Sunday, December 19, 2010
Getting into threading...
When I bought my Sherline lathe, I went for the loaded option. As I am finding out, it was a very good decision. I don't think I'd have been able to use at all it without the digital readout box. I understand how people in times pass could have used a micrometer to do measurements between cuts. I doubt that I could have had the patience, though.
After my last attempt at doing a deep drilling and cutting down a piece of aluminum bar stock, the next thing I wanted to do was use the threading attachment. Between Joe Martin's Sherline book, Tabletop machining and the Sherline Accessories Shop Guide I was able to puzzle out how to re-rig the lathe for threading. My motive in getting a threading attachment was to have the possibility to cut my own lead screws and thrust collars. The studding used in the Rapman and Mendel 3D printers, not to put too fine a point on it, suck the middle out of canned Vienna sausages. When you buy studding it is rarely, if ever, straight. When you try using it as a z-axis lead screw, it does not very pleasant things to your print quality.
As well, I am quite fond of the polymer pump design on the Rapman. My primary reason for wanting to do my own threads was to be able to make the threaded drive shafts for those, too.
The biggest shock for me in this adventure happened when the instructions book told me to demount the lathe motor. It turns out that you cut threads on the Sherline lathe with a hand-powered handle. Using it reminds me of my grandmother's old foot pedal powered Singer sewing machine that I learned to use when I was about four. It has a very similar, 19th century feel to it.
By and large the threading system design is quite good. The real pain in the tail, however, is that little black lever that you see below the spindle in the above picture. Getting that to work right had me taking the whole lathe apart about three times. Sherline needs to rethink that part of the design. It really sucks.
Other than that, the threading attachment was quite easy to use. It is set up to do standard and metric 60 degree threads. The carbide cutting tool did that quite easily.
For a first try I did a really coarse metric thread, 2 mm.
I figured that that deep a thread would require the most muscle. It was a bit tiring but not at all impossible.
For lead screws, the Sherline will handle about 15 inches of threading. If the diameter of the stock is less that about 9 mm, a longer unthreaded piece of stock can be snaked through the spindle. Given that manufactured lead screws about cost $1/cm and thrust collars typically cost $30-35, this capability will save me some money over the mid-term.