Framebuilders - Rack questions
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I eventually want to build my own frame (don't we all) but I'd like to hone my brazing skills by making a few racks (or a lot of racks!) My question is this; what are you guys using if/when you make your own racks? What tubing, stainless, solid Al, etc? If you have any pictures that you'd like to share, please post them up. I have an idea in my head but I still have details to work out before attempting to build it.
02-01-11, 08:54 PM
4130 steel. Common sources are Wick's or Aircraft Spruce. It's not worth using anything else. Stainless is generally not as strong as 4130. What kind of rack do you want to build? I've been building my first racks, and I found that if you search google images for porteur rack, you will find tons of builder sites with progress pictures. If you search for any other terms, you will get too much noise.
You might want to look at this recent thread (http://www.bikeforums.net/showthread.php/710461-rack-tubing-bending?p=12162454#post12162454)
I use 4130 also, but the big manufacturers also use stainless including on their expedition models. It costs about the same, and it doesn't need powder coating, which sucks up a lot of money. I agree it isn't as strong, it isn't as strong as hi tens, but it will work.
I don't think you learn much from brazing racks, other than racks. It is just so easy, you can flood a whole joint with one poke, and it doesn't have anything like the step by step build of a larger joint.
I would recommend doing exercises on pieces of 4130, and building piles of braze on braze. If you do the racks first, one thing is they may not fit you ultimate customs, and then you have these beautiful, expensive, racks sitting on bikes you want to send down the road.
Yeah I think the SS racks have thicker walls to compensate. At 3/8 diameter you are starting to get pretty stiff in both SS and cromo. But get a bunch of 1/4 and 3/8 x0.035 cromo and some round files.
Making racks are challenging in their own way. Mitering small tubes at an angle, having symmetrical sides, nice fillets, making sure the rack sits level in two planes, fixturing the tubes, bending, etc. Fun stuff.
02-02-11, 01:29 PM
seems to me that it's similar to brazing a brake bridge, it's not all that easy to get a nice looking joint without a batch of finishing.
I understand the concept of brazing with regards to using lugs (similar to doing plumbing) but with racks, would I be doing a fillet joint? I've welded a rollcage in a VW Bug drag car so I understand how to make the joint (I think) but I think welding with a MIG is slightly different than brazing....:)
Joints are easy. Fastest way for a one off first off, is to get a Nicholson 10" rat tail file, check it for 3/8" diameter, and just file the joints in there, real easy. Then you flux with some kind of silver flux, inside and then you hit it will heat, and touch the silver. If it is just the right heat and touch, a perfect little silver fillet pops in place. If it isn't, you steer it around, and it will probably pop into place thicker, or it will be a mess, speaking from the first try perspective here. always seemed to turn out strong enough. This is why it is easier than doing a bike frame joint because it just kinda happens fully formed. No need to tack it, and work quadrants, etc... I've tried welding racks a few times since I have Tig. I can't say I overly impressed myself. Haven't tried gas welding yet...
Your input has been very helpful guys, Thanks! Next question, best place to get tubing to build a rack? Maybe I'm missing something but it looks like there are a lot of people selling pre-made components (chainstays etc) and not just straight tubing.
If you're fabbing your own rack, you need raw tubular 4130 or SS. Check this recent thread (http://www.bikeforums.net/showthread.php/710461-rack-tubing-bending) for more info.
Whoops.... Somehow I missed that again.
02-03-11, 08:03 PM
I don't think I would build a rack with silver. It's not that great for building fillets, especially for a beginner. Been repairing a fastback seat cluster that was done with silver and cracked. I'm not impressed. Everything would have been much better if it had been done with bronze.
You look at some of the guys who build/built in silver, and their fillets are about the same size on the full size tubes. It's overkill on racks. Some of the self-proclaimed "best" rack builders do it. :) I think it's a perfect application, though if he has bronze and wants to use it, why not. You will need silver to do stainless, probably another knock on that material, right? I also use silver to attach stainless bearing points on my 4130 racks. Basically the most likely failure points anyway. Most racks are overbuilt, so I'm not worrying.
02-04-11, 07:02 PM
I assume they are using fillet pro or some other variety of 45% silver that will build a fillet. It's expensive, and you can't just heat it up and jam the rod in and get a good fillet.
If I ever build a stainless rack I'm going to use nickel silver, quite a bit cheaper than silver.
That is pretty much how it worked for me just using 45% safetysilv, of which I have pounds, and the white flux. Just seems to be a sweetspot where a fillet would pop in there. I also would end up with too much and a drip hanging there. I need a rack about every 5 years, so it isn't like this is some masterclass. I work a lot on the frame welding. And am nowhere near satisfied. When I started out with racks. I tried to weld them and it was disastrous. But it was as if what I was using with the silver was just made to do 3/8" tubing. Just hit it with the rod and pull it around with the flame.
02-05-11, 10:41 AM
I'm with you now, sounds like fun. Make a movie :)
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