TB and Martin – thanks for the suggestion re: drilling the counter-sinks for the cap-head bolts. I think that in retrospect I should have done this (God knows I have enough chewed up drills to grind flat) and made the part from scratch.
Sadly patience isn't one of my few virtues. I spent the day going with my first idea…
I started with some stainless square stock that was about the right size, and used my rotary table to mill out a 12mm round shoulder. I would have used the lathe for this, but…
The shoulder was drilled and tapped to M8 (which I didn't get concentric, as you can see). The setup was a bit shonky, hence the poor finish. And the collets everywhere, and the swath…. it was one of those days…
![20200208_145012.jpg 20200208_145012.jpg](data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==)
Note to self, when I can't find the spotting drill tomorrow, it's hiding in the t-slot…
As for the original plate, the chewed up M8 hole was drilled out to M12, and the new part inserted…
![20200208_144953.jpg 20200208_144953.jpg](data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==)
The idea is that the thread engages where it did previously, but there are many more threads than before, and the plate underneath spreads the load, hopefully relieving pressure on the crack. I did manage to get a nice tight fit.
![20200208_144958.jpg 20200208_144958.jpg](data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==)
The piccy above was before I ran some M3 screws through the part to fix it to the clamping plate. I added loctite for good measure, since I hope never to see this part again. Here it is fitted…
![20200208_163456.jpg 20200208_163456.jpg](data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==)
It looks close to the lead screw, but there is plenty of clearance.
Here's the new "shoulder bolt" for locking…
![20200208_163534.jpg 20200208_163534.jpg](data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==)
Ok it's just a regular bolt with a bushing, but it works well. It goes from loose to totally locked in less than half a turn, and it's a lot sturdier than the original.
There's still a lot of reassembly to do, but I've called it a day and opened a beer. In retrospect…
* I learnt a lot about how the lathe works.
* It was a great opportunity to give the lathe a decent clean
* The new clamp works better than the original, and should last a bit longer, given it was twice the number of threads. I also prefer using a spanner to lock the carriage, as I have plenty of spanners, but usually have to go looking for the alan key to lock the carriage with the old bolt. And I get more leverage with a spanner…
* It would have been a lot quicker to just make the part from scratch
* This was an entire day of my life I will never get back…
@Martin Wood, my fingers are shredded, there is no part in that thing that has been de-burred. If you have time to take it to bits and clean it up, it will be time well spent. On a positive note, the internals of the apron looked pretty clean and well made (not that I'm an expert), and it all came apart and went together again without issue. So I'm not complaning
Edited By Jed Martens on 08/02/2020 20:22:43