lathe bed sagging?

[yorgatron]

OK first off,all you guys who don't like Atlas lathes can spare me the whole "you oughtta get a real lathe blah blah blah" it ain't in the budget,besides which,my dad bought it new in 1954,so it has sentimental value as well.i've leveled the thing as best i can with my torpedo level.i'm trying to find a good level on ebay,would the cross-test no.134 be good for this? anyhow,i checked the bed with my 16" straightedge,the one i normally use for checking cyl.heads and main bores,and it seems to only contact the ends,with enough bow to slip a cigarette paper (Rizla @ .001 thickness,i roll my own with American Spirit) underneath.it does this just about anywhere i put the straightedge,near the headstock or near the tailstock end.there doesn't seem to be enough wear on the ways to account for this,and it makes me wonder if the bed itself could use a screw-jack under the middle to support it.it's the 54" bed,which translates to 36" between the centers,and it's mounted on a thick hardwood plank and cast iron legs that are both from the factory.thanks in advance for any help-george

[JCHannum]

In the first place, there is nothing wrong with an Atlas lathe. Yours is reasonably new, not being 50 years old yet. Does it have quick change gears? If so, so much the better.
A torpedo level is better than nothing, and better than the Starett No. 34. A good precision level such as the No. 98, minimum of 6" is what you should be using. The longer, the better.
With that said, how does your lathe perform? Are you having trouble with accuracy? What do you expect to get from the lathe?
0.001" is not bad for most work, depending on what you are trying to do. For the most part, you will be turning an inch or so to a diameter, and will not see the problem. Go ahead and use the lathe, and enjoy it until problems become apparent, then you can define them, and implement a solution. Jacking up the middle of the bed is likely to create more problems than it solves.

[Oso]

I think there is something on the Atlas part of the Clausing site about using shims to remove bow like that.

If it is bow, that is. If you were resting the straightedge entirely on unworn areas, 0.001 might be bow. But if you were on the carriage contact area in the middle and unworn parts at the headstock end, 0.001 is probably wear, and not bad at that.

Atlas are fine. On the light side, but fine.

[crypto]

Hi George,

My first lathe was an Atlas just like yours. I agree with Oso and JC it is a good lathe. Mine, a very well worn lathe, also came with the factory legs and wood top. I owned it for several years and it never occurred to me to check the bed for warp, I was just happy to have a lathe that performed as well as it did and keep in mind that at work I used EE Monarchs and toolroom quality lathes.

I most certainly agree with JC's opinion that jacking up the middle of the base could create more problems for you.

You could check the base for levelness and your floor for flatness perhaps a shim or two is needed. But I wouldn't bother with that small amount of sag. It just means that on a long, long cut your toolbit would drop 0.001" below center, (heck, normal wear could equal that).

[nheng]

George: As long as your front and rear ways have the same drop, your diameter error (from the 0.001 drop) is down in the 6th decimal place !
Den

[woodnmetalguy]

Just a thought - could there be a bow (high center) in the straightedge you're using? If that were the case you would see the 'sag' in all areas when measuring a perfectly flat surface. -- Dave

[yorgatron]

those are certainly some things to think about.granted,i may never need to do anything more accurate than .001,but it would be nice to know i could if i had to.there's no guarantee that my straightedge is really straight either,until i can find somebody with a surface plate i can check it on.i'm just worried that if i don't figure out what i'm doing wrong,it'll sag even more.for now i've taken to moving the tailstock and carriage as far as i can to the right hand side when i'm not using it,there was a time when this was in storage for about6 years,and they were parked in the middle of the bed,i'm thinking that may have caused the sag.oh well,i'm gonna go check the archives some more for this subject,there's 114 pages i have to go through!-george

[JCHannum]

Using a straight edge as you have described is not really capable of measuring to 0.001" anyway.
As Den has stated, if your bed does sag 0.001", any inaccuracy will probably be in the range of 0.000005" or less. Doubt that would present much of a problem.

[Evan]

George,

Leaving the carriage in the middle isn't going to make it sag permanently. The weight of the carriage is nowhere near enough to exceed the elastic limit of the metal and produce deformation. It will "sag" ever so slightly due to the weight but when the weight is moved/removed that sag goes away. Below the elastic limit metal acts as a spring and storing the carriage to the right won't make the slightest difference except for the additional wear from always putting it there.