Bending 1/2 inch tubing for seat stays

I’ve got a future project that needs the seatstays bent. Would something like this be possible?


It looks to be a 4” radius and says it’s made for thin wall 1/2” tubing. I plan on just buying straight gauge 1/2” tubing since the bike isn’t super fancy and I’m a beginner. I’m not a professional and am on a budget, so I’m just curious if it’s possible. Not if it’s a good idea. I’m full of bad ideas and I’m ok with that.

1 Like

Like usual, not speaking from experience here, but if you poke around Instagram there’s a few builders using pretty economical setups to bend seat stays. A 4" CLR is probably a bit tight, but if you can make a CLR somewhere in the ballpark of 10" work for your design you can get by with pretty basic tools.

Feather Cycles uses an old 700c rim:

Signal Cycles used a wood v-groove die:

Joel of Clockwork has a fancy looking bender, but the way it acts on the tube is very similar to a fork blade bender (v-groove die, lever arm that is eccentric to the CLR):

Joel’s dies are labelled as 10" CLR, so that’s where I got that value from. No idea what the minimum CLR is for a set up like this, but a fancy bender isn’t really required for SS’s unless you’re trying to get tight bends.

3 Likes

Thanks for posting that inspiration @photon ! crazy what you can do with a little creativity.

@Spencermon this has been the coolest bender mod I have seen:

@Seriousbicycles added a follow bar and a better “clamp” system

image

We have the same bender to do curved bridges. With thinner wall tubing (.035) you sometimes get some ripple artifacts on the inside of the bend. I think a follow-bar will mitigate that problem.

Pretty much everyone is using straight gauge rear ends! Its the “pro” thing to do!

4 Likes

I just use the shallowest of my three forkblade mandrels, with judicious hand pressure.

2 Likes

This bender is for 1/2" EMT (electrical metallic tubing, or at the hardware store it’s every man’s tubing). The nominal ID is 1/2", actually .62" and the OD is .71". That means your 1/2" tubing that’s actually 1/2" OD will fit loosely in the groove. If you already have the bender, and some spare tube to play with, give it a try. Otherwise, some of the other suggestions here will probably give you better results.

2 Likes

I was actually wondering if that was the case. I’m glad you spoke up. I didn’t have my calipers with me to measure so I didn’t buy it. I could go back and get it. It’s only $12. I wonder if a thick piece of leather would be ok to take up the space? I’ve had some ideas about making a v groove in a piece of wood that sits on the ground and acts like a follow bar. I might buy it because that’d be the cheapest experiment and if it works, great. If not, oh well. It’s only $12.

1 Like

Hard to go wrong for 12 bucks. If it doesn’t work, it’s the start of a new career as an electrician.

5 Likes

I bought it. Then I tested it. I only had a scrap piece of 1/2” x 1/16” tube to test, so this might not work for thinner walls, but it worked just fine for this tube. I used a broom handle and then placed the tube on the floor of a wooden deck so it sat in a little groove. Then I stood on the little foot position on the tool and pulled on the broom handle. I’m still going to make a leather piece to take up some gap and maybe increase accuracy.



6 Likes


I have this set of Ridgid instrument tubing benders. I have made several sets of 1/2 and 3/8 stays in .035 and .028 (child’s bike). You’re welcome to try this too if you want to swing by sometime. I think the CLR is 1.5” so it’s a pretty tight bend.

4 Likes

Those ridgid bender works fine.
Some examples from a rack , and seatstays

2 Likes

Better pictures



4 Likes

Really into those seat stays. With the radius matched bridge it almost looks as though they were bent from a single tube, wishbone style.

3 Likes

Thanks
Have to say that it was my intend, but it happened with luck.
The bridge just fell on the spot

2 Likes

Uploading: IMG_0310.jpeg…
Uploading: IMG_0312.jpeg…

4130 is pretty forgiving if you’re bending on a larger radius. I bend seat stays using a simple plywood mandrel based on instructions that came with my Henry James fixture for a plywood fork blade bender. It’s one of the most useful DIY tools in my shop. 10" clr, if I remember correctly. Just fix one end and off you go. I put some marks on it to help match two tubes to the same bend. No need for a follow bar or anything fancy. I have one of the Ridgid benders for tighter radius bends, but rarely use it.

5 Likes