Square or Round?

Hello, All!
Please correct me if I don't get the terms right, English is not my first language!
On a vertical mill, which is the preferred shape of the moving Z-axis
"collumn?" - square / rectangular or round and why?
Your input will be appreciated
With best regards, mweb. E-mail: snipped-for-privacy@home.com
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====================Everything else being equal, a square or rectangular column will tend to maintain better alignment in the x-y plane than a round column as the head is moved up and down, for example to allow tool changes.
That being said, note that a well built and aligned machine with a round column with key may well maintain better alignment during head movement than a cheaper [less rigid] machine with a square/rectangular column that is not accuratly machined and square to the table [x-y] plane.
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Too vague in your description. Is the entire column on linear rails, box ways or other moveable members, or is it a fixed column with a moveable quill within the housing?
--
Anthony

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Hello, Anthony! You wrote on Tue, 04 Jul 2006 17:19:42 GMT:
??>> Hello, All! ??>> ??>> Please correct me if I don't get the terms right, English is not my ??>> first language! ??>> ??>> On a vertical mill, which is the preferred shape of the moving Z-axis ??>> "collumn?" - square / rectangular or round and why? ??>> ??>> Your input will be appreciated ??>> A> Too vague in your description. Is the entire column on linear rails, A> box ways or other moveable members, or is it a fixed column with a A> moveable quill within the housing?
Basically a square or round fixed cast iron housing with a quill moving up/down. Spindle motor inside this quill.
Quill is aligned within the cast iron housing by 8 adjustable preciscion bearings. What concerns me is resistance to torsion and vibration, but I guess the bearing system will determine most of that.
From what has been answered so far it seems pretty 50/50. I would prefer a round quill for ease of machining.
You've probably guessed that I'm constructing a cnc mill.
With best regards, mweb. E-mail: snipped-for-privacy@home.com
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Most of what I have seen of the good mills out there that have a fixed- height table, have a moveable column for the Z axis. There is no quill per `se. The spindle, spindle motor, etc are contained within this column casting. The whole casting moves on ways (linear or box). To me, this would be the sensible way to go, as you get more mass damping to the tool.
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Anthony

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