Re: question about ways vs. shafting

Rick,

You will find both dovetail and box ways used on heavy duty machines,
made of cast parts as you have noticed. BUT....

You will also find many modern heavy duty machines with some version
of the "linear bearing" (shafts and bearing blocks) approach. Where
thomson round shafting and linear bearings used to dominate the motion
industry; improved manufacturing processes have given us the rise of
the "ground track" (thk type) linear bearing, which has a much higher
stiffness and load carrying capbility than was possible with the round
rails.

And therein lies your answer. Don't forget that when you are looking
at machines, you are likely looking at MANY stages of their
"evolution". So you see cast iron or steel dovetails or box ways on a
certain class of machine which is now made with linear rails...

During each "era", the "correct" choice was "slanted" toward some
accepted "ideal". The important thing is to notice that these "ideals"
are in a state of constant change.

Hope this helps.

Ballendo

P.S. Economics is ALWAYS a factor in manufacturing...

--- In CAD_CAM_EDM_DRO@y..., "Rick Miller" <apollo@a...> wrote:
> Hello,
> I'm relatively new to this forum and am laying out ideas for
building my own machine (CNC mill). My first thought in designing this
machine was to support travel of all axes on steel shafting, with
beaings & pillow blocks on the necessary parts. As I look at the
construction of larger CNC's, I see that they are all constructed by
means of ways (I believe this is the term for the 'dovetailed' slide)
rather than the shaft/bearing arrangement I have just described. Which
method is preferable, from an accuracy standpoint?
> I am inclined to believe the latter must be, as it is used on
the big machines and I can't imagine economics being a factor in those
large expensive things. Please correct me if I am wrong, and if anyone
would care to give me a brief explanation of this I would greatly
appreciate it.
>
> Thanks,
> Rick
>
>
> [Non-text portions of this message have been removed]