The DIY frame jig thread

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  • Found some time for dicking around in CAD, came up with this seattube beam fixture, with one on both sides it'd be bolted down with 6 clamps which might be a bit over the top. I priced it up in the calculator of fractory.com and 3 sets (2 of the seattube plates and 4 of the sliding plates each) would be 100 GBP. Not too bad?

    Couldn't be arsed to draw up the rest properly as I think your plan is perfect, only thing I'm unsure about is the dummy axle clamping situation, but would also depend on the axles used.


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  • Couple of things.

    Your price sounds off...
    Have you checked your DXF sizing? DXF files are unitless, they are essentially just a set of lines that the software follows. make sure before you export them they're in mm as that's what fractory use.

    The bit which has the arrow pointing to it is where all the flex is going to come from. The extrusion is by design quite stiff (high second moment of area). this means you'll get the best results using that stiffness to your advantage. A plate has quite a low second moment of area which means it'll be flexy.

    If you can mount the upright beam across the full width of the steel plate it'll support the plate and stop it flexing and you'll get a stiffer jig.


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  • re:pricing.

    • 20%tax + post
  • I was surprised too, cheaper even as I had 12 of the big ones and 6 of the small ones first. Dimensions are definitely in the right ballpark. Good points re: the design, I just drew the bare minimum and slapped a fillet on it. Was thinking of triangles like this, but my sketch blew up when I did that and I didn't think it'd make a difference for pricing.


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  • The arrow was supposed to be pointing to the airgap between the two bits of extrusion where all the load will be transferred through two thin plates. I lack paint skills.

    You want the bits of extrusion to clamp to each other face to face not cantilevered up on thin plates.

    Re:price
    You don't need S355, fixtures need stiffness not strength. Better steel gets you a better yield strength but the stiffness will be the same.

    That price will go down if you add more bits. Small orders are priced WAAY higher to account for set up and office time.

  • You want the bits of extrusion to clamp to each other face to face not cantilevered up on thin plates.

    But then it can't rotate? Am I missing something very obvious? The angle of that beam needs to be adjustable.

    I could do 3mm CR4 instead but it saves 5 quid on the entire order so figured I'd go for 4mm.

  • orange = main beam
    green = upright
    red = anchor points to upright

    The upright is anchored across the full width of the plate so that the stifness comes from the cross-section of the extrusion rather than relying on the cross-section of the plate. See how the upright goes across all of the metal plate?

    The same thing is happening with the main beam so the extrusions end up mating face to face. (with the plate acting kinda like a big washer)

  • MVI_4266

    This is what the wheels do. They were adjusted way too tight in this wee video. Have been loosened off now and run well, but i don't have video of that. :) They turn the extrusion into a big linear rail.

    Click the photo for video

  • Aha! Your previous comments make a lot more sense now. Should have room for that, I’ll give it a go this weekend.

  • Oh meant to say previous not precious. 👆

    I think this is better in some ways but worse in others, particularly in terms of clearance around the NDS bottom bracket. Maybe not the best avenue to go down?

    https://a360.co/3pLea8I


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  • Small orders are priced WAAY higher to account for set up and office time.

    This line of thinking had me painting 50 bookends a while ago. And deburring a lot of clamps because I forgot to tick the box. With the company I use here 1 piece tends to be about as expensive as 5 and then 25 is about double the price of 1.


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  • sweet clamps. group buy? were they all snapped up?

  • Yep, all gone. Was a bit hush hush as I felt bad about stealing Cobra's design. Initially planned on doing just 3 as a thank your for a friend. Happy to send you the files, these were 12mm alu.

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The DIY frame jig thread

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