Re: [ATM] draper machine

["Bob May" <rmay@nethere.com>]

Another thread asked the question of whether  thirty thou is too
much play and the general answer was no, it isn't too much play
in height. More important is to make sure that the motion is
smooth and doesn't suddenly rock back and forth and this is done
by making sure that the bearing is carrying a "side load".  What
this means is that a ball bearing is carrying a small load along
the direction of the shaft and thus, any slop in the bearing will
be taken up because the balls of bearing is riding on the  of the
race rather than bouncing around when they aren't carrying the
load of the bearing.  Bronze bearings are best done by tilting
the bearing a bit so that they stay on one side of the bearing.
Straight roller bearings are the worst type of bearing to use
because they just won't take a side load.  For a source of cheap
bearings, go look at auto front wheel bearings.  They are
designeed to be clamped together on a shaft and keep the whe4el
from wandering about.
If you feel that the wobble of the table is too much for your
tastes, pull the table off of the connector from the shaft and
put a paper or metal shim on the low side and get it to where you
want it to be.  Personally, a lot of fussing for no gain.
BTW, you made the right choice by going to a standard motor and
pulley system as you have no need of making fine adjustments of
speed in the system.  Speed changes will be of a much more major
change than what speed controls will really do.  It's like
machining on a lathe.  The book may say you want to do 900feet
poer second of speed for the cutter on the work.  This doesn't
mean that you have to do this but gives the "optimum speed"  for
production work.  If you wish to go slower, you may do soand if
you don't care too much about the cutter sharpness, you can go
faster as the metal will be getting hotter and the erosion of the
cutter will be higher.
Bob May
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