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Choosing Metal Lathe for Peculiar Purpose

tlgrimmy

Plastic
Joined
Sep 18, 2020
Good morning everybody! I have virtually no experience in the metal lathe department, though I do have a cross slide on my wood lathe and I understand the basic premise. I have quite a bit of experience in the woodworking department, however, and I am tooling up to make open back banjos more efficiently. Currently, I turn wood banjo rims on a wood lathe with a cross slide set up. It works reasonably well, but nearly every one of the banjo makers I have researched eventually converts to a metal lathe for this purpose. The added rigidity, cut quality, and ease of mounting to those larger chucks is really worth the switch.

I will also eventually be aiming to use the metal lathe to turn or true up brass tone rings, and potentially other round hardware involved in banjo rims. I really like 12" banjo rims, which require starting with 12.25" rim blanks, so probably a 13" swing would be the minimum size metal lathe for me to consider. I also don't need much distance between centers, so if I luck out and find a shorter bed lathe with a large swing, that would be ideal. I probably don't need to be spending $5k+ on a new or extremely high quality used lathe since I'm guessing wood and brass aren't exactly going to tax the capabilities of such a large lathe, however, I do want it to be accurate and have good cut quality to avoid excessive handwork after turning the part.

I thought I'd see what those of you with far more experience than me would recommend. I've heard of folks going with large older model lathes for great deals, newer Chinese and Taiwanese lathes, and some going the combo mill/lathe route, despite the shortcomings, due to the large swing in a small package that's often available.

Some options I've found so far:

Logan Lathe 14" - LOGAN LATHE - tools - by owner - sale

Dashin Prince 13" - 13''x40 metal lathe - tools - by owner - sale

Grizzly combo lathe / mill (would probably try for used) - Shop Tools and Machinery at Grizzly.com
 
GEt in front of one that you think will be big enough, with a part.

You may find you want a larger swing to be able to actually do work on a part very near the swing diamter

not that you need one as heavy as one with that swing would be
 
Seconded. Given your work envelope, I imagine you’ll wind up needing a much bigger lathe. Something in the 15-20” range to hold a 12”+/- part comfortable. You have to take into account the chuck jaws and their clearance to the lathe bed. Alternatively, you might be the perfect candidate for a smaller gap-bed machine. I’m not entirely sure what a banjo rim is... 12” seems too small to be the body of the instrument. Even still a lathe with the gap removed may still not be enough.

I may get harped on for this, but I would rather not chuck anything up bigger than the OD of my chuck. Meaning if 12.5” is the max stock size you can probably get away with that with a 12” chuck, but I wouldn’t go any bigger in diameter. 13” lathes don’t generally come with 12” chucks though. A 15” lathe MAY...

Lastly, as your purpose for initially buying the machine is solely for your banjo work, think about the speeds you’ll need to accommodate the materials you’ll likely use.

I hate to say it, but too many more restrictions and you’re gonna find yourself fully in “unicorn” territory. It seems to me you’re looking for no less than a 14-15” swing machine, that spins at least 1500 RPM. Your saving grace may or may not be bed length... I honestly don’t know if a lathe of that size will be easier or harder to find in a short bed length.



Best of luck.




Be safe and stay healthy




Jeremy
 
Thanks! I've heard they aren't all that great, but wasn't sure how they'd handle the wood and soft metals. Good to know.

To tie it woodworking, using a Grizzly anything is like trying to use any other Harbor Freight or similar cutting tool and expecting good results. Careful as even discussion of those is not always permitted here.

As for the combo machines, those are akin to a Shop Smith in the woodworking world. If you think a Shop Smith makes a nice wood lathe and a nice drill press then you might be ok with a combo machine, but I'm not a fan. I've used some "nicer" combo machines, and found them to be less functional than even a beat up/worn out nicer machine with a lot of years on it.

Often over-priced due to popularity, but older South Bend 10L and similar lathes, while not a highly solid metalworking machine, do have a decent reputation for lighter work. IMO they are an order of magnitude better than today's green imports. Aim for something of at least that quality, but in a size envelope appropriate for your work.
 
