22 October 2013

I had a bit of time between projects, so today I finally had a chance to do some infrastructure and tooling work that has been on the list for a long time. Firstly I got an extractor fan installed in the shop, so I won’t have to go through another winter opening the door every time I start brazing. Then I did some modification work on the follow-rest for the lathe. For the frames with integrated seatmasts, I’m not able to use a standard butted tube, as for one thing, they don’t generally come that long, and secondly, I need the butted section in the middle where the toptube joins the seatmast. I could just use a straight gauge piece of tubing, but that would be unnecessarily heavy. My solution is to start with a straight gauge 4130 cromoly tube, and use the lathe to selectively remove material from the outside to create a custom externally butted tube with the thicker sections where I need them. Doing this means a long section of tubing running between centers on the lathe, which requires the follow-rest just ahead of the cutting tool to stop the tube from bowing under cutting pressure. The follow-rest that was supplied with my lathe uses brass bushings to support the work piece. If these are kept lubricated then it works well, but they do still wear which causes two issues: The wear will match the size of tubing, which means a not great fit when used on a different size, and wear will occur (albeit a small amount) during a cut, making it harder to maintain tolerances. My solution to this was to remove the brass bushings and modify the supports to take a cartridge bearing, giving a rolling contact and no more wear. I’m looking forward to trying it out!

4 Comments

  1. Hi Rob

    Follow rest ?? Travelling steady surely !

    Andy

    You built a great pair of wheels for me years ago. I’m a friend of Duncan Alexander.

  2. Excellent behind the scenes post, Rob. This interest a fair few people.

  3. Rob,

    It’s always interesting to see the process, thanks for posting this.
    How much weight is typically removed from the seatmast using the lathe?

    -peter-

    • Thanks Peter – honestly I haven’t done a before and after weight in a while, but it is typically a 30-40% reduction.
      Best regards, Rob.

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