Just a quick project that I did around Christmas Time. I wanted some machinists jacks to support a slightly long piece that I'll be milling. So, I found some scrap pieces and figured out a design that would work (I think). These jacks are two stage, with the outer thread being a 2.0mm pitch and the inner 1.75mm. This means that by holding the top and bottom sections stationary I can turn the center part to obtain 0.25mm per revolution for fine adjustments. All threads would need to be single point cut. Firstly to ensure concentricity between the outer diameters and the threads and also because the thread sizes were complete odd-balls. The outer thread ended up as something like M31.5x2.0 and the inner was M20x1.75 (slightly less odd). First step was cutting up some sections to make a pair. I should have left the stock much longer and worked on each end as that would have made work holding a bit simpler. But for some reason I chose to cut lengths to leave about 10mm of waste. https://pic8.co/sh/myf3Cb.jpg The thick walled pipe was turned down to the outer dimension, then bored out to the minor diameter of the thread. This turned out to be a bit off my planned dimension (hence the odd-ball size) due to the inside being neither round nor central. Threading was carefully and trepidatiously done with a braised carbide threading bar. I needed to grind a little more relief in the bottom of this tool, so not sure what diameter of thread they expected me to cut with it as ground. Determining when the threads were "done" was a bit of a guessing game as I don't have any accurate means of measuring internal threads. In hindsight, I should have cut the external thread first and used it as a gauge. That is effectively what I ended up doing when the male threads wouldn't go after I had cut them. I had to put the outer parts back in and fiddle with the compound and crossfeed until I got the tool back in the thread. Very fiddly work. https://pic8.co/sh/ikEyQz.jpg Having cut (at least initially) the first set of threads, I set up the middle piece. This would need a matching 2.0mm pitch thread on the outside and a 1.75mm pitch thread on the inside all cut without moving the setup so I would maintain concentricity and not make a banana. https://pic8.co/sh/xftGBX.jpg https://pic8.co/sh/Lq88W5.jpg The final piece was relatively straight forward. Just threading a simple outer thread to match the inner one. https://pic8.co/sh/3nRJkO.jpg The parts were separated and cleaned up (along with lots of stuffing around to get the threads to fit nicely, I need more practice at this stuff) and fit together. https://pic8.co/sh/1iTMFm.jpg Each part was knurled to give some grip for adjusting. The inner parts were held on their threads in a 5C collet for this. The outer and middle parts were done together using a spacer ring to allow access to the middle section for knurling. https://pic8.co/sh/ba6jqI.jpg That was it. All done and working nicely. https://pic8.co/sh/Zypbf6.jpg ---- Here's a small sneak peak of what's in the works next. https://pic8.co/sh/xU89ur.jpg