featherbed frame

lcrken said:

I'm pretty sure all the Manx featherbeds were done with a silicon bronze filler, most likely from SIFbronze.

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Be careful here too, SIFBronze is reportedly from Suffolk Iron Foundries = SIF.
I've never seen the actual compostion of the bronze quoted.
Only that it can be built up into fillets.

So its not another brand of Tobin Bronze brazing rods = brass.

Anyone know ??
There are available endless varieties of bronzes, and bronze rod types.
Silicon bronze rods do use a fluoride type flux though....

The original SIFbronze #1 rod is still around, and the company says it is widely used for welding vehicle bodies, bicycle frames, and other tubular steel structures. The composition is 60% copper, 0.3% tin, 0.3% silicon, and the balance zinc. I don't know if that is the same rod used for the Manx frames, but it sound pretty likely.

Ken

That composition with mucho zinc actually makes it sound like brass, ??
and the normal brazing rod used for most vehicle and bicycle work.
Where wicking into spaces is an important property...

I'd have expected more silicon and much more tin ??

Hard to be sure which alloy was really used. I picked on SIFbronze #1 because it is one of the original rod compositions that is still available. The company describes it as well suited for general purpose brazing and bronze welding of steel, cast iron, etc. I know SIFbronze was frequently mentioned back in the day as a preferred filler rod for bronze welding frames, both mild steel and 531 alloy, but I've never seen any mention of which alloy rod was used. More recently, John Bradley mentioned in his book on motorcycle design and construction, that a good rod for bronze welding 531 frames was SIFbronze 101, which also has a high percentage of zinc, being 60% copper, 0.2% manganese, 0.1% silicon, 0.1% tin, and the balance zinc. These references explicitly call out bronze welding, in addition to brazing, as a suitable application. More info here, including some history of SIFbronze.

http://www.weldability-sif.com/pages/home.asp

I've just gone through Ken Spraysons autobiography again, and although he gives a lot of detail about construction of featherbed frames, including that all Manx frames were bronze welded Reynolds 531 tube, he never mentions the type of filler rod used.

Fascinating stuff. Interestingly, the Weldability-SIF site recommends one of their phosphor bronze rods for brazing and bronze welding with tig. I'll have to try that, but that will have to be another thread.

Ken

Working on 531 and T45 frames,on racers I found that the frame cracks next to the braze as though the heat weakens the tube,and in some cases you will be chasing the break,on my P11 with 531 tubing it had to be cut out and slugged at each end with new tube sprung in.We had a lot of trouble with Rickman frame cracking where the left hand frame gusset flows around the radius of the frame where the tube bends round, behind the clutch.this was a real pain as the whole motor and trans had to come out,virtually stripping the whole bike just to do a welding repair.Another pain part was the Rickman had at one time had oil circulating the frame,so the oil contaminated the welding as soon as the torch was applied.

From memory I believe the usual thing when steel welding a frame is to keep the heat in the joint using the torch and let it cool slowly. I think it has to do with the balance between austenite and martensite. All frames that I've been involved in have been bronze welded, and I don't think it matters what you do, flex with cause cracking. I think the bronze affects the steel when it penetrates. TIG welding looks the best to me, the heat is lower and more localised. I'd still keep an oxy-actetylene torch handy to play on the welds while they are cooling. If the frame is locked in the jig it shouldn't spring much when released if the welds cool slowly.
My Seeley frame is a MK3 which usually has a ladder brace in front of the motor. I use a curved piece of chrome-moly tube with the end brackets offset to allow a bit of spring when the motor bounces up and down. The distance back to the pivot is so large that I don't think there would be much stress concentration at the welds - the tubes would flex to accommodate it. The head steady has rose joints. I suggest that if it is too rigid in the vertical direction in the front, it must break.

acotrel said:

I think the bronze affects the steel when it penetrates.

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We need to find out exactly what 531 frames are welded with.?

I rather suspect that its only brass (the zinc in the brass to be precise) that 'penetrates' into the steel crystalline structure -
i.e. your martensites and austenites and pearlites...
Soldering (solder) and marine/copper and bronzes (but not brass) only stick to the surface to bond things together.
Brass as mentioned flows INTO the metallic crystalline steel lattice and contaminates it. And cannot be removed without cutting the affected areas out.
Rather than just filing and grinding and sanding and removing say a soldered or a coppered or a bronzed join.

Thats why all the references say to bronze weld Reynolds 531 tubing, not to braze it with brass....