What is the worst case of correctable bed twist you have seen?

hsracer201 · Nov 25, 2017

What is the worst case of correctable bed twist you have seen or fixed? I moved a reasonably accurate heavy 10 across my shop by lifting it from under the bed with a forklift and now it is cutting a taper that's close to .002" per inch. :eek:

(unsupported 1" diameter aluminum sticking out 3" yields .006" taper) I don't seem to be able to remove very much of it with just the front and back leveling bolt system on the tailstock end foot. Range of adjustment ceased before the goal was reached.

Any ideas, thoughts, suggestions? The diameter is smaller at the chuck jaws and grows larger as it goes down the machine. Anyone shim under one side of the foot itself?

Thanks.

Conrad Hoffman · Nov 25, 2017

I'm pretty sure my Logan was on a crooked floor for much of its early life. The bed twist isn't quite removable before one leg picks up. I have a big cast iron angle plate suspended from one corner by a piece of welding rod. Pulls it right down and alignment is perfect. One other thing of note. If a lathe cuts a taper when the bed is straight, say more than a few tenths, investigate the alignment of the headstock. Mine has a slight built in error and I had to shim it to get it perfect. Too much effort to scrape. Twisting the bed to correct a headstock-caused taper leads to problems like uneven carriage wear. It's a bad solution save for removing the last couple tenths of taper over 6-10 inches or so.

mach2 · Nov 25, 2017

Most lathes have a headstock alignment tolerance that allows slight taper so if in a facing cut unsupported by a tailstock will cut a slight concave. A convex face cut is not acceptable.

MrWhoopee · Nov 25, 2017

Had you checked the alignment in the same manner before moving? 1 in. diameter seems small for this test.

Richard King · Nov 25, 2017

How did you move it??? Is it on a wood bench or on a factory steel cabinet? Are you sure your adjusting the screw the right way as it's easy to turn it the wrong direction if you do not have the instruction manual. I have seen machines worn really bad and we adjust that screw and twist the bed a mile it seemed.

hsracer201 · Nov 25, 2017

MrWhoopee said:
Had you checked the alignment in the same manner before moving? 1 in. diameter seems small for this test.

Yes, when I got it 3 months ago I did a similar cut and it was less than .001" off over 3". That was the extent of it as I had other projects to keep me busy until now. I moved it out of the way until recently. Now it's really out of whack.

hsracer201 · Nov 25, 2017

Richard King said:
How did you move it??? Is it on a wood bench or on a factory steel cabinet? Are you sure your adjusting the screw the right way as it's easy to turn it the wrong direction if you do not have the instruction manual. I have seen machines worn really bad and we adjust that screw and twist the bed a mile it seemed.

I gently picked it up under the bed with a forklift. It's a 4.5' model on the nicer full metal cabinet with doors.

I've run the adjustment bolts fully from front to back and it just doesn't seem like there's enough pivot to accomplish much at all. It barely moves the bubble on my machinist level a couple notches. When I get home I think I'll pull the foot off and make sure everything is free.

Richard King · Nov 25, 2017

I recall I turned it the wrong way the first time I did it. Also can't recall if there were hold down screws on each side we had to loosen first. I'm looking for the procedure Steve Watkins found online on how to do it. Steve was the host of the first Texas rebuilding class we did 4 or 5 years ago and his SB 10 was worn out.

iwananew10K · Nov 25, 2017

Probably just the sheet metal cabinet is cocked.

Loosen the adjusters on the bed foot, and get the cabinet reasonably level.

Then move to the bed foot.

Those cabinets will flex like crazy.

mach2 · Nov 25, 2017

Check the floor for level too. It could be the new location is out a different way than the original location. Concrete is notorious for being out of level.

keithmech · Nov 25, 2017

same tool,material,speed/feed?with only taking 1 cut
both times,.Lots of variables here. I would check a bit more before panic sets in.

hsracer201 · Nov 25, 2017

iwananew10K said:
Probably just the sheet metal cabinet is cocked.

Loosen the adjusters on the bed foot, and get the cabinet reasonably level.

Then move to the bed foot.

Those cabinets will flex like crazy.

All I did was break the 4 foot to cabinet bolts loose and then the foot adjuster bolts suddenly had 8x more movement. Snugged the 4 bolts back down, took a cut and it was right at .001" over 6", basically back how it was before I picked it up.

I can go to bed happy, nothing is messed up. When you suddenly turn that much taper it makes your heart sink. I never dreamed the cabinet could be that bound up. Thanks for the suggestion.

DMF_TomB · Nov 26, 2017

hsracer201 said:
What is the worst case of correctable bed twist you have seen or fixed? I moved a reasonably accurate heavy 10 across my shop by lifting it from under the bed with a forklift and now it is cutting a taper that's close to .002" per inch. (unsupported 1" diameter aluminum sticking out 3" yields .006" taper) I don't seem to be able to remove very much of it with just the front and back leveling bolt system on the tailstock end foot. Range of adjustment ceased before the goal was reached.

Any ideas, thoughts, suggestions? The diameter is smaller at the chuck jaws and grows larger as it goes down the machine. Anyone shim under one side of the foot itself?

Thanks.

normally use a precision level at tool post shim (feeler gages) til reading level then move carriage and see if level changes. Starrett 98 level is 1 division about .005/12" or .004/10" so if within 1/4 division thats within .001" per 10"
.
until you shim or level the lathe bed you have no ideal if its actually twisted
.
medium sensitive level (.005 per foot) is used for measuring shims. a too sensitive level will be off scale and useless for 99.9% of machine setting up as it will read off scale most times and not tell you what shims you need

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What is the worst case of correctable bed twist you have seen?

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