Gears and Gear Materials (Rivarossi)

[peteski]

No, the worm is still brass.  But at least it is a brass motor worm running against a Delrin idler.  I would think that still has a much reduced friction with all the sliding pressure that goes on in a worm.

You misunderstood me.  To me "worm gear" is the gear that meshes with the worm (aka. worm-wheel).  I never call that gear an "idler" because it is not just an idler - it is part of the worm drive system. The worm gear's teeth are usually angled to match the angle of the worm's "tooth".

 What you have now is probably the most common desing for that drive - brass worm driving a plastic warm gear (worm wheel). It must have much less friction than brass worm and brass worm gear. Actually using the same material for the worm and the worm gear is not recommended design for such type of a drive.

So you are using a gear with straight teeth meshing with the worm?

[mmagliaro]

You misunderstood me.  To me "worm gear" is the gear that meshes with the worm (aka. worm-wheel).  I never call that gear an "idler" because it is not just an idler - it is part of the worm drive system. The worm gear's teeth are usually angled to match the angle of the worm's "tooth".

 What you have now is probably the most common desing for that drive - brass worm driving a plastic warm gear (worm wheel). It must have much less friction than brass worm and brass worm gear. Actually using the same material for the worm and the worm gear is not recommended design for such type of a drive.

So you are using a gear with straight teeth meshing with the worm?

Yes, the worm wheel is Delrin, the worm is brass.  I tend to say "idler" just because I know there is this confusion about the worm and the worm gear (worm wheel).  In the Rivarossi drive train, all the idlers are the same and one of them is driver by the motor worm.  There is no angle to the one that mates with the worm, even though strictly speaking, there is supposed to be.  In a RR x-8-x mechanism, there are 3 idlers (one between each pair of drivers) and the motor worm mates with one of them.  My supposition is that just by changing that one idler (the one that mates with the worm), the mechanism improves because MOST of the friction is at the worm.

I have a 4-6-2 and a 2-8-2 with my rebuilt motors in them.  And I have clocked their minimum speeds.  I'm going to change out just the one idler to Delrin and see if I see the same improvement I saw in the 0-8-0.  If I do, I'll consider two examples enough that it's not a coincidence.

My observations of these engines running slowly is that they stop when they hit a random "sticky spot" that makes the engine stall.  It is never in the same place in the driver rotation.   I have a sneaky suspicion that the brass-on-brass worm just isn't smooth enough.

[CRL]

More Worm gear...

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[peteski]

Thanks for the explanation Max.
I agree that brass-brass gear mesh will have more friction than brass-Delrin or Delrin-Delrin.  Those brass teeth are just machined, unpolished.  There is lots of microscopic roughness that causes friction.  I think it the teeth were polished, that would decrease friction, but still not as much as when using Delrin gears.

[mmagliaro]

Thanks for the explanation Max.
I agree that brass-brass gear mesh will have more friction than brass-Delrin or Delrin-Delrin.  Those brass teeth are just machined, unpolished.  There is lots of microscopic roughness that causes friction.  I think it the teeth were polished, that would decrease friction, but still not as much as when using Delrin gears.

I considered going at the teeth on those gears with strips of 2000 grit sandpaper, and then a polishing compound in an electric toothbrush.  I've used tricks like that before, and they do help.

[wazzou]

I remember being told Pearl Drops Toothpaste was pretty effective.

[peteski]

I remember being told Pearl Drops Toothpaste was pretty effective.

Yes, that trick is often mentioned.  Using brasive on a meshed set of workign gears seems ideal since it will polish the all the hard-to-get-to surfaces of the teeth that mesh.

I also remember seeing a strong statement in NWSL catalog stating that you can't break-in gears.  Hmmm . . . Mayne not break them in, but make the meshing surfaces smoother for reduced friction?

[mmagliaro]

After proving trying my Delrin gear idea in a 4-6-2, I am pretty convinced it's worthwhile to replace the one idler gear that mates to the worm with a Delrin one, as it also improved the 4-6-2's minimum speed and made it run quieter.  This gear thing has nothing to do with my armature/remotor project, but I'm glad I know this now.

An update to the motor project.
I struck upon another 3-pole skew-wound motor on eBay.  It appears to be the same exact size as what I've been using
in my Rivarossi experiments, but it has a dual shaft (which I don't really need), and is offered in two variants, complete with the actual Mabuchi part numbers, which I was able to decode using a chart on Mabuchi's website.  What I learned is that one version
is wound with 190 turns of #39 wire, and is rated at 29,000 RPM at 12v, and the other is 300 turns of #42 wire, rated at 21,000 RPM at 12v.  Recall that my hand-rewrapped arm used #42 wire, but had 460 turns.  I bought a batch of the slower ones.  I want to see if they are better than the stock armatures I am currently using, even though I don't expect them to be as good as hand-rewrapping the armature.

[peteski]

After proving trying my Delrin gear idea in a 4-6-2, I am pretty convinced it's worthwhile to replace the one idler gear that mates to the worm with a Delrin one, as it also improved the 4-6-2's minimum speed and made it run quieter. 

