Everything about bending tubes

I didn’t find any thread specifically about bending tubes, so I thought I would start one because I have quite a few questions. Feel free to move it or join it to another if it’s more appropriated. I separated my questions so that people can answer specifics and not search thru a wall of text.

1. Benders (types, brands, etc.)

First I’m curious to see people’s bending setups, what benders you’re using for what purpose and why. Myself, in the longer term, I would be interested in bending racks, handlebar and frame tubes. Doing some research, it seems like this would require 3 different benders: one for small diameter rack tubing, one with relatively tight radii for handlebars, and a third one for big swoopy frame tubes.

Tube benders such as the Pro-Tools or JD2 seem to be the ones I see more often:
Pro-Tools bender
From the few different models I found, these can generally bend tubes from 1/2" up to 2", with radii ranging from 3" to 7.5". This would technically cover both handlebar and frame tubes, although I feel one could want bigger radii for frame tubes for more gentle curvatures. I only say this based on me fooling around on BikeCAD making crazy bendy frames for the heck of it. I tried using common bend radii (Cobra Toob Bender as a reference) but in some cases I didn’t like the look of the a tighter radius, so I would just end up putting random radius numbers until I liked how it looked, sometimes getting to ridiculously big radii like 1000mm. I know you can have custom dies made, I believe Cobra do it, but if I want to make crazy swoopy frame tubes à la Oddity or Blacksheep, would a manual bender like the Pro-Tools be able to accommodate such big radii?

Another bending method I know about and used during my internship at T-Lab (Montreal Titanium frame manufacturer), is to use a hydraulic press with custom-made mold. They would CNC’d the mold to their specs and all I had to do was to take the straight tubes, put them in the mold and press 'em. This was actually pretty efficient and good for repeatability, but seems like a pricey setup. Not the press itself, but for the CNC’ing and being limited to specific molds.


2. Custom dies

Back to manual benders: if getting into custom dies territory, how do you know the limits? I tried finding info about minimum radii for a given tube OD and wall thickness and did found a rule of thumb, but it seemed to be for industrial use and may not be applicable to bike tubing. Even looking at the Pro-Tools die chart, the minimum wall thickness they recommend for all tubing OD is .049". So, without having do to a bunch of trial and errors with custom-made dies, how do you find the sweet spot? Do you just stay relatively conservative to make sure? Are there maximum bend radii?


3. Handlebar specifics

Lastly, I know one of the main problem with bending handlebars is the distance between the bends. I tried to model a simple riser bar on Fusion360 and quickly realized that this can be an issue depending on radii and bar design. Playing around with it I ended up with a workable model, but it got me thinking that there must be some kind of equation to find out the minimum bends distance? I imagine that the type of bender will also have an influence on that distance.

For single bend handlebars, like a bullmoose for example, again one could want bigger radii. In 3D, a 9" radius (biggest radius offered with the Cobra bender) looks nice on a bullmoose, but I’m not sure how well it translates in the real world. Anybody used the Cobra bender for a similar handlebar?

I probably have more questions but I’ll just start with that to get the ball rolling. Any insight is greatly appreciated!

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The standard at the moment is the Cobra TOOB bender. It has some flaws, but I think it’s the best bender out there for two reasons:

  • The follow bar (missing from JD2 style benders) constrains the tube, which prevents it from wrinkling with .035in tubing
  • You can do two chainstays and seatstays in tandem

I think the Cobra bender is best used as a CS, SS, and ST bender.

  • For handlebars, the bends can’t be placed close enough (65mm) and sharp enough for risers
  • For swoopy tubes, the 230mm is too sharp for big tubes (>35mm). It ovalizes the bend quite a bit in the large tubes.

I agree that swoopy tube bends look better with >500mm radii. The way the cobra works, the max radius is 230mm.

I call the style of bender you describe a clamshell mold. I have been told this is how James at Black Sheep gets the swoopy downtube radii, but I am skeptical.

Another style of bender is a tube roller. This is good for creating those long arches (~1000mm radii), Looks like James also made his own roller:

In this video, you can see moot’s DIY bender. Eyeballing it looks like a 400mm CLR

I also don’t think DIY dies are out of the question. Just for fun I did a quick quote with PCBWay for a 500CLR 22.2 die. $100 is not bad for a giant chunk of aluminum.


@Meriwether builds bikes without any straight tubes. He can chime in on his experiences.

