another beginner brazer
 

Hello folks
I'm thinking of learning how to braze and am thinking of doing a rack as my first project. I searched around and found a few good sites by people that have done this. Now I am at the point of chosing materials. I can't decide on stainless or4130 steel.

As I do not wish to spend too much money before I know if I will graduate to bigger projects, I will probably start with a couple small bottles of MAPP gas and a torch head. I'll get a decent bender and files. I have clamps, etc already.

What thickness of material (cromo and stainless) would be recommended for a small front rack to support 6-12 bottles of beer? I've seen that people recommend 4130 in either 3/8 X .035 or 3/8 X .028 and I've also seen 5/16 X .035 . What tubing is close in strength in stainless and can it be brazed with MAPP?

Finally, if I were to choose stainless, what grade would be ideal for an unpainted rack? 304? 316?

Thanks very much!
Allan Pollock

I'd stay clear of stainless for a first project, it's harder to work with and expensive.

look into an air-propane torch. They are hotter than plumbing torches. Heat is your friend.

thanks for the tips folks! I'll look into the torch (but price is a factor) and will use cromo as a first project.

Allan

would this one be useful?
http://www.canadiantire.ca/AST/brows...orch%2BKit.jsp

Allan

I'm not an expert on alternatives to oxy-acetylene. I've heard that the hardware store oxygen tanks run out fairly quickly. Also, in my previous post, I was thinking of air-acetylene, which avoids the expense of oxygen.

I was thinking about going with propane-oxygen, but then I got a good deal on a O/A torch. For my money, I wouldn't compromise. Building frames and even racks is fairly expensive, the torch/tanks for a decent setup are $400-600 and well worth it.

that's an order of magnitude above my budget, but I appreciate the advice.
Allan

Racks are one case where you can get away with SS. The reason is that racks are often silver brazed, and with your fuel choice that is pretty much your only serious option. You have to silver braze SS (or weld it), so you are already going down that path.

The other thing is that while SS is crap compared to 4130, unless of aero boutique quality, it seems to work for racks. Some big name guys use it, and it holds up. They are basically using brake line stuff, or the Aircraft Spruce stuff (I would personally choose the AS stuff). You essentially don't have a choice as to the wall thickness you use since it isn't really being sold within the structural size grid one gets with 4130 (no stainless for longerons, and for ribs, and for load pieces as with 4130). I think your main choice is 3/8", 1/16".

WIth 4130 you have a lot of choices, and you can't really specify a wall thickness. First, .028 tends to be for the light racks, however 5/16 and 3/8 tube are very different structurally, so the tube diameter has to be considered. You also have to separate the pieces that are being used perp to gravity, or radial to gravity. Just like a house frame, 2x4s for posts, and 2x12s (or all sorts of different dimentions for beams, depending on span). Another thing are parts being used as struts, they are loaded moreso in-line which is nice. Tension is normally kinder than compresion in in-line loading. Also, how are you taking the loads off? Are you turning elegant "drops" or mashing the tubing flat? And the design is a big factor, is it minimal looking or are there lots of load sharing parts.

I'm not suggesting you need to be a structural engineer to do this, but look at your design. If it carries more weight with less parts, and the horizontals are cantilevered a lot, use heavier walls, and heavier diameter. If it has a zillion little trusses, lighten the parts up. Put the weight where it maters, take it out where it doesn't.

With silver and any of the tubing up to 3/8" you can get by with mapp gas, but it won't be as easy as it would be with hotter torches. However, a cheap OA rig may not have the control you would want for doing this work and will be too expensive on larger projects if it uses bottles, so I would just give it a pass.

Oh, the obvious money saver with SS is that it can be finished naked. If you are coating it regardless then 4130 makes more sense.

I think this guy does SS racks. It is easy to copy the generalities of an SS rack, because there aren't many tubing options, so you pretty much know what it is about. One way to look at it very generally is that boring SS is not even up to regular structural steel numbers. So if you see someone's SS rack, and it seems to be 3/8", then it is probably 1/16" wall and if it was 4130 it could probably be 1/32 wall for the same design.

very useful, peter. I haven't completely settled on design yet, but I'm leaning toward something like this but with perhaps a second cross member
http://www.velo-orange.com/nimfrra.html

It's a small rack so loads will be limited but the fact that it'll attach to thee canti studs will be a limiting factor... also, I will not be squishing the tube...I'll cut a slit and braze some flat stock in there.

in the end, I'm guessing it'll carry a sixer but not a 12 of beer.

I think I'll start with a can of MAPP and some silver braze and probably use SS--there is a place in town that stocks quite a lot of SS and 4130 tubing, so here goes@

Thanks again!
Allan

http://www.robinmathercycles.co.uk/

Forgot the link...

