Seeking geared plastic axle

[mmagliaro]

This is what I have for my 0-6-0.  It is 20 tooth, 0.2 module.  I have an 0.2 module worm to match it.

But the gear is a little small in diameter, and it will probably require me to fit in an intermediate idler gear
in my frame to allow it to reach up to the worm.  I'd rather avoid that.   Does anyone know of a different
axle tube with a gear on it, CENTERED, not offset, that has a bigger diameter gear on it?   Ideally it will have
at least 20 teeth, but more would be even better.  It can be 0.3 mod or 0.4 mod.  That's fine.
In fact, a coarser gear would be easier to work with.  Aligning gears when you get down to 0.2 mod is tricky.

The axle tube in a Kato Mikado would be darn perfect, except that it is offset, and if I try to use it as a centered
gear, the tube on the "short side" is just too short.

(With my planned 4:1 reduction Faulhaber gearmotor, that gets me an overall 80:1 reduction, which is pretty nice.)

[narrowminded]

Do you have a good C/L spacing dimension as it exists?  I ask because in the next month or so I will be running some gears and once set up, with just a few program changes, may be able to make you something to fit your shaft spacing as is.  I'm working with 120 DP so it would need the worm too but proportionally 120 DP is very close, slightly larger than .2 MOD.  (In a modular number 120 DP translates to .2116 MOD.)  Is your worm just pressed or loctited on to the worm shaft?  And if so, what size is that shaft?   If the gods of luck are smiling on you, this might be no biggie.

Another option with that offset gear if it would work well otherwise might be to just bore out the existing muff and make an insertable sleeve through the gear.  That was basically what I had in my prototype where I was using a standard bought gear set that had a 2 mm bore through the gear. I made the muff as a reducing sleeve.

[mmagliaro]

I don't know the gear spacing yet.  I am figuring this out as I go along.  But I can already see that with
an 8mm diameter motor sitting above this in the frame, there is no way the worm and worm gear will touch.
I won't know that spacing, probably, for at least a month.

As for other specs...  The geared axle as I showed it has a 1.5mm bore and that's what I need because my axles
are 1.5mm
The worm gear on the motor shaft will also be bored for 1.5mm.

Right now, I know I can buy 0.2 mod gears in every size from 6 tooth up to 70 tooth, so when I figure out exactly how
I'm mounting the motor, I can just select an intermediate gear that will correctly fit in between and be done with it.
As long as it has fewer than 20 teeth, that will make things all the better because it will get me some more gear
reduction, which I'd be happy to have.  80:1 is nice, but I'd rather it be more like 100:1.

Thank you for your offer to make the gears for me, but I don't think I'll be ready with the specifics
you would need by the time you make them.

[narrowminded]

I don't know the gear spacing yet.  I am figuring this out as I go along. 

Got it. 

Right now, I know I can buy 0.2 mod gears in every size from 6 tooth up to 70 tooth, so when I figure out exactly how
I'm mounting the motor, I can just select an intermediate gear that will correctly fit in between and be done with it.
As long as it has fewer than 20 teeth, that will make things all the better because it will get me some more gear
reduction, which I'd be happy to have.  80:1 is nice, but I'd rather it be more like 100:1.

Take a minute and digest that.  Any intermediate gear or multiples of gears, with teeth numbering ten or one hundred or one thousand, won't change the final gearing. They can be used as you suggested, to fill space, and they will reverse shaft rotation each time they pass one gear to the next, but they won't change the ratio until you compound two gears of different size on one shaft.  That's easily missed at a glance but you'll see it if you think about it.

[mmagliaro]

Got it. 

Take a minute and digest that.  Any intermediate gear or multiples of gears, with teeth numbering ten or one hundred or one thousand, won't change the final gearing. They can be used as you suggested, to fill space, and they will reverse shaft rotation each time they pass one gear to the next, but they won't change the ratio until you compound two gears of different size on one shaft.  That's easily missed at a glance but you'll see it if you think about it.

