On Tue, 8 Aug 2017 05:45:19 -0000 (UTC), bob prohaska
wrote:

Phil Kangas wrote:

My South Bend 9" Model A is on a similar table but I put a
sheet of 3/16 5086 aluminum plate between the lathe and
the table top. It makes for a brighter work area and is not
affected by swarf and cutting oil. And is easy to clean too.
phil k.


Metal is neat, but it's expensive. And, it's not clear to me that
the greater stiffness is helpful; that's somewhat the question I'm
trying to pose: The lathe was manufactured straight and true. Is it
not better to let the lathe assume its natural shape, rather than
forcibly bolt it to something most likely of contours different from
those supporting it while it was made?

Metal, in particular has a high mechanical Q, so if the lathe is
inclined to chatter a metal plate won't provide much, or any, dissipation.

I do appreciate the value of rigid mounting to help convey acoustic
energy out of a structure; bolting a lathe down keeps it from ringing
like a bell, at the price of deflection or painstaking alignment. One
can also muffle a bell with a soft cushion, I think with less deflection.

Do you observe any particular tendency of the metal plate under your
lathe to vibrate (I realize it's a hard comparison to make...)

Thanks for writing!

bob prohaska
No matter how straight your lathe was when made it will twist some
when set on a surface that is not true. Then, if fastened down, it
will deform more. No matter what surface you are going to attach it to
the lathe will need to be leveled in order for it to cut straight. On
a wood desk it will change over time with temperature and humidity. So
bolt it to the desk top. Adding the 1/2" sheet of plywood won't
increase the stiffness of the mounting unless it is fastened to the
desk top in such a way as to be essentially part of the desk top.
Gluing it down properly would do this. Then the amount of stiffness
will be increased much more because the stifness goes up by the cube
of the thickness. In other words, a benchtop twice as thick is 8 times
as stiff.
Eric