Lathe form tool query

I want make a form tool to produce a series of 'humps' (similar to clock frame spacers ) on a piece of 6mm diameter stainless bar. Normally for a one off I would use files and emery but this time there are several to do and for cosmetic reasons I want to keep them all the same. I am thinking of making the form tool from a piece of gauge plate, by drilling a hole 2mm diameter at an appropriate angle to give relief to the cutting edge, mill away half of the diameter and then harden the plate by quenching in oil. Not sure if tempering is necessary as there are only 6 humps to form.

Any advice on the validity of this method would be most welcome, I have done the same in the past with brass but stainless is a whole new ball game for me.

Phil

Hi Philip,

Was one thing I don't think was mentioned that you could use an old part-off blade if you could grind the form using a router spindle with grinding bits or a bench grinder. That way you could get a HSS tool.

Michael W

Strangely that is a technique that I had considered but I don't have any experiences of using these small grinding points and to be honest I don't think I have ever seen one just 2mm in diameter.

Phil

Yes that is correct, especially where "stones" are concerned, like aluminium oxide or corundum. But there are very small diamond coated bits you can get. Perhaps they don't have the rigidity without a steel shank like the diamond ones.

PS. I got a decent "hilda" branded router drill off of banggood.com that can do 40k rpm, which would be necessary for such a small bit, that came with a load of small diamond grinding bits, was the best part of £30, but I would only do that if you were confident it was the only way. Don't spend money if you don't have to!

As for the validity of your suggested method, I don't see why it wouldn't work, just make sure to keep the RPM lowish for stainless on the lathe or it'll wreck the tool. 

Michael W

Edited By Michael-w on 05/04/2018 17:20:36

I think what I'd do is make a form tool to shape the space between the humps, by grinding inside radii either side of a central plunge form. That way the forming pressure's concentrated rather than divided. I think it'd be easier to make too - unless the sphericity of the 'humps' is critical, I'd try offhand grinding it from 1/4" square HSS.

A worn dremel cutting disc or even a thin cutting disk in the 4.5" angle grinder will give a reasonable half round cut out in the end of an HSS toolblank.

Thank you gentlemen, you have given me some food for thought. The quality of the advice given on this forum really is second to none. Also on the subject of quality, the accuracy the humps is not so important I just want to get them all the same, I'm going to do some experimenting over the next few days with some of these ideas and will report back in due course.

Phil