rediRrakaD, whether or not we have realized it yet, I think we are all heading there.
I took a trip over to the scrap yard to look around for some stock I'll need while working on the monolever arm.
Here's what I found from the left; two 3/4" hardened bolts for the shaft, one of which I hoped would work, a section of 2"x1/16" tube for a cross brace, a rusty piece of 1" square tube for a fixture brace, and a section of 3"x2"x3/16" rectangular tube to make up the main part of the fixture.
My idea was to have a T-shaped fixture made of heavy gauge rectangular tube that would clamp the front of the swingarm at the swingarm pivot bearings, and then to have an indexable end plate that duplicates the final drive mounting pattern to hold the rear of the arm. The indexing of the end plate would allow it to hold swingarms of differing lengths.
I made up these swingarm fixture drawings to work with:
bearing plug drawing
angle plate drawing
main arm drawing
The main arm acts as a stable base for the other parts and allows indexing of the angle plate at 25mm increments. Arms of 0, 50, 75, 100, and 125mm. I don't think 25mm worth the effort, and the two index holes at 50mm were actually an error in my drawing that I didn't catch until after I got the machining done.
The angle plate duplicates the mounting pattern of the final drive and holds the rear of the swingarm in position. The lower section of the plate has two 10mm chromed pins pressed in that allow precision positioning of the plate on the main arm. The pins provide the alignment, and two 13mm bolts provide the attachment force.
The bearing plugs fit into the bores of the swingarm pivot bearings and clamp the front of the swingarm in position. Two bolts with 15mm of the diameter turned down fit into the center hole of the plugs. These bolts then thread into nuts welded on the front risers of the fixture.
I found these concrete anchor bolts are a handy way to pull the swingarm bearing out of the race.
I decided to make the angle plate out of aluminum because aluminum is easy to work with, but I think now it would be better made of steel since it seems as it will wear fast. I bored out the big hole in the angle plate and drilled the holes with this setup.
Here's a detail of the main arm and angle plate. This gives a good view of the angle plate's alignment pins. The bolts fix the plate to the arm and are 1/2-20 UNF grade 8. The hole in the far end of the arm is to accept a bolt that will act as a jack screw
to keeps the swingarm from rotating on the front bearing plugs. I found I needed to reposition this hole outward as seen in other photos.
Anyway, after a while I had this collection of fixture parts assembled and ready for welding.
To get the arms aligned for welding I clamped them down to this piece of 3/8" aluminum plate.
I welded nuts onto the fixture at the bearing plugs and the jack screw. After welding I needed to chase the threads. This photo also shows the jack screw bolt and how I put a rounded profile on the top to get a constant contact area between the bolt and the swingarm when the bolt is turned.
And the finished fixture, its relly a heavy beast.
Here's another view with the arm installed. The idea for use is to set the angle plate at the 0 index, bolt an unmodified arm to the angle plate, then close up the bearing plugs, jack screw and top clamp such that the arm is held in place without any bending force, then cut the arm with a hacksaw and move the index plate to a new position.
After having the actual fixture and with some fitting of the arm to it I think the bearing plug method of holding the arm will be difficult to control accurately. I think it will be enough with some careful setup, but I think something with fixed alignment stops welded to the fixture may work better.