Machining stainless steel

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?

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

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

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

I would cut my losses and get it laser cut.

Dave

Tractor man, you have PM.

Mike

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

Regards Ian.

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

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