Frame repair.

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Beemerboff
Posts: 22
Joined: Thu Feb 08, 2018 12:11 am

Re: Frame repair.

Post by Beemerboff » Tue Mar 06, 2018 5:45 pm

I didn't say that frame repair was not possible, just that it took more skill and knowledge that most who were doing it had.
Pop learned his trade and skills with Rolls Royce and then the Royal Air Force.
After the war he and his brother set up a little engineering business , specialized welding and engineering for petrol heads.
He repaired a few frames, and converted a few more solid frames to swinging arms.
He wasn't a great fan of bending anything bent back straight, or heating anything cold formed.
Brazed lug frames were unbrazed, if necessary new lugs fitted , and bent tubes replaced..
All using part from the OE suppliers, Qualcast and Reynolds tubes.
With welded frames the preference was to cut out the bent portion and weld in a new section, suitably sleeved internally and sometimes externally, but there wasn't a lot that could sensibly done to anything other than mild damage, and very little to a thin wall high tensile steel bronze welded frame.
And of course even less to a aluminium one, ever with the equipment and knowledge to re heat treat them.
FWIW you cant re heat treat cold worked steel .
Phil Irving's Engineering book has actually been reprinted and Amazon has it for $30-
His Tuning For Speed is/was free to air somewhere.
Both are essential reading for anyone who works on bikes.
And also for anyone who would post learned comments on the net --------------.

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Zombie Master
Posts: 8129
Joined: Sun Aug 22, 2010 12:21 am
Location: Vancouver Island BC Canada

Re: Frame repair.

Post by Zombie Master » Tue Mar 06, 2018 6:14 pm

Pop sounds like the real deal, doing things the right way the first time.

Just because you can bend back a frame strait, doesn't mean it will stay that way.

Your dad's methods insured a true repair unlike the common BS artist.
Any and all disclaimers may apply

barryh
Posts: 490
Joined: Fri Oct 01, 2010 12:30 pm

Re: Frame repair.

Post by barryh » Wed Mar 07, 2018 5:09 am

So I get the principle that you can't use excessive heat on cold drawn tubing without weakening it. But just how much heat can you use. If brazing is OK then it must still be in the region of 650 - 800 C. I have a friend who is contemplating repairing a bicycle frame built with 531 tube and brazed lugs. Does he need to chose a particular brazing rod to keep the temperature down. It must also be tricky to get the old lugs off without overheating.
barry
Cheshire
England

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melville
Posts: 1384
Joined: Tue Aug 03, 2010 8:32 am

Re: Frame repair.

Post by melville » Wed Mar 07, 2018 7:19 am

barryh wrote:
Wed Mar 07, 2018 5:09 am
So I get the principle that you can't use excessive heat on cold drawn tubing without weakening it. But just how much heat can you use. If brazing is OK then it must still be in the region of 650 - 800 C. I have a friend who is contemplating repairing a bicycle frame built with 531 tube and brazed lugs. Does he need to chose a particular brazing rod to keep the temperature down. It must also be tricky to get the old lugs off without overheating.
Chuey can also comment on this. Yes, bicycle frame repair is quite sensitive to temperature. For frame repairs at the shop I used to work at, they'd usually cut out the bent tube first to see if the tube had been pinned into the lug to hold it together before it got brazed. Pinned frames were drilled through the lug and tube as they sat on a mockup jig and pins (nails) inserted into the holes. The pins would usually have 1/4" or so sitting inside the tube. A lot of older frames were pinned--like from 1980 and before.

Different builders have different favorite rod. Lower temperature is better, but IIRC they all melt between 1100 and 1300 deg F. That is below the critical temperature of most bicycle tubing but not very far below that temperature. Torch technique and even heating is more important.
Call me Mel. Some years ago- never mind how long precisely- having little or no money in my purse, and nothing particular to interest me at home, I thought I would ride about a little and see the other parts of the world.

barryh
Posts: 490
Joined: Fri Oct 01, 2010 12:30 pm

Re: Frame repair.

Post by barryh » Wed Mar 07, 2018 11:20 am

melville wrote:
Wed Mar 07, 2018 7:19 am
Pinned frames were drilled through the lug and tube as they sat on a mockup jig and pins (nails) inserted into the holes. The pins would usually have 1/4" or so sitting inside the tube. A lot of older frames were pinned--like from 1980 and before.

Different builders have different favorite rod. Lower temperature is better, but IIRC they all melt between 1100 and 1300 deg F.
The tubes are already cut short cut and I didn't see any pins which will help with getting the old tube and lugs off. The temperature range you quote is 600 -700 C so not so bad. He's a good engineer and has dozens of high quality bikes so I'm sure he'll manage.
barry
Cheshire
England

Beemerboff
Posts: 22
Joined: Thu Feb 08, 2018 12:11 am

Re: Frame repair.

Post by Beemerboff » Thu Mar 08, 2018 3:36 am

Remember that brazing - brass rods or spelter are quite different to bronze welding rods.
Both come in different temperature ranges, are used in quite different processes and with different fluxes and torches.
It is all in Phil Irving's Motorcycle Engineering book which was written by a quantified engineer from hands on experience and covers all the problems and mistakes which might be encountered in the design, assembly and jointing of steel frames.
Essential reading /knowledge for anyone anyone working on them, and at at $30- wont break the bank.
I didnt ever work in pops business as a paid employee. Apart from pocket money that is, and I had to work hard to get that!
My brother and cousins went into the business , I studied Structural Engineering and Estimation (Quantity Surveying) and worked in the Building and Civil Engineering industry for 50 years in a variety of roles.

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