hard to break. Increasing feed will help breaking.

A modest chip breaker coupled with positive rake, using HSS and a heavier feed and deeper cut will likely work. Slowing the spindle will multiply the available torque, which may overcome your lack of power. Adding coolant would be to advantage. Chip breakers can be ground specifically for a given task. A deep, broad breaker will roll nice coils. A narrower breaker will break the chip. Armed with those thoughts, experiment until you hit a winning combination. As a breaker deepens, it has the potential to increase demand for power unless a nice radius terminates the breaker. If the termination point is too abrupt, it can result in chip stacking and a broken tool.

My Graziano is equipped with a three horse motor. I can take .200" off per side with a .010" + feed without much effort (steel, running @ 500 rpm on a 2" diameter). I expect your lathe doesn't really have the power advertised.

H
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