Best Of New Brass EP-2 assembly & Mod clinic

[TiVoPrince]

Probably
useful for those of us skimming along to show a nice block diagram at the beginning of steps to help us luddites follow the action.  With the general design of modern plastic shell diesels where the side frames mount to trucks from the bottom, confusing me was an incredibly simple task...

[u18b]

Now  we move to one of the key improvements.

We've been trying all possible ways to reduce friction (and any annoying electrical shorts).

We've covered everything in the power truck except the worm gear-- the big gear that interfaces with the worm.  I have sometime called it the main drive gear- since (at least in my brain) it is the main gear that turns others and interfaces with the worm.



The stock gear is brass.  And I don't know if it is cast or turned, but I do know that some of the edges are rather sharp.

The teeth interface the worm, but the central portion can rub against the inner side walls of the geartower inside the truck frame.  I already filed the inside of the geartower smooth-- now how about the gear itself?

I very gently rub the gear on very fine and very worn out sandpaper.



I use a circular motion.  As before, what you discover is that the gear moves roughly at first, but then pretty quickly slides on the paper much easier.  What I've done is remove the sharp peaks and edges on the metal.

I do both sides.
I then BURNISH the gear outer surface by rubbing it hard and quickly on a piece of wood.  It gets a little hot on my finger.


When I've done this a while, the central raised section become more mirror-like.

Here is a before and after comparison.  I don't even need to tell you which side is stock and which side has been polished.


All of this together has reduced the friction in this truck dramatically.



But even though it runs MUCH better than a stock truck, it is still a bit noisy-- as all brass gears are.

Wouldn't it be great if we could find a Delryn plastic gear replacement?

Hmmmmmm.   

[Chris333]

Just for info that is not a "crown" gear:
http://en.wikipedia.org/wiki/Crown_gear

If it engages with the worm, then it is the "worm gear" 
http://en.wikipedia.org/wiki/Worm_drive

Gears are usually cut in long strips called gear sticks. You can buy the sticks from NWSL if you ask them. They are then sliced into thin usable gears. Looks like this one went through further milling after (or while) being sliced.

[u18b]

Corrected.
Thanks.

By the way, every Kumata loco in N scale except the Centipede uses this gear.

[peteski]

Just for info that is not a "crown" gear:
http://en.wikipedia.org/wiki/Crown_gear

If it engages with the worm, then it is the "worm gear" 
http://en.wikipedia.org/wiki/Worm_drive

Gears are usually cut in long strips called gear sticks. You can buy the sticks from NWSL if you ask them. They are then sliced into thin usable gears. Looks like this one went through further milling after (or while) being sliced.

Good info!  Crown gear looks like a crown. The worm gear covered here, as you stated, clearly has machining marks on it. I wonder if there is also another name for the worm gear  if it also meshes with the idlers or with the gears on the axles (like in this truck).

[Chris333]

I guess you could call a worm gear a spur gear as well?  Lots of times a worm gear teeth would be cut at an angle to mesh with the worm, but in most model trains they are cut straight just like a spur gear.

My one pet peeve was when people would call the worm the worm gear 

And as most know the worm is why we can't push our locomotives freely down the track.

This is the guy who told me how NWSL gear were made:
http://hon2jeff.blogspot.com/

[u18b]

And Tivo

You were right about clarity.

This is the kind of shot I should have ended the last section with.



You can see the little up-turned corners in this broader shot.

[peteski]

I guess you could call a worm gear a spur gear as well?  Lots of times a worm gear teeth would be cut at an angle to mesh with the worm, but in most model trains they are cut straight just like a spur gear.

My one pet peeve was when people would call the worm the worm gear 

I know what you mean about people calling the worm a worm-gear. 

Many of the contemporary models use a combination (hybrid?) gear which consists of the larger angled-tooth worm gear and a smaller straight-toothed spur gear which then engages with other spur gears in the truck.

I also have some Arnold models (both old and brand new) where all the gears have helical-cut teeth. They are not really thick enough to take a true advantage of the helical-cut gears (2 tooth surfaces are engaged at all times), but they still are probably the most optimal design where worm-gear is also a spur-gear in a model loco truck.

[TiVoPrince]

And Tivo

You were right about clarity.

This is the kind of shot I should have ended the last section with.



You can see the little up-turned corners in this broader shot.

Probably
just me.  Imposing my extremely limited knowledge of brass locomotive construction to the work of a master like yourself. 

I am humble before you, I still tend to give gears the Pearl Drops polish method.  I continue to jealously guard my very last bottle of the stuff.  Because it still needs to last my lifetime...

[u18b]

Well, it turns out there IS a Delryn gear out there we can use.

It just so happens that the worm gear (Atlas calls it a double gear) from the old old Atlas/Kato/Japan U25B has the same teeth and basic size as the brass KMT gear.

The only problems?

It is too fat and the center hole is too small.
Both problems which I can fix.

So I guess you could say I'm going to "kitbash" this gear.

There are two sides to this gear.  The secondary gear side and the smooth side.

