Capabilities of a 12" lathe

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RSG
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Capabilities of a 12" lathe

Post by RSG » Sat Mar 16, 2019 7:02 am

I'm unsure of the weight capabilities of my lathe so I thought I would ask the question here. As earlier discussed I am having the riser for my mill cast and I would like to dress the surfaces on my lathe instead of sending it out.

The part is 11.5" dia. x 5" deep with a wall thickness of around .65" I roughly calculate it to weigh around 45lbs.

My question - is a 12" x 36" lathe capable of holding and turning something that size realistically or should I be sending to someone with a bigger lathe.
Any advice would be appreciated.

Thanks in advance
Vision is not seeing things as they are, but as they will be.

earlgo
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Re: Capabilities of a 12" lathe

Post by earlgo » Sat Mar 16, 2019 8:34 am

That is not something I'd try on my 12"ATLAS. For one reason, the jaw depth on the 6" ATLAS 4 jaw is too shallow to grip responsibly and for another, the jaws won't open up that far.
If you are too far away from civilization, you might be able to face off and counterbore each end an inch or so deep, and then make plugs so the OD could be turned on centers to clean up. This assumes that the inside bore will not be seen or used. Keeping the counterbores aligned would take some thought but can be done.
Were I in that situation, I'd look for a buddy with a bigger lathe, or ask a local shop to do it, but then I have both available.
JMHO
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

John Hasler
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Re: Capabilities of a 12" lathe

Post by John Hasler » Sat Mar 16, 2019 11:03 am

Use a faceplate. Add features that you can drill for mounting holes if needed.

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NP317
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Re: Capabilities of a 12" lathe

Post by NP317 » Sat Mar 16, 2019 11:53 am

I would recommend a larger lathe to true the ends of your 11.5" diameter riser. Here's why:

I used my 12" Atlas lathe to turn the ends of the 8.5" diameter smokebox for my Mikado.
I had to fabricate a spider to hold the tube between centers, using the 4-jaw chuck expanded outward to hold the headstock end.
Also used back-gear for slowest speed, and freshly sharpened HSS tooling. It got the job done, but barely.
I also suggest that your tube will not clear the carriage support, leaving your tooling too far away to reach the tube edge.

It was a marginal setup, but worked for me. I now have a beefy 14-40 lathe with far greater capabilities.
I was convinced by the above described project...
~RussN
Smokebox1 small.jpg
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Richard_W
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Re: Capabilities of a 12" lathe

Post by Richard_W » Sat Mar 16, 2019 1:08 pm

Depends on which 12 lathe you have? If it fit in the lathe I would try it. If the center is hollow you may be able to give additional support with the tail stock center if needed?

If not, then a rotary table on the mill might be the place?

pete
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Re: Capabilities of a 12" lathe

Post by pete » Sat Mar 16, 2019 3:31 pm

Yep as John mentioned use the face plate if you can come up with a hole pattern in the part that matches the slot pattern in the face plate. It sounds Micky Mouse, but if I couldn't match the part hole pattern to those face plate slots I wouldn't hesitate to use even a wood lathe method and bolt the part to a couple of laminated 3/4" ply discs and using counter bores for the bolt heads and washers on the back side, then through bolt the ply to the face plate. Your only doing facing and a couple of short areas on the parts O.D. so the turning forces should be fairly light if you don't start making hogging cuts. As for the weight capabilities? Looking at what the good and of course expensive live centers are rated for as a maximum part weight then the head stock if it has the usual angular contact bearings should have no issues handling any part that physically fit's in the lathe. If the lathe had even minimal numbers based design work on it then it's built to with stand the maximum part weight plus the turning forces for anything that can fit and be turned in it.

Bolting the riser firmly to the face plate then the diameter to length ratio is fine. Being a hollow walled part it's at least possible you might see a chatter problem at some point. Cast iron will certainly help. But if it does happen? Even something like a bungee cord stretched and wrapped around the O.D. can change the harmonics enough to fix the problem. I suspect you (probably) won't see it happen since the riser is pretty short.

