Checking the wear on a lathe's bedways

[cheb]

It occured to me that before I spend time and effort on repairing the ML4's broken casting that it might be wise to see if the bedways are so badly worn as to make any other work pointless.

I'll have to edit this later, I've just been given something more urgent to do.

 

[AKN]

I remembered this from lathes.co.uk, hoping I’m not breaking rules by quoting directly, it is in the buying a lathe section.

”
Checking for wear
To track down a really good lathe needs a care and time. While virtually all the wearing parts - cross-slide screws and nuts, headstock roller bearings (but not plain bearings), broken gears, etc., can be replaced or remanufactured, one crucial element cannot be so easily fixed - a worn bed and saddle.
For example, on the popular Myford ML7 and Super 7 lathes, bed wear can be estimated by examining the bed's front vertical shear - that narrow band which runs along the front face (and, on other older, cheaper lathes, the front face of a V-edged way) . On early ML7 and Super 7 lathes the beds were milled and the machining marks very evident. As a bed wears these marks are slowly polished out - and it is but the job of a moment to examine the strip and compare the area near the chuck (where the greatest wear takes place) to that near the tailstock, where the marks may remain almost as they left the factory. Later Myford beds (and other makes) were ground, with a much finer finish, but even so the same rules apply: if the original grinding marks are visible near the chuck the chances are all will be well.
An essential practical test to confirm your observations is to position the carriage so that the toolpost is within 50 mm (2") of the chuck, grasp the front and back of the cross slide and attempt to twist the whole carriage on the bed. If it does twist - and so is very easy to move up and down the bed using the carriage handwheel, any gib strips will have been set on the loose side. Now try to move it all the way to the tailstock end and try the same test there. If the rock disappears it means that the bed is worn. What if the owner has adjusted the slides so that the bed is a good fit at the headstock end ? In that case, as you try to move it towards the tailstock, it will become stiff and, in the worst cases, go no more than halfway before locking up completely.
As some lathes, especially those with V and flat bedways, often have non-adjustable "keeper plates" at the front of the saddle and no means of taking up any slack and so wear is harder to detect. However, no matter what design of bed is used, there is one certain way to gauge wear - use the saddle lock nuts in the manner as described for the Myford lathe above. As V-bed lathes often develop a wear step near the chuck and this can be filed out by an unscrupulous owner, be sure to carry out the saddle lock test. “

 

[cheb]

Thanks, that's roughly what I was thinking.

 

[daedalusminos]

The usual would be to measure relative to an unworn surface -on many lathes the tailstock slides on it's own (relatively unworn) ways but that probably isn't the case on the ML4. You may be able to get an idea by measuring the thickness of the way relative to the underside and compare to the end furthest from the headstock.

 

[Pete.]

ML4? Throw it in a lake. If it floats, it's a good 'un

 

[cheb]

Harsh man, harsh.

Happily I'm close to the sea so it'll stand a better chance of floating.

 

[Anguz]

A worn lathe is still tons better than no lathe

 

[addjunkie]

Break-it for spares, youll be surprised what the bits sell for

 

[cheb]

I've already got a lathe, a Harrison. Very nice it is too.

The problem with breaking it for spares is the couriers out here being slow. The PO is good but uneconomic above 5kgs.