Ha ha ha.... That's right.  Of course!  Well then, 80:1 it will be... unless I can find a larger diameter axle tube gear with
more teeth.  Of course, if I go to 0.3 mod, I'll probably end up with only 20 or so teeth anyway, even with a large gear,
but I'd like that better.   
I have considered the idea of a double gear.  That's the usual design in steam locos.  Double gears are not as conveniently
or commonly available as plain old spur gears, however.  I have made my own by fixing two gears over a common shaft
and then drilling/pinning/glueing them.    If I were to *commit* to that design, I could use an axle tube with an
offset gear (which is why most of the commercial ones are offset in the first place.

I really liked the simplicity of a gearhead on a coreless just direct-driving the axle gear however. 
Few moving parts (at least the ones I have to worry about --- the gearhead is taken care of for me). 
Very little to get aligned.  Very little to go wrong. 

[Lemosteam]

Max, could you take two Mike tubes, machine off the teeth on one, take the second gear, cut off the tubes drill out the center to fit the OD of the tube of the first gear, and use brass pins to secure the gears to each other?

[narrowminded]

The next problem you would have if mating any gear to the worm or final drive gear is that as a worm gear it will have the teeth faces set at an angle to mate with the advancing angle of the worm and that angle is dictated by the diameter of the worm.  Any idler gear placed in the middle of the train should be a helical style, not a straight spur gear, with the helical angle matched to the worm which, again, is dictated by the worm diameter.  A single start worm always advances one tooth per revolution, but the ANGLE of the attack changes, is sharper, the smaller the worm diameter is.  It doesn't change the ratio but it DOES change the angle of the tooth (not the gear pressure angle but the worm angle). That may take some thinking and digesting but it's there if you think about it. (Ask if you're not seeing it.)  So, make sure that any worm or intermediate gear that you get is made to mate not just to the same MOD, but also the same DIAMETER of the worm that you have.  If not, get a matched set with the new manufacture's worm diameter but then the worm shaft and axle shaft centers change again based on the new worm pitch line.  And also, best to make sure whether it's a right hand or left hand set.  Most are right hand but that is not etched in any stone and would be a part of the basic spec for any gear you engage here, helical for use as an idler or just a new larger gear.  It's really not hard but they are details that matter.  You'll be good.

Summary:  Make sure any gears that you get, that will be mating in the train that starts at that worm, are intended to mate with a worm of that diameter and MOD.  One of the simpler options you might have if the dimensions worked out would be to use a second one of your existing final drive gears as an intermediate gear because all of these angles are already intended to mate.  And we know that it won't change the planned final drive gear ratio.  Hope that helps and maybe saves some later headache.

[mmagliaro]

John,
I follow what you're saying.   I *think* I could cut the tubes of a Mikado gear and bore it out to slip over the
tube of another.  It wouldn't be easy, though.  Getting a perfectly center-bored hole like that through plastic
is tough.  But yes, I can see how that would work.  It would get me the offset back to the center, and
it would be strong because it could be pinned sideways into what's left of the first gear that has the teeth
machined off.

Narrow:  Yes, I am aware of the worm tooth angle and the changes that come from the diameter.  Unfortunately,
I cannot get the Kato worm that goes with this axle tube gear.  They did make one, but it is out of production
and no longer available on their website.  So I am hoping that the worm I have will mate with this
gear okay.  Most the 0.3 mod "train gears" have the same pressure angle and other parameters.  So I am
hoping the same will be true for this case.

[narrowminded]

Even if that particular gear set or ratio isn't available I would think it's very possible that the same manufacturer may still use that MOD and that worm O.D. in another application.  If so, the worm gear would be suitable.  Might be worth a look and with the resource here you might be able to get worm diameter measurements if needed.  I'm sure you'll get it worked out.  And if you needed to get a straight and concentric bore through your existing gear that should be a relatively easy job for someone with a lathe.  I could help with that if it proved to be a stumbling block.   

