Machine Feet for my lathe

**cropwell** · 29-10-2014

I looked at precision levels and, as an amateur, I thought they are pricey for something I won't use much.
Then I got to thinking..... Why should a lathe be exactly level ? Everything is relative to the axis of the lathe. Basically you want the headstock to point to the tailstock and the carriage to tram to the axis.
So you need to ensure the bed is not distorted. No twist sag or bow. You also need to ensure that cutting forces don't cause distortion.
A lot of this checking could be done with a laser system that fits on the spindle pointing at a tailstock centre. If you can adjust out any wobble and get the laser to align on the axis when you turn the spindle 360deg then the first part is done. next you need to check the tool path is parallel to the axis by mounting a plate with a pinhole at tailstock centre and run the carriage up to the headstock. If the laser beam goes through the pinhole and shines on the tailstock the length of the travel, then all should be ok.
Let me know (politely) if I have got it wrong, I am not an engineer.

**Neale** · 29-10-2014

This levelling business set me wondering as well. I can think of a few reasons for doing it. One is that it puts the machine in exactly the same orientation as when it was originally ground, so you should be replicating the original accuracy. But I can't believe that you need a precision level to achieve that - I'm sure that you could get close enough with any decent level. But a precision level might be able to check for twist by checking in various places along the bed and save time spent in machining a test bar until you were very close. If you also set the machine very accurately, you could also use the level for setting work later? I've never done that, but I can see it might be useful on a milling machine.
By the way, don't use the tailstock for setting up. The initial setting up is all about getting the headstock aligned to the bed (or vice versa). That's why you don't use the tailstock when doing the initial checks. The tailstock is usually adjustable, and has to be aligned with the headstock and bed later. I wouldn't trust tailstock alignment on a fresh-from-the-factory machine.

**cropwell** · 30-10-2014

You are right about the tailstock as a primary reference it is inadequate. The first job would be to get the laser to point at a target at the tailstock end. When the dot doesn't move with the lathe turning (by hand) then the beam is directly on the axis. Then you can set up the tailstock centre, before checking the carriage. if you only want a relatively accurate level how about this one http://www.chronos.ltd.uk/cgi-bin/sh...html#a30316004
You can always put it on the bed, zero it and turn it 180deg to check for any slope.

**Neale** · 30-10-2014

A reasonable lathe is going to do better than 1 thou/20 micron accuracy - I'm not sure that a laser dot is small enough to do that well.

**cropwell** · 30-10-2014

The cheap laser pointers have quite a wide beam but you can shine it through a small aperture (pin hole). If you can make a 1 micron hole, then you have a 1 micron beam width, which would remain in good collimation over a couple of metres.