My 1st milling/turning job...

[jdm]

...is a new cross-slide nut for the SIEG C0 lathe (copy of the Unimat 3). I suspect the original is made of brass, as even with good lubrication I have replaced two already due to all threading gone. For the third one I decided to take the matter into my own hands, bought a 16mm bar of SAE660 phosphor bronze, which supposedly is the most wear-resistant grade, and doubled the threaded lenght from 10 to 20mm. The part can be made with the lathe only, but since my "big mini" lathe has a milling column, I decided to give it a try.

 

16mm dia is perfectly sized for making the part, incidentally is also the biggest that can be fitted in an ER25 collet. I used a square block because I was thinking I would have rotated it in the vise, which of course wasn't necessary, neither it was to mill side faces at all, but I did it anyway for practice. In milling videos you hear all the time "just measure/move/divide with your DRO", well my machine doesn't have one anymore, as the crappy heads had rotten away also due to carelessness by the previous owner. However for a simple part like this just measuring and looking at the handle dials is enough.

 

I then moved to the 4 jaws for turning and threading the top post. Centering the work was quite a struggle, as I scribed lines instead of indicating, thinking that would have saved time compared to using a dial indicator. Wrong, as I had to take awkward positions and too much eyeballing. Same story for the leadscrew hole. Note to myself: I need to make better "jaw pads" from copper.

 

Original nut is on the right, threads are visible but don't hold at all. I think I managed to be well within 0.05mm for all the sizes, but made some small mistakes and still have room for improving. The nut works nicely and is well aligned as long the cross-slide bolt is not tightened too much, in hindsight I should have left the post a bit taller for that adjustment, but will use a small washer for the purpose.

 

Last picture is of the new quick change tool post that I bought for the occasion of having the baby lathe working again. Specific for the type, not too expensive and well made by Soba in India, it was something long overdue.