Monthly Archives: December 2013

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.


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.

Bicycle frame jigs (1/4)

There are a handful of approaches to design a bicycle frame fixture. Taking advantage of Henry James knowledge from his website and my own researches I have ended up with this article about the existing possibilities. A lot of information spread all over the bike forums that somehow I wanted to gather and analyze.

Holland custom frame in an Anvil fixture.

Holland custom frame in an Anvil fixture

Jigs can be classified according to different criterias: professional solutions vs. hobbyists fixtures, horizontal configurations vs. vertical mountings, tack-only vs. fully weld frame jigs, mass-oriented production jigs vs. custom frame geometry units, beam inspired types vs. beamless jig designs, multipurpose and extensible jigs vs. simplified versions, the place where you start to assemble the tubes on the jig and so on.

Professional fixtures will provide full access to each joint for TIG welded and fillet brazed construction without the hassle of tacking and removing the frame in order to fully weld it apart. At the same time is easy to remove and replace the frame during the assembly process, especially important when using lugged construction or when we want the gravity to assist the welds, which is a good thing.

Jigs having vertical structural plates and/or members are superior to horizontal or backbone based models. Their individual clamping components are shorter, located closer to the joints and connections, hence stiffer than the same type of fixture that has to extend all the up from the base plate.

Homemade tack-only jigs are affordable if you are planning to build just lugged bicycle frames. Roomier units that provide enough clearance to fully weld the frame vertically on the jig can be achieved with DIY beam designs at the expense of more complexity when determining, for example, the BB drop as it will be “floating out in space”.

Pure beam style jigs for mass production (the ones used in BMX companies for example) have limited range of adjustment but work well and offer a lot of access for peanuts. On the other hand, jigs that combine compact plates and adjustable arms via extensions that hold the “bearing areas” (BB, HT and rear axle) generate almost endless geometry combinations with good clearance.

Fixtures made of beams are very rigid and provide great accuracy if we go for extruded aluminium profiles and machined parts. On the downside, aluminium can be considered a bit expensive compared to wood or traditional metallic square profiles.

A multipurpose jig will meet more framebuilders needs, for example integrating a fork building feature in the rear axle frame fixture, or offering motorcycle jig capabilities.

Finally choose the jig that makes the tubing logic assembly fancier for you. Building from the BB up is a better alternative in my opinion.

Here is a brief summary of the frame jig types according to their design:

No jig. This goes back a hundred years. Accuracy depends on craftsmanship, not tooling. Because no fixture is used, lugged joints often are pinned together by driving nails tightly into drilled holes in every joint. This holds the frame together, and hopefully keeps it in place during brazing.

Welding bicycle frames in an American factory (not named). Wood engraving Leipzig 1900.

Welding bicycles frames in an American factory in 1900

Flat surface. The frame is assembled on a flat plate which is larger than the frame, and made of granite, cast iron (steel) or aluminum, or for beginners, particle board or plywood. Fixtures consists of shims, vee blocks, or other holders that locate the tubes on the center line of the frame. Setup takes forever, and access is limited. Used for tacking only. A good choice for building your first frame considering a flat surface is also needed to check the alignment.

A flat surface, machined fixtures and a full size drawing is enough for precise framebuilding

Modified flat plate or vertical plate jig. Still intended only for tacking, The plate is shaped specifically for a range of common frame configurations in an attempt to provide better access. It has specially designed holders for head tube, rear axle, etc. but still with limited capabilities. Because intersecting tubes (HT and BB) and rear axle are clamped it can be mounted vertically.

A massive flat plate design that has been tailored to extreme dimensions

A massive flat plate design that has been tailored to extreme dimensions

Parallel beams jig. Here the plate is replaced with beams that are parallel to the head tube and seat tube. These beams rest on one or two cross beams that are intended to keep the structure flat. This style of jig is very sensitive to warping of the beams. Most beam materials are not inherently dimensionally stable, so internal stresses and external stresses from torch heat, etc., can lead to a loss of accuracy.

To use this style of jig you move and rotate the beams to set the jig up. The problem is that the beams are parallel to the tubes, limiting access just like the plate jigs. The net result is still a tacking jig without the simplicity of the plate jigs, or the access of the compact plate jigs.

The resulting jig is lighter and more portable than a flat plate design

The resulting jig is lighter and more portable than any flat plate design

Compact plate jig. On a compact plate jig, the plate is much smaller than the main triangle. Adjustable arms extend out to support the head tube, BB shell, and rear axle. Carefully designed, offers the best combination of clearance, rigidity, fast accurate set-up and versatility.

Because of the compact design, these jigs can be much lighter than other jigs, making it much easier to rotate the jig as you weld, and the jig takes up much less space in the shop.

Sputnik and Henry James professional frame fixture are ample proof of this design.

A rare variation of this style uses no plate at all, just a bunch of arms that support critical parts of the frame. Both Anvil and Bringheli jigs implement this design.

Sputnik stands out as one of the best choices

Sputnik stands out as one of the best choices

Bottom up or backbone jig. A narrow (4″-6″ wide) four foot long bar or beam is the base of this style of jig. The frame sits upright on this base. Along the base are supports for the BB shell, rear axle, and head tube. Additional supports may be added to hold the seat, top and down tubes.

Only the axle and BB shell which are close to the base are accurately held. All the other supports extend a relatively long distance from a very narrow base, so errors and tolerances are magnified. Set up is usually slow.

An almost jigless version of a frame fixture can be achieved thru this design. The method is proposed here following famous Paterek instructions.

The main disadvantage on this is that you never see the complete picture of the frame until you tack in the last tube. You can't set it up and then have a sanity check where you can see if it all makes sense

The main disadvantage on this is that you never see the complete picture of the frame until you tack in the last tube. You can’t set it up and then have a sanity check where you can see if it all makes sense

External jig or motorcycle jigs. A rectangular framework structure is sized so that the bike frame fits completely inside the structure. For this reason, these are sometimes referred to as “picture frame” jigs.

A foundation of a wide rail, multiple rails or table are built upwards with the jig fixtures supported from below. Arms extend inwards to support the head tube, BB shell, axle, and seat tube. Because the framework must be the largest of any style of jig, and because the framework members must be heavier to provide the stiffness this large size structure requires, these jigs are heavy and expensive. The inherent problem with this style is that the largest frame you can build is limited by the size of the framework. And, if you make the framework really large, the extensions that hold the bike frames must reach in much farther to build very small frames.

It is stable by itself without the need of mounting platforms.

A variation is a hybrid jig with a smaller framework offset to the rear with extension arms for the axle and/or head tube.

Supacustom bicycle and motorcycle frame jig

Supacustom bicycle and motorcycle frame jig