Fillet Brazed Bicycle Rack
 

Any recommendations on steel tubing thickness/diameter for a medium-duty fillet brazed rack? Sounds like a good place to practice, and I'll need one for the frame I'm making anyway.

Thanks,
Jim

5/16"x.035", give or take diameter or wall. Andy

Thanks andy!

I was going to suggest .028" wall, but that doubles the price

I've had great luck with 304 SS 5/16 x .028. Polishes up nicely and it's cheap.

6 ft. length for $8.70 from McMaster Carr, their part number is 8989K46

I'm going to try it

Are you using silver? I am going to try nickle silver.

I've used Ni-Ag for stainless racks. I found that it flowed poorly using the normal flux for brass. A specialized flux (from Cycle Design, but there are other sources) helped a lot; the filler flowed and wetted pretty much like brass.

interesting, is it on their web page?

apparently, nickel silver is ni-cu-zn

Yeah no Silver in Nickel-Silver, it get its name from its colour. It's like brass but with 10% Ni and less Cu. It's stronger and melts ~30C higher. The nice thing is that is doesn't tarnish at all, unlike silver. Here's a pic.

The flux is not on their webpage, I called. I have a bunch if you want a sample.

PS. normal flux works fine for Ni-silver and steel

Alex Wetmore has a bunch of great info on racks, tubing and how-to: http://alexwetmore.org/. Search rack building basics, I think.

I hadn't considered trying stainless for a rack, but the price of materials does seem to make it a winner.

Yes the materials cost the same plus you don't have to paint or plate the rack. A good polish is as expensive as chrome plating, but there is nothing wrong with a sanded or blasted finish. The downside is that SS is a harder to work with (cutting and brazing), and the ubiquitous 304 grade has lower yield strength than cromo. 316 is stronger but harder to come by (around here).

To the OP. Racks are great practice, and actually quite challenging to make (has to be level on two planes, centred, weird mitre angles, etc.), have fun!

the only think I'm concerned about is bending it in use. I finally got a bender for 5/16", and no 4130, plus we seem to have lost the local powdercoater so the stainless seems like a good plan.

From what I understand the yield is for the base material, formed pipes and tubes, work harden and are much stronger.

375 x 35 is the standard size for modern heavy touring gear. As far as getting the best fit on hardware, the 375 can be better, check your bags first.

Yeah, 56% ( BAg 7 ) and 45%.
Black flux.

Polish the tubing before bending and brazing, then go back and touch up when you finish filing.

I'm thinking about using LFB (I have a bunch not earmarked for anything). That'd rule out the SS, right?

The cromo seems a fair bit more expensive, would it make sense to practice with carbon steel, or will that be weak and heavy?

Stainless works fine with LFB and brass, just use a higher temp flux.
4130 and low carbon 1010, 1020 etc, weigh the same, and are equally stiff. 4130 is higher yield and UTS.
AISI 304 is roughly equal to C1025 in UTS and yield but is marginally less stiff with an E modulus of 28 mPSi, relative to steels at 30 mPSI.

I'd practice with low-carb electro welded tube and then build something real with stainless.

With the specialized Ni-Silver flux, LFB did (barely) wet stainless, and it flowed badly. I know because I noticed something was off then realised I picked the wrong filler rod. So I wouldn't recommend it.

If you want to use weaker steels, plan for a good triangulated design. But if you go for 3/8x0.035 tubing it is quite stiff to begin with so it should be okay.

MassiveD yes I read about the work hardening of stainless. My experience is that the 304 is easier to bend than 4130. For 3/8x0.035 it still requires a fair amount of ooomph mind you so I'm not concerned. For 1/4" tubes you can really tell the difference.

