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