I'm in trouble and ask for help, any advice welcome
I have an old lathe, the tailstock position is not correct and the centre is off axis.
There are some marks on the back of tailstock, the "0" seems out of phase, more 2 scratch to the side, maybe have been done later by hand.
Currently I got no double fixed point, no rectified bar, there is some way or tips for finding the correct alignement?
I take some picture
Make a set of alignment buttons, e.g...
In my construction notes in that article I indicate that the holes should be center-drilled. If your tailstock is badly out of alignment, then that operation may be problematic. A more accurate process would go like this...
Rough drill hole using tailstock
Bore hole to ensure its centered and cylindrical
Form 60 degree bevel on mouth of hole using compound rest
Once you've carefully made the buttons, save them. You'll need them to reset the tailstock the next time you set it over to turn a taper. [Although there are better ways than tailstock setover but that's not related to your problem.]
The button method. This is one of the easiest ways to do it. Once the buttons are made, put the small end of one in a collet or 4 jaw chuck, make sure it's running true. Put the other one on a center in the tailstock and bring the 2 big ends together. Measure across them horizontally with a mike as you adjust the tailstock side to side. When the reading across both buttons is the nominal diameter of the button, the tailstock is centered.
There are pretty easy adjustments for horizontal adjustment, but not vertical so hopefully that part is ok. If not, going up will definitely be easier than going down with the help of good shimstock.The fastest way I found to check alignment was to chuck a coaxial dial indicator up in my 3 jaw (assuming that the chuck is centered) and I put a piece of machined round stock in the tailstock chuck. Then its just a matter of moving the tailstock in and out to check for being true with the bed ways, and spinning the coax indicator around the round stock to get the tailstock centered with the spindle, making necessary adjustments to dial it in. Hope that helps.
Many good points have been made here. Here is my 2 cents:
Many years ago, my mentor taught me to turn a rod between centers, using a lathe dog (lathe dogs are cheap; every machinist should have several of different sizes.) This eliminated any error in my 3-jaw chuck. Also, by turning the rod end-to-end, I eliminated any error in the rod itself. Once I had turned the rod, I measured it for taper, using a good (calibrated) micrometer. After adjusting the tail stock accordingly, it was rinse & repeat, using the same rod. Eventually, the rod miked out equal in diameter along its entire length. Thus, the tail stock was aligned with the spindle's center & it was good to go.
This procedure can be a bit tedious, but it works. It eliminates errors that may be introduced by the chuck* and by the rod itself.
Good luck, and happy machining!
*run out error in a chuck is another matter, but it too can be fairly easily adjusted to run true to the spindle.
Last edited by Caldude53; 05-06-2017 at 02:35 PM. Reason: further thoughts to help clarity.
Nevertheless, it is tedious. Having a set of alignment buttons to get you close will minimize the time spent with precision alignment and, depending on what the work is, may themselves provide sufficient alignment.
Please allow me to say this... MERV KLOTZ you are a GENIUS!
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