Anybody Use Cerrobend or Wood's Metal for Bending Thinwall Tubes?

[jclay]

To accommodate plump tires and fenders l put a large bend in 22.2 ROR chainstays ( https://www.flickr.com/photos/216244...in/dateposted/ ). I use a home-made bending mandrel ( https://www.flickr.com/photos/216244...in/dateposted/ ) and for bending support have filled the stays with wax, a wax/sand mixture and with sand only; with the latter, one end is capped, the other has a nut brazed on and a bolt providing compression which I increase as I go, bit by bit. I've have had reasonable, if not 100% success with those methods, and I can't help wondering if Cerrobend or Wood's Metal would improve the results. Anybody here have direct experience to share? Given the chemistry of the alloys I'm particularly interested in how one works with these materials safely in a shop environment.

[e-RICHIE]

It might se simpler to use CX chainstays.

[VertigoCycles]

I've used it, wouldn't use it again. The problem isn't that it doesn't work...it does, but the whole process is a bit of a mess and you risk leaving some of it in the stays.

[jclay]

Thanks for the feedback.

It might se simpler to use CX chainstays.

Which ones do you have in mind? I've looked and nothing jumps out at me, at least in 22.2 round or ROR.

I've used it, wouldn't use it again. The problem isn't that it doesn't work...it does, but the whole process is a bit of a mess and you risk leaving some of it in the stays.

Cerrobend recommends coating the bore with olive oil or similar; did that not work so well as a release agent? I'm guessing that TIG on Ti is a lot more unforgiving of minuscule contaminants than brazing carbon steel...though I'm not keen on volatilizing any left over material.

Do you use a substitute?

Does anybody else reading this have experience with any sort of filler for this type of purpose? It's gotten to the point that I'm thinking that maybe using angular sand/tiny pebbles (rather than sand rounded by use in my sand blaster) in my wax/sand mix to form a matrix that's got more compressive strength. Wax/sand mix is messy but non-toxic and trivial to handle. Been thinking about that for a while; it might be the best next step.

[e-RICHIE]

Thanks for the feedback.



Which ones do you have in mind? I've looked and nothing jumps out at me, at least in 22.2 round or ROR.

.

The ones I use on RSCX frames, and import/distribute.
Mega clearance. No Blacksmithing on the shell. No weird.

Oh - you want round at the shell?
Never mind.

[jclay]

The ones I use on RSCX frames, and import/distribute.
Mega clearance. No Blacksmithing on the shell. No weird.

Oh - you want round at the shell?
Never mind.

Just visited your site; saw lugs, crowns, shells, lotsa stuff but I didn't see tubes. Where are they?

[e-RICHIE]

Just visited your site; saw lugs, crowns, shells, lotsa stuff but I didn't see tubes. Where are they?

It says to contact (email) me:
https://richardsachs.com/frame-building-kits/
https://richardsachs.com/shop-frame-building-kits/

[jclay]

In a 16x30 this is the closest thing I've ever seen but I haven't tried one: https://framebuildersupply.com/colle...all-length-470

I need to sketch it full size to check but I'm enamoured with it's flattened X-section.

In order to get the 60 to 65mm clearance I'm looking for ( https://www.flickr.com/photos/216244...in/dateposted/ ) without a lot of BB shell blacksmithing either the shell's CS socket angle needs to be greater than the 20 degrees provided by the Rene Herse shell, and then use a pretty large single bend (which I'm able to do), OR the chainstays need to look (especially at the BB end) much like the 29er linked above (which has a lot in common with old MTBs and balloon tire bikes and would accommodate MOL conventional shell spigot angles).

For the time being I'm still using 22.2 ROR and have had good results since going through a number of mandrel and process revisions. But I'm still interested in how others skin this particular cat (as in make 22.2 ROR work for these sorts of frames/tires/fenders).

My next stop will probably be the change to a larger, angular aggregate for my wax/rock bending support matrix....or maybe I'll go back to capping the small end, brazing a large nut on the big end and compressing sand via the bolt, tightening/re-compressing it at each incremental bend. It's slow but it works.

[VertigoCycles]

Cerrobend recommends coating the bore with olive oil or similar; did that not work so well as a release agent? I'm guessing that TIG on Ti is a lot more unforgiving of minuscule contaminants than brazing carbon steel...though I'm not keen on volatilizing any left over material.

Do you use a substitute?

Does anybody else reading this have experience with any sort of filler for this type of purpose? It's gotten to the point that I'm thinking that maybe using angular sand/tiny pebbles (rather than sand rounded by use in my sand blaster) in my wax/sand mix to form a matrix that's got more compressive strength. Wax/sand mix is messy but non-toxic and trivial to handle. Been thinking about that for a while; it might be the best next step.

I used mineral oil and tried olive oil. Maybe it'll be different for you if you have more space and time to deal with the process of filling and emptying the tubes as well as the additional cleaning required. I look at it like this...if you're doing it once or twice, it works but it's a lot of $$ in material for a one off. If it's something you plan on doing in multiples, the "cowboy" way to fill and remelt the cerrobend takes a long damn time and I'd never want to do it.

In addition to all that, it doesn't always readily separate from the oil when you melt it out. So you end up with a vessel of some sort with an amalgamation of oil and molten metal in it so you try to spoon out the oils. If you don't get it all, it can sometimes create little pockets of incongruous cerrobend in your stay, which if located somewhere in the bend, will muck with your bending setup.

If you have a halfway decent milling machine, a rotary table and a little time, make a proper bender with a follower for support instead of that fork blade bender thing that you have. Or better yet, find some round stays with the proper bend and give 'em a squish. It's been a while since I was an instructor at UBI but they had dozens of different stay profiles, and I'm fairly certain that they had something that would work in this situation without the squish in it. I'm 100% out of touch with what steel profiles are available, but I'd be shocked if something didn't already exist that fits the bill and needs minimal modification.

[jclay]

If you have a halfway decent milling machine, a rotary table and a little time, make a proper bender with a follower for support instead of that fork blade bender thing that you have. Or better yet, find some round stays with the proper bend and give 'em a squish. It's been a while since I was an instructor at UBI but they had dozens of different stay profiles, and I'm fairly certain that they had something that would work in this situation without the squish in it. I'm 100% out of touch with what steel profiles are available, but I'd be shocked if something didn't already exist that fits the bill and needs minimal modification.

Time aplenty but no mill. Starting with round stays is something I’ve considered and the bending operation will likely flatten them a little. Thanks for the benefit of your experience with all of this; using a brazed-on screw press to compact sand filler sounds like less trouble than fusible metals, if not as good. I think I’ll revert to that.