Where to get gear reducers with a flat ratio?

I've been looking for gear reducers for NEMA motors, but just about every one I've seen is either an odd ratio [99.05:1, labeled as 100:1], extremely high price [~$1285], or require a minimum quantity of 100 or so.
Is there a place I can get one with an even/flat ratio [actually 40:1, not 39.98:1]? Either NEMA 17 or 23 fits are just fine with me. I'm specifically looking for 40 and 20 to 1 ratios for 5 micron-step Z and 10 micron-step X and Y.

Side question: why do a large number of companies require you to request a quote? What is done different that a standard price isn't available?

Edited 1 time(s). Last edit at 08/18/2014 01:51PM by MrDoctorDIV.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

They want your contact information so they can either call you and try to make a sale, or bug you constantly until you order from them

The reason that the ratios are odd is often so that the teeth on one gear mesh against the same teeth on another gear infrequently. Otherwise the gears wear in a pattern that gets noisy and sloppy very quickly.

Pulley with a prime number of teeth are preferred, as they even out the belt wear.
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163.

You'll be hard pressed to find any gearbox (at a reasonable price) that will have little enough backlash to achieve a repeatable 5 or 10 micron resolution.
Also, other than wanting your contact details, most companies that quote rather than stating an outright price deal predominantly with large orders where the price is both quantity dependant and negotiable.

Thanks gary, after a tad bit of research on A2's point that makes perfect sense. I really hate odd numbers, but for that I think I'll break from my preferences and go for reason this time.

I see the point you make A2, I definitely learned something new, but I don't quite see how it would help in the case of positioning systems yet. Starts at one point, and regardless of teeth count of pulley and belt, when it goes back to the same position it will be at the same point of the belt and pulley. So no matter what it is going to be uneven and I don't even see how it would help spread wear among the places that do touch. Closed loops, I'm all over it, but I don't have any of those in my system. If I'm still missing it, please enlighten me, I don't want to be wrong about it.

LMColl, I don't need either of them to make it perfect each step, the Z-axis will never utilize layers 5 microns thin, but I as far as I know it'll be more accurate than micro-stepping down to that step size. Without micro-stepping I should be able to achieve higher speeds as well, right? Especially since it's an all-belt system?

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

Is there an odd gear ratio and pulley tooth count that would match up to even steps per mm [putting aside pulley/belt prime counts]?

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

Prime numbers are truly interesting and fun to play with. Gear ratio of 4.25:1 and 17 tooth pulley result in a nice even 25 steps/mm with a resolution of 40 microns. The ratio "resonates" at 17 base steps. Every multiple of 17 steps results in even number of microns traveled, no matter the pulley tooth count. The same type of math doesn't seem to work for ratio 5.18:1 and 37 tooth pulley. 4.25 ratio and anything including 17 seems to be the magic number for an even wearing gearbox.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

My numbers that I played with.




Is it more important to get an even [or at least low number of decimal places] steps per mm, or microns traveled per step, or should both be relatively flat? Any firmware could take a whole number of steps per mm, say 101. But would that create errors in the way it translates to distance traveled per step?

Edited 1 time(s). Last edit at 08/19/2014 12:32PM by MrDoctorDIV.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

Forget this idea with "even" steps. There is no such thing.

Example: my printer uses M8 rods, which are expected to have "even" 1280 steps/mm. In theory.

In practice, milled parts come out 0.5% smaller. I'd have to teach the controller to move "uneven" 1286 steps/mm. Or 1287, perhaps, who knows?

As long as you have a resolution smaller than 0.01 mm, there's no need to make a headache about wether your steps/mm has a decimal point in it or not.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Quote
MrDoctorDIV
I've been looking for gear reducers for NEMA motors, but just about every one I've seen is either an odd ratio [99.05:1, labeled as 100:1], extremely high price [~$1285], or require a minimum quantity of 100 or so.
Is there a place I can get one with an even/flat ratio [actually 40:1, not 39.98:1]? Either NEMA 17 or 23 fits are just fine with me. I'm specifically looking for 40 and 20 to 1 ratios for 5 micron-step Z and 10 micron-step X and Y.

Side question: why do a large number of companies require you to request a quote? What is done different that a standard price isn't available?

Whats got you wanting to do a gear reduction Doc? other than even steps. I ask because I have been contemplating it too to test a theory of smoother wall ( part profile) finishes. Instead of a "gear" reduction I was thinking about another set of pulleys and a belt to achieve the step down. Easy enough to configure. Also cost and backlash are kept to a minimum

Simplicity mostly. If I can keep it down to a single, closed loop belt, all the better for me. I'm paying the extra dollar to make this beast look as good as it prints. After looking at all of my options, however, I might have to break down and go with pathing reduction. Maybe I can do both, actually.. that's a bit too good of an idea. With a 4.25:1 gear reduction and 4:1 belt reduction, I can get the resolution I want at whole stepping and reduce the error produced by the cheaper gearbox backlash. A low 100 steps/mm, and high 10 microns/step, but I honestly don't need more than that. This is my larger format, not fine detail, printer.

That'll work for the Z anyways. X and Y axis should do just fine on an odd steps/mm, so higher gearing will be suitable, even though not even.

I'm aware, Traumflug. But the closer I get the better for me, personally. It's not a pure reasonable build. Actually, with all the harder paths I'm taking for simplicity and personal preferences, I'd have difficulty saying it's even half reasonable. I'm not so much building this for practicality reasons as I am making it a fun project. My imagination let to roam free, only reigned in by necessitated reasoning.

Edited 2 time(s). Last edit at 08/21/2014 10:34AM by MrDoctorDIV.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

[www.aliexpress.com]

Not sure what backlash there would be in the gearset, but they list 3d printing as an application use for this option. The drawback is the output rpm of 39mm/min. Unless you set your z height switch at the bed end, it will take about 5 min to move down to the bed. On the plus side...you'll never run into problems with torque...generating 97 nm @ 400mA current draw. :-)

Edited 1 time(s). Last edit at 08/22/2014 06:41PM by ShaneH.

I can get not only a higher ratio gearbox, but the motor to go with it for cheaper here.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus