Rutterbush Posted July 28, 2009 Share Posted July 28, 2009 Making a squared right angle bend (L shape) hasn't been a problem. I would like to know of a formula that gives a starting length so that when the iron is bent the legs work out to approximately the correct length. EXAMPLE: Use 1/2" x 1/2" square stock. I need one leg to be 11" from end of iron to outside end of bend. The second leg should be 15" from end of iron to outside end of bend. What length of iron do I start with to get these dimensions? Please point me in the right direction if it happens to be posted somewhere already. I am also interested in any other formulas for forging to size. Thanks Quote Link to comment Share on other sites More sharing options...
jeremy k Posted July 28, 2009 Share Posted July 28, 2009 I was showen to mark the side of the stock w/ a center punch mark as a reference as to where the center of the bend should be kept. This helps out alot during the forging to give you an idea as to where your bend is going, and once you get one done(or a few for more accurate approximations) you can measure the leg and make adjustments accordingly. - JK Quote Link to comment Share on other sites More sharing options...
johnptc Posted July 29, 2009 Share Posted July 29, 2009 without the math bend the first piece a little long and measure the results and you are good to go. note the length of the bar and the start point of the bend. when you have bent it you will know the gain/loss for the next pieces. i have bent a lot of tubing and always found a single test piece more accurate the the math. ime Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 29, 2009 Share Posted July 29, 2009 (edited) If you're not making a square corner bend then you need to know the radius of the bend. Length is pretty darn close to the centerline length. The radius makes a huge difference because it takes a "short-cut" across the corner. I usually use a little math and a test piece like John. But I also use CAD for most things. Edited July 29, 2009 by nakedanvil Quote Link to comment Share on other sites More sharing options...
brucegodlesky Posted July 29, 2009 Share Posted July 29, 2009 I don't remember the formula but Metalbender , who is a member here is really good at that stuff. Try emailing him Quote Link to comment Share on other sites More sharing options...
jeremy k Posted July 29, 2009 Share Posted July 29, 2009 I'm Sorry Rutterbush - I was thinking you were doing a forged square corner bend - JK Quote Link to comment Share on other sites More sharing options...
mcraigl Posted July 29, 2009 Share Posted July 29, 2009 My shot would be to mark the piece at 14 3/4" with a prick punch, and shoot for that being the center of my bend guessing that I'd pick up the other 1/4" from the thickness of the stock. Test piece is key in this situation I'd say. Quote Link to comment Share on other sites More sharing options...
Dave Leppo Posted July 29, 2009 Share Posted July 29, 2009 I work in the sheet metal design field, and predicting a sheet metal blank before it is bent is a similar challenge. You "gain" a set amount of material for each bend (for the reason that Grant mentioned, among other things), but this relies on press-brake tooling which is consistent. We have had to use experimental evidence to develop standards for each different thickness of material. Hence: use a jig to keep your bend parameters consistent, and bend one (or three) test piece(s) to learn what the difference between start and end will be. Start with a test piece say 12" long, bend it in the middle, measure the result. Do this three times if you are a patient person, and use the average as a CONSTANT of increase per bend. Keep in mind that measuring across the bend (from outside to outside) will add about Quote Link to comment Share on other sites More sharing options...
Sam Thompson Posted July 29, 2009 Share Posted July 29, 2009 There are a lot of these formulae in here:The Blacksmiths Craft Quote Link to comment Share on other sites More sharing options...
danielsmith Posted July 29, 2009 Share Posted July 29, 2009 hey rutterbush, i have two tricks i do for right angle bends. if using 1/2" square, 11" long, I would put a center punch mark at 10 3/4". put it exactly in the middle of the stock. then make the right angle bend with the center punch mark on the side. It should be lined up in the middle of an imaginary diagonal line drawn from the inside corner to the outside corner. this should give you 11" from outside corner to bottom. the idea is subtracting half of the width of the starting stock from the total length needed. check out "elementary forge practice" by John Lord Bacon. It has some great ideas on forging. the second trick i do is to forge a corner with plenty of stock to spare and then cut the piece to length. is that cheating? Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 29, 2009 Share Posted July 29, 2009 O.K. Now I think I understand the question better. I thought he meant he had no problem when doing a sharp bend. But i think he just meant he has no problem doing the bend, but now he wants to do the same in an accurate position. Test piece, punch-mark, go for it. Quote Link to comment Share on other sites More sharing options...
