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How To: rear frame fabrication

April 24, 2012

More of the ongoing restoration of the 1913 Veloce.   Here are some links to earlier articles.

 

The Veloce project had some damage to the rear frame tubes, just ahead of the rear axle.  The rear stand pivots on the dropouts (the lugs that hold the axle) and the stand has two legs which pivot up to rest on the bottom side of the chainstay tubes.  Starting the bike is done by pedaling while up on the rear stand, so the chainstay tubes see a bit of stress, and mine were crushed by the strain at some point in the last 99 years. 

 

An advert for Reynolds tubes circa 1920’s, with D tubes and oval tubes and some combination stays:reynolds tubes

While it would have been very simple to fill the dents with bronze and then paint over the repair, I wanted something stronger.  Knowing that my kids will eventually learn to ride on this bike leads me to make it as strong and safe as possible.  And the repair is fairly straightforward:  remove the tubes, make new ones, braze them in.  Except the tubes are not round, or square.  They are D shaped in their cross section.  These tubes are not easy to buy, but there are a few companies in the world that I found that make such tubes.  And they were glad to quote the manufacture of tube to the correct dimensions, if I wanted to buy the minimum order of 2 tons of tubing…

 

So, to make some D shaped tubing:  First step is to measure everything before cutting out the old tubes.  I traced the frame onto paper and kept it as a reference, marking the paper with the measurements from the steel parts. 

IMG_0756

 

Then cut open the tube to measure the diameter and flat dimension of the D and the wall thickness too:

IMG_0752

 

Buy some round tubes, and cut them with a slitting saw on the mill.  Some other guys have done this also, and they cut the tube with a cutoff wheel and a grinder.  That makes it tougher to get a good joint for welding, but it can work.

IMG_0669

 

Buy some flat bar to weld onto the round.  I used flat bar that was 2x thicker than the original D, as it made it easier to bend the tubing to shape after welding.  Thank you to John Quirke in Ireland for this tip and the general fabrication ideas!IMG_0671

 

Bryan down at Advanced Welding TIG’ed these for me after I did a lousy job on the sample pieces with my MIG.IMG_0809

 

Then it was time to bend them into shape and the cut to length.IMG_0811

 

Here was when things went bad.  I heated the tubing to almost red hot, and dropped it in my tubing bender and promptly crushed the tubing.    Luckily I had made up several feet extra of the D tubing, so I could experiment a bit.IMG_0822IMG_0820

 

Eventually I found that I could fill the inside of the tubing with a solid steel bar of D cross section.  They are available at steel yards and used for fabricating handrails on modern staircases.  With just a touch of grinding it dropped right inside the D.  I made it long enough to support the portion that was being bent, plus an inch or two on either side.  Now those portions are essentially solid bar stock and are very strong.   I did the ends too, the area that the rear stand support legs will hit against, so this exercise won’t have to be repeated sometime in the future.

 

Then the bending went fine.  Fixture it all up and measure a few times to make sure that the dummy axle is square to the rest of the frame, and then brazing it all back into one big piece:

IMG_0859

IMG_0866

It looks easy, and it almost was.  Not shown were the hours and hours of test cuts, test bends, grinding, welding, machining, making fixtures and the other fiddly little things are needed to make new parts fit old bikes.

 

And here is how the bike looked a few weeks ago.   Still a thousand things to finish, but it looks like a motorbike.1913 Veloce 500cc

 

Here is a whole different approach for making D tubing using a press. 

More How To articles can be found at this link.

17 Comments leave one →
  1. shaun permalink
    April 24, 2012 9:05 pm

    Nice post! I will likely never have to do something like this, but it was still very interestin’ and cool to read about. Thank you.
    I’m not sure I understand how the “D” shaped stock was removed, after you made the bends, unless the stock didn’t extend to the parts of the tubing that was being bent. In which case I don’t understand why the tubing at the bend didn’t collapse, as it did during the first experiment.
    Last: Is the rude pixie on the luggage rack an original fitment?