I'm sorry Max, but I cringe ever time you call the "worm-wheel" or "worm-gear" an "idler" regardless if it has skewed teeth or not.  If it engages the worm on at least one point, it should be called a worm-wheel or worm-gear.  If anything, I suppose it could call that gear worm-wheel/idler, but it's main function is a worm-wheel. Transferring the rotary motion to another gear under it is to me is its secondary purpose. Just IMO.

To me, idler gear (as the name implies) does nothing more than transferring rotary motion between 2 or more gears that are meshing with it.  The mesh with a worm results in a 90 degree change in transfer of motion.

There are models out there where the worm meshes directly with a gear on the driver's axle.  I woudl also call that a worm-wheel.

[narrowminded]

I'm sorry Max, but I cringe ever time you call the "worm-wheel" or "worm-gear" an "idler" regardless if it has skewed teeth or not.  If it engages the worm on at least one point, it should be called a worm-wheel or worm-gear.  If anything, I suppose it could call that gear worm-wheel/idler, but it's main function is a worm-wheel. Transferring the rotary motion to another gear under it is to me is its secondary purpose. Just IMO.

To me, idler gear (as the name implies) does nothing more than transferring rotary motion between 2 or more gears that are meshing with it.  The mesh with a worm results in a 90 degree change in transfer of motion.

There are models out there where the worm meshes directly with a gear on the driver's axle.  I woudl also call that a worm-wheel.

And because the worm gear (or worm wheel) is not used as the final drive, I see it appropriate to call it an idler gear as idler gears are used to bridge a space between one gear and another.  As pure idlers they would make no change in the final device gear ratio, which this gear does, so maybe there's a fine point to be made, but I would understand it either way.  It would be interesting to hear gear gurus preference in this.

This reminds me of one of my engineer father's pet peeves which was the accepted interchangeability (in some circles) of the terms "motor" and "engine".   A motor's source of power is electric, an engine's is fuel.  A race car had an "engine" and never had a "motor"... until recently.   A locomotive had an "engine" to drive the generator to finally drive the traction "motor".

[peteski]

And because the worm gear (or worm wheel) is not used as the final drive, I see it appropriate to call it an idler gear as idler gears are used to bridge a space between one gear and another.  As pure idlers they would make no change in the final device gear ratio, which this gear does, so maybe there's a fine point to be made, but I would understand it either way.  It would be interesting to hear gear gurus preference in this.

Do we have any gear-gurus here? 

So as you see it, the only time the gear meshing with a worm will be called worm-wheel is when it is used as the final drive (like that seldom used design where the worm directly drives the gear on the driver's axle)?  In any other design you are ok calling the worm-wheel an "idler"?

Actually this questionable nomenclature usually doesn't show up because in most N scale locos the worm-wheel is actually paired with an idler (as a double or compound gear). 

[rodsup9000]

Do we have any gear-gurus here? 

  I was taught (back in machine tool school in '75) that the "worm" was call a "worm" and the gear that it drove was a "worm gear" or "worm wheel". The other round gears with teeth on the outside were called "spur" gears. Gears with the teeth on the inside were called "internal spur gears" Most idlers that I've seen in the model railroad are "spur" gears. Then we can get into "idler", "drive" and "driven" gears. Compound gears are most generally two different spur gears and or worm gears mated together.

 If you want to get into ratio's, I can help a little there too.
 Hope this helps a little bit.

[peteski]

  I was taught (back in machine tool school in '75) that the "worm" was call a "worm" and the gear that it drove was a "worm gear" or "worm wheel". The other round gears with teeth on the outside were called "spur" gears. Gears with the teeth on the inside were called "internal spur gears" Most idlers that I've seen in the model railroad are "spur" gears. Then we can get into "idler", "drive" and "driven" gears. Compound gears are most generally two different spur gears and or worm gears mated together.

 If you want to get into ratio's, I can help a little there too.
 Hope this helps a little bit.

That does help out - thanks Rod.  It shows that the worm-gear will never be called an "idler", since it is a driven gear (and likely also a "drive" gear).

[mmagliaro]

An update on the project:
Peteski noted earlier his concern that when I press out the front bearing on the Rivarossi motor, and then press it back in from the outside, there might be some risk that it would pop out, because it no longer has the little "lip" on it as a retainer to keep it inside the can.  The "lip" is on the outside, where it doesn't do much good.  What I see now, looking at a bunch of these motors, is that usually, the front bearing is just a straight bronze tube with no "lip" at all.  It stays in purely by a friction press fit.  Since it is pressed into a metal nose, this works because the press can be quite tight.  In my photo, and in a few examples I have, the front bearing DOES have a lip.  I have no idea if this was because other people tampered with these over the years, or if there were manufacturing mistakes or variability at the factory.  But it makes sense to me that the REAR bearing, which is just in a plastic end cap, always has the lip on it on the inside to keep it from pressing through the plastic while the armature runs up against it.  And the front bearing doesn't need it.

As it happens, I have changed my procedure slightly, to just press the bearing back into the inside after machining it out.  As it turns out, I have enough room in the can to allow this, and it lets me use one or two fewer thrust washers in the front.

[woodone]

Going back to gears—— a worm gear mated with a worm wheel should never be made of the same material.
Same types of metal when put in contact with each other will gaul. Worm drives are much more quite than spur gear drives.
Be careful polishing worm gears- you could change the profile of the worm,
Going back to NWSL’s saying— you can’t wear a gear in, you will only wear it out.