Regearing a Kato Mikado

[mmagliaro]

As advertised, here is my first run-through at regearing a Kato Mikado.  I am very happy with the results.
The gear ratio changes from 36:1 to 52:1.  I spite of this, I'm not really sure it's worth it.
I can run a stock Mikado just as slowly as this one.   However, the top end speed is of course much reduced,
and the current draw drops significantly from 240 mA at 6v to about 150 mA.

I may go back and experiment some more.  Hans Starmans suggested I grind the pin off that holds the double gear, drill a hole,
and put in a proper-sized pin with the Bachmann gear on it (these comments will all make more sense after you view the photos below).
That would allow the gear mesh between the double gear and the idler to be more accurate, resulting in less noise and
probably better running.  It runs very well just the way it is, but I'm kind of "getting away with it", which isn't
the best way to build an engine.

Here is a video:
https://www.youtube.com/watch?v=_29-JGXJ-nA

Here is the story in pictures:







http://www.maxcowonline.com/photohost/katomikadoregearing/04GearBeforeAfter.jpg

[Chris333]

I was going to ask about the slop between the 10T and the stock gear, but in the photo it really doesn't look that bad.

Why can't Kato do these things?

[mmagliaro]

I was going to ask about the slop between the 10T and the stock gear, but in the photo it really doesn't look that bad.

Why can't Kato do these things?

The slop there is somewhat troublesome.  You really have to carefully get all this put together to keep those two gears from jamming.
The retainer over the worm, the gear plate under the chassis... all that stuff needs to be tight - none of that fooling around
loosening screws to see if it makes the mechanism run more freely.
But as long as you do that, it works.

The gear in the photo I kind of buggered up.  I made another one where all the teeth are clean and full-length.  But what I wouldn't
give for even .003" less distance between those two gears. 

The other thing to worry about is the extra undercut you have to
do under the idler.  As you can see in the photos, I cut more under that idler to make room for the bigger Bachmann gear
to spin under there.  If I move them closer together, I'd have to undercut more.   I think I could do it.
Hans suggested I cut that pin off and just drill a new hole with a pin that fits the Bachmann gear.  That would save me the hassle
of reaming out that gear.    That mesh is the source of all the increased noise.

Since this whole thing was a diversionary experiment, I will probably bite the bullet, pull it apart, and put in a new pin just to
see how much difference it makes.

[Chris333]

Just make the new pin eccentric. Put it in place with the gears and rotate till the mesh is perfect. Piece of cake 

[SkipGear]

I wonder if there is a smaller worm out there so you don't need to shim the motor. Maybe even a finer pitch worm and worm gear that is the same size. You could splice a 12t stock gear onto the finer worm and worm gear with a brass tube with a 2mm ID.

[mmagliaro]

I wonder if there is a smaller worm out there so you don't need to shim the motor. Maybe even a finer pitch worm and worm gear that is the same size. You could splice a 12t stock gear onto the finer worm and worm gear with a brass tube with a 2mm ID.

Most of the 4mm Kato diesel worms would mesh with that 0.30 mod gear, and Hans tells me the Kato 2-6-0 worm is 5mm, so that
might work.  But honestly, shimming the worm was pretty easy.  You can measure the outer diameter of the Bachmann gear,
do the same with the Kato gear, subtract the difference, and see that the worm needs to rise by .025"
It's not even a guessing game.  I tried it with .020", and sure enough, the worm mesh is too tight, and .025" is perfect.

There does not appear to be a problem getting the shell back on with the motor and worm jacked up by .025", because it's a small
amount (but I admit, it's close... the shell doesn't have much extra room in there).

I totally get you on using a finer worm.   That was my first thought.  Get an 0.2 module worm and gear, and then fine a 12T 0.3 mod
pinion and mate them together.  I calculated that keeping all the gear diameters exactly the same as what they are now
(to no need to move anything and no need to undercut), I could increase the gear ratio from 36:1 to 66:1.

But good luck finding an 0.2 module gear that is quite the right size.  I dug around the internet for days and found nothing.
You will find things are sorta kinda close, but nothing that is right.

Really, I was trying to find a commercial part that was as close to a drop-in upgrade as possible.   Unfortunately,
the Bachmann gear doesn't meet that goal because you have to cut and grind clearances to make it fit.
If I believed that enough people would want to actually buy the gear and do this upgrade, I would go to one of those
custom industrial manufacturers from China that advertise on alibaba and get them to make me a few hundred gears.
But I doubt the demand is there.

