Bicycle Framebuilding: Jig Design

Update (08/06/2109): Engineering Drawings!

Wow – someone has actually read this post and requested drawings! This seems only fair since not everyone can be expected to create an Onshape account to play with the model. I’ve created a drawing package. But…be warned – these drawings were originally only for my reference while making the jig! So, they likely contain lots of mistakes and some ambiguous/unclear/contradictory/inconsistent annotations and/or dimensions. For example, I’ve left out hidden lines on some parts if they’re too busy or confusing.

If you email me with feedback, I’ll do my best to fix them. The first file below is a 21-page pdf of size “B” drawings (easiest to print on 11″x17″). The two files after it are dxf files containing engravings (and reference geometry) for adjusting seat tube and head tube angles that need to be machined on a CNC mill.

To learn more about the design and its origins, continue reading below.


Every year in the spring, I teach a one-credit co-curricular in which 6 or 7 engineering students learn to build bicycle frames. We keep it pretty simple – we only work with steel, and students must either fillet braze or capillary braze (using lugged construction). No exotic materials. No TIG welding. Just good old fashioned oxy-acetylene brazing.

In years past, I’ve had the good fortune of being able to use a jig built by a predecessor of mine, but this year I wanted to build my own jig to tune up my machining skills again and to make some improvements to the previous design. I opted for a sort of “S”-shaped design with it’s closest commercially available cousin being the Arctos jig (pictured below). It seemed like a well-proven design, and I really like the way the bottom bracket pivot floats thanks to a clever dual-curved-slot design that puts the center point of the slot arcs at the center of the bottom bracket.

The commercially-available Arctos bicycle frame building jig. Image credit: Oscar Camarena

Thankfully, I did not have to start entirely from scratch in copying the Arctos design. There is a wonderfully detailed Instructable created by Instructable user “Tanner W” that I also referred to for basic dimensions and ideas about how to fabricate different parts of the jig.

The aspect of this project that I am most excited about is that it gave me an excuse to go deep on my new favorite CAD software, Onshape. If you’ve never heard of Onshape, imagine a marriage of Solidworks, Google Drive, and Github that runs entirely in your browser (that’s right, I said IN YOUR BROWSER). (As a Mac user, can I just say what an absolute pleasure it is not to have to boot into Windows or run a VM to work in CAD?) Ok, permit me a momentary diversion to highlight just some of the myriad reasons Onshape is a delight to use.

  • Sharing – You can share your models with any other Onshape user. This has been sooooo helpful for checking my students’ bicycle frame models before they started notching tubes. We can collaboratively edit their model from any machine and it just updates and works. It’s the little things, people.
  • Mating – Onshape’s mating system for assemblies is dramatically more intuitive to use once you get the basic concept (attaching coordinate frames to parts and specifying relations between those frames). I suppose it helps that I teach dynamics, though, so coordinate frames are very familiar to me.
  • Multi-part design – In a single “Part Studio,” you can design multiple parts very easily. This makes the creation of assemblies very easy.
  • Updates – New features are released continuously. No downloading new releases. No hotfixes. No agonizingly slow local installs.
  • FeatureScript – This is THE game-changer for Onshape. Using a very JavaScript-like language, users can create new features that are native (NATIVE, PEOPLE!). They even get UI icons that show up in the toolbar. Because they are native, they automatically update when you change geometry and rebuild the model. It’s unbelievable. In the design of my frame jig, I used a couple FeatureScripts – one to create 8020 extrusions and another to make standard cap screws.

Okay, enough blathering on about Onshape. If you’re interested in using my jig design or just checking it out, it is publicly shared on Onshape. You can view it without logging in, and it is copyable and exportable for all Onshape users. The Onshape document includes models for all custom and COTS parts, an assembly, and engineering drawings with dimensions. Aspects of the assembly could probably be improved. Despite years of CAD experience, I’m still pretty new to Onshape’s system, so I suspect there are better ways of doing some things. Also, the drawings are still fairly rough (no tolerances, for example), but should give you a starting point for fabrication.

My Arctos-inspired bicycle frame building jig.

If you’re interested in building my design, drop me a note to let me know what doesn’t make sense or could be improved in some way.

Stay tuned for Part 2 of this post with more photos of the finished jig, its constituent parts, and short descriptions of how I manufactured each of the custom parts.

13 Responses

    1. I’d be happy to share drawings with you. I’m on vacation at the moment, but when I get home I can add a link to the drawing package to this post.

