Forging round stock: any techniques for preventing or correcting corkscrew warps

N

Ninja Blacksmith

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Aug 26, 2012
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The project in question is a wakizashi that I am forging out of W1 steel round bar, and as round bar tends to do when hammered on, it developed a corkscrew warp as I worked my way up the bar. While still hammering it flat I tried - and tried to straighten it back out but with no luck, though after cutting the flatened section away and placing it back in the forge, I've had a little bit of success, but I'm not out of the woods yet. Before I finishtrying to get this warp out, are there any tips/tricks to correct it more efficiently, or is the only way to do it is with patience, a prayer for good hammerstrokes, and lots of fuel?
 
I dont know how others do it but I usually start off establishing a flat on two sides. I work this for a little bit then flip it up to hammer the top and bottom that are still half round. This straightens it out and makes it more square or rectangle. Then I go back to the original flat and start drawing it out some with occasional flipping it on its side to ensure it comes out even.

Hope that makes sense. Works for me but I am not the most experienced. Oh also make sure its hot enough and that you give the round plenty of time to ensure its all up to temp.

What size round are you playing with?
 
Actually, turning the round into square first may help me out a lot whenever I use the remaining piece of rod, it's too late for the one I'm working on right now - but it is almost straight again. I usually just start banging away after a segment has soaked for 1-2 mins at 1700+ F. Next time I will give your advice a try, Quint.:thumbup:

Oh; the rod I'm using is 3/4" diameter.
 
I would let it soak for a little while longer, it takes a while for round rod that thick to get even heat distribution atleast in my propane forge. May be different if your using coal or coke.
 
Are you using tongs or a handle? Tong control is an artform all its own. I have taken to welding handles onto everything... Round stock shouldn't corkscrew unless your technique is causing it to. Is your forge at 1700 or you think the steel is? That is about as cold as I would go... my starting is usually just shy of welding heat with round stock. It does take quite a while to soak up, and is a little tougher to get moving nice and even. I also work it down in sections. In other words, a little flat down both sides. Then a little more flat. etc etc etc. Instead of flattening a section then moving up the bar. Helps keep everything square as well.

It will be easier to get it flat once it is drawn out nice and thin actually. The thinner it is, the easier it is to get flat. If I have a bit of twist or wiggle in something that is still pretty thick, I try not to worry about it much. Now, spine to edge curve you need to kind of set up for so to speak. The edge side is going to grow as you draw it down obviously, so you get swayback. If you start off in the opposite direction, you wind up square after drawing the blade down.

I am no master of the forge myself, and struggle with some of the same things unless I remember to take my time and think everything through. It allegedly takes ~3000 repetitions for this stuff to become muscle memory. Along the tong lines... there is an old blacksmith here in town that makes fun of me. He says 'A bladesmith don't a blacksmith make...' Observing that those of us who forge blades from time to time often neglect the blacksmith's fundamentals...
 
Lucy: Once I get far enough up the rod that my gloves can't handle the heat, I use tongs or locking pliers (whichever I happen to have closest to me) - would gripping it by hand when I start out be the cause of corkscrewing? Right now I'm suspecting it is.

The forge gets hotter, it's only the steel that I wait for to reach 1700. The forge is mainly for the heat treatment of knives made via stock removal, but on rare occasion I try forging one to shape, so I don't really have near as much experience with a hammer and tongs as I do a grinder and file. I do appreciate the advice and it'll be put down in my notes.
 
I'm no forging expert, but I've picked up this jem


What you do to one side, you have to do to the other.

It's easier to keep it straight, than to straighten it after.
 
Thats exactly right count....

By hand you would probably be less likely to twist than with tongs. Unless you are really good with tongs... Without getting into a physics discussion, you are twisting the bar just a hair out of line each time. Usually it is your eye that is seeing it that way... It corkscrews because you are the same amount of 'off' on both sides you are flattening... That make sense? In other words both sides are twisting the same amount. Otherwise it would just have a curve one way or the other as being held flat out in front of you.

Are you working on the flat? If so, try putting some length in it first with a drawing hammer or a die. Not a lot... But a bit of length will also flatten a bit too. This has to be square on each strike as well.

Have you ever played with play-doh to get a feel for forging? Sounds dumb... but it works. Steel curves opposite the side that is getting longer. Steel doesnt compress. Even hot hot hot steel. When you strike, if you have the round bar twisted just slightly, or your hammer blow is off one way or the other (with respect to being square) the stock will start to curve away from the point where the most concentrated force was applied. Having the steel hotter makes it work a bit easier. Striking as hard as you can, you are likely to miss. And when you miss while swinging that hard it is a big miss. Hotter just helps.

Don't concern yourself with grain size and all that. You are going to normalize anyway so it will all pan out. As long as you aren't sparking off the surface you are good heat wise. I usually go for as hot as I can until I am detail working. I started with coal 20 years ago but dropped out for a long time. And now you could count the times I have forged off coal on one hand in the past three years. There is plenty of heat in coal, just a little more attention to the surface crud.

Again, I am by no means a master blacksmith either. And I try to use as much plainspeak as I can because thats how I learned.
 
Have you watched a step by step video or tutorial on how this is done?
The guys who do this daily are very methodical, and have a very particular order of operations that makes it work.
 
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