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@Daniel_Y there are at least two straight tubes on my bikes! :joy: I’m not as crazy as Blacksheep and Oddity though, they’re next level.

Oakes Mfg next door to Blacksheep in Ft Collins used to make the clamshell dies for a 2-ton HF hydraulic press and cost was about $1100 just for the dies. They were used for those dual bend down tubes or a kinked top tube klunker, and seat tubes. It’s not as easy as clamping the tube and squishing it though. Bending is a dark art that only some have the patience and cash to dive into completely. One wastes a lot of tubes learning what works and doesn’t. You need a variety of benders and dies for each part of the bike although the Cobra is extremely useful for seatstays, chainstays, seat tubes, even kinked top tubes, but you’ll need all those dies. No other bender can do that unless you have a Diacro and the knowledge of how to machine dies for it.

Anvil sold a bender I still use mostly for handlebars. The reason Blacksheep and Oddity and Myth and others have made their own benders is because nothing has the side clearance for riser bars. If you look closely at the videos people have done coming out of those shops you may be able to catch a glance at their setups but they tend to keep their designs out of the photos since it lets them do what they do. James is probably the most likely to share his setups.

Below is the Oakes one but their bike site is down, I think they got too busy during Covid and stopped making bike bits.

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Forgot to say, the JD-squared is not going to get long radius bends. It’ll fold thin wall tubes. The cheapest way to get those long radius bends are with either a Harbor Freight tube roller, and dies from SWAG Off-road, or SWAG also makes their own roller that’s better than the HF but a lot more $. You can do butted tubing in these but it’s hard to roll or bend heat treated stuff, doesn’t want to bend.

Automatic rollers are way easier and faster but cost a lot. Someone else makes a manual roller that Coconino has used for years but I can’t remember the name.

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James Blacksheep has a photo up of his ti-handlebar bending set up. Looks like a JD2 style bender with a massive lever and some grip tape on the ground haha

I have a strict :x: no swoops :x: rule on my frames, so I can’t speak on bending any frame tubes. But I do bend up a handful of bars every month.

For that I use a JD2 model 32 with a 3.5 clr die for .058 and thicker tubes. I have a 6.5 clr die that I’ll use on .049 tubes on the rare occasion I do a flat bar or something.

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For us more price-sensitive hobbyists, the venerable Chinese budget bender produces acceptable results when bending stays with a few simple modifications. I’ve bent 14mm and 19mm tubes, both with 0.9mm walls. There’s a little bit of flattening on the outside of the bend as the dies aren’t a perfect fit but it hasn’t rippled or kinked any tubes so far. I haven’t tested on a 25mm tube which is the largest supplied die. I’d say it’s worth a punt if your wallet’s feeling the strain and you can make it suit your application.

s-l500

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I have the same JD2 as @wzrd to bend CS and SS. No handlebars yet as I did not took the time to figure out phasing for the back and up sweeps.

I have 1/2, 5/8, 3/4 and 7/8 dies. 0.035 bend well with the 5.5CLR for the 7/8 and 3/4, and I have done some 0.028 with 3.5CLR 1/2 without problems too.

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I’m surprised the JD2 will bend 035! I thought I had tried 3/4”steel and didn’t have good results. Maybe I was trying to get too much bend. But I can bend 049 and 058 without crimping or too much flattening, all the way up to 1.25” unicrown fork blades.

The more expensive benders are great for bend quality and repeatability, but not needed. The bender isn’t the expensive part it’s all the dies you will need. I remember someone making custom hold blocks for the JD2 since the bolt that holds the tube in place isn’t great and can dent the tube.

For reference, that tube James is bending is thick wall Ti so within the specs that JD2 can do.

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Just FYI, these are the commonly used dies for our Cobra Bender:

CLR [mm] CLR [in] Tube Diameter Purpose
115 4.5 0.5 (12mm) Seat stays
115 4.5 0.625 (16mm) Seat stays
230 9 0.75 (19mm) Chainstays
230 9 0.875 (22mm) big steel chainstays and titanium chainstays
115 4.5 0.75 (19mm) tire clearance bend on gravel bikes
230 9 1.375 (35mm) Seat tubes

You could probably get away with using 115 for everything. However, I don’t like coldworking the tube more than you have to. The 230mm radii look nicer. Andrew at Bike Fab Supply can bend seat tubes for you, saving a die.