That looks like 5/16". Could be .028, or .035. .028 should be enough for most things that would do. Another thing to consider with the kind of stud mounted into the tube for the bridge, is the fit between something like that headless bolt and the tube. Check the ID chart for tubing and find a close fit. It will probably be a thicker wall than you would want elsewhere on the rack. Also, normally you want metric stuff, but you may need to check out your options, and how a 1/4" bolt would fit your bike, and your ID. Another option is to buy a metric drill bit or better still, a chucking reamer, and ream some tubing to your bolt.

Hey Allan,
I'm by no means a experiend brazer, but I decided to build myself some racks for the same reason you want to.

I used 4130 tubing from AS, some files, hacksaw, bender, etc... I used air/propane at first and it works okay, however I had to heat the joint for a long time and the flux would burn, complicating the brazing and clean up. I ''upgraded'' to air/MAPP recently and it works a bit better. I might try brazing with silver too for fun. Also, I'm using some very basic powdered borax flux mixed in water. Couldn't find anything else. Petepan1 you're in ON where do you get good paste flux for brass or silver?

Here is a pic of what I did last out of 1/4'' cromo. It mounts on the canti bosses with flimsly 2mm flat stock brazed in slots, and through the crown with a brazed bolt (I reamed 5/16'' tubing with a 1/4'' drill). It's got an integrated décaleur for a h-bar bag.

http://farm3.static.flickr.com/2425/...2d86eb8eb4.jpg

If you use a lot of different sizes or thicknesses of tubing, doesn`t that get a lot more expensive for a guy who isn`t buying in quantities and stockpiling? I mean, if you only buy a couple random lengths of one size/wall you`d have plenty for one rack and maybe another, whereas if you want to use four tubes you either have to buy a minimum of four lengths or pay "convenience" prices a bunch of for itsy bitsy pieces. Just my thoughts- every time I think about ordering "good stuff" for a project I change my mind and just use what`s already available, so I haven`t experienced that issue first hand.

Looking good, Tuz. I like the round side rails- definitely sets it apart from the factory stuff.

I don't think it is necesarry to make racks out of mixed tubing, Most of mine are all one size, being expedition type racks I wanted them to be tough and didn't care about the weight. It is worth thinking about structures though, particularly if you want to push the envelope at all. Touring racks aren't all that large since the panniers that go on them are really framed in addition. But porteur type racks both have the post and beam geometry, and the size where they might benefit from some tubing sellectivity. One could ask the same question about a bike, why not just use one size of tubing throughout?

I think it pays to start to think like an engineer, it will pay off over time. I certainly am not an engineer, but I'm not a linguist when I do crosswords either. The other day I read about this guy who sold ultralight plane plans, good plans. But he was very thrifty and specified 4130 tubing only where it was required. Circa WWI planes were made with Hi10, but the cost is about twice the weight. He was substituting Hi10/DOM with equal wall diameter, a big haircut. I was wondering what part in an airframe could be made of the DOM without weakening anything. It stands to reason the short transverse struts, and maybe the diagonals could be made of DOM. But I may be all wrong, it's just interesting to try to figure this stuff out, and pick up reference info wherever one can find it. Main advantage is you can learn something you didn't know, mention it on Frameforum, and get banned.

Cost wise, I buy by the foot, and can often pick up some pieces from offcut boxes. I don't think there is any significant cost difference in specifying different wall thicknesses or sizes, not for one-offs. In general, buying all one size, and full length pieces is the best yield, but many are getting this stuff delivered anyway, and for that mater I just got the 5.5' box in my lattest truck and a 20 footer will hang out quite a bit. :) Also one needs some weird sizes for splices, before you know it you have a whole box of windchimes from offcuts and lots of sellections.

I have one of those hardware store oxy/acetylene rigs...the acetylene runs out way before the oxygen. Also, getting a refill on the oxygen costs less than $10.

[QUOTE=tuz;9357439]

I'm by no means a experiend brazer, but I decided to build myself some racks for the same reason you want to.

I used 4130 tubing from AS, some files, hacksaw, bender, etc... ?

QUOTE]

Hi

I am wanting to do the same, build my own rack. How did u bend the metel, and was it hollow?
It looks good, I am hoping for a more substantial rack.

G

Yes I used 4130 cromoly, hollow of course. I bought this bender. There are some cheaper ones that also have the reference marks localize the 90* and 45* bends ad they are found in local harware stores. Thanks btw.

I know you want to start on something small, but aren't racks readily available from shops? I'm a beginner brazer too and I keep a water bucket and extingisher handy.

Yes- sort of. Building a custom rack exactly to fit a certain bike has some really big advantages over factory built, one size fits all racks. Besides having complete choice over beefiness VS lightness and size/shape/ extra features (like light mounts just where you need them), you avoid all those pvioing and slotted gizmos that serve to make it fit a huge variety of bikes. It results in a much sturdier rack pound for pound and MUCH cleaner. And that`s just the practical side of things. Much better is the knowledge that you`ve done it yourself. Besides that, what CAN`T you just buy off the shelf? There are reasons for just buying something rather than making your own, but the simple fact that it`s available doesn`t rank up high on the list of those reasons for me. Think of chocolate chip cookies, for example.