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CN Jigs Mods

Old 01-12-22, 11:38 AM
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Andrew R Stewart 
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CN Jigs Mods

I've decided to modify the tube holding design on these jigs and this thread will show my plans and progress. For reference see the initial thread on the ID of these jigs (which is still unknown). Cyclery North Frame Jigs ID help - Bike Forums

I never liked how these jigs held the tubes on such short pads and relied on the tube sides for planar alignment. The short support pads and "wall" more easily allowed some tube misalignment, in both planar and in angular aspects. Relying on the tube sides also limited these jigs to one set of tube diameters. Back in the day the tube diameters were far more standard but to make these jigs current they need to handle differing diameters.

So here's my design sketched out.

The tube support is an Al channel set to contact the tube on the top or bottom. Any diameter will retain the center plane. There will be a length of All Thread with a "finger" slid over the All Thread and able to be swung around onto the tube then snugged against it with a wing nut pushing the finger down. Not shown in the diagram are the riser pads that will be placed under the head tube holder blocks to reestablish their being on plane with the tubes' new height off the base plate.


Here's the new materials marked out and ready for the sawing before milling to spec. Two interesting points- First is that the Al plate is the last of the Mic6 plates I bought in 1980ish when I first began trying to make a jig. Back then I think the whole amount of plate cost me about $250. Today the cost would be well over $1000! Second is that after hand sawing the plate many times in the past for other projects and getting older and weaker I will be band sawing these cuts. I came so close to getting permission for another big power tool (a band saw) but decided to seek a friend's help. Tim has both horizontal and vertical band saws and I will use them tomorrow. The two chunks of steel are for another project, A forming die for head tube badges. More on this much later. Andy
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Old 01-15-22, 09:11 PM
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Progress today. Finished the front end jig mods.

Metal has been cut and finished to dimension. Initial fit ups of front end jig tube clamps.

Setting the tube channels parallel to the base.

The finished mods. I had to slightly readjust the tube holders to get both the same stand off as the HT and that the DT and TT will run very close to parallel.

I've started to look at the rear end jig and find some challenges that I hadn't seen before. The possibilities are brewing in the goal to allow this jig to also accept different tube diameters. Andy
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Old 01-21-22, 05:40 PM
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The rear jig is done, finally. A bit more involved than the front one. More tube support points and planes of function at play and more surfaces to clean up.

I decided to reduce the added stand off to 5/8", somewhat driven by the rear triangle/axle support design. New drop out "studs" to expand the spread to 137mm. The one detail that took some thinking about was the DT support.

The top and seat tube support clamps can slide and pivot on the jig's base plate, as was the case with the front end jig. Thus the only critical dimension is the tubes' stand off from the plate. But the DT support is fixed in place and with the want of varying tube diameters that the tube being held on its inner side meant that I couldn't align the tube support WRT the BB and have this alignment be consistent across the varying diameters. I finally came up with the idea of a single point contact with the tube, allowing the tube to rock a bit against the support. At first I was going to turn an hour glass shaped stud. In the end I decided to just use a flat support "V" with a fairly thin section, not knife like but close enough. Now the DT can remain centered at the shell, be held parallel to the jig base plate and have a clamp to contain the DT. The rest of the frame will rock this or that way to allow the DT and support to touch. The rest of the jig can be adjusted to suits the other contact points. Remember these jigs have no scales or angles, all tube to tube dimensions/angles are by mitering, a venier protractor and careful set up.

All in all I think the results are pretty nice. Soon I'll start up a frame with these jigs before offering them for sale, likely months from now. Andy



Note the cut away of the "V" to reduce the contact surface to a more point like amount.



These two supports are nearly the same as with the front end jig's


The BB support shaft can slide side to side. It's held in place with a set screw on the bottom of its mount.


The two drop out stand offs are of unequal lengths due to the jig's design. I stamped which side is which and the overall axle width. You can see the bright silver 5/8" spacer I placed in the sliding clamp to bring the rear end in line as before. The other tube supports are located with this amount in mind.
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Old 01-23-22, 11:22 AM
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What a fun project. Each time I use the tools I got from my first shop it brings back great memories of the mechanic showing me the ropes and time spend listening to Paul Harvey's 'The Rest Of The Story' on the radio. We'd all stop our work, grab a snack and listen, then have a bit of a chuckle and then get back to work. Fun memories.

Good dAy
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