2017 July 17    Metal & Shop  


Introduction




The punch is one of the simplest tools there is;  it's basically a cylinder of metal that gets hammered on at one end.  The other end could be pointy, flat, or some other shape.

It's not a wrought iron fence with a bunch of fancy scrolls.  It's just a punch.  Anyone could make one of these, couldn't they?

Well, that's what I used to think.  If you're getting started in metalworking, I highly recommend you read this article!

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A Piece of Scrap


It's a splined axle-something-or-other.  Perhaps a mower spindle?

Whatever it was, someone else thought it looked like a punch, too.  They hammered on it 'til both ends were rounded over.

I got it with a couple of rusty old tools, hoping it was at least medium-carbon steel. 





Spark Test


So, what kind of steel is it?

If you have known pieces of steel, you can grind them;  compare the sparks to your "unknown".  This sounds easy, but the sparks move so darned fast.

Unless you slow them down:



And then compare it to a known piece of low-carbon steel:




Aha!  So the axle, or whatever it is, is probably low-carbon steel.  As you can see, there's some branching, but not much.  The sparks are mostly straight lines. 



The Propane Forge


After trying different ideas, I found something that works OK for light forging.  With a good pile of firebrick and the right supports, it makes a usable propane forge.    (Potentially "way" dangerous if it's not built securely;  disclaimer.)

This might not be the most fuel-efficient method.  But it's quick, and I don't have the charcoal-forge welded up yet. 



This was the Mark Zero, junkyard-prototype, "don't try this at home" stage. 

Some people recommend computer-controlled gadgetry on your forge.  That stuff has its place, but I'm not interested in that right now.  It's either going to be coal, wood, charcoal... or at least a purely-mechanical gas forge.  I just want something simple.

If you do build one of these torch-forges, build the right support for it.  And find a completely secure way to anchor the nozzle, etc.  Also-- obviously-- pick the right location for the forge.  Shortly we're going to revisit this topic.


Hammer and Anvil


I got a chunk of rail at a flea market for cheap.  It looked as though someone broke it off a track, literally;  the end was jagged, but not from a cutting torch.  It took about an hour of grinding and cutting to fix it.  (Save a lot of time and buy a nicer one here...)  This was the anvil for today.

The hammer was a 16- or 20-ounce ball peen.  I find when the steel is half-inch diameter or less, that weight range is very usable.



Metal Shaping


The machined-down end had flat sides.  So I had to pound that into round.  Even at the correct heat, this took a while with my beginner skill-level.  (You blacksmiths with actual skill probably know what noob mistake I was making;  I should have hammered it to square, then octagon, and so on.)

As it started to get round, many taps with a 1-lb hammer worked better than a few slams with a heavy hammer.  The heavy hammer kept bending the metal. 

The light hammer worked, but the outside of the metal drew out more than the center.  Sometimes this is called "fish mouth".  For a pin punch or solid punch, that end-surface has to be made flat again. 

If you hammer the end flat, the metal will upset.  It will no longer be the dimensions you spent all that time trying to make.  (And it will probably bend some, too.)  So I had an idea.

Put it in a vise and hot-file it. 

When steel gets to a dull red heat, you can file it easily.  A worn-out file actually works well.


Precision Backyard Machining??


Chuck the thing in your power drill-- held securely by Vise Log, perhaps-- and you precisely file it down to a runout of only 0.001".  (Maybe not really .001, but I do have a brass punch that looks mighty good.  I've read that a decent Jacobs chuck can do 0.005", anyway.) 

But the punch is 1/2" steel;  it won't fit into the 3/8" chuck that I have.

So here's what I did instead.  I clamped the angle grinder in a vise.  Then I freehand-rotated the punch carefully against the wheel, a worn-out flap disc.  (Dangerous?  Probably.  Do this at your own risk.)  Sanded it down to a precision of "whatever looks good". 

It's still not perfectly round, but then again it's not a mower spindle anymore.



That leaves us with one problem.

How to harden mild steel?


Heat Treat


Hot-work punches don't need to be heat-treated, really.  Old-time blacksmiths made them out of wrought iron.  But if you're going to be rust-busting broken-off bolts, or center-punching cold steel, or things like that... you'll probably want to harden the metal.

