I don't know it this will help you but, 1st as far as the billet becoming a parallelogram this is bet prevented by forging at 90Deg angles by rotating your wrist to exactly 90deg to the face of the anvil (if it is a rhombus rather than a parallelogram it will be due to your hammers striking angle) this is something that the only way to learn is to practice.... a lot. The same is true for power hammers or a press. Also the sooner you notice it going out of wack and fix it the less distortion you will get. I first really learned to keep things square after getting an order for a railing that needed 200 c scrolls out of tapered 3/4 SQ. forging 400 tapers to a matching length will get you to learn you to keep things square....

That said I find for milti-bar twists patterns it isn't all the important if there is distortion in the layers. What is important is the evenness of the twists. Most of the time I forge my bars Round before twisting to prevent shearing and in cases where that is impractical I at the very least forge in a heavy chamfer on all of the corners. I haven't tried some of the higher layer multi bar patterns recently but I remember finding that the same held true for them. I have spacer blocks that bolt on to my hammer and my press and I use them to ensure that the bars are of uniform size before twisting. that and even heats go a long way to keeping the twists even. I genraly need to go back and tighten sections. I have used a torch for that but found that a pipe wrench with a second handle welded on works better , heat the section that is loose , clamp in the vice just past the loose section and use the wrench to tighten the loose sections by twisting from just past the loose section.

hope that helps some any way.

MP

If you're using a power hammer, (especially with tall stacks) and your dies are worn, or your guides aren't adjusted (causing your tup to splay relative to the anvil), you'll have this issue. I've got an issue with one of my hammers (75lb Old Style Bull), doing this heavily.

Moving around to to engage the dies 180 degrees (i.e. the other side of the dies) heat to heat can help mitigate this but ultimately you need to cure the cause.

The thinner you draw the billet before restack, the less of an issue this'll be. With W's, it actually encourages activity, and what I'll do is forge the corners down into a light (not as heavy on the diamond) octogon, until I get thin enough that the trapezoid disappears. This has a similar effect of encouraging the W's like using squaring dies on to smear the sides.

I don't do a lot of twists patterns personally, because I'm far far far down the end bar pattern rabbit hole atm, so I hope this info is actually relevant and helpful.

Another thing I'll add, is that chasing "homogeneity" in patterns, lends itself much more to press work than power hammer work. Personally, I prefer variance in more organic patterns, but if I were shooting for the opposite, I would use the hammer as little as possible and work with billets small enough to engage completely with press dies as much as possible.

That's helpful guys, I appreciate the thoughtful replies. Yup I've got an older bullhammer too and after a few years of use it has developed a bit of slop. Seems like the best thing to do is address the issue as soon as it reveals itself and not let it get away from me!

Check your dies also Derrick, I surface ground mine less than a year ago but just checked mine and they've got some wear already, that being said, if your bull is the same style as mine, most of the problem is likely the tup guide adjustment. The way the tup is mounted on this hammer just exacerbates the situation, since it acts as a lever across the guides to the cylinder. Great hammers but they take some TLC. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' />

I don't know if this helps you with getting the 90 degree twist over during forging, but it helped me a lot. I weld my billet onto a handle with a 1 inch square tube on the end. I align the square tube with the billet and use it to judge when the billet is exactly 90 degrees over. I also put a piece of marking tape on the end of the tube so I can keep track of where the billet is in terms of folds, layers, stacks, etc. by writing on the tape. I used to use just any piece of scrap rod for handles, but now I weld a piece of 3/8 solid square to the billet and weld that into the end of a 1 inch square tube (about 16 inches long). The tube has 1/4 inch holes drilled through the sides at random distances to let the heat escape. That keeps the handle cooler longer so I can keep working without having the stop and cool off the handle. That being said, straightening up the dies on the hammer is probably the root cause.

you can tell if it is the dies or technique, by if the bar is of 90deg on one facet or two (ie two sets of parallel sides or no parallel sides) if nothing is parallel then it is the dies.(or striking angle if working by hand)if two opposing facets are parallel but not at 90degs to the remaining facets it is technique.

MP

Thanks again guys. I just came back from the shop and this time out I was careful to run the billet evenly from both sides of the dies and sure enough it came out nice and square. So I'm thinking my issue had probably been caused by the hammer. Running the billet through from opposite ends during each heat seems to allow the issue to simply correct itself. It also seems that this is one of those things best addressed the very moment you notice it rather than letting it go and trying to fix it later.

Joshua - I really like your idea too. Very clever!