Is HSS for pivots a good idea?

dandydude

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Nov 30, 2014
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Hello everyone,

I was considering using HSS (cobalt) for palet Arbor pivots to go with jewel plain bearings? Has anyone done this before? Its easy to find because, I can cut it off a drill bit of the Dia I need. Just need to taper the end to a point. Isn't this better than hardening steel?

Any response appreciated...

Thanks
Dandy
 

John MacArthur

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Feb 13, 2007
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Dandy - I think you'd want to experiment a little. In my experience, the shank end of a drill bit is softer than the cutting end, as anyone who has ever had a bit grab and spin in the chuck knows. You can get drill stock or pin gages which probably are hard throughout the length. These might work for grinding to a point, or even shaping a pivot and polishing with a pivot polisher. Good luck,
Johnny
 

dandydude

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Dandy - I think you'd want to experiment a little. In my experience, the shank end of a drill bit is softer than the cutting end, as anyone who has ever had a bit grab and spin in the chuck knows. You can get drill stock or pin gages which probably are hard throughout the length. These might work for grinding to a point, or even shaping a pivot and polishing with a pivot polisher. Good luck,
Johnny
Dear John... Thank you for your reply. The drill bit I am using is not coated... It is a cobalt hss (M42) bit. Would that still have a difference in along the length?

Thanks
Dandy
 

measuretwice

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Jul 28, 2019
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John is right about the chucking end of drills. Drills are not suppose to be hardened, they wouldn't work very well in a chuck if they were. Think of what a no-no it is to hold an endmill in a drill chuck, that's because its hardened and the chuck's gripping power depends on the jaws getting a bit of a bite in soft material. If the end was hardened it would slip in the chuck

As for HSS is being better, I'd say no. There is nothing about HSS that makes it harder or better wearing than correctly heat treated tool steel....except it holds its temper at much high temperatures. This is crucial on a quickly revolving cutting edge, but hopefully a not a factor in a clock. :) Heat treating HSS is about impossible without being able to hold very exact temps whereas tool steel is forgiving and easily heat treated and tempered with a propane torch
 
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dandydude

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Nov 30, 2014
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John is right about the chucking end of drills. Drills are not suppose to be hardened, they wouldn't work very well in a chuck if they were. Think of what a no-no it is to hold an endmill in a drill chuck, that's because its hardened and the chuck's gripping power depends on the jaws getting a bit of a bite in soft material. If the end was hardened it would slip in the chuck

As for HSS is being better, I'd say no. There is nothing about HSS that makes it harder or better wearing than correctly heat treated tool steel....except it holds its temper at much high temperatures. This is crucial on a quickly revolving cutting edge, but hopefully a not a factor in a clock. :) Heat treating HSS is about impossible without being able to hold very exact temps whereas tool steel is forgiving and easily heat treated and tempered with a propane torch
Hello measuretwice,

I really would've assumed that hss with cobalt is way harder as they recommend those for stainless, whereas carbon steel for softer jobs. Thanks for the advice!

Dandy
 

measuretwice

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I really would've assumed that hss with cobalt is way harder as they recommend those for stainless, whereas carbon steel for softer jobs. Thanks for the advice!,
You're welcome. Its a common assumption, hss is better for so many applications, people think its better no matter what. On the Rockwell hardness scale at room temp they are very close to the same. Most of HSS's advantages stems from its ability to hold its hardness at a higher temp - ideal for a cutting tool. It can be advantageous for tools that don't face high temps but need to be ground - grinding doesn't temper the edge the way it will with carbon. None of this matters much matter for a pivot. Still, its moot imo as drill shanks are soft and heat treating hss requires some special equipment (the difference between success and failure is a very small temperature range)
 

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