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Fourth Axis Vs Lathe

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Chris H

Steel
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#1
I'm looking at the charter oak cnc machine, and debating the purchase of the 4th axis rotab they have vs purchasing a stand alone lathe. I'm well aware that the rotab isn't designed to be a lathe replacement, but that it can be is intriguing.

My main use for the mill and lathe is to make parts for motorcycles (and some cars), more functional parts than cosmetic doo-dads. I don't know that I would have a large use for a lathe, but I know there would be times when it would be nice. The trouble is, does "nice" justify the shop space for a machine that will sit covered most of the time, to say nothing of the cost. So, if the 4th axis is a viable small piece alternative, I could purchase it with the lathe money, save some actual dollars, and save a large footprint of space.

How good a surface can the rotab produce? How difficult is it to set up and remove off the table, with the tailstock? Other than the size limitations of the workspace, what other functional limitations are there of the rotab vs a dedicated lathe?
 

ch2co

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#2
I'm not familiar with the Rotab name. Just looked it up, and it looks like they have several types of good looking rotary tables, Which model were you thinking of? I would think that one of these would
benefit any milling machine that it would fit. BUT replacing a lathe with one seems over ambitious to me, but then thats just an newbe old man talking. I'd love to have one of these, but as a replacement to my lathe? I highly doubt it.

Chuck the grumpy old guy
 

Chris H

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#3
I'm not familiar with the Rotab name. Just looked it up, and it looks like they have several types of good looking rotary tables, Which model were you thinking of? I would think that one of these would
benefit any milling machine that it would fit. BUT replacing a lathe with one seems over ambitious to me, but then thats just an newbe old man talking. I'd love to have one of these, but as a replacement to my lathe? I highly doubt it.

Chuck the grumpy old guy
No, I'm not meaning a "Rotab" brand, just using the name like Xerox or Kleenex as shorthand for a rotary table. Sorry for the confusion.
 

RJSakowski

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#4
I have both rotary tables (8" and 12") and lathes. When I bought my Tormach, I bought the RT because I wanted 4th axis capability. I have used the 8" RT twice since 2011 and the 12" RT less than a half dozen times. In the same amount of time, I have used my lathes dozens if not hundreds of times.

Machining on a lathe can be inherently less expensive since tooling can be reground many times with a modest amount of equipment. It is somewhat limited to working in the round (some limited amount of milling can be done with a milling attachment). An RT equipped mill could not make a tapered shaft very well while this is a simple task for a lathe.

On the other hand, with a manual mill and a rotary table you can make all kinds of complex parts. Add CNC capability and the degree of complexity can be increased tremendously. Bottom line, it depends on what your projects are like. Personally, I would not want to give up my mill or my lathe but I could live without the RT.

Bob
 

David VanNorman

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#5
A rotary table does not a lathe make. I would have a lathe first . You can do more things on a lathe than you think.
 

Tony Wells

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#6
There is no valid comparison between the two, and one cannot substitute for the other except in extremely limited applicatons.
 

barnbwt

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#7
The real question, is whether you're making mostly round parts with a few flat features, or blocky parts with a few round features?

All but highly-optimized turning centers that barely qualify as 'lathes' won't do as great a job milling, simply due to the cantilevered part, but it isn't as big an issue since the spinning parts that can fit in a lathe chuck won't ever be big enough to require heavy fly-cutting or other powerful milling maneuvers. Likewise, I could see you driving yourself batty & burning out your 4th axis trying to get as good a turned surface finish as a lathe from an interrupted cutter like an endmill.

So the real question is which type of feature is more common, or more critical, for the parts you want to make?

TCB

"You can do more things on a lathe than you think."
Yeah, like realize how many mill-features you can't do for the parts you want to make. The inverse is also true for mills. You really do need both, at least in some capacity.
 

westsailpat

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#8
Bite the bullet and get both , or get the mill with fourth or semi fourth and save up and get a lathe . Once you get the lathe you will wonder how you got along with out it .
A little story (sorta' on topic) a long while back my best bud RonDog Gross-man asked if I wanted to go see his friends machine shop , well the friend turned out to be Sonny Bryant yes that Sonny of drag racing fame and crank shaft manufacturing . Sonny's machines were massive lathes and here is the interesting part he had them set up as milling centers . He held the crank billet in the lathe chuck and tail stock and the milling was done with live tooling . The only mill he had was a horizontal that was used used to center drill the billet .
 
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