Thread: Cheap and different lathe leveling method

Cheapest Way To Level a Lathe!!! - YouTube

(Just cut and past a link)
In theory that may work but I suspect that in practice the errors that he would have stacking up mean that his lathe is "level" more by luck than scientific measurement.
5 thou over 12" is not all that flash as a target either - the usual target is better than 3

To each their own.

Michael

Points for ingenuity I guess - and cheapness - but the main point of levelling is to get both ends of the bed the same, so you need to keep swapping the instrument from end to end as you make adjustments. Seems like that device would be cumbersome and slow for the bob to settle. Better than nothing though.

Thanks for posting the video up Michael!

I agree it looks cumbersome but I like the concept! When I get around to it I will post a review.

I think the biggest source of error is the suspension of the plumb bob. You would have to make sure that it is hung in such a way that the pivot point, centre of mass of the bob and the indicating point are all co-linear. A slight deviation and the bob may not behave repeatably.

Michael

Originally Posted by Michael G

I think the biggest source of error is the suspension of the plumb bob. You would have to make sure that it is hung in such a way that the pivot point, centre of mass of the bob and the indicating point are all co-linear. A slight deviation and the bob may not behave repeatably.

Michael

Would a pendulum give better repeatability?

Phil

How the heck can he resolve the out-of-plumb condition with any degree of precision? Master levels detect 0.0005" over ten inches (approximately, depending) There's no way that you could resolve that fine a value sighting a plumb bob.

On the other hand: if you could layout a projection of the spindle centre line precisely beneath the spindle, and had a plumb bob damped in a viscous medium which you could read precisely, you might have something. Meh.

Greg

Basic physics Greg. The longer the vertical rod the further away the pivot point is and the higher the accuracy. It then can become a comparator.
Unless I have completely stuffed it up. I wasn't real flash at physics.

Phil

Well, yeah, I suppose, but you'd need a pretty long pendulum in order to see what a level shows, wouldn't you? Plumb bobs and levels are all measuring the same thing after all, and with the same accuracy, just not the same precision.

And I am not claiming that plumb bobs don't have their places in machine set-up. I have three beautiful ornate ones for reasons I can't recall. My wife won't let me hang them on the Christmas tree...cast iron and bronze ornaments of a bygone era would look great I reckon.

The sort of thing I was alluding to was this -

Attachment 219358

You'd need to use a fine wire and make sure the suspension was a point rather than just twitching it through a hole. Similarly with the bob, the attachment point would be something similar rather than the old tyre weight tied with a bit of string that I use. The weight would need to be symmetrical of course.

To get 3 thou in 12", you would basically need to double his 72" (so it's now 12ft) to use a 32nd scale to discriminate. The other thing I would be worried about would be air currents. You'd almost want to run the bob line down a piece of PVC pipe to avoid drafts.

Of course, with a longer wire are you starting to move into the realm of Foucault's pendulum and so start getting movement from the motion of the earth?

It's all getting too complicated...

Michael

The plumb bob is an interesting idea and while it might not be perfect, if you have nothing better, hopefully its at least heading in the right direction.

Originally Posted by Greg Q

if you could layout a projection of the spindle centre line precisely beneath the spindle, and had a plumb bob damped in a viscous medium which you could read precisely, you might have something. Meh.

But then wouldn't you be twisting the bed to line up with any error in the bed/spindle alignment?

You could use wire and read off it with a scope like Phils........although that will likely cost you more than a level.

Stuart

Of course, if you had a microscope collection you could use a ruler in 64th's or even 100th's and either increase your accuracy or decrease the height of your pole.

(Maybe that's why Stuart has those microscopes - to compensate for having a smaller pole)

Michael

Its not poles that they are for looking at

Originally Posted by Stustoys

The plumb bob is an interesting idea and while it might not be perfect, if you have nothing better, hopefully its at least heading in the right direction.


But then wouldn't you be twisting the bed to line up with any error in the bed/spindle alignment?

You could use wire and read off it with a scope like Phils........although that will likely cost you more than a level.

Stuart

Yeah, the whole level thing should be a lot easier and more affordable than it is. When you describe the process of using a level to eliminate twist you make the faulty assumption that it is almost free, since the local gravity vector is nearly a constant and spirit levels are common as dirt. Too bad that such a theoretically simple instrument to check is so expensive.

Greg

Originally Posted by Stustoys

But then wouldn't you be twisting the bed to line up with any error in the bed/spindle

Stuart

I wanted to mention this alone: i reckon that the average lathe, with its seperate headstock, can be adjusted so that the extended spindle centerline becomes parallel with the bed ways. This is the optimum condition of geometrical accuracy, which yields an absolutely constant tool height compared to the workpiece in the machine. This should yield absolute dimensional accuracy, except for the fact that the world is made of rubber of one sort or another, including cast iron.

My lathe's headstock is part of the massive one piece casting that included the bed, so I have to reference every survey and every correction to the spindle centreline as measured from a test bar which is itself corrected for droop, even if the machinist isn't.