Let's start with the easiest.  The smooth side.



As you can see from that photo above, I removed basically the triangular portion in the center.  I used a file, then sand paper.  This is my reference side.  Once I get it like this, I don't mess with this side any more.

The secondary gear side is a bit trickier.



I file the inner gear down most of the way--- but not ALL the way.  We need some of that thickness.  I file, and then test fit into the geartower.

Once it fits slightly loosely in the geartower--- all that junk will cause too much friction.

So I take an Xacto knife and I hold it flat against the bigger outer gear, and cut into the teeth of the inner gear.  It goes easily (since I'm not cutting much).  When the easy runs out when it gets to the end of the teeth, I turn the blade up.
Like here.



I then make the same kind of move on the exact opposite side-  parallel.



I then rotate and do the same all round.  So now I have a square left.

I then cut the points of the square in a similar manner-- so now I have an 8 sided "stop sign".


That's as far as I need to go.

I then use a round file-- gently spinning it a bit to open up the center hole.



When I can easily get the headless retaining screw through it I stop.



The last step is to burnish everything as I did before, smoothing everything up.



It really is amazing how this improves the performance of Kumata locos.  I do this to all KMT locos I can.
It may not reduce friction over a polished brass gear, but it sure does make the loco quieter!

Just to make sure my mind wasn't playing a trick on me, I put the brass gear back into a loco and sure enough it was louder.
So this really works.

[peteski]

Excellent find!  That is pretty darn clever Ron!

BTW, it is Delrin (not Delryn  ).

[u18b]

Thanks Peteski

And thanks for the clarification on the name.

[u18b]

Time to turn attention to something boring but really important.

The Gearbox.



This gearbox is quintessentially Kumata.  Every KMT loco except the Centipede uses some variation of this 2-piece gearbox.  (in fact the Centipede would have been an outstanding loco if they HAD used this gearbox, instead of the piece of cr@p that it is-- but that is the subject of another thread.)

One of the things that is a little different about this new loco is that KMT plated the gearbox.
I can only guess, but maybe it was because the metal is (or is similar to) Zamac- which might degrade with time.  After all my research into KMT locos and studying all but one, I have observed that the 1983-84 locos do indeed sometimes have some Zamac degradation.  The other locos... not so much.

But there is a problem with this idea of plating which seems like a good idea....


Flash!  And sharp edges.  Study this photo carefully and look!

So I found that a pretty large amount of work was required to clean up this mess.

The worst edges are at the top where the box was plated first and THEN cut.
I filed the edges at a more rounded angle, being careful to get rid of all flash.



In fact I filed and rounded just about every edge-- at least on the outside.  Even the screw holes could have some crud that needed removing.



Now, there is one more thing I do to KMT locos for my sanity.  This has no bearing on the performance of the loco..... but since for most of this year I have assembled/disassembled/assembled/disassembled Kumata locos over and over again, I discovered that the gearbox can be frustrating to work with because the clearances with the main loco frame are so tight.

So a little trick I devised it to file the outer bottom edge at an angle to give me more room to get a gearbox half out (like for removing a truck without removing the headless screw.

I file at somewhere around a 35 degree angle (I'm not sure the exact angle and it doesn't matter.  It is just a better angle than in the dead middle- 45 degrees.



Someone might say--- Whoa!  What are you doing?
But the bottom metal piece only has one function- to keep the headless screw retainer from dropping down and the truck falling out.  So I can thin it down as long as I leave enough metal to retain the truck.



You can see from that shot that it helps to remove just a little bit from the end wings where the screws go.

This fuzzy end shot shows you that I have not even removed 50% of the thickness.



Now, since I'm going to all this trouble, I make sure the slot for the headless screw is cleaned out too.  Since this is the key MOST important surface, I'm working very lightly, holding the file as level as I can and I'm not trying to remove metal, just smooth over any flash or high spot.



While the inside surface is usually pretty smooth, I go over it too.



Here is a before and after photo.  Admittedly, it is not all that pretty, but it does improve the loco.



When installing the gearbox, once the screws are set, back them off a bit.  Then the whole box can lift just a little so the headless retaining screw can fit in.



Sigh.  Getting the headless screw in can be tricky.



Once it gets started, then it can be screwed in place.



And the screws tightened down.


It has taken a lot of work to get to this point.


Next, I can turn my attention to the drive train.

[superturbine]

Lookin good Ron,

[u18b]

I realized there was something very important I forgot to mention.
This would apply to any who also have the old NJ EP-2 from 1983.

As I said earlier, the walked solder joint is very delicate at the cab end.
Which is this end.


But tightening a screw requires a firm grip-- so that's dangerous.

The solution I sort of found out was to NOT hold the sides, but rather hold the power truck.
Further, I tilt the power truck until it hits the bottom of the frame.

So notice how I've tilting the truck so that it is tight up against the loco main frame.  Now, when I "bear down" in the screw, the pressure goes to the truck-- which I an supporting with my hand-- and not to the delicate walkway.