I am a frame builder AMA

Buy bent stays, or buy serious equipment (diacro or similar) theres not really an easy way to do it.

Do they sell bent stays for fat bike size tyres or does increasing the hub width get them around the tyre?

You'll normally need some sort of yoke, fat standard bb, wide axle, in various combinations depending on fatness. PMW is your friend here.

135mm rear +35mm = 170mm
73mm +35mm = 108mm
2.3 * 25.4 = 58mm, 58+ 35mm = 93mm

So stays designed for 2.3"s on a 73mm shell will need to angle in more to fit a 100mm shell, but wouldn't have the space for 4.0" even at the design angles.

And as @Emyr said you still need more bending on the stays to get around a 4/5 inch tyre. Do tube manufacturers produce fat bike ready stays or do they all require custom bending?

I've not seen any, but I've never built a fat bike.

What are the numbers? Can't get my head around them...

Fatbike would be 100mm or 120mm BSA shell, with OLD of 170 or 190mm for QR, 177 or 197 for thruaxle. The wider spec tends to be for ~5" tyres, but there are plenty of frames which use the 190 rear with a 100mm BB.

And the other numbers were 73mm BB, 135mm OLD and 2.3" tyre width, for normal MTBs.

Sorry I meant the sums:

135mm rear +35mm = 170mm
73mm +35mm = 108mm
2.3 * 25.4 = 58mm, 58+ 35mm = 93mm

Colombus advertise a fat bike chainstay and seatstay, it has a 12 degree bend from what I can remember

Selecting optimum tubesets for a given rider weight/riding style/frame size: rule of thumb, engineering analysis (whether complex or simple), or just based on stuff wot broke in the past? I know experienced builders often mix tubes from various manufacturers, but the whole process seems to be rather mystified.

Found them, thanks for everyones answers and advice.

There’s fat bike chainstays in the what’s new bit on ceeway

My TIG welder is a Cemont Arcotech TE150 AC/DC. For MIG I've got a Clarke MIG150TE. I fancy a new DC TIG welder with pulse though.

135mm rear +35mm = 170mm

Fatbike dropout is 35mm than MTB.

73mm +35mm = 108mm

Adding 35mm to the MTB BB shell gives you too wide a shell, by 8mm.

2.3 * 25.4 = 58mm, 58+ 35mm = 93mm

Assuming you just moved the stays apart 35mm, you'd only have clearance for 93mm of tyre.

Ahhh all clear! I spent an unreasonable amount of time looking at those numbers on sunday afternoon!

R tech ftw. Can't reccomend those guys enough.

Seconded on how great R-tech are and their machines are ace. Had one of the digital DC ones for just shy of a year and it's been totally hassle free.

I've got a gas-pipe Raleigh frame someone was kind enough to dump in my front garden: ideal practice fodder!

Should I strip the paint first, or just burn it off when I melt the joints?

have you had any injuries as a result of framebuilding?

I have put the hot end of the TIG rod into my mouth by accident more times than I care to mention

Burn paint off and then rub it back. Cleaner the better.

I slipped with a jewellers file and stuck it into my face, somehow in a nostril. That bled really badly.

Also, got a 30cm shard of carbon stuck in my hand, one end going in at the bottom of my palm, the other end coming out between my fingers on the other side of my hand. Felt a bit like what a cesarean would feel like id imagine. Stupidly I removed it myself, risking it snapping off and having the have my hand operated on. I no longer wipe carbon tubes down using the 'bash the bishop' method.

As is often the case, it's not the terrifying machines that can rip you limb from limb that get you, as you are always respectful around them, but rather the little things that you cut corners on that leave you bleeding.

There's a good way of avoiding that ;)

I bought some used torch kit, and planning to set up for oxy-propane brazing, but not sure what will be most useful here (and what's what actually) and what else I'll need to buy - any help?

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