Bicycle Frame Building Jig types for lugs, tacking & welding

TYPES OF FRAME BUILDING JIGS

There are only a handful of approaches to design a bicycle frame jig. During the development of the original Henry James Bicycle Frame Building Jig, I designed 10 jigs, and built 3 different ones. Having begun with a list like this one, most of my jigs were Compact Plate Jigs, as this style offers the best combination of features and benefits. Why this is so will become clear as you read the descriptions.
Here is a brief summary:

NO JIG:
This goes back a hundred years. The builder must be highly skilled, as accuracy depends on cratsmanship, not tooling. Because no fixture is used, lugged joints often are all pinned together by driving nails tightly into drilled holes in every joint. This holds the frame together, and hopefully keeps it aligned during brazing.

BASIC FLAT PLATE:
The frame is assembled on a flat plate which is larger than the frame, and made of steel or aluminum, or for hobbyists, particle board or plywood. Shims, vee blocks, or other holders locate the tubes on the center line of the frame. Setup takes forever, and access is limited. Usually used for tacking only. A good choice for building your first frame.

MODIFIED FLAT PLATE:
Still intended just for tacking, The plate is shaped specifically for a range of common frame configurations in an attempt to provide better access. Usually mounted vertically. Specially designed holders for head tube, rear axle, etc., try to provide more access, with limited success.

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.

COMPACT PLATE JIG:
The Henry James Universal Jig and ACCESS 100 Jig are of this type. Why? Because brazed lug construction requires good access all around the joints for full in-the-jig brazing. A compact plate jig, if carefully designed, offers the best combination of clearance, rigidity, fast accurate set-up and versatility. (As a result, the Henry James Jigs are the best all-around tacking jigs available for welded construction.) 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. A rare variation of this style uses no plate at all, just a bunch of arms that support critical parts of the frame.

The new Henry James ACCESS 100 Jig has a relatively small plate to maximize access, especially for welded and fillet brazed construction. Our "Universal" Jig has a slightly larger Plate that allows the use of versatile tube supports mounted on the Plate to locate and support the top, down and seat tubes. This makes it easy to remove and replace the frame during the assembly process, especially when using lugged construction.

Because the bike frame is bigger than the jig plate, these jigs can offer the best access to the joints. It is desirable for brazed lugged construction to build the complete frame in the Jig. Full joint access is essential. The Henry James Jigs offer clear access. This makes our Jigs the best tacking jig for welding bicycle frames.

Because of the compact design, these jigs can be much lighter than other jigs, making it much easier to rotate the jig as you work, and the jig takes up much less space in the shop. The ACCESS Jigs are perfectly balanced about their mounting arm, so it is easy to tip and tilt the frame and Jig, especially if you like to fully weld frames in the jig.

BOTTOM UP 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.

EXTERNAL JIG:
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.] 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.

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