On Fri, 14 Nov 2008 00:57:59 -0800, Michael Koblic wrote:
"Michael Koblic" mkoblic@... wrote ...
I like the shim idea. The problem is that these plates are of rather
inconsistent thickness and the depth of cut has to be adjusted
individually. I shall look at all these ideas tomorrow. Thanks,

A further thought occurred to me: A pack of cards! However, another
issue: To mill properly, I have to lock the spindle, right? I would have
thought that the change in Z-depth by the simple act of locking the
spindle is quite undesirable, especially as it is unpredictable and of
the order of 0.010". Am I wrong?

If you cut a groove or slot, or mill a horizontal surface,
then yes, the Z-axis should be locked -- ie, the fine-feed
meshed, the vertical gib tightened by handle on side of
head, and the limit block tight against the bottom of the
head. If you set the limit block first, that should keep
the depth from increasing beyond what you want.

In previous post, I wrote:

-- Attach a DTI or a digital caliper to indicate depth. Say you
want a 4mm or .157" deep hole in 5mm or .197" material. If you
zero the indicator when the tool tip touches the work, or set it
to -.001" when it touches a cigarette paper on the work, then
you will be at desired depth of cut when the indicator reads .157".

I forgot to mention the alternative of setting the zero so that
the indicator reads zero when you are at the desired depth. If
you do so, then varying thickness of metal you are drilling
into won't matter, as long as the surface not being drilled
through is clamped against the same reference surface each
time.

--
jiw