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Today, fork leg bottoms got cleaned up and packaged up to go to Maxton’s. That took a couple of hours
I then thought I would try and reverse the jaws in the three- jaw chuck on the lathe to take the 3.25” bar. Took me a while to realise the scroll gear inside the chuck is a spiral and the jaws will only engage with the gear teeth one way, then it took me a little while longer to realise that the jaws only close up completely if the jaws are replaced in their intended slots. Every day is a school day! The jaws and the chuck itself now have register punch marks.
My options for machining the bar are therefore the 4-jaw chuck or the plate with 4 sliding teeth. I spent a good hour and a half not managing to centralise the work piece in the 4-jaw chuck. Whichever way I adjusted the jaws, I always ended up with a runout of about 3mm on the end of the bar (about 150mm long). The run out was always in different places as I used a felt pen to highlight the high point and slackened off the jaw(s) opposite, when I tightened up again (from the high spot side) the high point had moved somewhere else.
I will have to buy some form of clamp to hold a dial gauge when I eventually get the bar square enough to finely adjust it but I would be pleased with a 1mm run out but I am nowhere near that yet. This does not bode well for turning the work piece round and machining a bearing cup from the other side.
I gave this up as a bad job and spent an hour or so vacuuming the garage.
P.S. while writing this I thought I will give it one more go and I have just been down to the garage and I managed to set the workpiece in the jaws with about 0.25mm run out. The trick I used was to wind the tail stock centre hard against the workpiece forcing it flush with the face of the chuck before tightening the jaws, measuring the projection of the jaws from the drum of the chuck with a Vernier caliper
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