# WWTP028: Seat Stay Bending



## jay_ntwr (Feb 15, 2008)

Well, this kind of sucks. This is my first "failure" in the project so far I think. I've had some things that I've messed up from lack of experience, mistakes, etc, but this is just total failure.

Oh well, that's ok, I'll survive.

I started with this little MDF jig I made in just a few minutes on the table saw and router table with a special 5/8" roundnose router bit I bought for the purpose:










I was hoping that I could just smash the stay into shape without any tricks like sticking brass rod in the tube, or ice, or anything else I've read about on here:










But it didn't work:


















Walt, these are looking like Nova stays huh:
https://www.cycle-frames.com/bicycl...MO-SEAT-STAY-16mm-x-0.8-SINGLE-TAPER-600.html

I'm going to order some more, work on my bender so that it has a roller instead I suppose. I was hoping not to have to make something like that, but had I had the whole day instead of an hour, I probably would have done that instead. Oh well, live and learn.


----------



## Walt (Jan 23, 2004)

*Just support the tube on the ends*

In my experience, if you just make some cradles that can swivel, then press the form into the stay, it'll work much better. You also should try to make your form a smooth curve, not have it come to a point.

I did a post about a bender I made (which subsequently was considerably improved, but worked great) here: http://waltworks.blogspot.com/2008/12/scrappie-my-new-tube-bender.html

I made some new mandrels for it as well: http://waltworks.blogspot.com/2009/01/more-bender-stuff.html

There's a whole new "spine" fixture as well, but I don't have any pictures of it. It's the same basic idea, just a little more sturdy and not made in <5 minutes.

Those seatstays I sent you are 16mm tapered ones, I think? They're most likely VERSS1 from True Temper, but the Nova 16mm ones (get .8mm wall for ease of non-wrinkled bending) will work fine.

-Walt


----------



## Francis Buxton (Apr 2, 2004)

Maybe try filling them with that fine white play sand (you can get it at Lowe's). My initial thought was that the radius on your bend was a little tight. I've been in your spot, though. I ruined a few nice chain/seat stays when I was too lazy to fill them with sand. Part of it was wanting to see what I could get away with, and part of it was simply being lazy and not wanting to deal with the sand. It taught me a $50 lesson.


----------



## pvd (Jan 4, 2006)

I use frozen water in the stay. It works like a charm. Next time I'm going to try freezing soapy water in the tube since it's supposed to work even better.

Bending stays is probably the most expensive part of learning to framebuild (aside from tooling). You end up scrapping a bunch of stays before you figure out all the tricks.


----------



## jay_ntwr (Feb 15, 2008)

Walt said:


> In my experience, if you just make some cradles that can swivel, then press the form into the stay, it'll work much better. You also should try to make your form a smooth curve, not have it come to a point.
> 
> I did a post about a bender I made (which subsequently was considerably improved, but worked great) here: http://waltworks.blogspot.com/2008/12/scrappie-my-new-tube-bender.html
> 
> ...


Well it looks like part of my problem was the 4" radius instead of 8" radius. Seems I had it in my mind that 4" was what I was looking for. That's an easy fix.

I admit I wasn't happy with the way I was doing this. I spent the day with my woman and ended up not having the time I wanted to spend on this to make something nice.

Walt, the VERSS1 sound right to me.... They also measure out to 600mm, so I'll call HJ and get some more on the way I suppose.

First, I think I'll work on my bending fixture and try to bend the last good one I have. If that works, then I only need to order 1 pair.

Thanks for the feedback, guys.

Also, if anyone wants to discuss hand mitering SS, I'm all ears. I used the screwed up one to test file and that's actually much more difficult than any of the other miters so far. I've got some ideas on how to do it so don't say anything in the event you'd rather see what I come up with on my own. However, I'm all ears.


----------



## jay_ntwr (Feb 15, 2008)

pvd said:


> I use frozen water in the stay. It works like a charm. Next time I'm going to try freezing soapy water in the tube since it's supposed to work even better.
> 
> Bending stays is probably the most expensive part of learning to framebuild (aside from tooling). You end up scrapping a bunch of stays before you figure out all the tricks.


