Machine Feet for my lathe

I think the levelling business is to take the worst of the twist out of the bed and bring it close to its original just-ground level of accuracy. However, that isn't going to guarantee the accuracy that the lathe should be able to achieve. Once it's levelled as accurately as you can manage, then you switch to the "machining" test - the test bar machined at both ends. As long as the bed is not worn, there shouldn't be any need for grinding. That's already been done and you are just tweaking out any slight twist that develops in the casting as it ages and stresses release. The instruction manual for my lathe - cast iron integral stand, etc - recommends the "machining" test after setting up with a level, and then rechecking over the next few months. I think the BH 600 will be second-hand (although rather newer than my lathe) so it's likely to be fairly stable by now. I would set it up with a level as close as you can get and then fine-tune by machining. I can't see any point in using self-levelling techniques as they still won't give you the ultimate accuracy although it will certainly help overcome the problems of an uneven floor when first installing.

I've just been to the smallest room where I do my best thinking and I thought, things can be relative to a datum or relative to each other.
So using gravity as the datum, a level is placed at the headstock end for example and that is brought into alignment with the ground.
Next everything else is brought into the same alignment either by making it relative to the ground or relative to the headstock. I would suggest relative to the headstock being the most accurate in this instance.
The tools required for alignment should therefore be chosen to achieve these requirements.

I think you're right, Eddy - the bed does not have to be level to micron accuracy to work OK. However, it's just easier to aim at "level" across and along it than to get to take out twist by making it the same amount off-plumb all along. As to accuracy required - and I'm thinking out loud here so no guarantee of logic! - then a bed that's as about as wide as the centre height will need to be levelled to about the same accuracy as the lathe could be expected to cut. Say, 1 thou in 12" would be pretty good. That's 1 in 12000, which is about 0.005deg. That's a pretty good level...

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Originally Posted by Neale

That's 1 in 12000, which is about 0.005deg. That's a pretty good level...

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So this level could be just the job then?

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Originally Posted by cncJim

And I found this "proper" level:-
300MM Precision Engineers Level
Accuracy 0.02mm/m (0.001°?)
£89.50
http://www.rdgtools.co.uk/cgi-bin/sh...%2ehtml#SID=63

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Looks it - could you lend it to me when you're done?

Just joking - I still think that "reasonably level" followed by a machining test is the way to go, but certainly a decent level should get you pretty close more quickly.

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Originally Posted by Neale

Looks it - could you lend it to me when you're done?

Just joking - I still think that "reasonably level" followed by a machining test is the way to go, but certainly a decent level should get you pretty close more quickly.

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I agree, i must admit though, with my inexperience I have no idea what "reasonably level" looks like! Machining test after levelling will be done - I think i will be following pretty much what the guy in the videos (that Lee shared) does.

Maybe when I get more comfortable with the machine (and actually make some cuts!)/get some experience/learn about what kind of accuracy I am happy with etc, my feelings about the process may change! :)

Cheers

Jim
(PS - Neale - If I do buy one you would be more than welcome to borrow it anytime!)

Yea, Jim hit the nail on the head it's about the lathe staying true over time, any foundation is only as good as it is level? Its counter productive to fight with inperfections if they can be mostly removed first, don't forget Tom uses those levels because he's got them and also uses them for other things.

.Me

I agree with the comments about the purpose of 'levelling' being to help maintain the accuracy of the machine by ensuring the bed isn't twisted. However I'd be careful with using the word 'level' as to me that word imply relative to the surface of the earth, which is a somewhat arbitrary reference (at least in this situation). So long as the bed isn't twisted it shouldn't really matter if it's tilted one way or the other, within reason. I guess it just happens that adjusting to 0° on your engineer's level is convenient...

Also bear in mind that if you're only ever going to be cutting fairly short parts on the lathe then you wont notice errors in diameter due to bed twist, so get it close but don't worry about it too much if you don't need it.