John Hasler
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Re: Capabilities of a 12" lathe

Post by John Hasler » Sat Mar 16, 2019 4:09 pm

Don't hesitate to drill extra holes in a faceplate. I wouldn't worry about the weight since the part is radially symmetrical. A plywood disk pressed into the center is one way to damp vibration. Even a piece of 2x4 wedged in there can help.

When I did the 8.5" base for my rotary table on my 9" Logan I used a boring bar on the O.D. I do have the advantage of a 2hp dc motor with a feedback controller so with the backgear I can get good torque down to 10 rpm.

RSG
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Re: Capabilities of a 12" lathe

Post by RSG » Sat Mar 16, 2019 9:05 pm

Thanks for the feedback guys. Good points made with some I hadn't thought of.

My face plate measures 10.5" dia. but I didn't measure the swing over the ways so it might be an issue as Russ mentions. Since the riser is so short I have to wonder if I really need to support it via the tailstock as John mentions.

Richard mentions using a rotary table, I was wondering the same thing. How about mounting it to my 8" rotary table and do it all on the mill?
Vision is not seeing things as they are, but as they will be.

Russ Hanscom
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Re: Capabilities of a 12" lathe

Post by Russ Hanscom » Sat Mar 16, 2019 10:01 pm

Support at both ends, you will be glad you did. I have done several similar objects, bolted to the faceplate at one end and some form of spider at the other end. The extra support is essential for stopping chatter.

whateg0
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Re: Capabilities of a 12" lathe

Post by whateg0 » Tue Mar 19, 2019 9:04 am

Russ Hanscom wrote:
Sat Mar 16, 2019 10:01 pm
Support at both ends, you will be glad you did. I have done several similar objects, bolted to the faceplate at one end and some form of spider at the other end. The extra support is essential for stopping chatter.
earlgo wrote:
Sat Mar 16, 2019 8:34 am
...If you are too far away from civilization, you might be able to face off and counterbore each end an inch or so deep, and then make plugs so the OD could be turned on centers to clean up. This assumes that the inside bore will not be seen or used. Keeping the counterbores aligned would take some thought but can be done...
JMHO
--earlgo
The issue I'd expect trying that on a 12" lathe is that the swing over the cross-slide is going to be substantially less than the 11.5" required.

I agree that a faceplate would be the best way forward, maybe even a sacraficial plate bolted to it. You'll only have a bit of clearance on the outside, so you may have to get creative to hold the part and still turn registration features on the inside. I might even do it in three setups, depending on how well you can hold it. First setup, to get some sort of registration that could interface with a mating surface on the faceplate and afford me a way of holding it more securely. Then, the second would turn it around to do the other end. The third would let me finish the work begun on the first setup.

Honestly, though, aside from the top and bottom surfaces being parallel, is the concentricity that critical? I would think not. It's not like, in use, one would rotate the ram and expect it to be in some pre-expected location, right? So, once it's locked down facing whichever direction, the work would be re-indicated in. So, the only two things I think I would really concern myself with are the top and bottom being parallel, and being able to bolt it together.

Dave

RSG
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Re: Capabilities of a 12" lathe

Post by RSG » Tue Mar 19, 2019 11:00 am

Whateg0,

Regarding your thoughts on the swing. I did some checking and found I can't do it on my lathe no matter how creative I get. I didn't figure I could get the cross-slide under it so I thought about maybe using a boring bar to finish the sides but even then I can't get the tooling out far enough.

I've resolved to taking it to my friends place where he has a 14" x 40"
Vision is not seeing things as they are, but as they will be.

whateg0
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Re: Capabilities of a 12" lathe

Post by whateg0 » Tue Mar 19, 2019 11:38 am

RSG wrote:
Tue Mar 19, 2019 11:00 am
Whateg0,

Regarding your thoughts on the swing. I did some checking and found I can't do it on my lathe no matter how creative I get. I didn't figure I could get the cross-slide under it so I thought about maybe using a boring bar to finish the sides but even then I can't get the tooling out far enough.

I've resolved to taking it to my friends place where he has a 14" x 40"
That's a good idea. I have at times had to get creative with how the tool post and tooling is situated on the compound. On my old lathe, I have even removed the compound at times, to both gain clearance, and allow attachment of the tool at an odd angle to reach back to the work.

Dave

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