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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Nonstandard steel tubes - please give some tips on how to bend.
Hi there!
I need to get information on what is the minimal bending radius for 1.9'' (48mm) OD steel tube with 0.079'' (2mm) wall thickness where bending angle won't be greater than 90 degrees. I'm planning on building my own tube bender dedicated for this kind of tubing. Tube bender should be similar to model presented on this page: http://www.blindchickenracing.com/To...bingbender.htm Since I live in Poland, having those tubes bent by someone else is not an option. Locations where this job could be done are way too distant and prices are too high. I've already spent some time trying to figure out the bend radius by myself but I've seen too many different opinions. I tried looking up this information on Pro-Tools website since I know they are selling dies for benders but there is no die suitable for me. I'm interested in minimal radius (CLR) that is possible without additional means like heating up tube walls or filling tube with dry sand. I hope this is clear description of what I need. Please forgive me if I made any language mistakes - English isn't my native language. Regards Lukasz |
#2
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If your bender is only half as good as your English, you'll have a
super bender. Best of luck with your project. Lewis. **************** |
#3
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You could do a whole book on the subject but here is the condensed
version: "degree of difficulty" is defined as the center line radius divided by the diameter. 6 and up is easy, 4 is ok, 2 is hard, 1 is VERY hard. This is really a function of how much the outer skin stretches in relation to the neutral axis that runs near the center of the tube. You are at 4, not too much of an issue. "Wall factor" is the diameter divided by the wall thickness. The higher the number,the more support you will need to keep the outer wall from collapsing and the inner wall from crumpling. 10 and less is pretty much self supporting, you are up at 24 to one, this will require substantial internal support. You can do it with a mandrel, cerobend (low temp metal) or sand. Sand is not very useful, it must be packed VERY hard. The bend die you need will need to be machined. If you only need to do a few (dozen) bends, you can make it from aluminum. A few hundred can be done with mild steel. Thousands will require hardened tool steel. The inner channel must be an exact fit for the tube, it must come up to the center of the tube. The edge walls need to be at least 4mm,6mm would be better. this means yours should be machined from a 60mm plate, a non trivial chunk of metal! standard practice is to spin a disk with proper groove, cut out the excess. Or cut it on a rotary table set on edge in a mill using a 48 mm roughing mill. This is very close to 1-7/8" if you could find a mill of that size it would be fast. Otherwise rough it then use a boring head to get the last cut. Slow and tedious. Try this site for some great information. You will need to register but it's worth it. http://www.toolsforbending.com/literature.asp Good luck. Lukasz Kucharski wrote: Hi there! I need to get information on what is the minimal bending radius for 1.9'' (48mm) OD steel tube with 0.079'' (2mm) wall thickness where bending angle won't be greater than 90 degrees. I'm planning on building my own tube bender dedicated for this kind of tubing. Tube bender should be similar to model presented on this page: http://www.blindchickenracing.com/To...bingbender.htm Since I live in Poland, having those tubes bent by someone else is not an option. Locations where this job could be done are way too distant and prices are too high. I've already spent some time trying to figure out the bend radius by myself but I've seen too many different opinions. I tried looking up this information on Pro-Tools website since I know they are selling dies for benders but there is no die suitable for me. I'm interested in minimal radius (CLR) that is possible without additional means like heating up tube walls or filling tube with dry sand. I hope this is clear description of what I need. Please forgive me if I made any language mistakes - English isn't my native language. Regards Lukasz |
#4
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"Wall factor" is the diameter divided by the wall thickness. The higher
the number,the more support you will need to keep the outer wall from collapsing and the inner wall from crumpling. 10 and less is pretty much self supporting, you are up at 24 to one, this will require substantial internal support. You can do it with a mandrel, cerobend (low temp metal) or sand. Sand is not very useful, it must be packed VERY hard. Thanks for your reply Roy. Thanks for lots of adequate information. The website you recommended is very helpful. I decided to build 5 x OD radius die just to be on the safe side. Unfortunately mandrel and cerobend are beyond my reach. I wonder if it's possible to fill the tube up with dry cement or maybe gypsum instead of sand. What do you think about this idea? Small grain substance like gypsum or cement wouldn't be hard to pack tightly or would it?. Regards Lukasz |
#5
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In the tube bending world, bend radius of a round tube is ALWAYS
described as the centerline of the tube. Bend radius of a square tube is ALWAYS described as the inside radius of the tube. Go figure. But using the proper nomenclature makes it easier to get assistance with your project. On the hbobbist level, we have tried the sand route with a hydraulic ram bender with marginal success. http://www.harborfreight.com/cpi/cta...emnumber=32888 bends over about 40 degrees would kink. And this is for a tube with heavier wall than yours. I think your idea of gypsum has merit. You want something that will clump and not flow under pressure. You will need to pack it very tight for a distance of at least 2 to 4 diameters past the bend area. You will need to have some sort of drill powered spring cutter to get the material out of there. If you decide that you want to build a bender like the one you mentioned, I think I would try and figure out some sort of mandrel inside the tube. The point where the bending occurs is well defined, about 1" from the point of contact with the straight die. Use a plug mandrel about .005" to .010" (.1mm to .3mm) smaller than the inside of the tube. It needs to be relieved a bit on the outside of the bend to conform to the newly formed bend. With this design, the mandrel does not move so it can be just a solid plug screwed into the end of a solid rod. You will need to have it easily adjustable for exact placement as well as well some sort of cam to pull it the first inch or two when you are done with the bend. Lukasz Kucharski wrote: "Wall factor" is the diameter divided by the wall thickness. The higher the number,the more support you will need to keep the outer wall from collapsing and the inner wall from crumpling. 10 and less is pretty much self supporting, you are up at 24 to one, this will require substantial internal support. You can do it with a mandrel, cerobend (low temp metal) or sand. Sand is not very useful, it must be packed VERY hard. Thanks for your reply Roy. Thanks for lots of adequate information. The website you recommended is very helpful. I decided to build 5 x OD radius die just to be on the safe side. Unfortunately mandrel and cerobend are beyond my reach. I wonder if it's possible to fill the tube up with dry cement or maybe gypsum instead of sand. What do you think about this idea? Small grain substance like gypsum or cement wouldn't be hard to pack tightly or would it?. Regards Lukasz |
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