I am a frame builder AMA

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  • If this is correct Merckx's bike at that time was on 265. If that's good enough for cornering when racing, with clearance required for wide pedal and cages, does a rando bike really need a higher BB (I understand it'll be just fine)?

  • I like my BB low. Nothing wrong with that. I am just saying 270 aint that high. Also depends on the wheel base. My cargo bike suffers badly from pedal strike, but it isn't a problem if you know it's a thing

  • My cargo bike suffers badly from pedal strike

    Those flat MTB pedals need a lot of clearance don't they. Now you'll know for the next one!

  • Yes for sure. BB is at 265mm I think. Turning with such a long wheel base seems to mean I get quite close to the ground. SPARKS have been made ;-)

  • AS @PhilDAS says, I think if I find a correctly dimensioned 4130 straight tube I should be able to make it work with some off the shelf headset parts. The trouble with a 44mm HT is that it doesn't leave much room for the rear brake hose to wrap around the steerer.
    I asked a Chinese CNC company and they quoted me $220 for a fully custom machined headtube which will just take the drop-bearings. Not crazy expensive once you factor in the cost of headset cups etc. Obviously, it's expensive if you fuck it up and have to order a second one...

  • A second one would be cheaper if you ordered them at the same time though... Half the cost is in the set up

  • Yes, most definitely. Time for a list ;)

  • haha im keen, sounds cool

  • Haven't properly dimensioned it, but it'd be something like this.


    1 Attachment

    • HT.PNG
  • Had a call with TBA yesterday to discuss my course which was generally positive, as in they're willing to help with my ideas but not take responsibility if they don't work (fair enough).
    I might abandon the wishbone in favour of concentrating on the headtube as the key feature and not messing that up.
    As a backup headtube option, I was looking for just some plain gauge tubing that might come in a suitable diameter and wall thickness, i.e. 58mmOD, 2mm wall. Anyone know of a good source?

  • What's your vital dimension?

    LASAero don't do 4130 that large, Aircraft Spruce do 2 1/4" or 2 1/2" but choice of wall thickness is pretty limited at that diameter.

  • Ideally, the finished piece should have 62mm OD, 55.95mm ID at the ends. I can machine the outside to remove some weight in the middle of the tube.

  • 2.5" x 0.12" wall thickness from Aircraft Spruce is pretty damned close?

  • Talking headtubes, what's the deal with mitreing a downtube to meet a tapered headtube?

    Having only done straight headtubes it seems like doing a tapered one will be hella difficult but maybe I'm over thinking it?

  • yeah they look awkward. Ive wanted to do one for a bit but havent got round to it. Also are there tapered heatsinks out there for tiggin?

  • Is it boric acid that some people use as flux?

    I knows its something acid!

    I tried it a while ago and wasn't overly enamored but fancy trying it again just for dipping my rods in.

  • Yep, that's the stuff. Matt swears by it. Never tried it myself.

  • Cheers.

    Just grabbed some off ebay.

    I remember when I was trying to make a paste with it it just didn't want to go where I wanted it to. Hopefully it sticks to a hot brass rod ok!

  • A drop of washing up liquid helps.

    I find it a right faff to wash off. Not sure if money saved on it, works out cheaper than time trying to get it off. I probably bake it on a bit much.

  • For the frame builders and tube connaisseurs. Can you convert a 1" ahead to quill stem by threading the fork and replacing the headset?

  • Yes, but it's not an easy job. There's a fair bit of metal to be removed, and that's hard work with a tapping die. Fork threads are normally cut on a lathe, but once the fork is built that's not really an option. Also, it's critical that the die is straight when it starts to cut the thread, otherwise the thread will go off-centre and weaken one side of the fork. It's not a job I'd want to do myself, but you may find someone out there who has the tools, skill and brute force to be able to do it.

  • Ah didn't think of it that way. I thought one would just take thread cutter and go for it. Maybe I should look at getting a custom ahead stem instead.

  • Surely easier to melt out the steerer and braze in a new one, then repaint the fork, than it would be to lathe turn threads on the steerer with it still attached to the crown.

  • Yes...

    That probably needs some justification.

    Internal diameter is of no consequence when designing/speccing a threadless steerer so a quill stem may not fit.

    A lot of steel 1 1/8" threadless steerers have an id of 1" so could accept a 25.4mm quill but the p2 fork I'm working on for a forumenger right now was 23.something millimetre and I found another fork in my collection that was slightly larger that.

    I suspect 1" threadless steerers will be similarly inconsistent.

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I am a frame builder AMA

Posted by Avatar for coldharbour @coldharbour

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