M41 tool steel questions

[Doug H]

I was at HGR Surplus yesterday to pick up a few items, and I happened across a box that included several used brazed carbide tools that I had absolutely no use for, but there was a box of 21 unused Crucible Rex 49 tool blanks there as well. I figured that for the price, I couldn't go wrong, so I picked them up as well. I tried to do a quick search on my phone, but couldn't really find anything until later. The information I have found so far shows them to be an M41 Ultra Hard steel.

I am on the road right now, and won't get back to my shop till later this week, but looking for whatever information I can find on sharpening and usage. The primary use will be as turning tools on my 11": Logan lathe, and I will probably set a couple of pieces aside for use in a 3" flycutter.

Does anyone have any advice going forward. I have a few HSS tools that I have been using, but they were random pieces that I have aquired and I have no idea of their individual qualities, so I just grind them on the bench and call it good. On the other hand, and maybe I am over thinking things, I hate to just start grinding away on these new pieces without having some sort of plan, or even knowing if they are appropriate for the use I have in mind.

 

[Mtndew]

I've used M42 HSS blanks when I was running engine lathes back in the day but not M41. Or maybe I did and don't remember, that's highly possible.
I would assume they are similar in properties where M42 would have more cobalt.

 

[Joe Henderson]

A little Logan will work well with HSS. You might want to think about brazed carbide for the fly cutter.

 

[Doug H]

Had an opportunity to just make some chips with that steel. First thing I would say is patience and a freshly dressed wheel are your friend when grinding bits. So far, the only one I have made is just a conventional turning bit with 5 degree rake angles. According to what I have read, this steel can take about 20% more speed than standard HSS, and is more tolerant of heat. My testing so far has shown that to be the case. It is also very durable when not abused, but push it too hard and you will smoke the cutting edge. Generally speaking, as long as you keep the speed reasonable, you can run some pretty aggressive cuts. When roughing, I just try to keep the chips straw colored. I made two cuts this evening to really push the boundaries, with basically identical removal rates, one with a very aggressive (for my lathe) 50 thousandths depth (.10 total) at .0125 feed. Ran it pretty slow for that, approx 40 rpm. The next cut I backed off the depth to 25 thousandths, but bumped the rate to .025, also at 40 rpm. Both cuts created deep blue/indigo chips, and I had some concern that I might smoke the bit, but it finished both cuts (approx 12" each). I inspected the cutting edge when I finished, and it showed no more wear that when making more conservative cuts, so I put it back on, and adjusted the machine to make a finish cut to clean up the bar.

Overall, I am quite impressed with the performance. It isn't in the same league as carbide, but it is far superior to any of my other mixed assortment of HSS, both in production and durability.

Time to start grinding bits. Figure I will grind one for cutting threads, one for cutting chamfers, and whatever else comes up

 

[sfriedberg]

HSS in general holds its temper up to a faint red heat, around 800-900F. In fact, while I do some in-shop heat treating, I can't heat treat HSS because my tempering oven doesn't get hot enough.
Of course, the cutting edge is going to be significantly hotter than the bulk of the cutter, so if your bit gets hot enough to blister your thumb, the edge may be toast. But you don't have to baby it the way you might carbon steel cutters. If you keep the chips (assuming steel) at a straw color, the edge should last for a very long time.
The SFM and material has a lot more to do with the heat going into your cutter than the DOC or feed. Rule of thumb: for aluminum, HSS might be happy as high as 600. For mild steel, 150 SFM. For tough tool steels, 50 SFM. If the chips are brown or blue, or you have any doubts, slow down. But DOC and feed can be whatever the HP and rigidity of your machine will support.

 

[eKretz]

Generally I agree: keep the chips silver to light straw with HSS and you'll be in good shape. Cutting oil/coolant is also very helpful for increased tool life. Use oil if you can't flood the sh!t out of the cutting zone so it's not getting very hot and quenching over and over.