Is this one of those rare circumstances where a riser block under the headstock and on the toolpost is actually appropriate?
Smooth controlled slides are desirable, but high cutting forces are not present. Lots of diameter needed, but not length.
 
Is this one of those rare circumstances where a riser block under the headstock and on the toolpost is actually appropriate?
Smooth controlled slides are desirable, but high cutting forces are not present. Lots of diameter needed, but not length.

I was wondering the same thing, op might even be able to add some riser blocks to his existing lathe, although he did not mention its size.
 
Going in a suboptimal direction, here. Large-swing lathes are big and heavy and power-hungry in places where you don't need them to exist nor eat at all.

WHEN.. you know in advance that the work will ALWAYS be (relatively) large diameter, and (VERY!) short on-axis..?

A conventional lathe is not what you need.

The whole "infrastucture" is optimized for a different purpose altogether.
You do not need a "bed", for example.

"Back in the day" this is what a "Tee" lathe was built for. They just do not happen to have ever been common.

So, too, vertical turning lathes. Better-yet, their modern "VMC" equivalent of the CNC tribe.

Cheap seats? A modified horizontal mill.

Yes, it would want some "frankenstein' adaptation.
Just not very much of it.

No, that is none of dificult, costly, damaging to its original purpose, hard to undo, confusing to set up or utilize, nor high-maintenance, going forward.

Dead-easy, rather.

Trivially low cost. TINY floorspace. Low mass to transport. Small power budget.

Close operator access for ease of set-up and ready access to controls.

Been done. Lots of times.

Some examples can be found "right here, on PM"

2CW
 
Is there a shortage of banjo's ?
How many Banjo's does the world (as we know it) really need ?
 
GEt in front of one that you think will be big enough, with a part.

You may find you want a larger swing to be able to actually do work on a part very near the swing diamter

not that you need one as heavy as one with that swing would be

Yeah, I'm thinking I'll bring a rim mounted to a makeshift wooden faceplate with a recess that the lathe chuck could expand out into to see how the clearances look. I feel ya, I'm a bit concerned a larger swing may be necessary.
 
As noted by others, a 12" swing lathe turning something 12" dia. is not a happy situation. You really need to be a 14" or more, and if it was me, I'd want 16" minimum.
 
Seconded. Given your work envelope, I imagine you’ll wind up needing a much bigger lathe. Something in the 15-20” range to hold a 12”+/- part comfortable. You have to take into account the chuck jaws and their clearance to the lathe bed. Alternatively, you might be the perfect candidate for a smaller gap-bed machine. I’m not entirely sure what a banjo rim is... 12” seems too small to be the body of the instrument. Even still a lathe with the gap removed may still not be enough.

I may get harped on for this, but I would rather not chuck anything up bigger than the OD of my chuck. Meaning if 12.5” is the max stock size you can probably get away with that with a 12” chuck, but I wouldn’t go any bigger in diameter. 13” lathes don’t generally come with 12” chucks though. A 15” lathe MAY...

Lastly, as your purpose for initially buying the machine is solely for your banjo work, think about the speeds you’ll need to accommodate the materials you’ll likely use.

I hate to say it, but too many more restrictions and you’re gonna find yourself fully in “unicorn” territory. It seems to me you’re looking for no less than a 14-15” swing machine, that spins at least 1500 RPM. Your saving grace may or may not be bed length... I honestly don’t know if a lathe of that size will be easier or harder to find in a short bed length.



Best of luck.




Be safe and stay healthy




Jeremy

Thanks! Yeah, at first I was just thinking of machining the OD with a chuck using specialty DIY cauls expanded outward to secure to the inside of the banjo rim, but I will end up needing to machine the ID as well, and even with creative fixturing, there's still going to be some of the cauls/chuck extending beyond the banjo rim, so a gap bed really would be necessary...dang! Fortunately, I'm turning them right now on my 12" wood lathe at just 400 rpm with the cross slide, so low speeds ought to be fine. The surface speed at 12" diameter at just 400 rpm is actually scooting along pretty quickly.
 
GEt in front of one that you think will be big enough, with a part.

You may find you want a larger swing to be able to actually do work on a part very near the swing diamter

not that you need one as heavy as one with that swing would be

Definitely starting to look that way. Thanks!
 








 
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