On Mon, 29 Oct 2007 20:54:19 -0400, Bill Schwab
wrote:
snip
should be] locked when using the RT, x/y back lash should have no
effect if you are using a test indicator.
I must respectfully disagree. I need to move the mill table to get away
from the axis, and I need to understand the backlash in order to make
use of the dials. Please set me straight if I'm spouting nonsense.
snip
No nonsense, just the use of the dials. I suggest moving the
table bases on the movement of the test indicator movement and
not the table dials for exactly this reason. When you do this
any backlash affect is eliminated.
Of course this refers only to centering the table, and if you are
offsetting the table after centering, for example to mill a face
cam, or drill holes based on radius and angular specification,
then you will need to [accurately] measure the table movement.
On many mills it is possible to adjust the nuts on the adjusting
screws, but the problem is that the adjusting screws generally
have considerable wear in the middle and not much on the ends, so
when the nuts are adjusted to fit the middle, the nuts are too
tight at the ends, and when right at the ends, too tight in the
middle.
There was a thread on lathe cross slides and most of the
comments/suggestions there will apply to your mill. This tends
to be a major operation involving either replacement of the table
adjusting screws, or turning the adjusting screws down to a
consistent [but not stock] thread pitch diameter and
replacing/fabricating/modifying the adjusting nuts.
A major problem is the use of ACME [price an one inch acme tap]
or nonstandard thread forms or specifications [e.g. left hand.]
There are some ways around this. You can "slick up" the screws
to a consistent pitch diameter and finish, and them mold a liner
in the existing nuts to the screws. The old-world-craftsmanship
way is to use babbitt, and the new get-it-done way is to use a
teflon/epoxy compound such as moglice.
for information on babbitt see
http://lindsaybks.com/
http://lindsaybks.com/bks7/babb/index.html
http://lindsaybks.com/bks4/babbitt/index.html
http://lindsaybks.com/dgjp/djgbk/babbitt/index.html
http://www.littlegianthammer.com/pdf...20Supplies.pdf
and for moglice see
http://www.practicalmachinist.com/cg...1;t=022744;p=0
http://www.cnczone.com/forums/archiv...php/t-422.html
http://www.moglice.com/newsite/frames/wroteframe.html
http://www.moglice.com/newsite/pages/wrotethebook.html
The cheap-screw way [my preferred process] is to mount long
stroke drop indicators on the x/y/z axis as required and use
these to measure table/head as required rather than the dials.
You can easily fabricate bolt on holders for the indicators, but
my experience is that either a magnetic back or a magnetic holder
such as a "mightymag" works just as well and allows you to more
easily reposition the indicator or use on another machine, such
as your lathe, as a tail stock depth indicator, cross slide
indicator or slide stop.
Most of the mill supplies will have suitable indicators and backs
some sources
http://hhip.com/products/product_vie...uctID=400-0001
http://hhip.com/products/product_vie...tID=401-0005-5
http://hhip.com/products/product_vie...tID=401-0004-2
The type of holder will depend on your mill/lathe configuration
and your personal preference.
Note if you get the screw on magnetic back with a plastic rear
cover for the indicator that these are prone to breakage if you
let these "snap" onto the machine.
Note that you can make up indicator extensions from 3/16 drill
rod [or aluminum] and use long 4X48 set screws loctited in holes
in the ends of the rods with 20-30% depth of thread to avoid
dealing with ultra small [for me at least] threads.
If it would be helpful, I can suggest a cheap-screw sensitive
drilling/tapping set-up for not too much money.
Good luck and let the group know how you make out.
Unka' George [George McDuffee]
============
Merchants have no country.
The mere spot they stand on
does not constitute so strong an attachment
as that from which they draw their gains.
Thomas Jefferson (1743-1826),
U.S. president. Letter, 17 March 1814.