Sunday, 15 July 2018

The new TR1 engine - a cylinder machining fixture for the lathe (part 24)

Now even if you haven't read of any updates on the engine build, this doesn't mean there hasn't been a lot going on. Unfortunately a lot of head scratching, using rude language and production of scrap-metal was involved.

My initial idea was to machine the cylinders on my lathe by clamping the cylinder between two T-shaped hats and support it on the tail-stock.


In order for this to work at all, two more pieces of the puzzle were missing: an outside boring bar and a new toolpost. But first it was necessary to find out, if all of the surface was reachable within the saddle's traverse.


With that established, the next step was to cut the bar to shape and also clearance it on the bandsaw prior to milling it to shape.


Subsequently a toolpost was required that was as close to the centre-bolt as possible, retaining as much of the travel of the saddle.





As you can see in this last picture, it did work and the surface finish wasn't too bad, but unfortunately the whole lot was lacking rigidity. So the next stop will be to fit a bearing and axle to the rear plate in order to make the whole lot run a lot stiffer.


... and that's what I did. Earlier today, I went back and changed the backplate to accomodate a 6001 bearing (it's what I had from a gearbox rebuild) and a rather stiff axle clamp in the tailpost's drillchuck.


Little mishap on the lathe as I was shooting for 27.95mm, but ended up with 28.00, which meant the bearing was more of a sliding fit.


Eight punchmarks later and the bearing is set nicely. 


An old toolbit held in the drill chuck will serve as an axle.



So what's the verdict: This mod improved rigidity no end and if smart me hadn't made the chuck-sided disk without a taper but a flat surface the cylinder could be pressed against, the final runout would have been superior to the 0.10mm runout I ended up with as soon as I applied some force causing the whole workpiece to start wobbling.

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