Pete, do you just freeze the end that you're working on? I figured I could just freeze half the stay and use a cork to seal it. I wasn't sure what it would take to split one but I'd think ease of splitting one is proportional to how full it is. Or is this a non-issue?


----------



## Smokebikes (Feb 2, 2008)

Nice bender Walt, thanks! :thumbsup:

"_Also, if anyone wants to discuss hand mitering SS_"..............try mitering them as a unit...that is, braze them together first with a bridge and file them at the same time.


----------



## jay_ntwr (Feb 15, 2008)

Smokebikes said:


> "_Also, if anyone wants to discuss hand mitering SS_"..............try mitering them as a unit...that is, braze them together first with a bridge and file them at the same time.


Yep, I was thinking of doing something like this. The plan wasn't to braze them though, but rather make a quick jig that will let me bolt them together and stick 'em in the vice as a unit rather than as single stays. Then, check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file/check/file. I'm good at check/file.


----------



## pvd (Jan 4, 2006)

Fill the whole stay. Cap with electrical tape (best I've found) and freeze it solid. The colder the better. Give it plenty of time, semi solid is not good at all.

You have to work quick. Handle the stay with a rag to avoid heating it up any. Have all your markings in place ahead of time so you go from freezer to bend as quick as you can.

I've only had one stay split. It's a good thing when it splits. That means the stay had a serious issue at the seam and you wouldn't want to use it anyway. It's pretty cool when it happens.


----------



## buildyourown (Dec 1, 2004)

How thick are those stays?
My method looks almost identical which I ripped off of Garro.
Check the link to my blog in my sig. I can't link to pics.
Anyways, I did 5/8" x .035 with ease to at least 25 deg. Cold.

The only thing that I may have done different was that my tool as alum and a perfect fit. If your MDF slot was oversized, then it would only be hitting on the edge of the tubing ang it would crimp. Is the stay exactly 5/8"? I used 5/8" straight gauge.


----------



## rbrstr (Oct 5, 2009)

The reason the tube crushed that way is because there is no support inside the tube. you are trying to stretch the skin on the outside of the bend whilst shrinking the skin on the inside of the bend all at the same time, something quite literally has to give

In the absence of a tube bender or a mandrel, filling the tube with sand is an excellent way of doing this. we have a cnc tube bender here and i still use sand bending sometimes for one offs. you need to weld caps onto the ends of the tubes(temporarily) and pack that sand in real,real tight with a stick or something. any fine,dry sand is good.


----------



## zipzit (Aug 3, 2005)

I sometimes wonder if less is more.. er... not so fancy.

I remember seeing this very simple jig for an S-bend chainstay. I noticed it on the very impressive Wolfhound Cycles 29er split wishbone build (Customer = Jay Carpenter)

See https://wolfhoundcycles.blogspot.com/2007/10/jay-carpenters-build.html

Comment from the blog:



> It has taken many attempts and a lot of sacrificed material to develop these chainstay forms, even though they look pretty cowboy, they actually do a pretty nice job of manipulating this specific Columbus Zona chainstay. As shown, I made one specifically for bikes with Slider drop-outs.





Photo of chainstay bender is at 
https://2.bp.blogspot.com/_cRA2LWYSP8Q/RwuCpl5aTII/AAAAAAAAAd8/uXkGJkLHxvQ/s1600-h/33.jpg

(Oops. I tried to post the photo via link straight up, but our friends at blogspot have the server locked from us folks doing that...) 
I'd save the photo on my own, but its not my original work. 

I thought it was a pretty nice bender design (assuming that it will work!)

One question... Can you use cheap electrical conduit to simulate and prove-out bender designs? Anybody done so? It might save a few bucks in the long run?

--zip.


----------



## Walt (Jan 23, 2004)

*I disagree*

I don't freeze, fill with sand, or otherwise support the insides of seatstays in any way when I bend them. Never had a problem with denting or wrinkling them. I think it's more about doing a reasonable radius bend and having all the contact points (mandrel/cradles/rollers/whatever) fit the stay well. Sand or ice can probably help you if you've got some problems in those areas, though.

