Re: Milltronics VM20 and VM17, woe is me


"PrecisionMachinisT" <Precisionmachinist@xxxxxxxxxxx> wrote in message
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"D Murphy" <spamto154@xxxxxxxxxxx> wrote in message
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Cliff <Clhuprich@xxxxxxx> wrote in
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On Tue, 29 Aug 2006 14:50:05 -0400, clutch@xxxxxxxxx wrote:

Black Dragon <bd@xxxxxxxxxxxxxx> wrote:

Anyway, back to the machine. Yesterday I was digging for the source
of some more positional error, and noticed that when I leaned on the
head it moved a few tenths. (was in the middle of picking up a work
piece with an indicator mounted on the spindle) That took me by
surprise. I reached out and pushed the head left to right with some
20-30lbs of force and got it to move a half a thou. More if I put
some body weight into it. Damn! The rotating mass of the motor,
spindle and tool probably creates more force (case study for BB and
Cliff? <g>) than me pushing on it. Now add varying cutting forces and
I've got inconsistent positional errors in every direction.

Wow. I guess when your service guy 'fixed' the alignment the rails
were not parallel. Something had to give riding that roller coaster.

Now the question is what. Maybe you can get the company to send
someone competent or better yet find someone competent to evaluate the
machine independantly. Document everything.

Gibs or spindle pre-load?

Gibs on linear ways?

It would be interesting to fool with the leveling bolts and see if you
can
get the column a bit more square to the table. But junque is junque no
matter how you slice it.


The collumn may be perfectly square...where you have problems with x y
drift
on varied tool length then it's generally because the spindle itself
wasn't
set properly.

Assuming x y are perp to each other, next is to shim a granite plate onto
the table....only now can you swing in the c axis--and then lastly is to
mill / scrape the actual table surface.

Or think cylindrical square--a very handy tool for machine setup and
fairly
inexpensive to fabricate if you don't have one already.


Actually, forgot...once that granite has been shimmed, now you use the
cylindrical square to bring in the collumn.

Then set the spindle, then finally you will mill in your table or pallet
surface....(oops more axes to worry about if it's a 4 or 5 axis machine)

This is actually quite the basic shittage--fwiw, gotta add that the larger
the machine tool, the more important it all becomes...and sadly, very few
individuals seem to grasp much of it at all these days.

--

SVL





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