How to install the app on iOS

Follow along with the video below to see how to install our site as a web app on your home screen.

Note: This feature may not be available in some browsers.

What's new
What's new

# OT - How big can a lathe swing?

• 29
• 1,082

#### GregSY

##### Diamond
I read this on another site and I am not sure what it means, but I can only suspect it is referring to a horizontal lathe, not vertical.

"The theoretical limit of a lathe is only limited by the Earth’s curve; a flat line of about 3.1 miles (5 km), after which point the lathe would be unable to do its job: making symmetrical changes to a rotating object.

After reading it a few times...it still doesn't make sense to me. If I made a lathe with a 40 mile swing, why couldn't I machine a disc that was 39.9 miles in daimeter?

Beats me, in theory. In practicality, maybe that swing is where there's some material breakdown that occurs?

Without doing any calculations, I'm suspecting that the midpoint of a 5 kilometer distance is where the arc and chord are separated far enough to unacceptably perturb the desired cylindrical surface of the workpiece.

If that is the concern, though, compensatory curvature of the lathe bed could be built into the lathe mechanically, a "rising and falling" toolpost could be used to compensate, or software compensation used if the lathe is CNC equipped.

No matter how big the lathe, the item you're trying to spin is always a bit too large.

That disc brake rotor you're cleaning up off your poor old mom's car to help her out would be 3.1 miles and 1/4", wouldn't it?

After reading it a few times...it still doesn't make sense to me. If I made a lathe with a 40 mile swing, why couldn't I machine a disc that was 39.9 miles in daimeter?
I agree it does not make sense, I dont see how the earths curve would have any effect on the swing. It could be a disc as tall as the moon and what would the earth curve have to do with it. Length on the other hand would become a problem when the curve of the earth started to effect the lathe straightness.
My2¢

If the earths curvature is limiting the size of your lathe then put your lathe out in space.

Simple problems require simple solutions

They are referring to the length of the lathe not the swing. So in an extreme case if you made a lathe that was 24,000 miles long (the circumference of the earth at the equator) the tail stock would be on your left the same as the head stock and if turning a shaft that length it would look straight but would actually be a circle. So a lathe three miles long is the theoretical limit before the lathe bed is no longer flat.

Now if the flat earth people are ever proven correct, problem solved!

I believe the two vertical towers of the golden gate bridge are about 6 inches further apart at the top then at the bottom. They are vertical, not parallel. Bill D

They are referring to the length of the lathe not the swing. So in an extreme case if you made a lathe that was 24,000 miles long (the circumference of the earth at the equator) the tail stock would be on your left the same as the head stock and if turning a shaft that length it would look straight but would actually be a circle. So a lathe three miles long is the theoretical limit before the lathe bed is no longer flat.

Now if the flat earth people are ever proven correct, problem solved!
What would a flat earther say the limit on length to be? Also 24k miles?
I know a guy who is a flat earther, maybe I should dial him up and ask....Or not, that is a big
can of worms with that dude...

Back before GPS, they used lasers for leveling fields, you had to move the tower every 1000 feet or you would create “dishes”. When the field was flooded, the water would conform to the curvature of the earth. But the ground being flat would result in the water being a couple inches deeper in the middle. Like the first slice off a tomato, thick in the middle and thin all around.

This would suggest that you will not even make it 1/4 mile before you start running into trouble

I still don't get it. If it is length, well....here is my Lathe o' Da World. 100,000 foot bed length. It has strong supports that are anchored in the USA, China, and California. Why wouldn't it work?

#### Attachments

• LODW.jpg
722.9 KB · Views: 25
I still don't get it. If it is length, well....here is my Lathe o' Da World. 100,000 foot bed length. It has strong supports that are anchored in the USA, China, and California. Why wouldn't it work?
You must believe in perpetual motion machines, don't you ?

-D

Last edited:
The earth is curved??

ToolCat

You must believe in perpetual motion machines, don't you ?

-D
That doesn't do anything in explaining why my Lathe o' Da World wouldn't work just fine. Perpetual motion? Of course not - there are rational explanations in place as to why that won't work. So tell us why the lathe won't work.

Not sure is my unanimous answer!, however what I know, the millwrights and surveyors had to compensate for a really long lathe, there was autocolimeters lasers and total stations all over the place, can’t imagine it was much but it was a thing, think the bed modules were out at 70’ or more.
They often compensated for earth diameter on the rolling mills, over a mile it was quite a chunk.
Someone wrote in the dirt on the surveyors van “ flat earth society, and put a tinfoil hat over thier amber flashing beacon, funny
Mark

It seems to me that as long as you compensated for curvature, there would be no reason you couldn't make a lathe as long as you wanted. A straight line exists independently of the Earth's curvature. You could make a lathe floating in outer space and it would work fine, as long as you kept it straight and, or course, tethered it to the Starship so it would have something to counteract the rotational torque.

Too much Shiner bro.
So you mean talking politics and religion is forbidden
but this stuff is not ?
Next you are going to tell me some BS like the lathe
has to be level so gravity pulls on it all the same way.

-D

You just haven't been the same ever since your fear of guns and love of drugs was exposed....try to stay in your own lane.

I still don't get it. If it is length, well....here is my Lathe o' Da World. 100,000 foot bed length. It has strong supports that are anchored in the USA, China, and California. Why wouldn't it work?

I think they're assuming the legs/cabinet of the lathe are perpendicular to the ways, and not angled to account for curvature of the earth.

It's a really stupid thought experiment.

Teachme I think it can be better described as a thoughtless experiment.
Bill D

Replies
377
Views
13K
Replies
129
Views
8K
Replies
24
Views
2K
Replies
10
Views
645
Replies
63
Views
3K