-Walt



rbrstr said:


> The reason the tube crushed that way is because there is no support inside the tube. you are trying to stretch the skin on the outside of the bend whilst shrinking the skin on the inside of the bend all at the same time, something quite literally has to give
> 
> In the absence of a tube bender or a mandrel, filling the tube with sand is an excellent way of doing this. we have a cnc tube bender here and i still use sand bending sometimes for one offs. you need to weld caps onto the ends of the tubes(temporarily) and pack that sand in real,real tight with a stick or something. any fine,dry sand is good.


----------



## rocwandrer (Oct 19, 2008)

I do my small diameter tubing bends with old double walled rim wheels. I have a 406 (~7.5" radius), 559 (~10" radius) and 622 (~11" radius). I just hose clamp the tube to the rim, place the tube on the ground, put my weight on the top of the wheel, and roll the wheel onto the tube. Starts and stops don't show this way like they do with some other simple methods, so you can fine tune the bend over multiple passes. The juggernaut S-bend seatstays (16mm x0.7mm wall, tapered) were done this way, and they came out awesome. Actually, for this easy bending stuff, I think I just bent the tube around the rim in my vice.


----------



## shiggy (Dec 19, 1998)

zipzit said:


> I sometimes wonder if less is more.. er... not so fancy.
> 
> I remember seeing this very simple jig for an S-bend chainstay. I noticed it on the very impressive Wolfhound Cycles 29er split wishbone build (Customer = Jay Carpenter)
> 
> ...



Those stays are way flatter than I would want. Some would call it crushed. I like the basic tooling idea, though.


----------



## shiggy (Dec 19, 1998)

rocwandrer said:


> I do my small diameter tubing bends with old double walled rim wheels. I have a 406 (~7.5" radius), 559 (~10" radius) and 622 (~11" radius). I just hose clamp the tube to the rim, place the tube on the ground, put my weight on the top of the wheel, and roll the wheel onto the tube. Starts and stops don't show this way like they do with some other simple methods, so you can fine tune the bend over multiple passes. The juggernaut S-bend seatstays (16mm x0.7mm wall, tapered) were done this way, and they came out awesome. Actually, for this easy bending stuff, I think I just bent the tube around the rim in my vice.


Nice tip. I will have to give it a try.


----------



## Hubcap Cycles (Sep 6, 2009)

Here is a picture of the bender that I made to do stays. I wanted it to be repeatable, so there is an adjustable stop for the hydraulic ram and a stop for length. Most of the top dies have a 4 inch radius and the bottom dies pivot. There is also a die spring under the bottom dies to give back pressure,(I'm still trying to decide if the spring makes a difference). No problem bending .028. 
Cheers,
Hub
http://Hubcapcycles.com


----------



## edoz (Jan 16, 2004)

Speaking of Garro's ideas, he told me about shoving a bunch of brass rod inside the tube to provide inside support. Works like a charm, but if you're doing tig you may not have any on hand.


----------



## jay_ntwr (Feb 15, 2008)

edoz said:


> Speaking of Garro's ideas, he told me about shoving a bunch of brass rod inside the tube to provide inside support. Works like a charm, but if you're doing tig you may not have any on hand.


Eric, yeah, I've had a few folks tell me that and of course, I don't have any brass rod. I know it's cheap, but when you've got power tools, stays, desire, beer, and no brass rod, well, they're getting bent that night.

FWIW, I did "modify" my setup a bit the other night and re-bent the already ruined stay supporting the ends differently. It worked nicely, even on the 4" radius.

So I have an idea of how I want to make the next bender and just need time to do it now. Hopefully I'll get started on that next week. I may pick up some brass rod at the LWS if I get the chance.

As Peter mentioned though, I feel like I need to ruin a bunch of these to learn about what is and isn't possible. Just making one bend for #1 is fine and I hope to get there in the next pass, but being able to do some s-bends would be nice for #2 or #3. I'm sure I'll need the brass rod for those.


