Alright guys, I think this thread is a little over-do. I do not claim to be the fore-front authority on any of this. By all means, if anyone has anything to add, please do it.
What is a "Jig" or "Fixture"?
Jigs, also known as fixtures, or positioners, are devices made to assist and ease the fabrication of pretty much anything. They don't even have to be for fabrication. You could have a fixture made to ensure the straight and trueness of a frame or other part, where the sole purpose of it is to make sure the part fits the fixture. That way you know everything is exactly how it is suppose to be, and not bent or twisted any way.
Jigs can be home made, or bought from 3rd parties. Do a quick search on ebay for "frame jig" and you'll find a few auctions for Chopper frame fixtures. In most cases, the fixtures are made in house however.
Fixtures are typically made out of material considerably heavier and tougher then whatever the fixture is for. This is to ensure that there is no chance for any twisting or distoration that might effect the exactness of the fixture. Fixtures may, or may not have adjustments depending on what the designer had in mind when they made them. Fixtures for small parts like suspension links would probably not be adjustable. Something like a swingarm jig likely would be, because of the interest in varying lengths. That way you dont have to have a whole new fixture for a +2, +4, +6, etc. You'd just have the fixture made in such a way that the carrier portion of the fixture would be moved back to the +2, +4, +6, etc places.
Making a "Fixed" Jig.
I've come across the need for a fixed position jig for the suspension components of the 85-86 250R frames, for my 500R conversions. The reason being, is when I do the swaps, its necessary to cut out the bottom tube that the shock linkage bolts to. And in order to exactly duplicate that positioning when the new U shaped tubing is welded in, I needed a fixture. Now, let me clarify slightly. You dont *have* to have a fixture, but it sure makes it easier. The first time I did thise I just C-clamped the shock linkage in place to the swingarm. Which worked OK, but the C-clamps were in the way, and if you undid them one time, the whole thing was out then and would never be the same. The whole point of a jig is for consistency, and as a time saver. So, here is what I made.
What each piece does, is fit INBETWEEN the mounts on the frame. So its emulating whatever would normally fit into the frame. The top of the shock, the linkage wish bone, the chain roller, and well an actual piece of swingarm. This way, when you bolt the thing into place, all you've got to do is bolt your brackets to the outside of these pieces and weld them onto the frame. Then everything is exactly where it needs to be. On my particular application the 2 bottom pieces are what I'll be the most concerned with. It was important however, that I didn't just weld the 2 pieces I was worried about to the bottom of that piece of swingarm, without having a piece ran to the top shock mount. If I wouldn't have have had that 3rd reference point, the fixture could have "spun" any direction, and all the bottom positioning would have been out. By adding on the bar to the top shock mount, everything is absolutely solid and there is no movement. When its bolted in from the swingarm bolt and the top shock bolt, it aint going anywheres.
So here is what my ugly (but very functional) fixed position jig looks like in the 250R frame:
I'll be the first guy to admit, I tend to OVERTHINK EVERYTHING! But this was really simple to make. I turned the spacer to fit the top shock mount first. Welded on a piece of tube. Welded it to the piece of swingarm (Remember, the exact length of the tube, and where it fell at on the swingarm was more or less totally irrelevant because the space between pivot area, and the top shock mount would still be the same) And then I did the same process on the bottom. Turned bushings for the 2 area. The linkage brackets, and the chain roller. Then I attached those to the piece of swingarm in the pivot area however I could. The tubes arent centered or anything, again, it is irelevant because the spacing between the points is the same. It doesnt matter if its a bent in a U shape between the two, the ends are still in the same place.
So thats all I really have to add for the time being. I know tht fixtures and jigs in general are sort of "trade secret" type stuff, but I encourage anyone that has one to post it up and explain what its for, and how it works. Doesn't even have to be trike related. Happy fabbing!
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