Blog

90 Deg Shift

bicycle, workshop0 comments

A while ago I was fortunate enough to be gifted ‘The plate jig’ from John at cycle Underground. He had used it to build all of his frames  and before that it belonged to and was fabricated by Frank Phillips, it has some serious history behind it and has built a hell of a lot off beautiful frames. Originally I fabricated a flat bench on wheels that the plate sat on horizontally. I have used it this way for some time now but it was never very practical or easy to use in this position so I decided to build a new stand for it. Due to space restraints where the jig is housed I also wanted to have it mounted to the wall the other requirement was that it be able to rotate 360 deg. To this end I had taken a very large bearing from a  screw jack system that was fabricated for a job but never used, we threw out the screw jacks (a real shame as they where beautifully made with machined brass screws but they were far to big and heavy to be practical) but I could not bring my self to throw out the bearings, even though I had no idea what I was going to do with a 95mm race and 10mm dia ball bearings.

I was toying around with how to mount the jig plate to the frame I was going to build, John originally had it mounted on a floor stand and the plate rotated via a bolt thru the back of the frame into a taped hole on the centre of the jig, this worked fine but was always a bit cumbersome to use as the friction of steel on steel and the placement of the bolt made it awkward to undo it while holding a lit torch in one hand and rotate and lock off with the other. I pulled that big bearing out of the draw that had been collecting dust and scratched my head about how to weld the races to a piece of  plate steel.

The issues I faced where the weight of the plate it is VERY heavy it would be in excess of 120 kg so I certainly didn’t want it to let go any where, then there was how to attach the stainless steel bearing races to the plate steel I was using for the backing plates, and lastly how I was going to mount the unit to the wall.

The first thing I need to do was see if I could fix the bearings to the plate, as if this proved to not be able to be done then I would have to redesign and come up with a different approach to the problem. I talked to a few of the guys I work with nutting out whether to tig the races on but I was worried that the intense heat would warp the races and this was what every one else thought as well. The air conditioning guy who also happens to be a master welder told me to use a 15% silver rods and braze the rings on to the plate. 15% silver is not common or cheap but I use it when I build fillet brazed frames with very light weight tube sets. So it was out with some sticks of silver and much flux. At first I tried to heat the plate steel from underneath to get it hot enough to take the silver thru the stain less on top (stainless gets a hot a lot quicker than steel and carries the heat a lot further so less heat is required) but even with my biggest torch I could not get enough heat into the piece, so after soaking the flux off and cleaning and prepping the pieces I had a go from the top this time went much better cleanly washed in and with no distortion to the race, repeated the process on the other plate and race .

Then I had to find the centre of the bearing so that when the unit is mounted it runs true. To do this I measured the ID of the race drew up a round template on auto cad with a centre mark, printed it and cut it out placed it in the ring, I now had my centre mark. I drilled to size then to make sure the other race matched it I  put the bearing together and ran the drill thru to mark the second race centre. I then trimmed the excess steel from the plate that was going to mount on to the back of the jig to a round shape, roughed the shape out on the band saw then fitted the unit in the lathe and machined it to size.

From here it was a matter of taking some measurements to work out how high from the floor the unit needed to sit, that done and I was docking steel to size, drilling a lot of mounting holes and then welding the pieces together. I had planed to tig the unit but I had a big heavy fabrication job coming up and I was planing to using a new to me stick welder so I thought this would be a good test for the unit. It turned out not to be the best decision as the welder was not running properly, it laid down more than enough metal for the strength of the weld but was not very clean and thew a lot of spatter around the sides of the weld.  I switched to the old faithful oxy torch ( or the gentlemans welder as I call it ) laid up the rest of the frame with nickel bronze (strong stuff).

With every thing welded and cleaned gave it a coat of kill rust, then a lick of black  paint, fitted it together and marked out where I was going to fit it on the wall. 6 holes later and with the help of two big mates we lifted it up while another mate fitted the bolts. (bloody thing sure aint light, there was much cursing from my mates and promises of the rounds of beer I was going to buy to make up for making them sweat like this) .

It is all in place now and im just mittering up some tubes and ill test it out over the next few days.

Leave a Reply