re:Termites, tree, box ways

John H writes:
I took a look at the pictures of the Tree mill, that is one mongo piece of
iron, any clues as to the weight? Is there any major advantage of box ways
over dovetails? I saw on the Beaver mill I am looking at they use one
slightly raised ridge as one the ways on the x axis and then the other is
much higher. Is this idea to limit the amount of delicate cutting needed
with dovetail mills? I was thinking perhaps the more substantial raised way
is used to carry the load and the other is just a guide. Are the designs
actually based on any physical properties of how they'll behave or is it
more just how they can be bothered making them?


There is quite a literature regarding the design of machine tool ways. One
good one is
Design Principles of Metal-Cutting Machine Tools, by F. Koenigsberger, 1964.
There are sure to be other similar books. This one I found in the local
university library.
It goes into great mathmatical detail about the relative merits of various
sorts of ways, cutting forces, stiffness, spindles, and so on.

Another good book is Foundations of Ultraprecision Mechanism Design, by
Smith & Chetwynd, 1992. This books takes machine design, including ways, to
a level of precision sufficient to get nanometer precision.

So, the machine tool designer has available mathmatical tools to optimize
the design of ways. Does he use them, or just copy what everyone else is
doing?

There is also quite a literature on bearings in addition to what is in the
above book, such as Hydrostatic Bearings, 1970, and Ball and Roller
Bearings, Eschmann, Hasbargen, Weigand, 1985.

I've had some fun making linear air bearings, but certainly nothing stiff
enough to be used for machining. Getting friction very low while
maintaining stiffness is quite a trick. None of the books seem to have a
really universal solution.


Elliot B