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Posted by D Sherman [72.47.9.228] on Tuesday, July 19, 2011 at 13:47:23 :
In Reply to: lathe help posted by mannyc [68.165.89.2] on Tuesday, July 19, 2011 at 12:12:23 :
I agree that a basic lathe is a really handy tool, even if you're not a very good machinist (I'm not). "Cleaning up sealing surfaces" is tricky. I would stick with speedi-sleeves for that. To do it on a lathe you need a tool post grinder, which isn't cheap, and then you have grinding grit that's liable to get into the various important nicely-finished surfaces on your lathe. I have been using a 12x36 Chinese one, the same that Jet, Grizzly, and everybody else sells for years and it does the job for me on small stuff. Cost $1200, but these days they're about $2200. I have a much bigger Victor lathe I'm in the process of setting up now.
There are loads of used lathes for sale, and as far as I'm concerned for "farmer grade" work, it matters less what make it is than what size it is and how worn out it is. You aren't going to be using it for production so you probably won't put any additional wear on it, but lots of used lathes and mills were "rode hard and put away wet" and it shows. You don't want to buy someone else's headaches. A worn-out lead screw, for example, will be no end of frustration. I would honestly rather have a brand new chinese lathe than a worn-out South Bend or Clausing lathe. A big advantage of buying a used lathe, if it's not worn out, is that you can usually make a deal on the tooling to go with it, which generally is work about as much money as the machine itself.
There is a whole lot of skill and magic in getting a nice finish with any kind of machine work, and I'll admit I don't know how to do it and am only improving slowly. The good part is that most general repair stuff doesn't need a particularly smooth finish. Often times you make a part to fit some other part, like a new pin to replace a worn-out pin or a bushing to tighten up a worn hole. If the thing gets pressed in, tool marks even help it hold better. On a spacer or a collar, the surface finish doesn't really matter at all. If the outside of a pin or the groove in a pulley needs to be very smooth, you can make it a few thousandths over-sized, and polish it with emery cloth on a roll while its spinning fairly fast in the lathe. If you really work at it, you can get a good sealing surface on a shaft that way, but I'd rather just spend $20 on a speedi-sleeve.
A lathe is definitely one of those tools that I didn't know how useful it was until I got it. I would say it's more useful than a milling machine for repair work because most of what wears out is rotating parts, pins, and bushings, all of which can be made on a lathe. Threading is definitely trickier. I only use the lathe for cutting odd-ball or large-diameter threads, and only fairly coarse ones at that. I have not been able to cut a decent thread on anything much smaller than 5/8-11 myself. Inside threading is even trickier than outside threading.
No matter what kind of lathe you buy, you need to start out with a realistic idea of how long and how large in diameter your workpieces will be. There's no way to stretch a lathe if it's too small. On the other hand, price, weight, and power requirement go up quickly with increasing size. Simply changing the chucks on a larger lathe can be a piece of work if you're not built like a gorilla. Even a modest-sized chuck is easily 100 pounds and you have to bend over awkwardly to pick it up and put it in place which is hard on your back.
The nominal measurements given in the data sheets are much larger than what you can realistically work with. A "36" lathe will not machine a 36" long shaft, for example, unless it's thin enough to go inside the hollow headstock. Most lathes have a removable section near the headstock to allow it to handle slightly larger diameters, but it's a hassle to take it out and put it back in. A lathe that could handle PW brake drums, for example, is not something you set on top of a workbench and plug into the wall.
My thinking with tools is it's better to have a decent tool that is adequate for doing most jobs, which a 12x36" lathe is, than not have the tool at all, while aspiring to get a wonderful one someday.
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