What to do if my mystery steel is eating my HSS

[dabear3428]

Speed?

Fly cutter even at a slow rpm is traveling fast.

A carbide end mill can go faster, but it requires rigid mill and hp to bite.

We just start SLOW, increase if needed, but slow speeds to not generate the heat that destroys things.

Shallow cuts also.

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2" flycutter and 1000 rpm? too fast?

 

[WobblyHand]

More than 5 X too fast for HSS. This is why you are burning up the HSS.

Actually drop it down to 170 RPM or so if low carbon, maybe half that for alloy steel.

Cutting speeds for steels are much lower than for aluminum. Around 90-100 SFM (surface feet per minute) for low carbon steel. Each material has its own recommended SFM. Required RPM can be determined by

RPM = 12 * SFM / ( diameter [inches] * pi ), or approximately by

approx RPM = 4 * SFM/(cutter diameter in inches)

If you follow this general rule, your HSS tooling will thank you. It's ok to run slower for HSS than the formula says. It's not ok, as you found out, to run 5 x faster than the formula. Carbide tooling can run faster, about 3-4 x, depending on the material.

Hope this helps. I was literally burned by this when I first started machining.

 

[dabear3428]

More than 5 X too fast for HSS. This is why you are burning up the HSS.

Actually drop it down to 170 RPM or so if low carbon, maybe half that for alloy steel.

Cutting speeds for steels are much lower than for aluminum. Around 90-100 SFM (surface feet per minute) for low carbon steel. Each material has its own recommended SFM. Required RPM can be determined by

RPM = 12 * SFM / ( diameter [inches] * pi ), or approximately by

approx RPM = 4 * SFM/(cutter diameter in inches)

If you follow this general rule, your HSS tooling will thank you. It's ok to run slower for HSS than the formula says. It's not ok, as you found out, to run 5 x faster than the formula. Carbide tooling can run faster, about 3-4 x, depending on the material.

Hope this helps. I was literally burned by this when I first started machining.

thanks, makes sense.

 

[koenbro]

Same phenomenon of hardening of the cutting edge happens with plasma cutting, and if I remember correctly, it is called nitridation.


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[dabear3428]

well the good thing is that HSS is cheap and learning to grind it is a useful skill, i like sharpening that much better than trying to re-grind end mills.

 

[dabear3428]

More than 5 X too fast for HSS. This is why you are burning up the HSS.

Actually drop it down to 170 RPM or so if low carbon, maybe half that for alloy steel.

Cutting speeds for steels are much lower than for aluminum. Around 90-100 SFM (surface feet per minute) for low carbon steel. Each material has its own recommended SFM. Required RPM can be determined by

RPM = 12 * SFM / ( diameter [inches] * pi ), or approximately by

approx RPM = 4 * SFM/(cutter diameter in inches)

If you follow this general rule, your HSS tooling will thank you. It's ok to run slower for HSS than the formula says. It's not ok, as you found out, to run 5 x faster than the formula. Carbide tooling can run faster, about 3-4 x, depending on the material.

Hope this helps. I was literally burned by this when I first started machining.

i guess that this would apply to my HSS end mill? so 800rpm or less for the 12mm (1/2")?

 

[WobblyHand]

i guess that this would apply to my HSS end mill? so 800rpm or less for the 12mm (1/2")?

Yes, this equation is valid for any size HSS end mill or fly cutter with the correct value for SFM.

Spin a cutter too fast on a material with low SFM requirement, and watch them "burn up". Spin a cutter near the recommended speeds and they'll last a long long time. That's assuming the material has not been flame or plasma cut or welded which can cause local hardening.

 

[woodchucker]

hit it with an angle grinder first to get under the hardened flame cut area.
I don't bother with flame cut anymore until I grind it clean.
I went through a lot of brazed on carbide trying to go through it on the lathe. The next time I ground it, and it was much easier.

 

[tailstock4]

Flame cuts on mild steel can be pretty tough. They will tear up almost anything on a rotary tool. A shaper is the way to go if you have one. There are few things that shapers are really good at, and this is one of them.

With a shaper you have to get the cutting tool under the dross. You also have to grind the tool in such a way that that the tip strikes first and by the time it hits the cutting edge it is already being peeled up - in other words, a positive rate.

I had to do several blocks like the one in the shaper vice in the pictures below. I could cut quite a few of them before I had to pull the tool out and re-hone it. Then I’d do another stack.

I also recommend staying away from Chinese or Indian highspeed steel. There are still a few places you can find better stuff. I’ve bought high speed steel from Griggs Steel. They have a good selection. They aren’t cheap, but it cuts way down on regrinding.

 

[durableoreo]

About the mystery metal... you might be better off with a known material. Technically, you're learning, but is it getting you closer to your machining goals? This may be a curmudgeon "take" but wouldn't you be better served if you design, draw, and make a part rather than wrestle with troublesome materials? The most intractable problem in machining is materials that wreck cutters. I remember one project that involved making parts out of ingots of some terrible material. Excellent machinists were reduced to changing inserts every 15 min. I know there's lots of people who use found material but IMO it's... varsity. It's too hard and depressing of a problem for the beginners. It's the pallet wood of the machinist world. I watch Jeremy (see below) too, so I'm not hating on anyone, but I think most people will get to their goals faster and more happily with known material. Also, Stephan Gotteswinter mentioned that all of his material is labeled, even the small scraps. So learning from the best, I've started labeling stuff. Known materials makes everything better.