Best Of SP&S 4-6-2 #626 Project

[Loren Perry]

Great craftsmanship, Max! You're doing things "the hard way" compared to a lot of us lesser-skilled modelers but the results speak for themselves. Very imaginative solutions, too!

[mmagliaro]

Carl, Jason, Loren, and all, Thank you for being so kind and believe me, I am pushing hard on this one
to try to do the best I can do.  Loren, you are right, I am trying very hard on this one to
make everything be soldered, screwed, and disassemble-able.   Normally, I would use more glue and plastic,
and I probably won't go to these lengths again.   On this one, I just thought I would push hard to make this
an "engineered" model.

And by the way, thank YOU, Loren.  Where the heck would I be without all these handy Gold Medal parts!

As a quick update, I wired the tender across tonight and took it out for its maiden voyage.  It had a stupid bind
in the worm, which was an easy fix.  Now, it runs and tracks fairly well.   The pilot truck has a wheel that's dragging
and it can only get down a little under 5 mph.  I will be tuning now.  I know it can do much better than that
with the geartrain that's in it.   

But overall, it runs pretty good for its first time out.

One thing I didn't expect... the headlight is BLINDING!  I mean... BLINDING.  That little SMD LED is so bright that it hurts
to look at it.   Perhaps a bit of something cloudy painted over it would tone it down and diffuse the light a little.
(No way am I tearing out that little circuit board with those magnet wires and trying to change the resistor!)

[Lemosteam]

Max, simply spectacular.  Love the center brake shoe bit.

[peteski]

One thing I didn't expect... the headlight is BLINDING!  I mean... BLINDING.  That little SMD LED is so bright that it hurts
to look at it.   Perhaps a bit of something cloudy painted over it would tone it down and diffuse the light a little.
(No way am I tearing out that little circuit board with those magnet wires and trying to change the resistor!)

In your writeup of the LED install you tested the LED and you seemed to be satisfied with its brightness. 

But if it is too bright, why not just add a 2nd current limiting resistor, elsewhere in the circuit?  After all, it is in series with the other parts of the circuit, so it can be inserted in any location.  Also, there is absolutely no need to use giant 1/8 or 1/4 Watt through-hole resistors.  A much smaller, SMD resistor will work perfectly well!  I often use 1206 size (sometimes even 0805 size).  Those should have no problem dissipating the heat.

You could install it on the circuit board which is inserted in the chassis or even splice it inline with one of the wire leads (then put some heat-shrink tubing over it or some liquid electrical tape.

To verify the power dissipation, here are some calculations. Assuming that your LED.s Vf is around 3V and you have 12V track power, that will yield 9V across your 680 ohm resistor.  That results in 9 / 680 = 13mA of current going through the resistor (and the rest of your LED circuit. That is in fact rather a lot for a white LED. If I place LEDs directly in a headlight housing (or using a very short light-pipe) I usually run them at around 5mA.

The power dissipated by your resistor is 9 * 0.013 = 0.117 W. You could have safely used a 1206 size SMD resistor.

To make the calculation really easy, if you were to add another 680 ohm resistor in series in that circuit then the total resistance would be 1360 ohm.  The current would be 9 / 1360 = 6.6mA (probably a brightness you would find satisfactory).  Since each of the resistors now has only 4.5V across it, and the current is now only 6.6mA, the power dissipation on each resistor would now be 4.5 * 0.0066 = 0.03 W per resistor. That is three hundreds of a Watt. You could safely use a smaller 0805 or even a tiny 0603 size SMD resistor.  Those values are also for 12V track power. IN real life the track voltages will be lower, so the dissipated power will also be lower.

Calculating values in an LED circuit is nothing more than basic math. 

[mmagliaro]

Yes, I know, Peteski.  I set the resistor so that the LED would have good brightness at low voltages, so it
looks good even when the engine is just barely moving (remember, this is all straight DC).
Yes, yes, I could put a regulator or zener circuit in there. 

Anyway, I chose the resistor so that the LED would look good at low voltages and not burn out at 12v, with
plenty of margin for safety.  It draws about 11 ma at 12v.