I think that most people would have trouble using lfb with stainless. I know people have done it and apparently gotten away with it, but cruft precipitates out of the stainless at brazing temps. This will present difficulties for beginning brazers

Thanks for all of the info! I'll do a bit of hunting and maybe use some larger diameter low carbon steel to make something good enough for groceries. Then, once the bike is done, I can go back and make something out of stainless or chromo if I'm not sick of projects ;-)

VRB- Very good plan! I'll be interested in whether you change the design the second time around. Due to knowledge gleamed from building or using the first rack. Andy.

just spent a half hour polishing tubing on the lathe. Fun

I assume you know your prices, but 4130 is actually cheaper/same in my nook. People, not very many of them, do want the stuff, the supplier is online in the US, good price discovery. That sets prices here also. Seems few people want the erw in those sizes, so it costs more. Go figure. Worst case it might be a dollar a foot cheaper for the erw doesn't add up all that much when you are talking 10 feet.

So anyone else who is watching, and wants to do this, be sure to check your local prices. Another example: buying 4130 straight wall tubing is not always cheaper for frame parts than the butted tubes, particularly in the main triangle. Making one's own bottom bracket isn't a big money saver. Making drops out of 4130 plate, etc...

Which brand of nickle rods are you folks using? I bought allstate's 11 (flux coated, natch) and used it to braze a whole bunch of stuff and I thought it flowed lovely compared to the bronze/brass that I had previously used for ornamental steel work. I have a 10ft piece of 1/4 stainless I've started to bend into a small rear rack to hold a light and tool kit... kind of a knock-off the small racks the French seemed to love back in the day. I'll try and remember to post picture when I finish it... the .25 stuff bends so easily too I just carefully wrap it around round things to get my shapes...

The guy at my LWS raves about the Allstate 11. I should give it a try but if I remember right it was pricey with a large min. order. I use the GasFlux rod, it's pretty good. Let us know how well the Allstate 11 brazes on stainless.

I paid 30$ for a pound from my local air liquide dealer... I had to wait a month for it or something dumb like that but compared to actual silver it seemed like a deal. Have you bought any tubing from aircraft spruce in Brantford? Unfortunately I quit my job as a brazer to pursue something else so I'll be without torches for a month or so until I get my new workshop setup and torches/welder up from the states... but then I'll do up that rack I have bent and I'll likely get a front porteur out of 3/8" done up in the next month or two, depending on busy I am with this steel mill gig I'm on.

Aircraft Spruce is selling the best 4130 right now. All the other guys are getting Chinese stuff that is often pitted, I saw a discussion of plating not working well on some racks because the tubing was pitted.

Yes I get my cromo and stainless from Aircraft Spruce in Brantford. I did get a few tubes showing some pitting but for the most part it's great stuff.

BTW regarding Allstate 11. The LWS has a little booklet saying it has a working range from 650C to 950C, with a remelt at 950C. That it works well with 2-4 thou radial clearance... Sounds pretty cool!

Just got 3 36" chromo tubes in the mail, 5/16 .035. They actually ended up throwing in about 10" of it for free. Not bad!

I've also got a tube of 1/4 and a cheap bender on the way.

I've got some sketches together for what it'll look like. I think it's going to be good, but I need to figure out where I use the heavy duty stuff and where I use the light stuff.

Which areas would you say are under the most strain? My thought is that I can use the heavier stuff for three "covered wagon" style arches and use the lighter stuff for the crossbar that the panier attaches to, since it's supported at three points. Thoughts? Should I use a heavier piece for the crosspiece?

The racks that i've broke is nearly always at the attachment mounts near the drop outs. This is typically where the greatest bending loads are (from the loaded rake swaying side-to-side).

Hmmm... that mirrors what I've seen at the shop. Since I've got tubing that will nest, maybe I'll add a bit of 1/4 tubing inside the 5/16 right around the dropout area... taper it so that it doesn't create a stress riser at the end...

If I'm brazing a rod right along the side of the vertical struts of the rack... does it make sense to miter the side of it a bit to increase the contact area, or am I better off keeping both whole and just building up a nice big fillet?

Thanks,
Jim