Tool Grinding Question

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rmac
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Tool Grinding Question

Post by rmac »

The other day I wanted to turn some little thumbscrews as shown in the drawing. I ground a little bullnose-looking form tool to make the neck. It worked fine for that cosmetic feature, but it made me wonder how you'd grind a similar tool if getting the shape exactly exactly right was more important. Any hints? Is it simply a matter of going slow and being careful?

-- Russell Mac

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Harold_V
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Re: Tool Grinding Question

Post by Harold_V »

There are form dressers available for those who have need, but they're pricey.

A comparator helps when grinding to close tolerances, as does good vision. With care, a form can be ground within a thou or two by hand. I generally use my Starrett radius gauges for the task and have been known to make a custom radius with a divider, scratching through thin brass shim stock. Any port in a storm.

H
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RSG
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Re: Tool Grinding Question

Post by RSG »

I know it's not practical advice but I've been having great success with my fiber laser. I mark the top of the blank and grind up to it, then final dress it. You could try doing something similar with layout dye and a scriber.
Vision is not seeing things as they are, but as they will be.
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rmac
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Re: Tool Grinding Question

Post by rmac »

So no real magic, I guess. Thanks, guys.

-- Russell Mac
Fasturn
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Re: Tool Grinding Question

Post by Fasturn »

In your case a .150 drill blank / hard pin. Mount it @ 10-12 degrees rake in a square blank. Did this many times and it will cut.
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arborist
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Re: Tool Grinding Question

Post by arborist »

Fasturn wrote: Sun Oct 02, 2022 6:33 pmMount it @ 10-12 degrees rake in a square blank.
This is more for completeness than in any way disagreeing with you, but if you mount it like that, you are no longer turning a circular arc, but an elliptical one.

With a nearby CAD, you could overlay the two and see what the actual difference is, no doubt extremely small.
Fasturn
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Re: Tool Grinding Question

Post by Fasturn »

arborist wrote: Mon Oct 03, 2022 7:20 am
Fasturn wrote: Sun Oct 02, 2022 6:33 pmMount it @ 10-12 degrees rake in a square blank.
This is more for completeness than in any way disagreeing with you, but if you mount it like that, you are no longer turning a circular arc, but an elliptical one.

With a nearby CAD, you could overlay the two and see what the actual difference is, no doubt extremely small.
You are correct, but for knob good enough. Being old school hand grinder it would be HSS + 5 minutes on a bench grinder. Becoming a lost Art with insert tools. Just giving the OP something to ponder, if not comfortable with hand or ? Grinding.

Hey...you are the first to quote me on this site.
Congrats , new to this forum !! :D
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rmac
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Re: Tool Grinding Question

Post by rmac »

Fasturn wrote: Sun Oct 02, 2022 6:33 pm In your case a .150 drill blank / hard pin. Mount it @ 10-12 degrees rake in a square blank. Did this many times and it will cut.
Good idea! Thanks.

-- Russell Mac
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