I may just clamp across with a zener and resistor near that little board.  That would let the LED pop on at
low voltage, but hit a "shelf" so it can only go so bright.

[mmagliaro]

Max, simply spectacular.  Love the center brake shoe bit.

Thanks, man!  On the Atlantic, I used a similar trick, only the underframe was metal, so I didn't sink the shoe
into the plate.  I hold it on with the screw.  It's okay, but it means that if you take out the screw and remove
the plate, the brake shoe comes off.  So when you put it back together, you have to reposition the brake shoe.
I tried to improve on that idea, and this is the result.  Now, the brake shoe stays put independent of the cover plate screw.

[mmagliaro]

Hello again everyone.   I have a lot of photos this time, so I'm going to do it in two posts.
Hold off posting until I get the next "Part 2" post up.  It will hopefully be shortly after this one.

This first segment covers 2 subjects:
1. Tender wiring, test running of the engine, and revising the pilot coupler
2. Making and mounting the domes


1. Wiring, Test Run, New Coupler






Some interim running exposed a problem in the front coupler.  The original Microtrains Z scale coupler
box interfered with the swing of the pilot truck.  After attempting to trim it as best I could, I had to resort
to just cutting the entire coupler box away, heat melting the coupler halves together, and being
content with a non-working coupler.  Then I discovered the "Bowser Buckler" coupler.

PGE_Modeller (Greg Kennelly) was kind enough to spot me a few of these.  You can only get them
on an entire truck.  So I cut the coupler off, and removed almost the entire back of the coupler box.
Unlike the MTL 905, these remain fully functional as long as there is a bit of wall on the left and right
for the coupler whiskers to press against.  So now I have a working front coupler again, that is actually
a bit smaller and even more in scale than the MTL was.



Finally, here is some video of the test running of the engine.  I posted this in another thread, but I want the
record of this project to be complete, so here it is:

2. Domes

Now comes the process of making the two very distinctively-shaped domes for this engine.  I considered
making them by taking some domes off other engines, and filing or adding strips and wraps of styrene to
make the contours.  But I really wanted to try turning them from brass this time, something I have never done.

















That's my stepson's little finger posed in there...

[mmagliaro]

...and now Part 2 of today's update.

In this segment, I build the tender oil bunker and the rear tender platform.















































So, that's it for this time.  Next up will be lots and lots of rivet detail all over this engine, appliances on the boiler,
and also the numerous pipes and lines.   

[PGE_Modeller]

Looking fantastic, Max!  Well done!!

Cheers,

[peteski]

Very educational (again). Especially the fabrication of the domes.

[Chris333]

I bought my lathe just to be able to turn domes for my Erie 0-6-0. I haven't even tried yet    But this gives me hope.

[mmagliaro]

I bought my lathe just to be able to turn domes for my Erie 0-6-0. I haven't even tried yet    But this gives me hope.

Heh, if I had a lathe, I would use it.   I am a total machining idiot, as anyone who is a machinist can tell
by how I use my mill.  But heck, it works.   Supporting the turning brass from only one end in the collet
like I did is not ideal.  But I used a collet holder (not a chuck, which would have too much play in it) and
the brass was short, so it worked out.

[peteski]

Supporting the turning brass from only one end in the collet
like I did is not ideal. 

Not at all!  Many turning operations using a lathe are done that way (if the stock is thick and short enough to minimize deflection).  I often do that on my lathe.

[Lemosteam]

Max. this is quietly turing into a museum quality piece of work.  Beautiful.  As far as macining goes- whatever works, as long as it is safe.

[Chris333]

Heh, if I had a lathe, I would use it.   I am a total machining idiot, as anyone who is a machinist can tell
by how I use my mill.  But heck, it works.   Supporting the turning brass from only one end in the collet
like I did is not ideal.  But I used a collet holder (not a chuck, which would have too much play in it) and
the brass was short, so it worked out.

Oh I doubt I would have used the tail stock for something like this. But I never thought of just shaping tool steel. I was to busy thinking I needed a cross compound slider and a round over tool. I would have used the collet as well 

Also on my last vandy tender I just tried to patch up where I scratched in a new bunker, you just started everything new so no seams to deal with.