Gear rack sources for small quantities?

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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we use a place called union iron for building rack & pinion slide gates.. quite a bit cheaper than McMC here's a number 800-333-5148
hth Rob
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snipped-for-privacy@SOuthernVERmont.NyET says...

Check with Motion Industries or other power transmission distributors in your area. They're usually a bit cheaper than McMaster, though often not enough to bother on small orders.

Have you considered replacing the cables with a timing belt drive? That's generally the most cost effective choice where high speeds and accelerations, and moderate accuracy and stiffness are required. Breco has pretty good engineering info, it looks like it's available online.
http://www.brecoflex.com/?CATID=1
Ned Simmons
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Ned,
Timing belts would also be my choice for this application. They are remakably strong....steel cable reinforced...and quite accurate. They can be obtained in a variety of widths. Properly pre-tensioned they work well with good life expectancy. Industrial application is in the X,Y,Z axes drives for rectilinear robots and pick & place automated devices.
Wolfgang
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snipped-for-privacy@hotmail.com says...

Here's a system I designed and built about a year ago. The linear slide and timing belt drive, minus motor and controls, came as a preassembled unit from Item.
http://www.suscom-maine.net/~nsimmons/news/Washer01.jpg
Ned
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says...

Ned - I'm not the OP, but thanks for posting that link. The design info will come in quite handy for an upcoming project.
Mike
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I have, though that also requires (due to belt pitches available and sprocket-sizes) some additional reduction (thus complexity) of the drive to maintain resolution and power at present levels. A complete re-drive (which might resolve that another way) is probably not on the menu for this machine at this time or ever - if it can be made to work better, it might manage to buy itself a friend eventually, and get retired to doing more 3D input scanning and less cutting. Thus far it's been strictly a hobby-use money sink. Fun, but less fun when it goes off and starts ruining wood by not being where it thinks it is.
I get a bit squirrelly when dealing with places that have no price information available until you specify everything and get a quote (how can I make cost dependent engineering choices to specify things without some idea of costs ahead of time?), which was one vote in favor of gear systems, but given lots of replies supporting/suggesting/preferring the belt conversion, I'll give that more thought and try to figure out what components a quote might include without having any cost info - if it comes out way above gears, I guess I'll know something at that point.
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snipped-for-privacy@SOuthernVERmont.NyET says...

McMaster carries urethane belting on open lengths in a couple pitches and widths as well as matching pulleys. Even if they don't stock exactly what you need the prices should get you in the ballpark. The belts and pulleys aren't too expensive, but accessories like idlers and clamping profiles are pricey enough that making your own may make sense.
When comparing to a rack and pinion system don't forget to account for the difficulty in mounting and aligning a long rack.
Ned Simmons
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There is a cheapskate alternative to a rack. Weld a piece of bicycle chain layed edgewise along your part (or braze, or whatever) and use a bicycle sprocket to interface with it. Probably not good for your application but really cheap ..
GWE
Ecnerwal wrote:

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Ecnerwal wrote:

Don't spin the ball screw or Acme screw. Spin the nut. Just like the big guys do.
Belts or Acme with spinning nut sounds like the way to go though. Pete
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