Best Of Spokane, Portland and Seattle (SP&S) 0-6-0 Project

[nscaleSPF2]

Max, your video looks a lot like the original one that I shot of the PRR B6.  Microscopic bits of metal got picked up by the traction tire, and I could not wash them off.  I wasn't careful enough about controlling this byproduct of the Dremel work, and it got into everything; a few bits even got into the paint on the boiler.  A new set of traction tires solved the issue.

[mmagliaro]

Max, your video looks a lot like the original one that I shot of the PRR B6.  Microscopic bits of metal got picked up by the traction tire, and I could not wash them off.  I wasn't careful enough about controlling this byproduct of the Dremel work, and it got into everything; a few bits even got into the paint on the boiler.  A new set of traction tires solved the issue.

Jim, that's a good thought, but unfortunately, I already tried that (changing the tires).  Thanks!

[mmagliaro]

I have since tweaked the quartering, but not in a way you'd expect.  I wondered if freeing up the cranks on the center driver would allow the quartering to work better, (the quartering would only have to be perfect on the 4 outermost drivers).

So I removed the two center pins and yes, the engine runs a bit smoother and more uniformly, and I can get it to run even slower.   I put the cranks back in, but without their little sleeves, so that the center wheel has a bit of slop in its rod holes.  This allows the rod to pull the center wheel around to keep it in time with the others,  while still having a little slop around the crankpins which freed up the mechanism.

The result?
It can now sustainably run at 0.45 mph (whereas before it could only run at about 0.8 mph)
If you're wondering how ridiculously slow that is, it means it would take over 8 minutes to move two feet.  I really don't think it's a quartering issue. 

I think part of the visual problem is the large top-heavy nature of this engine.
Recall that in my previous test videos, this thing didn't have the cab or cylinders on it.  Now it does.  And the cab is quite wide and high compared to the engine.  So any slight side-to-side or up/down wiggle in the frame is amplified by that big boxy cab sitting on top.  I made a little red reference line on the frame above each rear driver, so I could watch how the frame potentially moved up and down relative to the wheel, and I must say, it's moving up and down by .005" at most.  It is barely visible.  But that cab makes it more obvious.

I may still do some tinkering with a spring or shim in one driver to see if I can stabilize it more.

[peteski]

I wonder if running the loco on one of those test stands would aid in pinpointing the source of the problem?

[mmagliaro]

I wonder if running the loco on one of those test stands would aid in pinpointing the source of the problem?

Peteski,
I've got a set of those Bachrus rollers.  I use them from time to time and I did use them on this problem.
After several days of angst, including pulling all the rods and valve gear and running it without to see if the problem
was really quartering or the the one rear geared driver, or who-knows-what, here's what I found:

1. The traction tire was part of the problem.  I have to slice a Kato Mikado tire a hair thinner to fit into my grooves
because these drivers are so darn fine-scale narrow.  And I had a thin spot on the tire.  Moreover, the tire was getting
a little pinched down in the bottom of the groove so it had some non-uniformity to it here and there.  I added a strip
of tape into the bottom of the traction tire groove so the tire itself would ride a little higher in the groove.  That got its surface
smoothed out.

2. I realized that the center driver crankpins don't really need to precisely quarter that center driver at all.  Drivers
#1 and #3, assuming they are quartered right, will carry the rods around and carry that center driver around just
fine even if there is some slop in the rod hole on that center driver.  In fact, it's better if there IS some slop on that
center rod hole because it removes one point of finicky restriction on the rod's motion.  So I removed the little
hypodermic needle sleeves around the crank screws on the center driver.  That didn't do anything for the lifting
problem, but it made the whole engine gain an extra edge of smoothness at ultra-low speeds (we're talking well below
1 mph here).

3. One bearing on the front driver set had a little back-and-forth slop in its pocket.  Yes, you always need a little because
the bearings need to be able to float around.  But this was more than the other 5 bearings.   What would happen
is that at one point in the driver rotation, when that front driver was being "pulled" by the rod,  instead of the wheel rotating,
the bearing would pull toward the rear.  So instead of the wheel rotating at that critical moment, it would stay put for an instant while
the bearing pulled rearward and took up the slack.  That caused a slight bind because now the wheel hadn't rotated to
where it was supposed to be, and would all of a sudden "catch up" with a quick "tug" of movement.  So I shimmed a couple
of thou of slop out of that bearing to eliminate this.

All of this involved several days of taking drivers in and out, rods on and off, tires on and off, shims in, shims out, ugh.
Lots of trial and error with combinations of things.

The end result is that I think it is now better.  It's not perfect.  There are still small undulations to the motion of the body here
and there, but I do think it's better.  The nice side benefit is that it can run slower than it used to.  About 0.9 mph
the bottom end before, and now I can get it down to 0.5 mph.  (Either one of these is quite ridiculous.  Nobody is going to
sit still for an engine moving that slowly.  But it's nice for smooth starts and stops.)

I'll post a new video later tonight or tomorrow, and you can all cast new stones.   

[Lemosteam]

We can't let any criticism slip on this loco because of its importance to the N Scale world.

[wazzou]

I'll post a new video later tonight or tomorrow, and you can all cast new stones.   

Sorry Max, but I assumed you wouldn't be happy with it if it were noticeable to the mortals.   

