Frustration

[BlasterJoe]

Hello all,

I have been working on making my own hammer. This is my first attempt ever with something this big. I used a piece of trans axle I found and just kind of went for it. After about a day and a half of work it all blew up in my face. I think I need to make a better eye punch. I made a drift but figured I could just drive a cold chisel I made from an old pry bar. Was it spreading too much too fast? I tried to keep yellow heat when driving it but it did stick a few time and took some doing to get it out. 

[Jackdawg]

bad luck! Looks like you had a fair of work invested in it when it went too.

 

[SLAG]

Really good luck, overall your face is still fine.

SLAG. 

[turbo7]

Your drift is too square, try for a more oval shape.

[BlasterJoe]

The crack happened pre drift. I was just trying to get the hole punched. 

[Kozzy]

Too sharp on the corners.  

Imagine bending a piece of flat bar to 90 degrees in a vice.  If you make a really tight bend, the outer edge of that bend has to stretch.  If the bend is too tight a radius, that stretching will be so severe that the outer surface of the metal can't deform well enough and will crack.  Ductility has limits (even at yellow heat)

That is exactly the same thing that is happening on your hammer blank.  When you are driving the punch, the sharp corners are causing the metal to stretch more than it is capable of which starts a corner crack.  Once you have even a tiny start, it will progress to the point of catastrophic.  

Same kind of thing happens when drawing shells (not meaning bullet shells in presswork, any cupped shape)  from sheet in a punch press.  You have to keep the radii large. Plus they usually do the forming in several stages rather than one single forming hit--progressive forming dies.  You are doing similar "progressive die work" with reheating and driving the punch a little more with each heat.  Like sheet forming, you can't do too much in one shot and you can't be too severe (sharp cornered) with the early forming progressions.  In your case, the "forming die" (punch) should be nearly round early on (round distributes the forming stresses most evenly) and then progress to the more sharp corners ONLY at the very last of the forming operations.  

Sorry to get wordy there but I can't seem to find a good photo on the inter-tubes to use as an example

[Frosty]

Ayup, sharp corners on an inside bend cause "cold shuts." The forces applied to punch or drift the piece are concentrated at the corners just like they are at the score marks when cutting glass.

Also you'll have better luck with a proper slitting chisel or a punch than a cold chisel. Take a look at Brian Brazeal's slitting punch design, they are very effective and not hard to make.

Punching should be done in stages, alternating sides unless you have the power to punch through in one go. Take a look at the eye in your hammer head now. Note the taper and as expected how it matches the chisel. Driving the chisel from this side maximizes the contact surface and moving metal is about psi, not total force. Max contact surface equals max friction and minimum psi, just the opposite of what you want. Now visualize driving the chisel from the other side, the taper is reversed so the contact area is minimized for minimum friction and maximum psi.

Aligning the slitter on opposite sides is the real trick so drill a pilot hole(s). Using a slitter generally profiled like a cold chisel drill two pilot holes, one for each end of the chisel face. This will do 3 important things: First it gives you hard, matched marks on opposite sides of the hammer. Second, the chisel will follow the pilot holes, force ALWAYS follows the path of leas resistance. Third, the pilot holes relieve stress at the corners sort of getting the jump on cold shuts. This won't last if the corners of your slitter are sharp but you'll have better luck and if you rounded your slitter you're golden.

The last important thing to remember slitting and punching is lube. Wax is pretty good, it starts slippery and burns to carbon and remains a decent release agent for the punch. I like graphite it's VERY slippery and doesn't burn at less than ridiculously high temps. Keep the punch/slitter, etc. cool and lubed.

Only drive it a couple blows at a time, 2-3 is plenty then cool and lube it. If you let the tool get hot in the work it will jam. Things EXPAND when they get hot so if you've driven something into the hammer head, then let it get hot and expand it WILL GET TIGHTER. Once the hammer head cools it will shrink more than the tool.

If the tool gets too jammed to remove without damaging  get out the torch. Stand the work on the tool in a can of water and heat the work with the torch. This will heat the work while the water keeps the tool cool maximizing the chances of getting the tool out.

Frosty The Lucky.