I'm gonna talk about one of the downsides to buying used equipment. The too-long-didn't-read version is simply this: "if you consider a used machine, ensure it comes with every possible accessory you might need, OR ensure that it's standardized enough that common aftermarket accessories will fit it."
The rest is details, examples, and supporting evidence.
My lathe was built in the 1970s by the one of the predecessor factories which later became the SIEG group in Taiwan. For those who aren't familiar with the company, Shanghai Industrial Electric Group (this may not be the correct acronym - the company doesn't talk much about its early history, because it's all embarrassing) is the manufacturing source for Gizzly, Jet, Enco (now defunct), Turn-Pro (MSC's house brand), Rong Fu, and many other brands of low-cost machine tools.
In the early days, before the existence of Jet and Grizzly, everything SIEG made was junk. Eventually, with the help of (semi-) modern manufacturing and quality control methods, their quality began to rise. Even so, Grizzly and Jet have a two-step manufacturing process, with the final finishing and quality control being done in the states. They are still inferior to the best machines made by the mainstream famous brands, but the newer machines can be entirely adequate for many hobbyists and many small businesses. I worked in a high-technology laser factory for a few years, and we used a cheap Rong Fu mill to cut open bad laser tubes to examine them, it was good enough.
Sadly, mine is not one of the newer machines.
Several times in recent years I have wished for the ability to turn items between centers on my lathe, but I do not have a center or other fixtures (ie; lathe dog plate and lathe dogs) to fit my lathe spindle. Very well, I decided this morning I would start learning about my lathe spindle and what things I would need to fix up my spindle with a center. A secondary goal was to find out how difficult / practical it might be to fit my spindle with a collet closer (which I would almost certainly have to make from scratch, but there are multiple designs and projects for making them, including a very nice one in Home Shop Machinists magazine about ten years ago...)
So next, I'm gonna blather a little about lathe spindles and chucks and other accessories.
At present, there are at least five different styles of spindle on lathe headstocks, and each style comes in several sizes.
In the earliest days of lathes, chucks and dog plates were attached to the spindle by the simple expedient of threading both and assembling the chuck onto the spindle like a nut onto a bolt.
But this method had serious problems, one of which my high school metal shop teacher lectured us about over and over. And despite his lectures, I once witnessed exactly what is described next, first-hand, and it was every bit as exciting as described even with a "small" chuck weighing only 75 lbs or so...
"Although cheap to manufacture and perfectly adequate for most purposes, especially amateur use, threads do have serious limitations centred around safety, rigidity and ease of removal and replacement. To take just one example: a threaded fitting cannot safely be run backwards and, whilst a chuck might happily stay in place as a lathe accelerates up to top speed in reverse, once there it cannot be so easily stopped. Legion are the number of serious accidents caused where an operator has stated a lathe in reverse, realised his mistake, and then (without thinking) applied the spindle brake. Once the chuck starts to unscrew the workman can do nothing but watch in horror as the 200 lb mass, rotating at 800 rpm, accelerates down the length of the workshop, smashing machines and people unfortunate enough to be in its way." -- from http://www.lathes.co.uk
One of the clever dodges that was dreamed up to address this is the cam-lock spindle (standards: DIN 55029, ANSI B 5.9 & ISO 702/I)
My lathe is equipped with a D1-4 cam-lock spindle, and when I bought it used, 30 years after it was made, it came with just one 3-jaw scroll chuck; no spindle center, no dog plate for use with said center, and no 4-jaw chuck.
Sadly, the internal bore shape of the spindle is not defined in any of the cam-lock standards!
My spindle does have a taper of some kind inside, but the spindle bore is quite large (3.5 - 4.0 cm or so) and any regular center which fits it would be enormous, so I assume there is some other equippage which fits the spindle and then accepts normal centers... I just don't have that item.
That internal taper - I haven't determined what it is - does suggest strongly that a collet closer could be fitted, which is nice, but that's not my priority rght now, having centers is.
The next step is probably to identify that internal taper using a dial test indicator mounted on the saddle; n thousands of radial change over N distance converts easily to an angle with either high school trigonometry (which I can never remember) or the trig tables in Machinery's Handbook*.
If I get really desperate, I'll hop into the forums for either Home Shop Machinist or Practical Machinist, but I gotta tell ya: there are helpful folks in those forums, and there are some real elitist assholes who have zero interest in being supportive of beginners, which to me is a baffling attitude - so if you tread those halls, tread with care and be prepared for a few of the denizens to shit on you. For me, those forums have become a last resort, I'm more likely to watch four hours of YouTube videos looking for the answer than I am to spend one hour reading those forums. YMMV.
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* if you don't know about Machinery's Handbook, you need to; I'm gonna
write up a piece on it in my next entry.
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