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I use the HF roller for my top tubes with the stock 1" and 1.5"dies. Using 28.6 or 31.8 tubes with a 1.5" die results in an ovalized and curved tube, which I find pleasing to the eye and the results are reasonably uniform. Using butted tubing is kind of a pain, because the nature of the roller leaves a few inches on each end that don’t pass through the dies. I weld two tubes together end to end and weld a 6" piece of sacrificial chromoly to each end of the assembly and then run the whole thing through. It’s a lot of work compared to using a straight tube off the shelf!

For the simple bends I do in seat stays using .035 chromoly, or the tips of pre-bent stays, I find it sufficient to use a plywood fork blade bender. It’s from the plans that came with my Henry James frame fixture. I have two, I think they are 10" and 8" CLR. Easy to make another for a particular bend if you have a jigsaw or band saw handy. There’s a light groove for the tube to follow as you bend it and no follow bar or anything. It is so simple and low tech, but it works fine!

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I’ve bent a good number of stays with the cobra tube bender, and I am a big fan of it for that purpose. I couldn’t make the bikes that I am making without it. There is definitely a learning curve, and I scrapped some tube along the way.

I have:
5/8 115 die
7/8 115,170,230 dies

I’m bending .049", tubing, and you could definitely get away with just the 115 die for that wall thickness, but the 230 and 170 are nice to have.


left is 230 at the BB and the rest 115. right is all 115.

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I have a Diacro #2 bender that I’ve made my own dies for. Bending 1” .035 4130 under 6” CLR is challenging. I wasted a lot of material experimenting but at this point I’ve worked through the problems and have created some satisfactory results.
Clockwork has a bunch of pics on Flickr that helped a lot.






I’m on the road with the family, I’ll upload more pics when I get back. Tdotbike on instagram for more bike addiction related photos.

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I would love to see a photo if you have one. I imagine the larger the CLR, the less fancy your bender needs to be. I was thinking a 9in CLR 3D printed die could work. @sunshine.fab had decent luck with a 4in CLR and 3D printed dies: 3D printed bending die notes - #25 by sunshine.fab

I use a JMR rotary draw bender, very similar to a JD2. I can bend handlebars, CS, and SS. It does great with 5/8” .035 chromoly on a 3” CLR and the 7/8” .058 and I would suspect it does fine with .049. However bending 3/4” .035 with my 3.5” die can produce less than desirable results.

To mitigate a ripple on that tube size (3/4x.035) it is imperative to keep pressure on the bend (good practice regardless) when moving between ratchet positions, also if the tube slips at all, you’ll end up with ripples.

I want a large radius die for the crank arm bend on CS, but that would require a different bender. I’d like something similar to the anvil or the one shown at the moots factory. Both those look fairly similar to fork raking benders.

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Here is a pic of the plans and another of my bender with a piece of 1/2" chromoly for scale. I was wrong, the main size is 12" radius but I have a couple smaller ones that I have used for tighter bends. I think I used a scrap of steerer rather than the pipe nipple specified. The groove in the plywood doesn’t need to be super deep to keep the bend in line. Also, I usually have no trouble just using the tube as a lever - no cheater bar needed.


My main use for this bending die is for a simple bend on seat stays where they meet the seat tube. Sometimes I also want a little curve at the dropout, too. In that case I leave the stay a little long and trim it after bending, like this.

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oh wow, that is pretty epic, a paper template, 1989 copyright. Such a simple tool gives you such elegant curves. I’ll try to give that design an update with 3D printing and laser cutting when I get a chance

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Curtis just put up a video on the Retrotec Instagram page showing his roller in action, making s-bend down tubes. Pretty sweet tool and the result is impressive. It’s almost like he’s been honing his craft for the last 30 years…
https://www.instagram.com/reel/Cpyou7NArtv/?igshid=YmMyMTA2M2Y=

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I just saw that also. Neat setup.

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Oh wow lots of great insight, thanks everyone!

Great tool indeed. In school I worked with a sheet metal roller bender and we couldn’t really set it to a precise radius, just kinda eyeballing or referring to a drawing, is it the same for a tube roller bender like this? Looking at the video it does look like he stops a few times to compare it to a drawing or something of the sort.

Didn’t see that thread, very useful too!

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Related to this thread, I recently acquired a Di-Acro bender and am trying to figure out the best way to get it set up to bend simple handlebars. I’ll need to create a new bend die, clamp, and follow bar. Is the de-facto way of doing this to use a ball endmill and a rotary table? Do most folks use aluminum or is steel/stainless a more robust solution?

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