[Closed] DIY/home brazing

Jeez, an opportunity to flame me...missed?

We're waiting for the 'diy/home firefighting' follow up 😉

Blowtorch won't be hot enough - oxy-propane will be good enough for silver-soldering small parts, you can even braze with it though it's fussier apparently.

I had my first oxy-acetylene kit in my garage - downside of that is you need to pay cylinder rental.

Hmmm, artisan brazed cutlery. Nice.

Blowtorch, I assume MAPP? For small parts using silver solder it's fine.

Anything larger - fillets, brass, proper bike building - the blowtorch CAN get it hot enough but it takes such a long time to get up to temperature that the heat spreads out and you end up with an enormous heat affected zone.

If you MUST do it, put a heavy bit of steel or similar close behind your workpiece to act as a heat reflector. It'll heat up quicker.

The flames on blowtorches are also way too large, will be very difficult to get heat to go to the right place, and you might find when you add brass or silver it wets out far too much.

Edit: Speak nicely to someone and borrow a proper torch.

Ta all. Looks like a PITA at home...I assume oxy propane kit would cost a few £?

Much of a muchness with oxyacetylene for kit cost - so a few hundred for regulators, torch, hoses. Not sure how it works with cylinders, some people use oxy generators, so budget a few hundred more for that.

By comparison, I pay about £45 per month rental for oxyacetylene cylinders.

The bigger thing is you'll burn through a lot of gas and materials when learning, especially if you're teaching yourself.

Keep an eye out on ebay for schools selling off old kit. Unfortunately a lot of school DT departments are getting rid of old metal work/woodwork kit and focusing on laser and 3D printers, etc. A school local to us was selling full brazing sets (obviously excluding gas cylinders) for pennies.

Can you not just get a job at Shand to satisfy your DIY needs? And after last week surely they can't get anymore criticism for the standard of the work.

Keep an eye out on ebay for schools selling off old kit. Unfortunately a lot of school DT departments are getting rid of old metal work/woodwork kit and focusing on laser and 3D printers, etc.

It's ridiculous - a friend decided to retrain as a tech studies teacher, for his student project he needed to machine a bit of steel then braze it to something. He wasn't allowed to do any of that, he had to come use my kit to finish his student project.

Look at hearth brazing to do some brazing with out oxy fuel mix. Never tried it but read somewhere they use it at mercian.

Hearth brazing is pretty old-school - great for lugs, not so much for fillet brazing or braze-ons. It's usually still oxy-fuel though.

I believe my ancient mercian frame was hearth brazed

You can see the nails in the bottom bracket shell

What are you up to Al? First it's ovens and now brazing. Got a mega project planned?

Avoids parts of burghy just in case
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I use oxy-propane with an oxygen concentrator - mail me if you want some more info (it was £245 for an ex-medical concentrator from Tuffnell glass).

MAPP is fine for silver solder bits and bobs (not big lugs or fillets). It is hot enough for moderately big tubes with silver (often use it for temporary tacking stays together before mitring) - generally faster than cranking up the oxy con. Swivel head means you can keep bottle upright.
http://www.go-system.co.uk/catalog/product/view/id/254/category/22/

I always fancied a Flamefast brazing hearth (like you get in school workshops - not like bike factory brazing hearths) but never convinced it would be hot or controllable enough for brass fillets (they are propane / natural gas + built in compressed air and lots of safety cutouts)

Didn't think you were meant to use MAPP for anything structural, it has a high concentration of hydrogen and potentially leads to brittle joints...

I think the hydrogen is only a problem for welding steel and not a problem at soldering / brazing temperatures. Same problem exists with propane which is why it only gets used for steel cutting and heating not actual welding.

I don't think what you buy as "MAPP" is actually MAPP anyway (it is MAPP substitute which is LPG plus other stuff).

I believe my ancient mercian frame was hearth brazed

You can see the nails in the bottom bracket shell

Those are pins to hold the tubes to the lugs while brazing - doesn't necessarily mean a frame was hearth brazed. It's an alternative to tacking joints in the jig (or if you're building without a jig).

