Checking bed twist

[DPittman]

Using a machinist level across the top of the tailstock and then sliding the tailstock along the bed should show any bed twist...no?

Don

 

[Dabbler]

if each bed rail is ALSO level,,,

 

[DPittman]

Well that's basically what I want to measure...or at least the relative levelness/eveness of one end to the other

 

[Dabbler]

You check the level of the bed on each rail at 3 points; each end and the centre. Then you use the level across the ways, either by sliding or by taking intermittent measurements along the bed. If all are level, then there is no twist detectable. After that, you take a test bar and cut along a longish section of the bar: 12" or more on a 36" lathe, etc. By measuring for taper you can fine tune your lathe.

 

[DPittman]

So I should explain why I would ever want to attempt the way I suggested....is because the ways that the tailstock ride on are above the carriage ways and therefore I can not lay a level across them. I block t he ways up to check with level but I can not see why the tailstock itself could not be used to check level/twist.

 

[Dabbler]

Ah... It may well work! I've never tried to do it that way. It *might* yield a more accurate result if the level were on a machined rather than painted surface... I am moving my lathe in the next two weeks and I'll try it both ways and compare.

To obtain accurate results , you can use a 1/4" parallel with a 1-2-3 block on top. the 1-2-3 block provides a surface for the level and the parallels can go most anywhere. It is not enough to just to check across the ways. Checking along the ways is important as well.

 

[Dennis P]

Another option is to use a pendulum setup to check lathe bed twist. Very easy to make and no special(machinist level) required and still quite accurate. I don't have a picture of the setup I made but there is a video on youtube link below

I personally would not use the tailstock sliding back and forth, I prefer to lay it right on top of the bed ways.
Worked very well for me and thought id share
Good luck

 

[Dabbler]

I looked at Dale's video when it first came out and thought of it for this thread, but I don't think it is nearly as accurate as the machinist's level technique. Mind you, it might be 'good enough'!!