[peteski]

Max,
While I don't have a Kato Mikado chassis in front of me, I'm pretty sure that the worm is not meshing with any of the gears which mesh with the gear on the driver. Those gears have teeth perpendicular to the side of the gear. The gear which meshes with the worm is a combination gear:  The larger one is the one one which meshes with the worm (and it has angled teeth). Then the smaller gear has straight teeth which mesh with the other gears which eventually mesh with the gear on the driver's axle.  I think that each gear in that combination gear has different module (and the worm gear has angled teeth for proper mesh with the worm).  So, I'm not sure if you'll be able to have the worm mesh directly with the gear on the axle (or an idler gear which then meshes with the axle-gear).

[Lemosteam]

Max, you could chuck the gear into your mill and mill the right size hole in dead on center. Like a tailstock chuck on a lathe, only vertical.

Also, if you remember from my little empty frame dual worm test loco with the magnets, the worm in the 11.103 meshes perfectly with the kato drivers.

[mmagliaro]

Peteski,
The Kato worm meshes with a double gear, which meshes with an idler and then the axle gear.
All of them are 0.3 mod.

And looking at them, to be honest, I do not think any of them have angled teeth, even the one that meshes
with the worm.

Be that as it may, the axle tube gear I am currently using comes from the Kato SD-40-2 "mid production" (among others).  And although the worm isn't available anymore, it turns out that Kato still had the truck, including
the worm, universal shaft, and of course, all the intermediate gears.  So I ordered one.  Let's see how they
do it.  I can certainly use whatever gears they did to get down from the worm to the axle.
I can see from a photo of the truck that the worm sits in a tower above the wheels, so there has to
be at least one idler in there.

[narrowminded]

If the gear in mesh has a very narrow face you can get away with it and and just let it run with that misalignment.  That's exactly what Bachmann does in many of their basic models.  They just misalign a very narrow worm gear utilizing a MOD that affords a relatively large tooth, therefore tolerates a generously sloppy fit, and let the truck turn.  No universal, no anything but the misalignment at the worm afforded by the generous clearance and generous oversizing of the parts.  That will tend to be noisy running as the gear friction and smoothness fluctuates with the mesh variations but they have accepted that condition and have sufficient motor power and component size to tolerate those variations.  Your device doesn't turn like that so doesn't require those sloppy fits or gear abuses so you might be able to optimize the fit and run nicely with those parts. You're not asking it to absorb those running fit variations so a sweet spot might be found that's very smooth and quiet running.  And noisy is a relative term anyway.   I still think a little more time researching your options to assure a device with the precision you've strived for this far would be worth it but I'm sure you'll come up with something that works well.  Hopefully these posts are helpful in your deliberations.  

[mmagliaro]

Narrow:

Yep.  From what I see, I think they are just "gettin' away with it", and it works, so why not?

My impression from looking at the gears in most commercial locos is that even the ones that
run well, like the Mikado, are still using gears that allow for a lot of playing fast and loose with
the way gears are supposed to fit.  After all, a smooth brass worm running against a Delrin worm wheel at 0.3 mod
is probably just going to push along without wearing anything out (and in fact, in Kato's case at least, without
making much noise).  A little slop and some slippery plastic goes a long way especially when the forces are
so small compared to what the teeth on those gears can really withstand and the load they are under.

You and others have mentioned this before.  The gearing and drive components in most engines is
fantastically overbuilt compared to actual load they have to bear.  And in the world of commercial locos,
keeping costs down, reliability up, and the ability to tolerate dirt, grease, cat hair and everything else trumps
making ultra-precise mechanisms.

I will see what's inside that Kato truck when I get it.  Whatever gears are in there, they have obviously decided that
they fit and mesh okay.  So if I take their worm, their truck tower gear, and their axle gear, I'd be shocked if it
didn't work.   

[peteski]

Max, is this the truck (and worm) you are talking about?


In that case yes, the straight teeth do mesh with the worm.

Funny thing is that the old A-forum post the above photo came also had a discussion between me and a gear expert about straight vs. angled teeth on the gear meshing with the worm.  That was on page one of this thread