[mmagliaro]

Let me be clear here.  NONE of your criticisms are unwelcome, at least not by me.  I appreciate everyone taking the time to notice and to think about possible solutions.
I am still working on something with it, so the video will have to be delayed until I am done.

In the end, if there is a slight undulation in it that I cannot get rid of, that will be that.  But I want to try investigate all
avenues before I conclude that it is the best I can do .  At that point, imperfections or not, I will move on.

It makes one really appreciate how hard it is to create a mass-produced set of parts that can be spit out by an automated process and assembled thousands of times by humans, without having flaws like this.  One at a time is one thing.  A manufacturing process to make thousands... wow.

[peteski]

It makes one really appreciate how hard it is to create a mass-produced set of parts that can be spit out by an automated process and assembled thousands of times by humans, without having flaws like this.  One at a time is one thing.  A manufacturing process to make thousands... wow.

Actually, manufacturers have it much easier than you cobbling your  model from bits of metal and very limited tools at your disposal.

In the old days the masters for making molds were made in much larger scale (which is easier to work with) by craftsman who did this stuff for living (40 hours/week) - not as a hobby. They also had fully-equipped machine shops at their disposal, and it wasnt a single person designing all the parts - they had teams of people collaborating on a model.

Nowadays, the design phase, and often mold-making is done virtually (CAD/CAM) where everything can be made to fit perfectly without even producing a prototype.  Then 3D printer prototypes are made to verify the design.

Then all the parts are made by machines in high volume. The only labor-intensive process is for some factory worker to assemble all the parts together into a RTR model. And then quality control.

Even then, those high-tech high-volume models look and perform less than stellar.  We all know what manufacturers I am talking about. 

So what you are doing stands out even more - you are a single human making your model out of bits of solder brass, cut mostly by hand and soldered/glued together.  Your modeling accomplishment is much more impressive than any commercially made model.  Give yourself credit where credit is due.

[narrowminded]

What Peteski said.   And in this scale a couple of thousandths eccentricity on a rotating part actually will show perceptible movement.  What you have done is pretty amazing and then when considering what you've done it with, it becomes astounding!

[mmagliaro]

What Peteski said.   And in this scale a couple of thousandths eccentricity on a rotating part actually will show perceptible movement.  What you have done is pretty amazing and then when considering what you've done it with, it becomes astounding!

Thank you, sir!  And thank you all!

Actually, I don't think a couple of thousandths will show to our eyes.   The Kato Mikado drivers, for example, run about .002" to .003" out of true when I test them with a dial indicator (and that same dial indicator running on a piece of machined round stock in that same mill shows .000 deviation so it's amazingly good considering it's just a low-end mini-mill.  Just have to keep everything gibbed and locked down well.  I think what we're seeing here is more like a .010" error.  That's when it really starts to show up.
And then you've got this bit boiler and cab accentuating every tiny flaw in the wheels, like a giant pendulum clock swinging above the wheels.

[up1950s]

Geex Max , I am lucky if I can get anything to run smoothly at 50 SMPH . Did you learn this on earth or the advanced planet you came from ?

[Chris333]

I just saw a series of photos showing an Erie shop working on a set of drive rods. After they were done machining they hung the whole assembled rods from chains at each pin hole. Each chain had a scale and the rod had to be perfectly level. They took the reading of each scale to adjust the counter weights because machining would change the weight of the metal. 

[mmagliaro]

I just saw a series of photos showing an Erie shop working on a set of drive rods. After they were done machining they hung the whole assembled rods from chains at each pin hole. Each chain had a scale and the rod had to be perfectly level. They took the reading of each scale to adjust the counter weights because machining would change the weight of the metal. 

Fortunately, in the N Scale world, we don't have to worry about eccentric forces imposed on the wheels by the rod!  The rod just has to push and nudge on each side at the 90-degree points to keep the wheels moving around smoothly at every point in the rotation.   Easier said than done.  (which means I'm still working on it and am not satisfied yet).

[Cajonpassfan]

Fortunately, in the N Scale world, we don't have to worry about eccentric forces imposed on the wheels by the rod!  The rod just has to push and nudge on each side at the 90-degree points to keep the wheels moving around smoothly at every point in the rotation.   Easier said than done.  (which means I'm still working on it and am not satisfied yet).

Well, no dynamic augment to worry about, that's for sure. But, I've often wondered whether "quartering" is the optimal setup given the dynamics of a model (rather than prototype) steam locomotive. Bear with me here please...

On a real (two cylinder) steam locomotive the pins have to be offset at 90 degrees to eliminate dead spots and to balance the whole shebang. Four points on a circle evenly split between piston travel extremes on each side, two and two. On models, we tend to follow suit to be prototypical, although there's no mechanical reason to do so (and since we cannot see both sides of a steam locomotive at the same time, perhaps no aesthetic reason, either, other than it just seems wrong not to). So I wonder whether on a model, given the necessary slop in axle bearings, the 90 degree offset actually creates unnecessary lateral forces on the wheel/axle assembly and whether we'd be better off, mechanically speaking, with some other ratio; 120? 180? 0?

Max, I'm in awe of your workmanship on this loco and I would not dream of suggesting that you do anything on it other that what you've done. My thoughts are generic and perhaps food for thought for some other future steam project. It's also quite possible that I'm missing something. Am I?
Regards, Otto K.