The melted pitch is a good idea. But, I remember seeing brass instrument brass tubes being bent after water was frozen inside. It can't can't compress like pitch. It can't move like large bearings or sand. I look forward to see your work and your answer to this problem.
Small mandrel bender
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dr_kingston
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Water pressure will not remove the crush or kinks in the pipe as Keith has discribed. Anything hydraulic has the same pressure in all directions. Steel balls forced through the pipe with the effected area heated will work.
Cheers Dale
johnny1320
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my intension was to use hydraulic pressure to stop the pipe from collapsing during bending, not to un kink after the fact, but I do think the ball method is the way to go, I would anneal the pipe and try that first. and heat if that didn't work.
I have bent aluminum, 304 stainless and titanium on machines with a mandrel, wiper die and follower. The mandrels all had between 1 and 4 "balls" that would allow the mandrel to extend past the tangent point of the radius. Even with that it was at times pretty difficult to avoid the hump. The primary hand-bending machine had a 4:1 mechanical advantage built into it which helped when bending larger diameters. There was also a hydraulic extractor for the mandrel if needed. I agree the wiper die would be a real challenge to make but would help smooth the bend. I have never tried the various "packing" techniques but am intrigued by the frozen water idea. It looks like you are almost there with your bender. I look forward to seeing the finished product.
One other thing I just noticed. It doesn't appear you are using a clamp block to hold the tubing. Part of the cause for the "hump" is the tubing slipping during the bend and not being completely drawn along the mandrel. In other words, the tubing should be pulled along the mandrel and not just held against the radius.
Steve C.
Steve C.
johnny1320
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I have seen this method as well but they add soap to the water to make it flexable or else the ice just cracks.
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True, but using gases to inflate pipes is dangerous. There's a reason boilers are pressure tested with water. Look at the Mythbusters episode where a cylinder containing gas under pressure penetrates two cement block walls when the valve is sheered off.
Lohring Miller
dr_kingston
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Hi Lohring,
I use CO2 gas so that I can heat the effected area to remove the distortion. Hydraulic testing of boilers has always been the norm but this process will not do the job we are asking. I do not use 3000 psi, I have done jobs with as little as 50 psi to blow out 1mm thick steel tube and pipe diameters up to 50mm.
The Mythbusters get it right sometimes.
Cheers Dale
In this thread http://www.homemodelenginemachinist.com/f31/1-4-scale-v8-first-project-13548/index3.html Keith uses Cerrosafe "Woods Metal" low temp alloy to fill his pipes before bending. And judging from his results it worked pretty good !!
Scott
Scott
johnny1320
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Yes they did turn out nice, but Keith5700 was the one that started this thread to improve on the method.
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I've not had chance to try any new ideas out yet, as some of you may have noticed , I'm back on the V8 for the time being.
The discussion on this thread is very interesting however, and there are some things I want to try out when I get the time. The first thing will be to check if the tube is sliding back when pulling round the die, and causing the distortion, as has been suggested.
It would probably need a redesign and a new die to get a clamp on the tube in this area, but would be worth it if this was the cause.
The Cerrobend idea gave good results, but was very time consuming and extremely messy.
Cheers.
The discussion on this thread is very interesting however, and there are some things I want to try out when I get the time. The first thing will be to check if the tube is sliding back when pulling round the die, and causing the distortion, as has been suggested.
It would probably need a redesign and a new die to get a clamp on the tube in this area, but would be worth it if this was the cause.
The Cerrobend idea gave good results, but was very time consuming and extremely messy.
Cheers.
You may have a look at the way music instrument maker now repair dents in brass saxs, trumpets or others instruments : with a strong neo magnet outside and a polished steel ball inside (many videos on the Net). It looks really magic with thin brass, but with steel the magnet would not work so well...
ie this video
[ame]http://www.youtube.com/watch?v=LJi_QzGY--k[/ame]
ie this video
[ame]http://www.youtube.com/watch?v=LJi_QzGY--k[/ame]
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Hi Keith
I've been reading up pre-bending some small copper pipe. Suggestions are filling the tube with salt and plugging it. Perhaps better thanks sand as its finer, as long as its flushed well. Also have a look at "woods metal", I haven't used this but perhaps others could comment?
Bob..
I've been reading up pre-bending some small copper pipe. Suggestions are filling the tube with salt and plugging it. Perhaps better thanks sand as its finer, as long as its flushed well. Also have a look at "woods metal", I haven't used this but perhaps others could comment?
Bob..
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Hi Bob,
Woods metal is another name for Cerrobend, or low melting point metal, which is what I have been using before the mandrel bender.
As for sand or salt or ice,etc. which could be packed into the tube before bending, I just can't believe that this method would do anything positive, when I take into account the massive forces involved when pulling the tube round the die.
The way I look at it in my head is that the thing that's inside the pipe would need to be rigid enough to prevent kinking the tube if I was to give ita good clout with a steel hammer.
The steel mandrel would, of course, but I can't imagine anything deformable would.
Cheers.
Woods metal is another name for Cerrobend, or low melting point metal, which is what I have been using before the mandrel bender.
As for sand or salt or ice,etc. which could be packed into the tube before bending, I just can't believe that this method would do anything positive, when I take into account the massive forces involved when pulling the tube round the die.
The way I look at it in my head is that the thing that's inside the pipe would need to be rigid enough to prevent kinking the tube if I was to give ita good clout with a steel hammer.
The steel mandrel would, of course, but I can't imagine anything deformable would.
Cheers.
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