Frame Jigs

Frame Jigs

My first frame jig was 3x8’ with a 2x4 frame. The 2x4s standing upright holding the bike frame had to be identical in size and where the centerline of the tubing would pass through. This required making a jig to cut and drill a pilot hole in each one. Then different size hole saws were used matching common bike tube diameters. It didn’t matter that you had a 1.125” meeting a 1.25” tube the centers would line up because the pilot bit for the hole saws hit the exact same spot on each piece. Next a hole was drilled about 3” down through, what would be the top of this homemade clamp, on each side of ‘tube hole’.Then the ‘tube hole’ was cut in half. Long wood screws would drop down through the top ‘cap’ and clamp a specific dia. tube in place. Small L-brackets held the base of each clamp to the table. See pic to get a better understanding.

Lesson learned:

Never completely weld a frame while it is locked in a jig. Tack weld the joints and pull frame out of the jig.

Check alignment, make adjustments, weld ONE joint only

Etc, etc….

I welded the first frame in the jig and although I could not see it at first I knew something wasn’t quite right. I found the problem when I gave it the water puddle alignment test. This test is by no means 100% accurate it’s just a quick and simple way to help detect an alignment problem. Check the axels first before you try this. See that they are sitting properly in the drop outs on both sides.

Ride slowly through a small water puddle weaving the front tire slightly. Go back and take a good look at the pattern each of the tires made. Now try it again riding as straight as you can. If you kept it straight you should see only one tire track and pattern coming out of the puddle as they center on each other. If the pattern looks slightly wider or you can see the pattern of one tire edge running consistently to the side of the other there’s probably a wheel alignment mismatch.

I did a lot of research on different frame jigs and I liked the metal version at the bottom of the page from the WISIL site. I thought it could be better and kept my eyes open for something that would be easy to fabricate.

I stumbled onto this electronics equipment rack that was being sent to the trash. The heavy duty 7’ long aluminum side rails are straight as an arrow having

threaded holes evenly spaced along both sides of the rail. I use one complete rail as a base and the second rail has been cut into lengths to form uprights. These upright pieces along with the rack’s original stabilizing cross members can be centered on the base rail or bolted to the sides of the rail to hold frame parts in alignment. I verify the alignment with metal straight edges, squares and a digital micrometer. (not to mention the infamous front to rear string test)

Pics to the right and below show how this is assembled. Dropouts are centered on threaded rod. Upright pieces placed to the side of the rail are directly bolted to it but pieces centered on the rail are held in place with short mending straps.