Re: [CAD_CAM_EDM_DRO] Stepper Motor Axial Travel under compression

In a message dated 3/9/2008 2:14:22 A.M. Central Daylight Time,
dc812@... writes:

2) How have other folks isolated the lead screw so as to avoid this axial
play under load?<<
In building several stepper-motor-controlled machines, I have read much
product-manufacturers' lit on this topic, some of which have admirable drawings
and/or photos. Ideally, the screw is in "double-compound" ball-bearings at
ONE end, and at least a good deep-groove ball-bearing at the other.

The stepper might be connected to that screw via timing-belt, if ABSOLUTE
per-step or per-tooth accuracy is not absolutely important. Or, use a good
"spider coupler" which is sufficiently axially-tolerant to allow the axial-slop
the DESIGN of the stepper requires, yet has NO rotary slop. Some kinds have
compliant, even rubber, "spiders" (webs?) which are right-TIGHT when
assembled, so angular misalignment is tolerated, if slight, but there is no "rotary
slop". No, do NOT even THINK of using the motor-bearings as screw-bearings
on the "motor-end"!

I had the best "precision luck" with dual (and "opposing") angular-contact
ball-bearings (bring money!) which "pressed onto" the journals at the
lead-screw on ONE end, and fit into a "bearing block" that allowed "taking up slop" so
that there was a bit of axial "pre-load". Not so much that it caused
immediate wear and/or strain on the rest of the machine, but enough that "linear
wiggle" was imperceptible/immeasurable.

For light stuff like, say, a PLOTTER, a single ABEC-7 deep-groove BB at both
ends of the lead-screws might be adequate, as there would be no "tooling
forces" on the lead-screws.

You might do well "just asking questions and holding-off until enough of
them have been answered for you, before you go cutting-up expensive materials
and parts" but i'td be MY bet you best BEGIN fiddling with some "light stuff"
like plotters, small X-Y router-tables, or Sherline toys, etc., before you
aspire to cut up any precision 38 mm dia. ground ball-screws, etc. on 1.5 x 3
meter X-Y tables with 1 hp steppers or servos! A "goof" on a SINGLE 3 meter
screw can cost you more than $1000! Jan Rowland




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