NeatGuy Posted July 29, 2009 Share Posted July 29, 2009 if you are working with inside dimensions then simply add up your segment lengths. If you are working with outside dimensions then you can subtract a thickness for each outside bend or simply convert all your dimensions to inside dimensions. there is also a formula : Ba = A/360 X 2pi(R+kt) where Ba = bend allowance (in) subtract off total length for each bend. A = bend anglen (deg) R = bend radius (in) t = metal thickness (in) k = constant neutral axis location (a value of .5 places this in the centre of the material) brad Quote Link to comment Share on other sites More sharing options...
Charlotte Posted July 29, 2009 Share Posted July 29, 2009 Neat Guy Thanks! i just copied that to my file of stuff I should know but forget every time. Excellent! Quote Link to comment Share on other sites More sharing options...
CRAFTBENDER Posted July 29, 2009 Share Posted July 29, 2009 When you bend metal it compresses on the inside and stretches on the outside. There is a place where it neither compresses nor stretches. This place is 44% of metal thickness, so if you add the bend radius to 44% of metal thickness and multiply by Pi you will have the amount of material in 180 degrees of bend. 90 degrees is what you are looking for so you divide by two. In a formed piece you have flat places and bends, so you figure how long the flat places are and of course the bends. In this case you have 11 inches by 15 inches, both outside dimensions. So lets figure using a 1/2 inch radius. First we subtract one material and a bend radius from 11 inches, so one flat leg will be 10 inches to where the bend starts. We subtract a material and a radius from 15 inches and we get 14 inches of flat leg. So now we figure the material in the bend. .44x .5 material thickness equals .22 plus .5 bend radius equals .72 times 3.14159 equals 2.262 divided by 2 gives us 90 degrees of bend which is 1.131. So 10 inch flat plus 1.131 in bend plus 14 flat gives us the developed length of 25.13. This simple formula has served me well for over 40 years Quote Link to comment Share on other sites More sharing options...
CRAFTBENDER Posted July 29, 2009 Share Posted July 29, 2009 I don't remember the formula but Metalbender , who is a member here is really good at that stuff. Try emailing him Hello to my good friend Bruce. Craftbender just got back from Texas. Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 29, 2009 Share Posted July 29, 2009 (edited) I've gotten by with centerline (50%) for many years, close enough for a blacksmith. Otherwise I just fit things together with Vise-gripCAD. Using centerline I get 25.1781. Less than 1/16" different than using 44%. I know you are right with 44%, but when you got bends going left, right and up and down it's easier to keep track of the centerline. Edited July 29, 2009 by nakedanvil Quote Link to comment Share on other sites More sharing options...
Dave Hammer Posted July 29, 2009 Share Posted July 29, 2009 You guys have WAY too much time on your hands..... :-) Quote Link to comment Share on other sites More sharing options...
Dragons lair Posted July 30, 2009 Share Posted July 30, 2009 I also use the 50%. It ain't rocket building Ken Quote Link to comment Share on other sites More sharing options...
Sam Thompson Posted July 30, 2009 Share Posted July 30, 2009 The difference between a blacksmith and an engineer is about one-eighth of an inch. Quote Link to comment Share on other sites More sharing options...
Dragons lair Posted July 30, 2009 Share Posted July 30, 2009 Engineers I have to deal with think 1/8 .125 is .120 out of spec. This on a large welded frame. Every dimension was a 3(dismal) places. Anybody got a .409 drill? Hole centered on a 13.137 piece of sq tube. Its done can I retire now? Ken Quote Link to comment Share on other sites More sharing options...
Rutterbush Posted July 30, 2009 Author Share Posted July 30, 2009 Well, I appreciate every answer. What I asked about was the squared corner. Bend, hit end of one leg of the bar to drive it into the corner to upset, hit the opposite outside of corner to square up, repeat until 1/2" x 1/2" looks like it could have been cut and welded into 90 Quote Link to comment Share on other sites More sharing options...
Sam Thompson Posted July 30, 2009 Share Posted July 30, 2009 As far as I'm concerned drills come in three sizes:small, medium and large. Quote Link to comment Share on other sites More sharing options...
DClaville Posted July 30, 2009 Share Posted July 30, 2009 As far as I'm concerned drills come in three sizes:small, medium and large. what is that thing a drill you speak of?? hmm most be how you call what we call a hot round punch ;) Quote Link to comment Share on other sites More sharing options...
Finnr Posted July 30, 2009 Share Posted July 30, 2009 Drill! Drill!!!! We don't need no stinking drills!!!! Well maybe now and then. Finnr Quote Link to comment Share on other sites More sharing options...
brucegodlesky Posted July 30, 2009 Share Posted July 30, 2009 Hey Riley! Welcome back! Quote Link to comment Share on other sites More sharing options...
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