Brian
The Sigma-Jones, like the BCA and the similar machines, is a bit of an odd duck. Its not really a jig borer more an instrument makers light mill. Of necessity, given the class of work it was made for, it was built to the sort of accuracy associated with proper jig borers. It will work fine with small milling cutters but unless you do the right sort of work the thing is an unmitigated pain in the butt to use. I was very happy to swop my Ultra version for a square column Chinee mill despite all the "customer paid, passed QC" issues that came in the box as a Brucie bonus!
For general purpose use the two major problems are the limited vertical axis daylight / travel and the poor grip of the collets on milling cutters. Limited vertical daylight and travel can make setting up for drilling hard work. Need short drills rather than standard jobbers length in most sizes. Not really room for a vice on anything much over 1" thick. Hafta think about the extension of the vertical slideway below the main casting too. Its very easy to end up with an impossible job because the only way to get the cutter over the right part of the workpiece involves passing a higher bit under the end of the slideway and it simply won't go! The simple small knurled hand wheel collet tightener severely limits the grip. Cutters over 1/4" will slip on you if you attempt anything approaching normal feeds and cuts. Not every time but it will get you.
I consider the relatively low speeds unforgivable. You simply can't run the sizes of cutters it prefers to use at anything like the correct speed. Makes for slow work and its easy to break cutters if your attention wanders. The less said about the belt drive system when inclining the head the better. Mine put me on Santas naughty list more than a few times and that had been modified with a swivelling motor mount so the pulleys could be got closer to the same plane. The man who sold it to me was very proud of this modification which "made life much easier". If that was easier lord preserve me from the standard system.
Now given the number built and used it can't be a totally rubbish machine. Bottom line is it does what it does well enough given its era. But it doesn't do well out of its niche. You need to be sure that what you need it for falls reasonably close to that niche if you are every going to be happy with it. Its a deceptive machine if your acquaintance with mills is limited beacuse it looks as if it can handle much larger work than it is designed to or capable of.
Clive.
Edited By Clive Foster on 23/11/2016 17:46:27
Edited By Clive Foster on 23/11/2016 17:47:40