DIY lathe design question

[MontanaLon]

I think it is a matter of compromises. If you were to design the ideal lathe, you would want rigidity in buckets. Think about having a need to make 1 part a million times. You could and likely would design a machine dedicated to that single part. Let's say that part is a bolt and for the sake of the exercise, that you couldn't make the bolt any other way. It would need so much power and any extra would be wasted. It would need a lot of rigidity so it would be heavily built. Ideally, the tool holder would be mounted with the range of motion needed to create the piece and all other aspects of it would be built for rigidity and nothing else. It would likely be mounted in a far more rigid fashion than resting on rails with a piece of iron bolted onto the bottom acting to keep it from moving in any direction but that required to complete the part.

You would likely end up with a machine that is recognizable as a lathe only vaguely. But it really would be a lathe at heart.

Now imagine you need to build a different part. Larger, smaller, even with a different thread pitch. You would need a whole new machine to do it. For someone making a million of the same thing, a new dedicated machine might make sense.

But if you aren't making a million of anything and need to make all sorts of parts using the same machine then you start making compromises. Bigger, smaller, etc. Everything is a trade off.

 

[savarin]

and dont forget there are slant bed lathes and vertical lathes.
My vertical lathe was the drill press using hand held tools.
It worked for aluminium.

 

[Choiliefan]

The c1916 book "Lathe Design - construction and operation" by Oscar Perrigo goes into it pretty well.
Perrigo knew his stuff.
A quick search came up with a pdf: https://archive.org/details/lathedesignconst00perrrich/page/n6
The chapter on bed/way construction starts on page 69.

 

[Stefants]

The c1916 book "Lathe Design - construction and operation" by Oscar Perrigo goes into it pretty well.
Perrigo knew his stuff.
A quick search came up with a pdf: https://archive.org/details/lathedesignconst00perrrich/page/n6
The chapter on bed/way construction starts on page 69.

Yes, that book seems pretty solid. The symmetric diagram I originally posted was from p77. But I didn’t see any reference there to anything other than symmetric being preferred in general as a matter of “strength, rigidity, and stability.” I’d love an explanation to go with the assertion.

 

[Choiliefan]

IIRC some 60's LeBlond sales literature has a diagram and some blurb as to why they changed the front angle for a deeper bearing surface.
Will post if I can find it.

 

[Choiliefan]

c1958 Leblond catalog:


http://www.vintagemachinery.org/pubs/2102/16487.pdf

 

[hman]

My vertical lathe was the drill press using hand held tools. It worked for aluminium.

My first "lathe" was a drill press and a Dremel grinder.

PS to Stefants - I'd offer a SWAG to the effect that symmetrical (spindle centered over bed ways) lathes are largely a matter of design simplification. As long as the front bed way is strong enough to withstand the anticipated cutting forces, the rear way can be placed wherever it's easy (simple) to do so. And of course, there's the added factor that many (most?) lathes have an inverted V way in front and a flat way on the rear, unlike the first diagram you included. I can see where the inverted V helps prevent the carriage from moving sideways (toward the operator) under cutting forces. And having a flat rear way reduces the need for precise location (and therefore expense) that twin Vs would require.

I'm definitely not a tool designer. But I find this whole discussion very interesting. Thanks for bringing it up!

 

[francist]

My first "lathe" was a drill press and a Dremel grinder.

Luxury! Here's "my" first lathe.....



Powered off an old clothesline pulley hanging from the ceiling and a length of cord around the workpiece.....
One hand pulled the cord, the other hand hand the chisel. Some dexterity was required!

 

[hman]

Almost a classic "tree" lathe! Love it!

 

[savarin]

Sheer luxury, we ad ta tie part ta wagon wheel an run along wi chisel ta make tha cut.