----------



## rustola (Jan 15, 2008)

edoz said:


> Speaking of Garro's ideas, he told me about shoving a bunch of brass rod inside the tube to provide inside support. Works like a charm, but if you're doing tig you may not have any on hand.


TIG filler rod works just fine as well.


----------



## jay_ntwr (Feb 15, 2008)

rustola said:


> TIG filler rod works just fine as well.


Duh, I can't believe I didn't think of that. :madman:

Sometimes it's the simple solution that is elusive.

Thanks for that tip.


----------



## Evil4bc (Apr 13, 2004)

Hubcap- Freeking cool little machine you made there !


----------



## NorseRider (Feb 9, 2004)

PVD: How was the bends on the Yo Eddy's done? 3/4" 4130, is'nt it? Quite sharp bend too.

Truls


----------



## Schmitty (Sep 7, 2008)

NorseRider said:


> PVD: How was the bends on the Yo Eddy's done? 3/4" 4130, is'nt it? Quite sharp bend too.
> 
> Truls


Quite by accident, I duplicated the FAT beds exactly with a geared Rigid bender.. 8" rad if I recall but may be 6", can check if you like. .035 only though, any thinner and I had problems, even packed with blasting sand.

I was trying to run short stays, full gears, and room for 650/2.3, and that 'FAT bend' actually solved all the issues. Of course I added some more bends fo no good reason other than b/c I wanted too, and also rotor clearance.

-Schmitty-


----------



## rocwandrer (Oct 19, 2008)

pvd said:


> Fill the whole stay. Cap with electrical tape (best I've found) and freeze it solid. The colder the better. Give it plenty of time, semi solid is not good at all.
> 
> You have to work quick. Handle the stay with a rag to avoid heating it up any. Have all your markings in place ahead of time so you go from freezer to bend as quick as you can.
> 
> I've only had one stay split. It's a good thing when it splits. That means the stay had a serious issue at the seam and you wouldn't want to use it anyway. It's pretty cool when it happens.


i don't remember what the diameter threshold was but, I figured -20 water expending the steel as much as it likes with no ice compression was still well below the elastic limit of the steel for 1.25" tube. That means the tube will look the same if you freeze the water in it and thaw it out, no yielding. Smaller diameters would have more safety factor than bigger ones. If you blew out a seat stay (which i bend without filling, incidentally), it was *seriously* defective.


----------



## pvd (Jan 4, 2006)

NorseRider said:


> PVD: How was the bends on the Yo Eddy's done? 3/4" 4130, is'nt it?


At FCC, 3/4" and 5/8" tube was bent. We used a Di Acro No.2. I belive over a 3" radius mandrel. Absolutely the best way to bend round tubes.

Drew at Engin recently set one of these up - http://www.flickr.com/photos/engincycles/sets/72157603259388609/


----------



## OldHouseMan (Dec 7, 2006)

I'm no frame builder but I bend a lot of hydraulic tubing at work and need to be pretty precise, for smaller sized tube I use one of these and for bigger material and if I need it to look nice I use this.. The hand bender is pretty cheep but the Parker bender is kinda spendy. The thinnest tube we bend is .049 wall and either of these benders wont make kinks and I've never done any of the funky stuff like freeze or fill the tubes with anything. Maybe the tubes on bikes are more fragile.


----------



## Schmitty (Sep 7, 2008)

pvd said:


> At FCC, 3/4" and 5/8" tube was bent. We used a Di Acro No.2. I belive over a 3" radius mandrel. Absolutely the best way to bend round tubes.
> 
> Drew at Engin recently set one of these up - http://www.flickr.com/photos/engincycles/sets/72157603259388609/


Here they are.

As for the other post about Parker benders, the hand benders don't work, but the Parker 420 (!) 60:1 worm gear bender works really well. Typical bs though parts are rare and very spendy, and not easily made.

-Schmitty-


----------



## buildyourown (Dec 1, 2004)

Hydraulic tubing is a lot softer than and more ductile than Cro-moly. It is also much heavier wall. .049 is a lot different than 3/4" x .035.


