Machining stainless steel

[Mike CrossfieldParticipant @mikecrossfield92481]

[Mike CrossfieldParticipant @mikecrossfield92481]

Perhaps unwisely, I agreed to make a kitchen utensil for my sister in law. It's a potato masher – basically a disc with a pattern of slots, mounted on the end of a shaft with a handle on the other end. Yes, I know you can buy such things, but I'm tasked with copying the design of a much-loved tool which has finally expired, and which is no longer availed commercially

Anyway, I thought that stainless steel was the right material to use, so a rummage in the scrap bin brought a suitable sized piece of 2mm plate to the surface. Now, I have little experience of working with stainless, but my attempts to machine this plate have been less than satisfactory. After just 1 slot with a new 5 mm carbide slot drill running at 500rpm the cutter has lost its edge, and the slot is very ragged. I guess the problem is the material work hardening. Am I using an unsuitable grade of material, or is my technique wrong? Is there a free machining version of stainless sheet?

[Tractor manParticipant @tractorman]

Buy her a potato ricer. Her mash will be better and her arms less tired.
Will never go back to a spud squasher.

[Anonymous]

It can depend on the grade. Can we assume that the stainless is austenitic, ie, 300 series? If that is the case then 303 machines well, and can be obtained in a free machining version. I've also found that 316 is straightforward, but 304 is horrid, and very difficult to get a good finish.

In terms of work hardening the key is to keep the cutter cutting! Feedrates need to be fairly agressive;and any hesitation and you're lost. With carbide tooling you may be able to recover, but HSS simply won't cut after the stainless has work hardened.

Andrew

[Frances IoMParticipant @francesiom58905]

the scrap bin at my metal suppliers often contains SS with 316 being by far the most common and is I think is that generally used in food handling – some end of bars are upto to 6″ diameter and generally about 3-8mm thick – this can be worked in a small mill with HSS or carbide (it polishes up very well), drilled relatively easily with HSS-Co drills and smaller rods on the lathe turned with very sharp HSS tools but once workhardened very difficult to do much with unless you can get in at end and remove the hardened surface – the merchant uses a saw with copious coolant whilst cutting

[Thor 🇳🇴Participant @thor]

Hi Mike,

Austenitic stainless steel isn't easy to machine. 500 RPM isn't very fast for a 5mm carbide slot drill, for carbide you run the slot drill faster. Have a look at the LMS calculator. You need to feed the slot drill, if it starts rubbing the material work hardens very fast. I usually drill a pilot hole at the start of the slot first.

Thor

[Mike CrossfieldParticipant @mikecrossfield92481]

Thanks chaps.

Sounds as though I need to source a few square inches of 303 or 316 sheet, and run the mill a bit faster.

Mike

[Tractor manParticipant @tractorman]

Mike I have a circular slug of stainless steel cut from a plate I used to make a chimney flue. It drills easily and is about 3mm thick. I’ll take a snap and mail it you. It’s about r inch sis I think. Might do the job. Mick

[Dave Smith 14Participant @davesmith14]

I would cut my losses and get it laser cut.

Dave

[Mike CrossfieldParticipant @mikecrossfield92481]

Tractor man, you have PM.

Mike

[CirclipParticipant @circlip]

316L and either punch the slots or get them waterjet cut.

Regards Ian.

[Ady1Participant @ady1]

Looking at the profile I would guess that the heads of stainless potato mashers are produced on giant 200 plus ton stamping machines, not on a lathe/mill

[MWParticipant @mw27036]

If and likely this stuff is cold rolled, it is possible to anneal and stress relieve 304 by heating to around 1000C and quenching it very quickly, as is common to do with austenitic steels.

Michael W

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