Basically, for repairs and brazing, you need quite a bit of concentrated heat - only really oxyacetylene can do that.

I always fancied a Flamefast brazing hearth (like you get in school workshops - not like bike factory brazing hearths) but never convinced it would be hot or controllable enough for brass fillets (they are propane / natural gas + built in compressed air and lots of safety cutouts)

No they're not really. Fine for silver soldering and we also use ours for heating up pewter for casting. I have tried brazing on it, but you need to heat for ages to get the steel up to temp so the brass will flow.
Much easier to use the oxy-acetylene set-up next to it 😉

Thanks ajantom - I suspected it would be the case with Flamefast fuel-air stuff.

Oxy propane works fine for all brazing tasks - plenty of people use it for framebuilding, including lots of factories when lugs were mass market. I seem to remember at Bespoked 2013 that the European guy doing the live brazing demo struggled using Bike Academy's Oxy-acet as he normally built with propane back home.

However Ben is correct - it just isn't as nice to use as Oxy-Acetylene (but a bbq propane cylinder in a home setting is a lot easier to explain to the insurance company).

Oxy-propane is fine for smaller work, but it doesn't get as hot as Oxy-Acetylene, and won't work for bigger brazes.
We've had huge rows at work over this, as one of our customers won't let us take Acetylene on site, but we can't braze 4" copper pipe using propane as it doesn't produce enough heat..

Can you silver solder it? I bult a bunch of copper heat exchanger things a while ago, used silver for them.

No, it is refrigeration pipework on Naval ships and Submarines.
It has to be brazed with the correct grade of rod (high silver content) and you just can't keep a 4" pipe hot enough to get a nice even flow if you use propane.

OMG Holy Tread Resurrection!

Is MAPP + heat hearth + silver solder gonna work to replace DT and TT for an old lugged frame?

Back to work, place will hopefully be busier today 😛

OMG Holy Tread Resurrection!

Is MAPP + heat hearth + silver solder gonna work to replace DT and TT for an old lugged frame?

I doubt it - the frame might have been brazed to start with, and undoing lugs needs more heat and lots more heat control than doing them in the first place. To be honest, unless the lugs are really worth saving, it's much easier to make a new front end - and you could do that with MAPP + silver.

Ta, I'd still need to undo the existing joins tho?

Shame MAPP won't do fillet brazing 😥

Yes, but half the number of existing joins to undo. I do it by cutting the tubes about 1cm from the lugs, then looking inside to make sure there's no pins, then carefully cutting a slot before unbrazing.

You might be able to do it entirely mechanically, with a small Dremel bit and lots of time. Easier with the BB shell, you cn just use a half-round file to file inside the lug, but the ST gets in the way when you do that with the TT.

So you mean grind out the remainder of the tubing with the dremel/file?

Yes. BB shell won't be too hard - could even do it with an expanding reamer if you want to be posh. The top lug will be the tricky one, getting the tube out of the corners.

I might even be tempted not to bother - if this is a bike for you and you're determined to do it yourself, you could sleeve it. Cut the TT right around the edge of the lug, fit a new tube that's got the same o/d as the i/d of the old top tube, then clop it off 2" from the lug and fit a new TT slipped over the stub. Would look the same, be a little bit heavier, should all be do-able with silver with care.

Or even depending on tube diameters, ignore the last stage and have a smaller diameter TT, assuming you can get HT lugs of the right size (or shim that end too).

pretty sure years ago there was an attachment for arc welders that enabled brazing

Had one when I was a student - I wouldn't let one within a metric mile of a bike frame 😉

Everything that Ben said. Especially the bit about arc welder brazing......

I've had much more success removing dropouts, bits of tube etc cold (hacksaw, file, Dremel). Un-brazing a lug needs a lot of heat over a large area - there might be something on youtube showing it being done. I've even struggled removing brazed canti bosses to then discover a tack weld buried under the brass.

Thanks all and good tip too Ben, tubing is a bit undersize!...can I find something to fit though...

It's not worth much, just a 80s 531c frame, but at 1.8kg it'd ride nice if I could fix it cheaply (and learn/amuse myself while doing so).