Bind in Kato Mikado

[mmagliaro]

This applies to the Mikado I am using for my W-5 project, by the way.

As good as it appears to run, there is a point where I can definitely see a bind at one point in every rotation of the drivers.

First, the situation:

Recall that on the Mikado:
1. Only drivers 1, 3 are connected by the siderods.  2,4 are geared only
2. I have tweaked an tweaked the quartering between 1,3 and it is as good as the ol' Mark I Eyeball
can get it.  Remember, #1 driver on the Mikado is on a smooth round axle, so it can indeed be out of quarter,
although I have never seen this happen. 

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I have even dropped in a separate pair of the #1 #3 driving axles from another engine, and the problem is the same.
This really tells me it is not quartering.

It is at one point in the driver rotation every time, so that eliminates the worm (which rotates many times for each rotation
of the drivers.

Looked over the gears on the drivers (2,3,4) and I do not see any particle in there. 
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Any suggestions of where I might look?   Darn frustrating.  I don't think I've ever seen a Mikado run anything less
than smooth as oil.

I suppose I could swap out geared drivers 2,4, which are not connected to the rods, just to see if there is some microscopic
flaw in the gears that I simply don't see.

[Lemosteam]

I assume you cleaned the idlers inside the mech?  Also maybe a burr on one of them catching something inside the casting?

[mmagliaro]

I assume you cleaned the idlers inside the mech?  Also maybe a burr on one of them catching something inside the casting?

John, that's a good suggestion.
 
I have now found that if I remove drivers 2,4 outright, and just run the engine on 1,3, the problem is still there.
And having swapped out the 1,3 set once with no improvement, this pretty much eliminates
all the bearings, axles, and gears on the axles, as well as the quartering.

But the idlers... hmmmm    I will check.  Thanks.

[peteski]

Aren't the idlers smaller in diameter than the gears on the driver's axles? If they are, wouldn't the binding occur at an interval different than the driver rotation?

What happens if you remove the siderods?

[SkipGear]

Are you running the mech with or without the valve gear attached? If ithe valve gear is still on the loco then I doubt it's driver related at all. Probably a bind in the cross head slide.

[mmagliaro]

Good suggestions, thank you guys.

Pulled the valve sliders and valve gear, and since the #3 crankpin is part of the valve gear, I
fashioned a temporary crankpin from some square styene so that I could test it just with the siderods.
(I should point out that I've gone through all this before).

Anyway, on just the siderods, the bind is still there, but there was a slight but definite improvement
without the valve gear on there.  The bind wasn't quite as pronounced.

Removed the siderods completely.  The bind is still there.  But now I observe something that goes back
to what Peteski hinted at:  the bind is no longer at the same point in the driver rotation.

The motor will rotate many times with smooth operation, then slow down a lot (but keep moving) for
quite a few rotations, then speed up.   This sure is starting to smell like a problem in the idlers being
the main cause, with perhaps some friction from the valve gear or siderod making the problem worse,
but the fundamental problem is not the rods or valve gear.

I'll be back here after I check the idlers, pick the teeth, and look for burrs.

[mmagliaro]

I finally found the source of the trouble.
With all rods and valve gear off, the bind was still there.
I pulled all the drivers and ran the frame on the bench (just the motor and idler gears),
after picking through the idlers and finding no debris or burrs.

The worm bearings were flat-out tight in the frame and the worm was quite snug between the two
bearings.   Checking another Mikado mechanism (because I through the worm was supposed
to wiggle and float a little), sure enough, the bearings could wiggle a bit between the frame halves,
and the worm itself could move fore and aft just a bit between the bearings.

I removed the worm/bearings (I had to actually loosen the frame screws to get it out of there!).  I filed a little
play into the channels on the sides of the bearings which let the bearings and worm wiggle a bit.
Reassembled, and the bind was gone.   

Next: lousy slip/pulling even with a traction tire driver.   I found that the trailing truck was quite snug
against the drawbar and underside of the mechanism, so it was actually lifting up on the rear just a touch.
I filed the trailing truck tongue a bit so it could float up and down without lifting the engine, and
now it can pull 20 cars up the grade like it should.

TONY:
I'm not sure the Maxon 1024 is going to be the answer.  As powerful as it is, the engine still slows considerably
on grades with a 20-car train and that's not good.   I am going to mull this over, but I think I am going to
have to revert to a shorter motor with a 4:1 gearhead to get the power I want.

[Lemosteam]

By the way gents, i picked up some 1mm, 1.5mm and 2mm K&S tubing last night.  The bad news is that the tubing is sized to the O.D. and each has a 0.225mm wall thickness.  That calculates to 0.55mm, 1.05mm and 1.55mm ID, respectively.  So for those metric motor shafts, the extra 0.05mm of clearance is too loose and the tubing will be cocked or eccentric.  Boo hiss...

[brokemoto]

It pays to read all steam topics.  None of my Kato Mikados show this problem.  I do, however, have several Atlas/Microace moguls that show it.  I wonder if the problem is a lack of play in the worm.  I will disassemble one to see.  Thanks for the heads-up, Max.

[SkipGear]

By the way gents, i picked up some 1mm, 1.5mm and 2mm K&S tubing last night.  The bad news is that the tubing is sized to the O.D. and each has a 0.225mm wall thickness.  That calculates to 0.55mm, 1.05mm and 1.55mm ID, respectively.  So for those metric motor shafts, the extra 0.05mm of clearance is too loose and the tubing will be cocked or eccentric.  Boo hiss...

