RE: [CAD_CAM_EDM_DRO] thermal expansion

There are quite a number of machines which run hollow columns and flood them
with fluid. It can be pumped throughout the machine and controlled with a
small thermostatic heater. An easy way to solve frame motion. Ball screw
growth is different, but big machines will normally stretch them which
reduces much of the thermal growth factor. I think you need a pretty beefy
frame to provide any significant tension on the ball screw.

Greg

-----Original Message-----
From: Les Watts [mailto:leswatts@...]
Sent: Monday, January 27, 2003 5:06 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] thermal expansion

Of common materials silica glass and fused quartz have low thermal
coeficients. Quartz is about 25 times lower than steel and 50 times
lower than aluminum.

There are many exotic materials that have essentially ZERO thermal
coefficient. Many are ceramics that combine materials such that one
shrinks with heat and the other expands. Aluminum titanate is an example...
it is used in automotive turbochargers.

It is an issue with tools like my large cnc gantry router... if the heat
is off in the winter it shrinks about 25 thousandths in length!!
One of these days I need to get EMC to perform thermal compensation.
I think it is already there somewhere in the code. In the meantime I
will just have to keep the shop nice and comfy just like when I calibrated
it.

Les


Les
Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.alltel.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.alltel.net/~leswatts/shop.html
Surplus cnc for sale:
http://www.alltel.net/~leswatts/forsale.html

----- Original Message -----
From: "Elliot Burke" <elliot@...>
To: "CAD_CAM_EDM_DRO" <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, January 27, 2003 2:06 PM
Subject: [CAD_CAM_EDM_DRO] re:Re: Re: vibration damping materials


> the esteemed Les Watts writes:
>
> >I would like to recommend Dr. Slocums book "Precision Machine Design".
> >It's pretty much the bible on designing machine tools, and it has
sections
> >on viscous and inertial damping of them. It belongs in the library
> >of anyone building such things. In general it has very little math, but
the
> >sections on damping have a lot, although it is not difficult. It can
> explain
> >such things better that I can in a short post.
>
> thanks for the tip. I just ordered this book on Amazon and hope to learn
> from it in a few days.
>
> A new project involves holding relative positions of components to better
> than 100 nm while a large boom is happening nearby. Frankly, I had no
idea
> how to do this in anything other than a brute force way.
>
> Do you know of resources on ultra stable materials? Telescope mirror
makers
> have worked on this problem quite a bit, I wonder if there are others with
> similar needs and analytic skills?
>
> Telescope makers like glass/ceramic materials. Fabrication of this stuff
is
> no picnic. It would be interesting to see how cast iron and granite
compare
> in stability, both thermal and in the various elastic and inelastic
> deformations.
>
> There was a mirror maker a few years ago (don't know if they are still
> around) who made mirrors by sandwiching short lengths of borosilicate
glass
> tubing packed tightly between sheets of the same borosilicate glass. When
> heated, soft glass tubing expanded to make hexagons and fused to the face
> plates. The internal pressure in the hexagons kept the faceplates from
> sagging (much). The air between the glass tubes escaped through properly
> spaced holes. This made a very light stiff mirror. Expansion was rather
> high compared to some of the better materials though.
>
> regards-
> Elliot B.
>
>
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