    • April 24, 2012 10:25 pm

      I left the solid D bars inside the tubing, they were trapped there after bending. So in those short sections, it is essentially solid bar stock. A few pounds heavier than stock hollow tubing, but much stronger!

      The cock-a-snoot is an aftermarket accessory that I found on ebay last year. A funny little guy, who reminds us not to be too serious.

      Ciao,
      Pete

  2. Anonymous permalink
    April 24, 2012 10:17 pm

    I am impressed, You make it look so easy

  3. Anonymous permalink
    April 24, 2012 10:20 pm

    Looks great Pete. Can’t wait to see it running. Hopefully my Pope will be together by then…
    Brian H. in Santa Cruz

  4. April 24, 2012 10:26 pm

    Fab! Thanks, Paul

  5. Anonymous permalink
    April 24, 2012 11:37 pm

    Beautifully done, and a joy to behold – plenty of hours of work went into that job! She’s coming on well, and a quick trial assembly is the icing on the cake! Keep up the momentum and she will soon be running!

  6. May 9, 2012 6:36 pm

    Dammit Pete, you’re hired. As my personal mechanic you’ll have no pay and long hours but you’ll sure get a lot of gratitude. Let me know when you can start. Reading your posts remind me how much of a mechanical muppet I am and how far I have to go.

  7. May 16, 2012 7:27 am

    Hi Pete,

    where do I order that brilliant devil that sits on the carrier?

    • May 16, 2012 8:56 am

      Ha John! He’s a fun addition to the bike. I found him on eBayUK. Do a search for “cock a snoot” or some variation on that spelling.

  8. Lou poleete permalink
    August 14, 2012 7:44 pm

    Hi can you help me out with my bike plz I hav the same bike and I need some pics of the rear frame with measurements and tubing size of top and bottom tubes and pic of the rear drop outs ty n gb

  9. Lou poleete permalink
    August 14, 2012 7:45 pm

    Hi can you help me out with my bike plz I hav the same bike and I need some pics of the rear frame with measurements and tubing size of top and bottom tubes and pic of the rear drop outs my email pollou8.1@netzero.com ty n gb

    • August 14, 2012 8:11 pm

      Hi Lou. I’d be glad to help. I’m buried with work right now, but I’ll try to get into the shop and measure it and snap some pics late this week.

  10. Nick Smith permalink
    March 1, 2015 2:22 pm

    Another tip for stopping the tube from collapsing is to fill with Woods Metal – a low-melting-point alloy (about 100 deg C). This sets to a solid which is string enough to resist compression at the bend, but malleable enough to allow the bend to be made.

    Once you’re done, it’s just a matter of heating up the tube over a suitable receptacle to catch the molten alloy.

    I got a tubing place to put some round 16SWG tube through a pair of odd rollers – flat one side, and larger than the OD of the tube the other, and got a decent D-section.

    The most difficult part was getting them to make time to do a small batch.

    Nick

    • March 1, 2015 7:39 pm

      That is great Nick. I only recently learned of those low melting point metals and all their uses. And I’m glad you were able to find a shop that would roll your tube. I thought about making my own rollers and giving it a try, but it seemed like even more effort than the other method. Can you send some photos of your project? It is always fun to share reader’s bikes!🙂

      • Nick Smith permalink
        March 3, 2015 12:28 pm

        Thanks for the reply, Pete. Not sure how to put pics up here.

        I had to do a couple of larger-radius bends than yours, but once I’d made a jig up I was able to pull them using the length of the piece of tube I had to do the work.
        Usual story – a day to make the jig, five minutes to make the one-off part required!
        I’ve gone on to re-use the Woods metal for handlebar bends and the like, and it’s worked each time. There’s a few common sense handling tips that I worked out along the way (generally after the fact…)
        The link to the Douglas page shows some astonishing engineering, but how do you get the wooden former out of the bent tubes?

        The rolling mill seemed pretty matter-of-fact about the job – they measured the circumference of the sample D tube I showed them, and got the diameter of the round equivalent from that.
        I wish I’d asked for more of the two sizes they made – had no idea it would be such a big deal to have a repeat order. It does make the idea of some rollers increasingly attractive…

        Nick

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