I like Chris's eccentric pin idea,  in a different way that seems utterly foolhardy, but I'm going to try it because
I have nothing to lose.  I already have the gear bored out to 2mm so I will reuse the bored gear.
 (I have other gears, so I could use a new one, but I want to try this).

It should be possible to just partially cut that existing pin right at its base, perhaps halfway through, grab it with some needlenose
pliers, and give it a gentle twist toward the idler gear, and voila, the tooth gap will be closed.  That will also move the
gear slightly downward so the worm can come back down somewhat.  A little JB in there after settling on the correct position should
keep it solid after that.  And what the heck, if it snaps off, I'll just drill a hole and put a new pin in it.
I doubt it will break.  Remember, we are talking about moving that pin only .003" or .005" at the most.

[Chris333]

If you get an eccentric pin to work I will need to set up a pillow for when I fall out of my chair!

[mmagliaro]

If you get an eccentric pin to work I will need to set up a pillow for when I fall out of my chair!

But twisting the pin is even easier!  Think about it.   You just graze the base of that pin with a very thin cut-off disk
(the .010 or .015 type, not the standard chunk Dremel ones).  Cut through maybe halfway.
Now, you grab the pin with some smooth jawed needlenose, give a gentle twist toward the idler,
and it will surely move a little.  Pop the gears on there, see how the mesh is, then tweak the pin this way or that if you need to.
Once the mesh is perfect, set a little JB in there at the base of that pin, and you're set.
I really don't think it will be that hard.  The only risk is that I'll discover the metal is too brittle and snap off the pin.
If that happens, oh well, I was going to drill and put a new pin in there anyway.

[peteski]

If you get an eccentric pin to work I will need to set up a pillow for when I fall out of my chair!

+1
But I'm willing to be dazzled. 

[mmagliaro]

Well, I don't know how "dazzling" this is, but it does work.
I undercut the pin, twisted it a bit, then polished everything up with 800 grit sandpaper (like I did before),
and reassembled.   It definitely seemed to me like I could put the mechanism back together and it was less "fussy".
Whereas before, I really had to make sure everything was in there "just so" and everything was tight or I would get gear jams,
now I just "threw it together", dropping in the parts, turn the screws in not particularly tight, and run it.

Another thing I thought of just on a whim, and I really like it: a cheap kid's electric toothbrush and some automobile polishing compound.
I polished the insides of the frame where I did all that grinding and mangling, and I polished the gear itself to try to smooth
up those slightly ratty edges left by the sanding.  The engine definitely runs quieter.
I don't think it will ever be as quiet as a stock Mikado, but then, my gears are spinning a lot faster and I sure can't file and fit
to achieve the same smoothness that Kato can at the factory.

Oh... one final important data point.
A stock Mikado at 10 volts runs at about 111 mph.  This regeared version runs at 78.
Current on the stock engine at this speed is 275 mA.  The regeared one is 175 mA.

Here are some photos:

[victor miranda]

well, you are heading into the tough stuff anyway.

file the worm wheel shaft flat to the frame.
drill a 1.5mm hole where you need to set the double gear.

I doubt you will be off by too much.

there is a place where the double gear can be centered
so the wormshaft  and motor will not need shims.

you already know the wormwheel center needs to go down 25 thous
the only question is how far sideways does the center need move?
my guess with the mark 1 eyeball is about 10 thous to the front.

... 'course the project goes from simple replace part to careful drilling.

it looks to me like it is worth the effort.

victor

[mmagliaro]

But but but... Victor... it's working!  You want me to drill and re-pin it now???   

I think the only "drop-in" solution would be to get a custom-made double gear that is 0.20 mod on the big part,
with a new, smaller-diameter 0.20 mod worm to match, and .030 mod on the smaller part. 

If they were made the correct size, they could actually drop in
with no modification to the mechanism at all.  But ugh... the manufacturing costs. 
I have actually been checking into this.   I'd be looking at $500 and that's if nothing goes wrong and the first
run of gears comes out correct.

Now Kato... with their vast resources and in-house manufacturing, could certainly do this and sell an upgrade gear set.
But why would they?

[peteski]

Now Kato... with their vast resources and in-house manufacturing, could certainly do this and sell an upgrade gear set.
But why would they?

Indeed.
Besides, that would take all the fun away from modelers like you who actually enjoy making this type of modifications. 

[Chris333]

So you just twisted the stock cast on pin    Yikes what if it snapped off?

[Chris333]

But why would they?

Yeah they'll just put in a coreless motor to make up for the lack of gearing.