Milling HSS

Anyone tried this? I’ve done a tiny amount of turning HSS on my Mini lathe with carbide tools and it’s worked out ok. As I’m also an occasional wood turner I’ve decided it may be useful to be able to do some modest milling of HSS as well for custom cutters.

I ask because I noticed that some carbide mills are only specified to cut materials to only fairly modest hardness levels so probably not up to milling HSS?

Anyone have experience that can offer any insights?

Andrew Johnston is your man but carbide will do it, shallow depth of cut. Carbide cutters come in different grades to suit different hardness of material so one for the harder stuff would be best, APT have some reasonably priced ones

Edited By JasonB on 29/10/2021 20:34:08

More of a question than an answer, but could you heat the HSS to reduce hardness the reheat and quench after milling?

I've never tried this.

Obviously HSS can be annealed & re-hardened but it's a high temperature operation which not all industrial heat treat companies can manage successfully so unlikely an amateur job but I'm sure someone will prove me wrong.

Tony

Milling HSS with carbide cutters works fine. Here's an involute form being CNC milled on the end of a length of 1/4" square HSS, to be used for shaping an internal gear:

The key seems to be high surface speeds, relatively small DOC and decent feedrates. My working hypothesis is that these conditions mean that the shear zone is at red heat so the chip is fairly soft. Experiments with turning hardened silver steel showed that the bulk hardness was unaffected despite the swarf coming off red hot. Given that most of the heat generated is contained in the swarf, combined with the high surface speed, ensures that the bulk material doesn't get hot enough to anneal it.

The milling cutter shown above is by Garr. I used them because my local tool emporium stocked them. They were fine on aluminium but tended to wear quickly on mild steel, so I swapped to Guhring and then to YG. If they can cut HSS then most carbide cutters should be fine. When turning hardened silver steel a standard carbide CCMT insert worked but didn't look happy afterwards. A CBN insert worked beautifully and left a great finish, but one needs to sit down before looking at CBN prices.

From reading, M42 HSS, the hardening of HSS can be a complex procedure requiring temperatures and equipment unlikely to be found in home, or many professional, workshops.

Andrew

Thanks for that. I will give it a try as planned as soon as the material arrives. It sounds though that I may need to be a bit choosey about which cutters to buy.

By modern standards, this 1922 Thesis is very brief : **LINK**

https://scholarsmine.mst.edu/masters_theses/5036/

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Although it is clearly not a direct response to Vic’s practical question, it contains some useful information about High Speed Steels.

MichaelG.

Well I took it very slowly and managed to do what I wanted to. I would like to hog off one end of the blank a bit in order to put a handle on it but my two insert cutter wasn’t really up to it. I expect I’ll grind the majority off and then maybe clean it up a bit on the mill. Gosh, wouldn’t it be nice to have the cash and space for a surface grinder!?