    2. Hi Mark,

      I’ve updated the post to include a drawing package and a couple of DXF files necessary to precisely machine the angle markings for the head and seat tube adjustments. Please let me know what you think.

  1. Dear Aaron,

    many thanks for sharing such niche plans online. I really appreciate this!
    May I ask you some questions about the jig?

    I’m on the way to plan mine at the moment – similar to your design.
    I’ve never worked on bike frame jig nor I have access to one at the moment.

    1) Have you ever build a frame with your jig yet? Are you satisfied with it?

    2) Could you please share with me your unmounting procedure? So how can you get the frame out of the jig?

    Many thanks for your answers.

    Best regards from Switzerland
    Matt

    1. Matt,

      Thanks for the inquiry.
      1) Yes, I and about a half-dozen college engineering students have built frames using this jig (and a full complement of machine/metrology tools).
      2) The cones that retain the seat and head tubes are adjustable (that’s what the orange handles in the model are for), so they can be loosened and moved up and down the 80/20 rail. There is also a collar on the “bottom bracket axle” that can be loosened to allow the BB plug to be slid out of the BB shell. Once the cones and BB plug are out of the way, loosening the rear dummy axle will let you rotate the frame about the bottom bracket. You can then slide it off the bottom bracket axle perpendicular to the plane of the jig.

      BTW, I don’t recommend fully brazing a frame on the jig. You will want to tack it on the jig, then do various checks for planarity of the front triangle, symmetry of the rear triangles, etc. “Cold-setting” (bending) the brazed frame into alignment will be easier than trying the same with a fully brazed frame. I just do full brazing on a Park stand.

      If you haven’t already, I highly recommend checking out Tim Paterek’s framebuilding manual (and DVDs if you can afford ’em). It’s very accessible and lays out nicely a solid process to go from tube stock to a fully brazed (fillet or capillary) frame whether you’ve got a jig or not.

      Good luck!

  2. Dear Aaron,

    many thanks for your answer and tips. Hopefully, I can find somewhere Tim’s P. DVD’s.

    In the meantime may I ask you another question? I can’t figure out what the blue small part on the dummy axle support is actually – the one with just two screws attached to the 40×80 extrusion. Is it just to close the 40×80 extrusion? Or has it any other technical purpose that I’m not aware of?

    Many thanks.

    Best regards
    Matt

    1. You are correct – it’s just there to cover the end of the 40×80 extrusion. Purely aesthetic – you can leave it out if you like.

  3. Hello and good day – this is outstanding and just awesome.

    Can we dl the plans and work on the frame-builder-jig!? This is just awesome

    many many thanks for all you did!

    steel-biker

    1. Thank you for the compliment! You are most welcome to download the plans and build a version for yourself. The links to download the files are in the post after the second paragraph of text.

  4. hi there – many many thanks for the great summary on this super-interesting topic.

    you offer the plans to work on this. One question – can we work out the mechanical parts – the critical ones like the two files . – ( the dxf files containing engravings (and reference geometry) for adjusting seat tube and head tube angles that need to be machined on a CNC mill.)

    these tow parts:

    – Head Tube Angle TicksDownload
    – Seat Tube Angle TicksDownload

    can we work on this two parts – with a 3d printer – or are these parts “mission-critical” so that we need to have them

    love to hear from you

    martin
    ps – keep up the great work – it rocks!!!

    1. Hi, Martin. I would say not it’s not a great idea to 3D print those parts. Handling performance is pretty sensitive to head tube angle. The seat tube is less sensitive, but that plate has a slot that a steel dowel pin rides in. That geometry is pretty important because it’s set up to have the seat tube rotate about the center of the bottom bracket shell by having the curved slots in the seat tube adjustment block part and the seat tube support plate part share the the same center (the bottom bracket shell center). I’d also be worried about it wearing out quickly from friction of the sliding dowel pin, which would exacerbate any accuracy issues.

      Thanks for the compliment on the jig. I’m glad it’s helpful to you.

      Cheers,
      Aaron

    1. Hello Matan,

      I’m afraid I can’t sell any of the jigs I’ve made. I use the facilities and other resources at the college where I teach to make them, and I feel like it would be unethical for me to profit personally from selling one. With the documentation package I’ve provided you could probably hire a competent machinist to make one for you, though. I’d be happy to provide clarifications if that’s the route you choose to go.

      Thanks,
      Aaron

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