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Tubes and bending

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Tubes and bending

Old 07-15-21, 01:00 PM
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lejo
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Tubes and bending

Hi all. New on this forum. Hope to get som tip regarding choice of tubes and/or bending.

I am currently exploring a design which require a slightly upward bend on the top tube and the down tube must have a s curve below the head tube and down to the horisontal line going back to the BB.

My Columbus tube supplier does not recomend bending top/down tube for their type og tubes. So, what tubes are used to achive bends and still preserving quality and frame integrety? I do have a proffesional/industry bending machine available but i do not have the equipment or experience to go through annealing and cool down procedures.

Any tip appreciated. Thanks.
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Old 07-15-21, 03:39 PM
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unterhausen
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Welcome to the forum. What's an OG tube?

I think going with a non heat treated tube might work. I have only ever bent 4130 straight gauge though.
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Old 07-15-21, 05:23 PM
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Originally Posted by unterhausen View Post
Welcome to the forum. What's an OG tube?

I think going with a non heat treated tube might work. I have only ever bent 4130 straight gauge though.
Sorry,typo. Og = of (type of tubes which is Columbus tubes)
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Old 07-15-21, 07:43 PM
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Okay. I think that heat treated tubes and butted tubes can cause a problem. Although I'm sure some people have bent butted tubes. The problem is it might get expensive if they buckle

Columbus sells some tubes that aren't heat treated
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Old 07-15-21, 09:49 PM
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I'm not sure what the OP has access to, but my tubing bender doesn't do particularly well with the ends of the tubes. I think it also distorts the tubing slightly.

Anyway, one could get a better bend with straight tubing and discarding a few inches at each end.
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Old 07-16-21, 01:43 AM
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lejo
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Originally Posted by unterhausen View Post
Okay. I think that heat treated tubes and butted tubes can cause a problem. Although I'm sure some people have bent butted tubes. The problem is it might get expensive if they buckle

Columbus sells some tubes that aren't heat treated
Yes, and i would like to avoid sending $$ out the window :-) When you see some of the custom designs today or the old magificent Shwinns it must be possible. I would like to create a Shwinn (ish) design and that would require a slightly vent toptube and downtube. I am not worried about tube bending machinery. Have access to computer operated equipment. Just want to avvoid sourcing expensive tubes that will get damaged from bending. Might be possible to fill them with compact dry fine sand before bending though.

The plan is to set up a frame for EL crank and incorprate the battery into a Shwinn lookalike tank in the frame. I have alot of experience in fabricating gastanks and fenders for custom Harleys so not conserned about that either. TIG and/or brazing should also be ok.
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Old 07-16-21, 04:56 AM
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Your best bet is to go with straight gauge .035" 4130 tubes. It's not worth saving the few grams that a butted tube will save and you will get reliable bends with the proper equipment.
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Old 07-16-21, 05:23 AM
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lejo
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Originally Posted by dsaul View Post
Your best bet is to go with straight gauge .035" 4130 tubes. It's not worth saving the few grams that a butted tube will save and you will get reliable bends with the proper equipment.
Thanks! I just got a reply from Renoylds tubes also. They siggested their 631 tube. I guess the cost for a 631 is higher for similat 4130 thickness..
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Old 07-16-21, 06:56 AM
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The cost might not be higher until you start buckling tubes. Although if you are bending in the non-butted part, it might not be too bad. However, it's harder to successfully bend thin tubing.
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Old 07-16-21, 07:28 AM
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Yes, but the 631 is plain straight gauge. I see that the cost for 1 3/8 with 1mm thickness is EUR22.52 pr meter or 19.44 annealed.
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Old 07-16-21, 09:04 AM
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I didn't know 631 came in straight gauge.
1 3/8 at 1mm is very thick, can you get .9mm? How much was the 631? Or are you quoting the price for 631?
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Old 07-16-21, 09:59 AM
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You don't say what the bike is used for so, that may change the following. As mentioned, 1-3/8 1mm 4130 tubing is VERY stout and heavy! You will have much better success trying to bend smaller tubes like 1" for the top tube and 1.125 for the downtube. If you're using straight gauge 1mm walled tubes for these the risk of buckling is much lower, they will be certainly stiff enough and the frame will be somewhat less of a boat anchor. The Schwinn Stingray/paperboy bikes used quite heavy gauge, mild steel tubing in small diameters which would make your job much easier.
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Old 07-16-21, 03:46 PM
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@DUANdr. Thanks. Good tip. The bike is for road use with EL crank.


The prices i mentioned are from the catalogue per meter in euros, and 631 is straight gauge per info from Reynolds but im sure they also du butted versions.
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Old 07-17-21, 12:17 PM
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Originally Posted by lejo View Post
@DUANdr. Thanks. Good tip. The bike is for road use with EL crank.


The prices i mentioned are from the catalogue per meter in euros, and 631 is straight gauge per info from Reynolds but im sure they also du butted versions.
Yeah, I'm just saying that 631 is going to be pretty difficult to bend (it's very strong) and it doesn't likely come in thick walls like the old Schwinns. You'll likely go through a fair bit before you get satisfactory bends - be prepared. Bending tubing is one of the more difficult processes in framebuilding. Please post up progress and the tools you use.
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Old 07-17-21, 01:08 PM
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Originally Posted by duanedr View Post
Yeah, I'm just saying that 631 is going to be pretty difficult to bend (it's very strong) and it doesn't likely come in thick walls like the old Schwinns. You'll likely go through a fair bit before you get satisfactory bends - be prepared. Bending tubing is one of the more difficult processes in framebuilding. Please post up progress and the tools you use.
Will do. Now im off for some holiday first. Then resume the build in August. Have a good summer
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Old 07-17-21, 04:10 PM
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Originally Posted by unterhausen View Post
I didn't know 631 came in straight gauge.
1 3/8 at 1mm is very thick, can you get .9mm? How much was the 631? Or are you quoting the price for 631?
I think that's a head-tube. Some of these are supplied very long and they're the only non-butted tubes in the Reynolds catalogue. Also those dimensions work out to a 34mm ID (which is HT sized).
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Old 07-17-21, 10:33 PM
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Good catch. I think it would take hydraulics to bend a head tube. Or an incredibly long lever arm.
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