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  • Paralysis from over analysis. Such an evil rabbit hole to slide into... Yes, he could of built a live steam locomotive before ever noticing that taper his lathe is cutting!

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    • Originally posted by RB211 View Post
      Paralysis from over analysis. Such an evil rabbit hole to slide into... Yes, he could of built a live steam locomotive before ever noticing that taper his lathe is cutting!
      No argument on the paralysis issue. Been there, done that and fretted over what the shirt should look like....

      I'm sort of thinking that a live steam engine would be where the taper issue would likely cause things to come to a head though. I'd be quite perturbed if my cylinder bore came out tapered or if the crankshaft journals on each end came out a few thou different despite using the same cross slide setting.

      I also think that knowing is half the battle. Sort of like how I "worked around" my own taper issue for so long. I still got the job done but only because I knew it tended to turn tapered and allowed for it... .Doesn't mean I had to like the situation though.

      Chilliwack BC, Canada

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      • Now that he has the machine tuned up a bit he can stop using brass and start working with silver and gold.

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        • Given that it came from a printing plant it wouldn't surprise me if the lathe is eventually able to run quite true. It'll take some tweaking and tuning which they had done at the printers. Repeating my previous post: I do believe it is a good idea to eliminate bed twist as much as possible, but it is also important to check for tailstock offset later on. I think its crucial to have it bolted down solid in its permanent location before doing anything.

          About cutting a test bar on the cheap, try and get say a 1-1/2" black pipe nipple about 10" long from home depot or lowes or the hardware store... should work. And like they say, use a dead sharp tool with the barest shaving cuts. I'll bet you can get it into a thou or less on a 10" length, with enough time and tweaking. Since commercial printers require accuracy.
          25 miles north of Buffalo NY, USA

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          • I know it sounds like I'm tooting my own horn again but with my setup that used mounting studs and seated the machine on riser nuts and washers on the studs I found it easy peasy to tune the bed to a lot less than .001/10". I started out with something like .001/10" as a goal I hoped to achieve. But the ability to work the seating and hold down nuts to a very fine degree soon had me gleefully chasing down tenths of a thou. With fixed size shim stock it might be harder but I believe it would still be doable to get to well under .001/10". But due to the need to play with various sizes to get a thou or two changes in the pack it would be a fussy bit of work. Doable but fussy..... And with the need to have a variety of different shim thicknesses on hand.
            Chilliwack BC, Canada

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            • Originally posted by nickel-city-fab View Post

              Hahahahha Truer words were never spoken...

              I do refrain from posting a lot because I worry about information overload, or going in the wrong direction in someone elses thread, and things like that. I do believe it is a good idea to eliminate bed twist as much as possible, but it is also important to check for tailstock offset later on. I think its crucial to have it bolted down solid in its permanent location before doing anything.

              About cutting a test bar on the cheap, try and get say a 1-1/2" black pipe nipple about 10" long from home depot or lowes or the hardware store... should work. And like they say, use a dead sharp tool with the barest shaving cuts.
              I actually have some of that laying around, made shelf brackets with them. So that stuff is pretty “true” as bought? I figured it would be too thin to be much use here...

              certainly cheaper than buying a brass bar.

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              • Originally posted by connor1 View Post

                I actually have some of that laying around, made shelf brackets with them. So that stuff is pretty “true” as bought? I figured it would be too thin to be much use here...

                certainly cheaper than buying a brass bar.
                Overall pipe isn't really true, but a 10" length shouldn't be too bad. It'll probably take a couple of cuts to "clean up" enough to use. Figure if you're taking cuts of only .003 deep the pipe is plenty thick enough. Basically I would just keep taking skim cuts till its cutting all the way around, down the length of it, then measure. You'll need a really sharp bit for that.
                25 miles north of Buffalo NY, USA

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                • A good test of the bit being sharp enough and proper geometry and the feed rate correct is when you back off the cut and the tip does not cut a spiral of additional material. It's really not as hard as it sounds to get there either.

                  The key with the bar stock or a good thick wall piece of pipe is that you want the stock to fit into the hole in your chuck so it beds down for the whole length of the jaws. So whatever size the hole in the body of the chuck might be that's a good size. And cut the threaded part off first so you don't have that acting as a spacer.

                  Now even with this you may not want to use a 10" length. You still only want the part sticking out the jaws to be about maximum 5x the diameter for length. And really 4x is better. But with your micrometer you're good to chase that down to easily a half thou and most of us even without the 10ths vernier can "guess" at 1/4 thou amounts. So even if you can only use 1.25" OD stock that's still a 6" stick out and you have the chance of getting down to around .0005 over 12" if you can see a difference between the collars of 1/4 a division. And if you can only manage 1" stock into the chuck and a 4 and a little stickout that's still potentially .0007'ish over 12". And still not shabby at all. And with keener eyes maybe still manage .0005/12" with a 4" testing bar.

                  Don't try to go anything more than 5D for length though. It'll start getting too flexible and you run the risk that even a super small skim cut will push the bar away by a tenth or two and fake you out.

                  If you got a four jaw and it has a bigger center body hole I'd also suggest using that instead. The bigger the diameter you use the stiffer the bar or pipe will be and also the longer it can be. So by all means use the option that permits the largest stock you can manage

                  The whole point of roughly relieving the part in the middle between the collars a little is that it saves you having to stand around for a VERY SLOW fine feed pass for the whole length when all you need is the two ends. But if you're using pipe don't go nuts on how far you relieve things. Find out how much of a cut you need to make it circular and then feed in another .01 and run the roughing pass. If you need a little more later on then run a second roughing pass between the collars.
                  Chilliwack BC, Canada

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                  • Click image for larger version

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ID:	1874812 Sorry to fall off the radar for so long after you all were so helpful. Here is a pic of the last collar test I did. I used black pipe to avoid offense! My brass bar is safely in one of the drawers until I find a use for it. I’m doing some work on a motorcycle crank so I am about to start another thread relating to that, so I’m sure we’ll talk soon!

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