Re: Precision level needed or not?

glenn brooks <brooks.glenn@...>

What I learned from my old worn out big iron Standard Modern 12” lathe, was that there are really two kinds of bed twist: most common on heavily used, old machines is bed wear - and related machine wear. The other thing is simply uneven flooring, causing the bed casting to sag and twist out of shape over time.  

If your machine exhibits signs of wear from its decades of life, all the parts will be worn in concert with each other - underneath the tail stock, cross slide, bearings, lead screws and of course the ways - likely having the most wear just outside where the chuck sits.  

So the challenge is to straighten the ways to counteract a possible sloping floor, and then, twist the bed to counteract all the wear - eventually finding the sweet spot that most resembles the original true surface of the ways.  

That’s the main reason I like to use a level (and a straight edge). It’s fairly easy to assess various amounts of twist in the different segments of the bed with a level. Hard to do with other methods...


On Jun 15, 2019, at 3:38 PM, Jim_B <jim@...> wrote:

When setting up a lathe to remove twisting you do not EVER use a tailstock. 
Please read “Rollies Dads Method”

Sent from my MacBook
Jim B.

On Jun 15, 2019, at 1:32 PM, eddie.draper@... via Groups.Io <eddie.draper@...> wrote:

Yes, it is possible to determine whether measurement differences between ends of an alignment bar are due to tailstock offset or bed twist.  Betwen centres:  Tailstock offset.  Held in chuck or otherwise directly coupled to the headstock mandrel:  Bed twist.



On Saturday, 15 June 2019, 03:13:48 BST, Steven H via Groups.Io <stevesmachining@...> wrote:

Another fellow earlier today said no, an alignment bar between centers won’t do for determining bed twist. Would just be useful for tailstock alignment. A check of eBay shows precision machinists levels starting at less than $30, but “you usually get what you pay for”.

Steve Haskell
> On Jun 14, 2019, at 9:32 PM, Stephen Bartlett via Groups.Io <> wrote:
> Is it possible to discern whether a measurement difference between ends of an alignment bar is due to tailstock misalignment or bed twist?
> I guess the first thing is to get the tailstock alignment correct with the tailstock right at at the headstock.
> When I got my lathe back about 1968 it had very little bed wear and I have not put too many miles on it.
> In practice I have never paid much attention to twist because I do not generally work with long stock.  Years ago I borrowed a precision level from work and leveled the bed.  I moved in 1985 and since the bed had an adjustable tail end base I just loosened the set screws to let it settle out and then snugged them again, tightening each a little at a time, back and forth.  It is on a heavy steel cabinet.
> I looked at the Edge Technology web site.  Much of their product line is affordable for a hobby situation.
> Steve Bartlett
> From: Steven H
> Date: Thu, 13 Jun 2019 23:09:02 EDT
> What you are describing - an alignment bar placed between centers - is one way of checking and setting the tailstock alignment both horizontally and vertically. These alignment bars are commercially available - Edge Technology makes one that is 12??? long. Don???t know if such an item could be used to check for lathe bed twist, but if the idea would work, the bar should be max length the lathe can hold between centers.
> Steve Haskell

Jim B

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