If the machine is robust enough a heavy feed rate can actually reduce tool wear as the tool is cooler biting into fresh metal getting less time to take heat from the swarf which may well be heated to blue at recommended speed. Colin

All the hobby supply houses sell HSS but the problem is you don't know exactly what you're getting.

I bought some M42 from Cromwell a while back but I've yet to see if it actually cuts any better.

Drills and milling cutters are HSS and the type used varies. M35 and 42 have been around for a long time. M42 tends to be too expensive in my view M35 not too bad really considering it will generally stay sharper for longer than the cheap stuff. M35 is sometimes described as 5% cobalt or HSSE. From just a cutting perspective the higher cobalt content allows higher cutting speeds before heat at the cutting edge spoils the temper. That also helps when the tools are ground. It's very easy to wreck the temper of some of them during grinding. It's best to not take advantage of the higher cutting speeds at home unless people wants to resharpen often.

The M's as I understand it are American designations. HSS has traditionally been sold by manufactures name with the ingredients on the side of the packet they were in. Frustrating if a brand was excellent but is no longer around.

It's worth looking in Cromwell's clearance section for tool bits. Names keep changing when new stocks come in so they seem to sell the last of the earlier ones there. Harry???? on Ebay sells M35 tools bits. One of the few that do.

When it gets to stellite and tantung g and crobalt etc cutting temperatures can go up again. If used at normal cutting speeds what ever those are they should stay sharp even longer. Some of these shouldn't be chilled in water when ground as they may fracture.

Cutting speeds really are just somebodies idea of speeds that will give their idea of a reasonable tool life.

John

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