I need about 30 feet of rack gear (2x12' + 1x6', or 5x6' which seems to
be what's actually available) and 3 spur gears for a project (upgrading
my old cable-drive CNC (woodoworking) router to gear drive). More
expensive, fancier options are relegated to fantasy, I think. I did
consider things like Acme screw drives, but the increased rotating mass
seems like a problem, as is the flopping length of the 12 foot longer
axis. Ballscrews are a post-lottery-winning option only, I think.

Of MSC and McMaster, McMaster is a bit cheaper for this item.

I suspect that for the limited purchase size they may be the only
sensible option, but thought I'd throw it out here to ask if there are
any other suppliers friendly to HSM/small orders that might have better
prices.

I suppose I might as well also get some input/commentary on design
parameters and/or stupid design choices I might be making. When (some
aeons ago) the makeer of my router made this change, they chose 14.5
degree 20 pitch racks. For a variety of reasons, mostly cash related, I
did not upgrade when they had an upgrade kit available. I think they
claimed less lash with 14.5 than with 20 degree - I don't know if that
has any basis in reality. The old drive system was steppers driving
cables, the first form of the gear upgrade was steppers driving belts
driving spur gears, the latest went to servo drive. Given that I would
be happy to get the admittedly slow/weak stepper system working pretty
much the same as it does with cables, but without the cable slip errors
it sometimes gets, I'm inclined to ride the hairy edge of rack gear
engagement and use the steppers to direct drive a 15 tooth spur gear on
a 20 tooth rack, producing the same power and resolution I get now - 3/4
inch per full revolution. The added complexity and opportunity for lash
in the step-down system was going to a seemingly not-much-bigger gear of
about 20 teeth. I could also direct dive 20 teeth with some loss of
resolution and power.

I understand that small spur gears are supposed to be evil (prone to
shearing teeth, etc). Loads are not stunningly high - stall force on the
unit as built now is something like 30-40 lbs. I really have no idea how
hard I would be pushing a 15 tooth 20 pitch spur (standard width seems
to be 3/8 inch for 14.5 degree) if I loaded it to 40 lbs...I gather that
brass or bronze gears running on the steel rack might have better wear
behavior than steel on steel, but be weaker, as would plastic gears.

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