What tool to use please

[Sam Longley 1Participant @samlongley1]

Posted by SillyOldDuffer on 18/02/2021 21:33:34:

Sam may be guilty of cruelty to machine tools if this job is typical!

. About 60 RPM for 85mm diameter.

Dave

that is the second suggestion of sub 100 RPM in this thread.I am not sure that the lathe can run with enough power at that speed as it is the variable speed version not belt drive. I expect 200 RPM will be minimum.

However, I will give it a go.in the morning but it will have to be very light cuts

Thanks.

[Martin DowingParticipant @martindowing58466]

Posted by SillyOldDuffer on 18/02/2021 21:33:34:

Sam may be guilty of cruelty to machine tools if this job is typical!

Stainless 316 is on my avoid list because it work hardens. That roughly shaped octagon causes difficult interrupted cuts likely to break carbide, which is otherwise a better bet than HSS. 316 conducts heat poorly causing HSS to overheat and blunt quickly. The web recommends flood cooling HSS and 316 and also making sure the HSS stays sharp throughout the cutting. About 60 RPM for 85mm diameter.

Before turning it, I'd round the blank more with an angle grinder and remove the hangers on. Then very light cuts with carbide at about 200 rpm until the circle is formed, at which point go in a bit harder. I'd expect the disc to work harden as the tool rubs either side of the peaks, but carbide should cope without breaking provided it's not asked to chop metal too quickly.

Holding the blank is tricky too: it needs to be rigid with no chance of coming loose. Not sure what to suggest. I would try super-gluing to a fat mandrel as well as bolting. A problem with bolting as shown is shock loads tend to loosen the nut.

Dave

I have done many details from this material.

Have found it quite pleasant to work with, it gives nice surface finish ex knife unlike many lower quality carbon steels (BDMS comes to mind…)

I have only a small lathe (ML 7) yet I can make 2.5mm cuts at 0.004 inch/rev on 40-60 mm bars of it with normal front tooling. As long as HSS is sharp no trouble is observed. Small Chinese 6 mm carbide inserts worth 0.3 queed each are doing real wonders on this material and they are lasting long. With carbides I cut dry, with HSS I use paintbrush cooling.

When drilling, drill must be sharp or it *will* work harden indeed. If it does work harden during drilling then Ghinese carbide spot drill worth few queeds and designed for 55 HRc will invariably resolve problem. Nevertheless *sharp* 16mm drill may be applied directly with no predrilling and it works well.

Parting must be done with sharp HSS tool or it doesn't work at all. 35mm bar have been parted off in my ML7.

I have made 3-1/2 inch deep, blind bore in 100mm diameter piece of this material held in 4-jaw. Taken some time but result was very good indeed.

Martin

[HopperParticipant @hopper]

Posted by Sam Longley 1 on 18/02/2021 22:18:59:

Posted by SillyOldDuffer on 18/02/2021 21:33:34:

Sam may be guilty of cruelty to machine tools if this job is typical!

. About 60 RPM for 85mm diameter.

Dave

that is the second suggestion of sub 100 RPM in this thread.I am not sure that the lathe can run with enough power at that speed as it is the variable speed version not belt drive. I expect 200 RPM will be minimum.

However, I will give it a go.in the morning but it will have to be very light cuts

Thanks.

Forget about using HSS at 200rpm on that diameter of stainless. The edge will burn off it in very quick order. Best go straight to carbide.

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