Brass KMT Centipede Re-powering

[Bob Bufkin]

So you got your hands on one of these POS.  Can't wait to see the end results.

And I have 3 brass Trainmasters laying around gathering dust if your intereste in one.

[u18b]

Like I said, using plastic gearboxes required running a jumper wire from the trucks to the motor.



After running this for a while, I found a trouble spot.
My custom frame tended to short on the trucks at the edges.

So I cut the frame back all the way to my screw holes.
No more shorting on the frame and trucks.



So this is then the finished chassis that Kumata SHOULD have placed under the Centipede.



How does it run?

Actually, very well.  Just a little big louder than I wanted-- but hey, brass is rarely quiet.
Flywheel effect works.
No stalls.

And it can easily pull 15 passenger cars by itself.

[pnolan48]

And that things runs!? OK, it does. This thread is a classic bash after my own heart. Who cares what it looks like as long as it runs. Thanks, Ron, you are making my evenings, and encouraging me to do similar bashes.

[johnh35]

What's that old saying about a fine line between genius and insanity.....lol! Nice work!

[mmagliaro]

Ugly?
Ron, I think it's beautiful.

I worry a little about your new idler gears spinning on steel shafts that are running in plastic gearboxes.
I suppose if the gear mostly spins around the axle and the axle itself doesn't spin much, it would hold up.
Won't the axles wear those holes in the gearboxes bigger after a while?   How tough is that plastic?

But anyway, great job.  I think the parts are carefully made and it looks really good.

I love your choice of motor.  That old LL skew-wound motor is as simple and cheap as they come,
and yet, it packs a LOT of power and runs at slow RPMs.  It's a much better motor than it looks.

[central.vermont]

Ron,
It's always entertaining as well as educational when watching your brass reworks!! One question though is how did you fasten the motor? Is it just sitting there or did you put a screw into it from the bottom?

Jon

[u18b]

Ugly?
Ron, I think it's beautiful.

I worry a little about your new idler gears spinning on steel shafts that are running in plastic gearboxes.
I suppose if the gear mostly spins around the axle and the axle itself doesn't spin much, it would hold up.
Won't the axles wear those holes in the gearboxes bigger after a while?   How tough is that plastic?

Max,  I'm not understanding.  3 things come to my mind- not sure which you are referring to.

1.  There is one plastic double gear I added down in the geartower. (that is probably not what you're talking about.).
Anyway, that is Delryn plastic and it is tough as nails.  I'm using it just like Kato designed it.

The housing around it is brass.  Here is another shot of the geartower.


2.  The plastic worm boxes I cast from Alumilite.  The don't hold an idler gear.  They hold the worm.

Now if that is what you are talking about, yes, that plastic is not tough enough for constant wear.
But the shaft has bearings.

Those bearings sit in the frame of the plastic.

YOu can see them in this shot.  From left to right are...
bearing
2 washers
worm
1 washer
bearing

So the shaft spins in the bearings.

There COULD be a wear problem as you describe if the bearings themselves start spinning in the gearbox slots-- and I have seen that with stock KMT locos.  In fact, KMT commonly placed epoxy on the outer edge of the bearings to glue them to the gearbox.



3.  If you are referring to the idler gear in the actual truck itself.
That is brass and I did not mess with that.

You can see that big brass idler gear here.

[u18b]

Ron,
It's always entertaining as well as educational when watching your brass reworks!! One question though is how did you fasten the motor? Is it just sitting there or did you put a screw into it from the bottom?

Jon

Jon.

Not very glamorous.

It is just superglued in place.  Of course with small amounts around the housing edges.... didn't want glue to get into the motor.

So there are two consequences of that decision.

1.  The glue may age and break on day.  When that happens, there will be a terrible rattling sound from the motor rattling- but the motor won't go anywhere since those RS-3 u-joints will hold it in place.

2.  Maintenance might be a bit tougher.  The motor would have to be broken loose to do something with it.

But this is not really a problem since the most common maintenance that is required will be oiling the bearings- and they are in plain sight.   The only reason to break the motor loose would be to change the motor brushes or if the motor fails altogether.

