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re-hardening the tip of a center punch


 
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BarnyardEngineering
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PostPosted: Mon Dec 04, 2017 8:19 am    Post subject: re-hardening the tip of a center punch Reply to specific post Reply with quote

Trying to make some marks with the trusty old center punch yesterday, and it got dull. Sharpened it on the grinder like I have many times before, went back to making marks, and in ONE hit, the tip was mashed round again!

Apparently I've ground through all the hardened material at the end of the punch. Any reason I can't heat the tip up cherry red, just the tip mind you, and quench in oil or something to harden it back up?
 
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kcm.MN
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PostPosted: Mon Dec 04, 2017 9:08 am    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

First off, you need to know whether the steel should be quenched by oil, water, or a gas like air. There's a lot of Youtube videos out there about tempering knife and axe edges, but this site will quickly go over the variables you may encounter.
https://www.wikihow.com/Harden-Steel
 
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BarnyardEngineering
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PostPosted: Mon Dec 04, 2017 9:53 am    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

More trouble than it's worth. I'll just buy a new center punch.
 
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Stan in Oly, WA
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PostPosted: Mon Dec 04, 2017 10:51 am    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

BarnyardEngineering; If you're going to buy a new punch anyway, and the one you have is now useless, then what have you got to lose by trying to harden it the simple way you described? It will either work or it won't.

Stan
 
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Steve@Advance
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PostPosted: Mon Dec 04, 2017 12:40 pm    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

I never realized they were hardened just on the tip.

Maybe the ones I buy are not a good a grade.

Any chance the part you are punching is harder than the punch?
 
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TimV
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PostPosted: Mon Dec 04, 2017 1:34 pm    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

Barnyard Engineering--no reason you can't try--it will either work or it won't, and if it doesn't you can always try again. The chances of it being water-quenched are remote, so use oil of whatever variation you would typically use for such projects if you have a favorite. I use canola oil for my quenching, but even regular motor oil will work in a pinch, and of course quenching oils are available, but hardly worth buying for such a simple project if you don't already have some around. When you're done, test it with a file to see if the file bites in or skates on the metal. I have also used Kasenite to case-harden punch tips before, but I don't believe it's available anymore and I have not heard good things about Cherry Red, the case hardening compound that's supposed to be a replacement for it, though I have no experience with it myself.
 
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Stan in Oly, WA
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PostPosted: Mon Dec 04, 2017 2:36 pm    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

TimV; I saw something on TV years ago showing that the parts for Kalashnikovs made by hand in tribal areas of Pakistan were quenched in oil-based paint. I guess you use what you've got.

Stan
 
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Janicholson
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PostPosted: Mon Dec 04, 2017 6:06 pm    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

Our students make center punches for an exercise. 1144 stress proof steel. Heat the tip to cherry red and quench it If oil
doesn't do it, use water. Only an inch will do it. Jim
 
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Bret4207
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PostPosted: Tue Dec 05, 2017 5:43 am    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

BarnyardEngineering wrote:
(quoted from post at 13:19:47 12/04/17) Trying to make some marks with the trusty old center punch yesterday, and it got dull. Sharpened it on the grinder like I have many times before, went back to making marks, and in ONE hit, the tip was mashed round again!

Apparently I've ground through all the hardened material at the end of the punch. Any reason I can't heat the tip up cherry red, just the tip mind you, and quench in oil or something to harden it back up?


Heat it red, quench and cool. Then draw the temper down by heating the end you hit and watching the color run up the punch (you will probably have to polish the scale off after quenching to do this) until you see the tip area start to yellow/brown, then quench again. That's the basics of doing the job. There are videos out there that give you a better look at the process. Works the same with good quality screw drivers.
 
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dr sportster
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PostPosted: Tue Dec 05, 2017 9:25 am    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

It seems to me on the TV show Forged in Fire the blade smiths who do best understand the heat treating of the metal. It should work well.
 
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Stan in Oly, WA
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PostPosted: Tue Dec 05, 2017 10:02 am    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

Bret; That's perfectly clear with the punch, but not so clear for a screwdriver. Where do you apply the heat on a screwdriver to draw the temper down without damaging the handle? Just part way up the shaft, I'm guessing, but since that's so different from what you described for the punch I thought I'd ask.

Stan
 
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mjbrown
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PostPosted: Tue Dec 05, 2017 11:09 am    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

Heat the cutting end to the austentic temperature (non magnetic). Quench in water to about 1" back from the end. Quickly make a light pass on a grinder to make a bright spot on the bevel then watch as heat from the shank moves up to the cutting edge. The bright spot you ground will turn to straw color then to purple now quench it cool. The first quench makes the steel hard but brittle. Drawing the heat back into the cutting edge and quenching at the purple color keeps the hardness but makes it tough so it wont shatter when you try to use it.
 
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Dave H (MI)
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PostPosted: Tue Dec 05, 2017 1:19 pm    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

Now you got the idea!!!
 
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Bret4207
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PostPosted: Wed Dec 06, 2017 6:03 am    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

CVPost-Stan in Oly, WA wrote:
(quoted from post at 15:02:21 12/05/17) Bret; That's perfectly clear with the punch, but not so clear for a screwdriver. Where do you apply the heat on a screwdriver to draw the temper down without damaging the handle? Just part way up the shaft, I'm guessing, but since that's so different from what you described for the punch I thought I'd ask.

Stan


Stan, the way I do it is to heat the shaft like you said. It's a problem on stubby's, but I don't use many of them! Laughing
 
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John Garner
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PostPosted: Wed Dec 06, 2017 1:43 pm    Post subject: Re: re-hardening the tip of a center punch Reply to specific post Reply with quote

A countertop toaster-oven makes a good furnace for tempering (aka drawing) hardened steel.
 
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