----------



## DWF (Jan 12, 2004)

The biggest problem I see most folks having is trying to bend the tube over a too small radius. Too small a radius forces the bend to occur in a small area and over stresses the tube resulting in ovalizing, buckling, waves, or failure. In my experience, it is very rare in bike building that you need a radius smaller than 11". The other important part of the puzzle is that you support the tube around its circumference and place the bending load to the tube DIRECTLY over where it contacts the die through the mandrel and not at some point off the die.

As an example, this is my old style bender. That tube is an Deda EOM 16.5 (heat treated) 19mm seat stay with a .4mm wall.


----------



## Schmitty (Sep 7, 2008)

You gotta know there's about 20 more products you could sell the hell out of......what a tease.


-Schmitty-


----------



## pvd (Jan 4, 2006)

DWF said:


> In my experience, it is very rare in bike building that you need a radius smaller than 11".


The bike I'm working on right now will hopefully have a double bent ovalized stay around the chainring and tire using a 4" radius. 5.25" radius was too big to make the design come together. In general, I prefer tighter bends to lazy bends. I'm bending out of need rather than astetics and I need all the space I can get usually.


----------



## DWF (Jan 12, 2004)

pvd said:


> The bike I'm working on right now will hopefully have a double bent ovalized stay around the chainring and tire using a 4" radius. 5.25" radius was too big to make the design come together. In general, I prefer tighter bends to lazy bends. I'm bending out of need rather than astetics and I need all the space I can get usually.


I just haven't had that problem. On a 29er, unless I do a bent seat tube design, the tire hits the seat tube before I have an issue getting the chainstay around the tire. Of course I don't get the whole fat tire on a big wheeled bikes anyway. BTW, a long radius bend isn't about aesthetics, it's a real mechanical/structural issue when bending thin wall tubing. Bending = thinning.


----------



## Linnaeus (May 17, 2009)

I've got a DiAcro #2, but haven't got any dies (yet) for larger diameter stock. Luckily I saw they are still available.


----------



## NorseRider (Feb 9, 2004)

I've been looking at this one going at ebay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290361308738&ssPageName=STRK:MEWAX:IT - But was thinking that I could as well just make one myself based on the same design but with an adjustable following die that kept the tube close to the mandrel, then Steven (Shand) showed me this: http://www.lindsaybks.com/dgjp/djgbk/pipe/index.html So when I have time I will make something like the latter from scrap in the shop.

Truls


----------



## jay_ntwr (Feb 15, 2008)

I had a couple of hours this weekend, so I dragged out all the WWing stuff and made a new bender:


























The posts are 7/8 x 0.035 4130 that I had laying around. This worked way better than the last one as the pushers can pivot. The mandrel (not pictured) was supposed to be 8" radius but after sanding it on the belt sander (the band saw made a mess out of the MDF, I should have changed blades but was lazy) then it ended up being more like a 10" radius I'd think. It's a 20 degree bender meaning that it only bends 20 degrees max, but with spring back, it's less. I figured I could easily make these in 2 degree increments so that I could control the amount of bend very easily and consistently. MDF is cheap. Stays aren't.

I went ahead and ordered more stays and am confident that I can bend the next set pretty easily. Sorry, I forgot to take pictures of the result from this bender, but it was good. I actually tried those pushers on the old mandrel (pictured above, failed to snap shots of the new one, sorry) and crinkled it too, so yes, a 4" is too tight even with the good pushers. What was cool is that I bent it back the other way and it took the wrinkle out and the other side was ok.

I'd think that HDPE would be a great "pusher" material if I could get some in 1-1/2" on the cheap. I used to have access to sheets of that stuff, now, not so much. The MDF has too much static friction. I've got some ideas though on how to fix that.

This really was just a mock up, it's not square, all kinds of problems, but it worked and it was more Proof of Concept for me than anything. It gets the job done though and I'll just have to wait for some stays to show before I move on. Sorry it's been a while since my last update. I've been traveling on business the past few weeks. It was great meeting a certain future builder on here during one of those trips. You guys are going to be stoked when you see what he's up to. That's all for now.


----------