[u18b]

OK, I figured out the casting.

The metal had a high surface tension.  Thus it is impossible to cast it in a mold that is called a "flat". 

For example, this is a Flat.   The TOP surface is designed to be flat.  So you pour your material in there in excess and then place a flat lid over it.  The excess runs out and you let it harden.



Thus one surface is flat when you pull it out.

This is a one-part mold and the easiest to work with.  Great for getting started in casting plastic.

But metal won't work in this mold.  The surface tension makes the metal pull toward itself so it just won't go down into all the crevices.

So since I have a few molds to work with for this project, I tried an experiment and it worked.

This mold was fatter.  And I could still use my flat RTV roof to go with it for a 3-D two part mold.



So I took my Xacto knife and cut a funnel out of one side.   This mold will be poured from one end- the part will be sideways.  I also cut a small channel for air to get out.  So metal will flow down the funnel, and air will come out the small hole until metal comes out the small hole too.

I built a little contraption to hold the two mold pieces together since it would be too hot for my fingers.

I heated the two mold parts in my toaster oven for a couple of minutes at low heat (under 200).  I wanted to be pouring liquid metal into a HOT mold so that the liquid would not immediately be cooled by a cool mold and clog up the flow.

I melted the Temp-Lo alloy in a little pan on low heat on the stove.  I guess this stuff melts probably around 180 since years ago I remember this stuff and being said to melt in boiling water (212 F).   I then poured the melted alloy into the mold.  I rapped the contraption a little once or twice to try to get any bubbles to rise.

I then let it sit and cool for about 10 minutes or so until the top was hard.



When it had solidified but was still warm, I placed it in cold water to cool it faster.
Pulled the two parts of the mold apart.  (you can now see the flat lid).




Here I have broken off the air channel excess metal, and I'm trying to lift the metal from the mold to break it free.



Now it is coming loose.



It worked.  Not bad.  No bubble holes.


I trimmed off the funnel excess.
This metal is a little coarse for use as casting something really nice (like a steam boiler shell), but it is great for my purposes.



Now I'll cast another, and file it down to smooth it up.

[u18b]

I installed my new castings in my Centipede.
It worked.



Nice to have this back-up plan for work with Kumata locos.
There are about 4 or 5 different gearboxes.  Now I need to make molds of as many as I can.

The ones in the Alco era are the worst about deteriorating.  I rarely see the gearboxes in an RS-3, RS-2, RSC-4/5, or RS-1 that look decent.

[mmagliaro]

Whoa.... cast metal gearboxes.   Cool.

Ron, I misunderstood and then figured it out when I looked back through the photos again.  Right,
the Delrin idler's axle is in the little brass box you made, not in the plastic.   
Just... ha... nevermind        It should work forever.

If you're any concerned about the superglued motor, use JB Weld instead.  It won't break.  And as strong as it is,
if you just lay some along the two seams at the base of the motor where it touches the frame,
you can always get it loose just by running a hot soldering iron along the JB.  It will melt and let go easily.

[pnolan48]

Ron,

Suppliers for the molding materials and low temp alloys? I think most good silicon molding materials such as MoldStar 30 will do OK; let me know if I'm wrong. I've googled low temp alloys but can't make much sense of the sites.

[u18b]

Pete, I have not done much beyond a little looking...

But when I get ready to buy, it will probably be these folks I found on the web.

http://www.csalloys.com/products.html

What they do not have on this site is the relative hardness.
For example, melting point of lead is a whopping 621 F,  but it is a very soft metal.

Pewter has a lower melting point in the area of 400 F.  But it can still be pretty soft.

On the other hand, that old Walthers Temp-lo melts around 180-200 F but  is fairly hard.   It is still soft enough to drill with no problems, but it takes a lot of effort to bend it.



What I don't know is what alloy the CS sells is fairly hard.

[pnolan48]

Ah, Walthers. Doh. I'll see if they still sell it.

[eric220]

Lookin' good, Ron!

Your competition has slipped again.

http://www.broadway-limited.com/schedule.aspx

August for the Centipede and "fall" for the M1.