First I was thinking of "pack carburizing", but that requires clay and stuff that I didn't have handy.

Next idea:  Gunter's Super Quench.  5 gallons water, 5 lbs table salt, 32 ounces Dawn dishwashing liquid, and some dishwasher rinse aid. 




When ready to use, stir the bucket so the liquid is moving.  Heat the metal to 1550 degrees F (bright red to orange) and quench. 

So I mixed up about five gallons of this in a pail.  And I rebuilt the propane forge outside. 

Makeshift, but at least this one was not sitting on plywood.



You'll want these when operating the forge, and some welding gloves.  I used wolf-jaw tongs to move the punch to and from the forge.  They also worked OK for moving hot firebricks, but only the thin kind.

I put the whole punch inside the brick chamber and heated it for quite a while.  Twenty minutes?  Only the end nearest the torch got to a glowing heat.  Maybe that's a sign of improper forge design;  but hey, it's a pile o' bricks thrown together in five minutes.



When the punch end looked orange, I removed it and quenched it in the Super Quench, stirring constantly.  Then, into a pail of plain water. 



Did It Work??


1550 F is about the same color as embers in a wood fire:  glowing orange.  Look for these colors in the shade;  direct sunlight obscures them. 

To verify the temp, I really should have had a good high-temperature IR thermometer.  I don't know about programmable gas flow controllers and all that, but I'll grant you that a pyrometer would be very good for learning what color corresponds to what temperature. 

So anyway, did the Super Quench work?  Well, I tested the cold metal by tapping on it lightly with an 8-ounce hammer.  The edges started to cold-work, easily.  This shouldn't happen with correctly-hardened steel.  And a file didn't skate off it.  I won't say it was like butter, but I still think something went wrong.

Probably it's simple:  I didn't heat the metal enough. 

If you only heat the end, the rest of the metal is a heatsink.  So, the part that was at the right temperature... might not be, just ten seconds later.

"Weedburner Forge Mk 1" was semi-fail.  It didn't bring the entire punch to orange-hot.  It might have got there after an hour on full-blast, but that's too slow.  Some forges can heat 1/2" stock to yellow in two or three minutes.  (Yeah I know;  someone has a forge that can do that in 10 seconds...)



More About Propane Forges


Weedburner torches don't do very well with back pressure.  That brick oven you build around the nozzle will generate lots of it... unless you leave the other end open. 

That may not be the right type of flow, either.  All that throughput is carrying away heat energy with it.  It may work better if the propane flame goes in from the side of the forge, not the end.  Turbulent flow is really complex;  the easiest way is simply "change something and see what happens".

Opinions are mixed on the use of weed burners for blacksmithing;  some people say these require more oxygen, while others say they are too oxidizing already. 

The pieces developed a lot of scale.  Those guys might have been right about "too oxidizing":




This may be why the steel didn't harden much in the Super Quench.  In an old book I've read about heavy scale causing problems.  And somewhere I've read talk of putting extra fuel (charcoal, wood pellets, coal) into the firebrick chamber.  I don't know if that will help, but it might. 

The back-pressure thing seems to be correct, for sure.  This will cause the flame to sputter.  To fix that, try setting the nozzle back a little ways from the bricks.



Smart Solution


If you want to get forging and heat-treating metal right now, the methods I've tried so far will not get you there fast enough.  And if you want to build a "proper" forge... well, you may not need computer-controlled gas valves or anything like that.  But it's still going to take some time with a pyrometer.  Try something, check the temperatures, try something different, repeat.

You can do all this, and it might work great.  Or, you might find it's a challenge to heat simple steel punch to orange in 20 minutes. 

The smartest move would be to get yourself a ready-made forge.  For larger stuff, get one of the bigger propane forges.  You will save a lot of time and money in the long run. 




Conclusion


This was a look at making a solid punch using very basic blacksmithing and grinding. 

Super Quench should work for the heat treating, but I think I didn't heat the metal enough.  And the oxide scale, that's also bad.  The makeshift gas forge was the limiting factor, I think.

This little exercise has made me appreciate a good set of factory-made punches.  If I want to do work that demands a perfectly dependable tool, I'd use something like that.  But making your own is a good way to appreciate just how much technology goes into one of the simplest-looking tools on earth.


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