lejo

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.

unterhausen

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.

lejo

Sorry,typo. Og = of (type of tubes which is Columbus tubes)

unterhausen

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

CliffordK

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.

lejo

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 Harley’s so not conserned about that either. TIG and/or brazing should also be ok.

dsaul

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.

lejo

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..

unterhausen

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.

lejo

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.

unterhausen

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?

duanedr 

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.

lejo

@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 i’m sure they also du butted versions.

duanedr 

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.

lejo

Will do. Now i’m off for some holiday first. Then resume the build in August. Have a good summer

guy153

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).

unterhausen

Good catch. I think it would take hydraulics to bend a head tube. Or an incredibly long lever arm.

SilversSpeed

Bending 4130 is pretty straight forward. You don't need to anneal it after bending. It CAN be done but is not necessary for many applications. I used to build roll cages for cars and annealing is not necessary. Even tube chassis cars and bikes are often not annealed. They are built jigs for accuracy and welded.

Devin Rickey

I might be a bit late in this discussion, but thought I would share some recent experience bending seat stays for the first time. They are straight gauge, but tapered 4130. Roughly 1/2" diameter at the bend area and approx. 1 mm wall thickness. I filled them with sand and bent them in my vise over the post (tried to post a pic, but am too new...). They came out reasonably well for such a low tech approach. There is a small flat spot on the inside of the bend. I will be trying a different approach on the next ones...

unterhausen

Welcome to the forum.

Devin Rickey

Thank you Unterhausen! Glad to be here!

guy153

Please post pictures when you can! Bending SS is something I'm still researching. It's often something that it's quite useful to have.

Devin Rickey

Will do!

Devin Rickey

Here are the pics of my "bender"... Note the small flats on the inside of the bend in the second pic.

duanedr 

For 1/2" tubing like that one of the hand held tubing benders works really well.
I'm not associated with the listing but something like this. Also, I grease the follower shoe and mandrel with a very thin coating of thick grease. You'll avoid that flat spot on the inside of the tube.
Ridgid No.398 1/2” Tubing Bender | eBay