Bicycle frame jigs (2/4)


The election of a frame fixture is not just a matter of budget. It is obvious that if you are going to produce few amateur frames a flat surface or a beam design jig will suit you. If you circulate large amounts of kind of the same type you should ponder over switching to something that ease the assembly and welding at the expense of less versatility.

Potential frame builders have the mistaken idea that the jig must be extremely accurate, built like a precision timepiece and yet possess immense strength for bending and holding the tubing sections in position for welding but in fact the base structure of the jig, sometimes called the backbone, bed, table, base table, face table or frame face can be almost any relative rigid structure. As long as the backbone is level in all directions the real precision and accuracy will come about through the fabrication of the fixtures that attach to this substructure (backbone) and then will be adjusted and secured to position and hold the tubing and parts in place during the fabrication of the frame.

A modified flat plate is enough for welding a bicycle frame

A modified flat plate is enough for welding a bicycle frame

For around 300$ you can start to think about it. In old Europe, for less than 400€ I’m struggling to find the right materials to accomplish my project. I guess this continent is not that cool anymore, isn´t it?

Don´t forget that choosing a frame jig is closely related to the welding technique. For example, brazed lugged construction requires the most from a jig. Full access to each joint is critical. When using lugs, most builders prefer to braze the complete frame in the jig unlike lugsless construction where jigs are used only to tack at 2 to 4 spots on each joint.

Silver brazing a lugged frame

Silver brazing a lugged frame

Consider most jigs offer limited access to one side of the frame. On top of that, if you are gas welding just forget about tackling the job on a cheap parallel beam jig for example. The heat coming from the torch will deform beam materials affecting our setup.

Nowadays TIG welding has become the superstar for joining the tubes of a frame. Both bicycle factories and custom workshops uses it on a daily basis. SMAW, GMAW, FCAW SAW are others common types of arc welding procedures but useless because of the thin-walled bicycles tubes.

Automated robot welder at Merida - Taiwan tacking a full suspension frame.

Automated TIG robot welder at Merida – Taiwan tacking a full suspension aluminium frame. Hand-welded frames are still far superior.

Besides TIG (that uses electricity), gas welding (oxyacetylene for example) is also possible, been the standard for 70 years. As good as it is, gas welding cannot compete with TIG. Anyway, oxy-fuel is still required for brazing, either fillet brazing (bronze weld) or brazing lugs (silver weld). These realiable and old-fashioned methods are still popular between cycle enthusiasts, that’s why you have to keep them in mind for your future jig plans.

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Checking the chain stays

So far: budget, quantity and welding procedures have been taken into account. The quality of a frame depends more on your miters, the time you spend fine tuning the geometry and your welds rather on an expensive jig, that can offer good accuracy of course. Amazing frames can be produced with simple tooling and great skills.

But there are also few considerations about the bicycles you are going to build and how you want to work in order to select the right jig:

  • What are the limitations in the seat tube area? Does the top of the seat tube have to be square cut? If it does, you can’t pre-shape the seat tube top, or use a seat lug with an internal ledge for a cut to length seat tube.

  • Does the seat tube holder arrangement pivot about the center of the BB shell? If so, you can’t build with the seat tube offset from the axis of the shell.

  • Can you easily build interrupted seat tube designs? These are common and unavoidable with rear suspension frames.

  • Are you in the mood of ISP? If you are, size the jig up accordingly or fabricate an extension.

  • How versatile is the rear axle arrangement? Most jigs come with one axle for only one spacing. You have to pay extra for any other spacings. 130mm road frames and 135mm mountain frames eclipse other preferences. How do they do 120 mm track spacing, or 126 mm old road spacing (for restoration, repairs, or using classic parts), or 145 mm if the jig also builds tandems, or the new MTB standard142xM12, or 165-170mm for fat bikes?

  • How do they handle the inevitable pull-in of the rear dropouts?

  • Do you want to build the frame from the BB up?

  • How do you build forks? A fork building feature could be integrated in a design. The rear dropout holder doubles as the front dropout holder in the Henry James Universal frame jig for example. A separate professional fork jig usually costs about $500. You don’t usually build forks? That is all the more reason to have one built in for when you do need one!

  • Can you build the occasional tandem on the jig? An attachment of some sort must be used, and you should not expect the adapted jig to be good for a tandem specialist.

  • How do you mount it? Because of the jig weight and bulk, most jigs require an expensive and complex mounting system that can increase your costs.

  • How portable is it? How much storage space does it need? TIG welding is not a straightforward skill. You might want to set up a frame in the jig, then single-handedly put it in your vehicle and take it to a full-time professional welding shop (an easy way to get perfect welds) for tacking while you wait. Even on a moveable stand, most jigs take up a lot of space.

2 responses to “Bicycle frame jigs (2/4)

  1. Lo conozco, fíjate que era el siguiente artículo 3/3: frame jigs existentes en el mercado . No es muy preciso ni muy resistente. Creo que con soldadura fuerte lo haces papilla en unos cuantos montajes. Y te lo paran aduanas.

    En realidad como explico para fabricar cuadros sólo necesitas una mesa perfectamente plana y utensilios accesorios de verificación.

    Mejor éste, el clásico beam design con perfilería de aluminio extruído 8020. Todo un hit entre montadores caseros:

    http://www.instructables.com/id/A-simple-bicycle-frame-jig/

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