Easy to turn but hard to mill

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Duder321
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Easy to turn but hard to mill

Post by Duder321 »

A while ago I bought some 12-14" chunks of 2.75" shafting for little more than shipping. The least rusty of them has a really shiny finish in spots that looks like chrome so I'm guessing it to have been some sort of hydraulic ram or similar. I've used it for a couple projects with no issues - all lathe work.

The stuff bandsaws just fine turns with HSS ok and turns with carbide really well. All ops are fine even at the outermost edge where there's possibly chrome or some case or induction hardening.

Today I cutoff a length with the saw after I had done some turning and went to the mill to face and put some slots in the end I had just sawn. The stuff ripped the corner off a really good cobalt roughing end mill and damn near melted a HSS 2-flute. All proper speeds, no chatter, just metal that wouldn't move and severe heat quickly to follow and then tool destruction :evil: .

I had to resort to using a brazed carbide tool in my flycutter at 0.003" max DOC to flatten the face. Now I have to mill the slot and I'm scared to kill more end mills.

What gives? Any ideas?
SteveM
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Re: Easy to turn but hard to mill

Post by SteveM »

is there a possibility that the sawing operation work-hardened the end?

If you milled a surface that was not machined, like the side, would that work, or do you see the same behavior?

Steve
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ctwo
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Re: Easy to turn but hard to mill

Post by ctwo »

Steel can smell fear. That's my hypothesis.
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warmstrong1955
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Re: Easy to turn but hard to mill

Post by warmstrong1955 »

Most hydraulic & air cylinder stems are made of chrome plated 1045. There are two basic flavors however.
Case hardened, and thru hardened. The depth of the case hardening is variable.
With both types I have worked with, the case hardened tends to have more hard spots. Many are easy to see on the ends, even after facing. Little shiny spots toward the OD.
The thru hardened does it to, but not so frequently.
The thickness of the plating is also variable, and generally not a big deal.
Sharp tools seem to make up for all. And when you get to the OD for threading, the variances in hardness are gone. Flaws seem to be closer to the major OD.

Bill
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warmstrong1955
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Re: Easy to turn but hard to mill

Post by warmstrong1955 »

ctwo wrote:Steel can smell fear. That's my hypothesis.
If this is true....you must start moving and machining faster than the speed of smell.....

;)
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Russ Hanscom
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Re: Easy to turn but hard to mill

Post by Russ Hanscom »

With chrome plating, I was always told to make the first metal removal pass deep enough to get under the plating.
EOsteam
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Re: Easy to turn but hard to mill

Post by EOsteam »

Reference this post and try the carbide and soluble oil as a coolant. It worked well on 1095 spring steel.

http://www.chaski.org/homemachinist/vie ... 4&t=105037

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Patio
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Re: Easy to turn but hard to mill

Post by Patio »

If you are melting anything, your speeds are to fast, IMHO.
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woodguy
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Re: Easy to turn but hard to mill

Post by woodguy »

I'd put the piece in my wood stove - get it good and hot and allow the stove to cool overnight. Then try it on the mill. I used to buy scrapyard shafting which was hardened by some unknown (to me) process and annealing the stock in this way always left it machinable.
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GlennW
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Re: Easy to turn but hard to mill

Post by GlennW »

Patio wrote:If you are melting anything, your speeds are to fast, IMHO.
That's where I was at with it.

You say "All proper speeds", but how can that be if you have no idea what the alloy and temper are and you are destroying cutters?
Glenn

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Glenn Brooks
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Re: Easy to turn but hard to mill

Post by Glenn Brooks »

Recently I turned a bunch of old 3" junk yard shafting and experienced the same thing - hard spots on the surface , often in proximity to old keyways. Finally, I realized - theorized anyway - that the hard pockets were caused by work hardening whilst the shafting was initially in service in some past industrial setting. Sounds like what you are experiencing also.

I was able to get under the worst of it on my big lathe -.025" DOC where necessary, and found wonderful high quality steel underneath.

If you can't turn it, then second the suggestion for annealing. Or keeping cutting new pieces until you find a section that doesn't have these characteristics.

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Duder321
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Re: Easy to turn but hard to mill

Post by Duder321 »

Thanks everybody for the responses and ideas. I haven't had a chance to go and look into it more but I have some ideas now when I have time. Basing my proper speed on guessing it's 1045 or CrMo of some sort coupled with the fact that using (HSS) 65-70 sfpm yielded good results on the lathe. But - the comment about the shiny streaks was insightful because I do see some bands in the end I faced on the lathe that are more shiny - mostly at the first 0.050" from the edge and then intermittent spots a little deeper. Maybe some intermittent hard spots and I just got lucky to cut into a good section of them. I've got the other end with a saw cut still so I'll play with that first and see what I can learn.
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