Discussion:
Surface grinder question
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Peter Fairbrother
7 years ago
Permalink
How do surface grinders move the wheel (or table?) to give micron
positioning diferences?

I would have thought that a straight thread wouldn't work. Is there some
other secret?

Ta

Peter Fairbrother
David Billington
7 years ago
Permalink
Post by Peter Fairbrother
How do surface grinders move the wheel (or table?) to give micron
positioning diferences?
I would have thought that a straight thread wouldn't work. Is there
some other secret?
Ta
Peter Fairbrother
Peter,

    My Exe surface grinder has a lift screw, looks like square or
trapezoidal thread, of 0.1" pitch and is driven through a 2:1 reduction
bevel from a large 9" diameter handwheel with 50 graduations so each
division is 0.0001" (2.54 microns).
David Billington
7 years ago
Permalink
Post by David Billington
Post by Peter Fairbrother
How do surface grinders move the wheel (or table?) to give micron
positioning diferences?
I would have thought that a straight thread wouldn't work. Is there
some other secret?
Ta
Peter Fairbrother
Peter,
    My Exe surface grinder has a lift screw, looks like square or
trapezoidal thread, of 0.1" pitch and is driven through a 2:1
reduction bevel from a large 9" diameter handwheel with 50 graduations
so each division is 0.0001" (2.54 microns).
Correction the handwheel is marked 0 to 49 with tenth divisions between
those so 500 marks on the wheel so even finer precision.
David Billington
7 years ago
Permalink
...
I'll get this right eventually, not been a great day for thinking. It is
as I said originally each division is 0.0001" of an inch as 2 turns of
the 500 division handwheel moves the head 0.1".
Mark Rand
7 years ago
Permalink
Post by Peter Fairbrother
How do surface grinders move the wheel (or table?) to give micron
positioning diferences?
I would have thought that a straight thread wouldn't work. Is there some
other secret?
Ta
Peter Fairbrother
It tends to be an ACME or trapezoidal screw lifting the head. It's always
under load from the considerable weight of the head, so backlash isn't a
problem. Even though the screws and nuts can suffer significant wear over the
years (especially if there isn't an automatic lubrication mechanism), the wear
over short distances will be consistent, so a properly geared screw can
produce very high precision movements. Silly as it might seem, the slight
vibration that is inherent in running the machine ensures that any slack will
be taken up.

Note that a heavy cut can lift the wheel-head within the 'play' of the screw
and nut. This is one reason for doing a spark-out pass at the end of the job,

Mark Rand
--
RTFM
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