Jon Kerr

Complete Beginner

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I have read more than a few posts where the person says that they don't bother to harden and temper their punches and drifts. Just normalize and go. I'm just starting out myself so I'm somewhat confused about it. I've been reading up on punch making in the forums here and most agree that the punch just needs to be harder than the hot material you're punching through. I would err on the side of too soft vs. too hard.

Pnut

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Ok thanks Pnut. I'm confused too.

Can anyone please recommend a procedure for normalizing (if necessary), hardening, and tempering a 4140 punch? (in laymans terms, please).

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Well you are looking at a place where folks are trying to get the maximum price for their stuff; don't expect to find many deals.

I generally do better talking with folks to find the "I've had one of those; it's been out in the shed for decades---you want it?" deals.  Takes longer generally.  Sometimes other blacksmiths will help beginners along; just remember they KNOW what the stuff is worth! Jumble sales, boot sales---ask folks that have stuff that look like it comes from someplace that might have a hand crank blower if there is one at home.

Worst case scenario build a double lung bellows!  You can use tarpaulin canvas for the "leathers".  I liked my double lunged bellows better than my hand crank---just took up a lot of space as I couldn't mount it in the roof trusses. 

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Everything I can find says 4140 is oil quenched. Quenching it in water may be the reason it cracked. I would try warmed vegetable oil and temper it fairly soft.  Will you be tempering in an oven or running colors

Pnut

Edited by pnut

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Jon, I would not try to harden it and temper it. I would just forge it, lay it aside to cool and use as is. You're going to use it on hat metal and that will take your hardening and tempering out.

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I've done interrupted tip quenches for 4140 slot punches in water (a couple of seconds in then double that in air, repeat till looks black then abrade surface and watch for the temper colors).  Still prefer to quench them in oil with a full quench except the striking end.  I like my punches to last, and I have bent  longer ones in the past (particularly those with sections under 1/2" diameter).  Ideally I don't let my punches or drifts hot enough to lose their temper, except at the business end when they get stuck, or are going through especially thick material.  If they do get that hot I try to re-heat treat them.

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9 hours ago, Latticino said:

I like my punches to last, and I have bent  longer ones in the past

I agree. I too harden and temper my hot work tools. The whole tool holds up better.

With 4140 I draw the struck end to a purple  after annealing and hardening to keep it from mushrooming quite so fast. The shank is usually annealed. The working end is annealed, hardened and differetially tempered to about a half inch or less to a straw on the tip. You will lose the straw, but the end is easy to reharden etc and the rest of the tool stays as is. 

The other reason is because you are new to heat treating and the only way to learn it is to do it. 

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Thanks everyone for the advice. Think I'll go with Lattucino and Anvil's advice as, as Anvil says, I need to learn to heat treat anyway.

Anvil- So, for a 4140 punch- you are quenching only half inch on the tip? Do you use Water or Oil? Then quickly polishing and watch the colours run to straw at the tip?

I guess best practice is still to do as JHCC says and repeat the quench/polish/colour run until the colours stop running, to ensure the shank never gets hardened?

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That is  one option. Another option is to do a full quench in oil, and then heat the middle to run the tempering colors out to the end. A plumbers torch is good for this: it gives very good control, and you can heat the struck end a little bit hotter than the business to temper it a bit more and thus make it a bit softer.

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Mark Aspry gave a demo at the IBA conference last year including punch making. I know he was using tool steel, I forget the type, but he would quench in water, moving the punch up and down vigorously. The last inch stayed submerged, while next half inch was moving in and out of the water to make a transition zone. He would the polish and let the colors run and repeat unit the heat was gone. He was also very insistent on heat treating punches.

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Hi Goods- that's essentially exactly what I did (with the depths and movements exactly as you describe).

What I definitely got wrong was that I heated the material way beyond critical temp before quenching (I forgot the "non magnetic" bit.). I also didn't do any normalising after forging to relieve any stresses/ improve grain structure. It does seem from online research that 4140 requires oil, also.

 

I'm going to repeat my try; but this time, I will do a normalising cycle, quench in OIL at the proper critical temperature, and polish and run the colour repeatedly until the material has cooled. Hopefully this will result in no cracks!

 

I'd really like to get this right so I can work on a set of long lasting punches to give myself some options in future.

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I've been struggling to find a nice (cheap/free) quench bucket for a while (with a lid, to stop the canola oil going rancid so fast).

Fortunately, I just sold the first axe I made, for £50! So I've treated myself to a very nice 25L (6 gallon) quench bucket with lid and handles (for £17. Gulp!).... and ordered 20L of oil to pour into it.

I'll definitely be making more bits to sell to fund my new habit....

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Plastic wrap laid on the surface of the oil will slow down oxidation which is what causes oil to go rancid. You want to prevent the surface from coming in contact with air.

Pnut

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6 hours ago, Jon Kerr said:

you are quenching only half inch on the tip? Do you use Water or Oil?

Not quite on hardening the tip. The end of your punch is tapered to whatever diameter the tip is. So bring the whole tapered portion up to just above critical temp. Critical temp is where you lose magnetism. Then quench about half or so of the taper in oil for 4140. Put it in vertically and move it up and down, not sideways. 

Now with sandpaper or file, quickly polish the taper good enough to watch the colors run. When you get the color you want and this color is about half inch long, put your tool in a can of water a bit more than half inch deep. This will stop the color run on the working end. 

This method is called the reserve heat method as you use the quench heat(in reserve) to run the colors.

JHCC's way works fine as well by adding heat after hardening. 

I prefer the reserve heat method as it saves a bit of time and there is no need for any other tools than your forge.

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