Cut your adapter to size, then place it in a 3 jaw chuck and tighten. That will take up the extra couple thousandths of play.

[Lemosteam]

Tony, are you suggesting to use the chuck to crush the tube onto the motor shaft, or to resize the tubing before I out it on the shaft?

[peteski]

Nice detective work Max!
But I wonder: Kato Mikado has been around for quite a while, and it seems to be a well-designed and reliable model.  But the problem you found could indicate a design problem which should afflict all the models. Yet, most modelers consider these locos to be excellent runners.  I wonder why yours was a bit different.

Thinking about this some more, could the brass worm be cut a bit too long?  That is something that could have happening during the manufacturing process.  Shortening the worm might have also solved the problem.  I wonder if you have a caliper and multiple Mikados.  Would it be worth measuring the length of the worms in them to see if the one that was binding was a bit longer?

[mmagliaro]

Peteski,
I think, funny as it sounds, that this Mikado mechanism is just a "lemon".  I am as surprised as anyone that there would be enough variation in Kato's casting process such that the bearings are tight in that frame.  So it makes me wonder if somebody who had this before me dropped it, bent it, or otherwise mucked around with it.

In fact, when I started with this mechanism, the worm was so tight that the motor wouldn't turn.
I had to break it free and put drops of oil on each end.  I noticed at the time that it fit just-so against
the bearings, but I figured Kato's fit was designed to be that way, not that this was an anomaly.

The bearings, the tight worm, and the trailing truck having no play in the tongue are all things I've never seen
in a Mikado.

At this point, I'm sure I'm switching to a gearhead.  The question is to use a 1024 or a 1017.  I can make the gearhead
fit onto both, and I have several Maxon 16:1 gearheads that I have cut down and converted to 4:1.
(When I get a chance, I'll do a photo tutorial on that one.  The higher-ratio gearheads, which are useless to us,
seem to come up on eBay more commonly and cheaply than the 4:1, so being able to cut them down is handy.)

If I go with the 1024, the motor will stick into the cab somewhat, and there won't be any backhead.  But with cab curtains or doors, I can hide it.  I suppose I'll try both and see what the difference in power and smoothness is.
Wish I could have kept that flywheel, but oh well.

........
Oh, and on those metric tubings, I looked them up after you guys mentioned them.   1.5mm - 2x.225 gets you 1.05mm
Tony's idea of squeezing it in a 3-jaw truck looks workable.  That should uniformly squeeze it so it stays round
and will snugly fit on a 1.0mm shaft.   Unfortunately, some Faulhabers have 0.8mm shafts, not 1.0.
I don't know, guys.  I think holding a diamond file or cutoff disk against the motor shaft to knock a little off
so it can fit inside whatever tubing you have, and then running the file against the outside of the tubing to take
it down to whatever outer diameter you need, are fairly easy things to do, and then you end up with a perfect fit.
Those motor bearings are awfully good so the shafts come out quite true.

[Loren Perry]

I'm glad you finally traced down the problem, Max. Before I read your solution, I was about to suggest a close look at the molded plastic brake hangers. On one of my engines, a hanger had somehow been bent a few thousandths of an inch forward, just enough the make contact with a driver tire when the rods were pushing rearward. There was just enough free play in the driver bearings to allow the wheel to move a couple of thousandths of an inch fore-and-aft and when the side rods were on the backstroke, the tire would rub lightly on the brake shoe. An easy fix once I found it. Related to this is a slightly out-of-round traction tire that makes momentary contact with the brake shoe - I've found this problem, too.

[mmagliaro]

I'm glad you finally traced down the problem, Max. Before I read your solution, I was about to suggest a close look at the molded plastic brake hangers. On one of my engines, a hanger had somehow been bent a few thousandths of an inch forward, just enough the make contact with a driver tire when the rods were pushing rearward. There was just enough free play in the driver bearings to allow the wheel to move a couple of thousandths of an inch fore-and-aft and when the side rods were on the backstroke, the tire would rub lightly on the brake shoe. An easy fix once I found it. Related to this is a slightly out-of-round traction tire that makes momentary contact with the brake shoe - I've found this problem, too.

Oh!   Thank you Loren.  I completely forgot.  Yes, this engine had this problem too.
In fact, the brake shoes are so close to all the wheels that most of them could ever so slightly touch.
I ran a round Dremel bit against each brake shoe face to take a little off so they wouldn't hit.
Not only did the brake shoes touch the wheel treads, but they could touch the FLANGES too, as
the axles slid back and forth, and here's why:  The Kato Mikado is gauged way too narrow, like many
engines.  I used a wheel puller to correct the gauge of all the driver sets.  But ones you do that, the drivers
are slightly farther apart on each axle then they are when they come from the factory.  this lets them
slide back and forth in the chassis more than they used to, and that allows their flanges to touch
the brake shoes.  You have to be very careful to spread each wheel on the axle just a touch
to correct the gauge.  Don't just do it on one side.  Otherwise, the axle can slide too much, and
the gear on the axle can touch the insides of the frame, causing more friction.

Whew... Anyway.  Yes, this was yet another thing I had to fix - the brake shoes.  Thanks for reminding me.