Help with Kumata Trainmaster Reconstruction

[mmagliaro]

Well, if it were mine, I'd forget the whole idea of threds.
Could you not just use a piece of steel rod, and rebore things to make it fit?

Assuming you are not doing this with precision milling equipment....  here's a suggestion:

You don't want play here.  So I would not count on just taking a stock piece of steel rod or music wire.
A better bet would be to choose a convenient size of drillbit, one that will be just a little bigger than the current
bore in the gear and the truck holes.  Let's call that drillbit "A". 

The drill rod will give you a very precise, hardened steel pin that will not wear.  VERY important.

Bore out the gear hole and the two truck frame holes, with one size SMALLER  than that, call this drillbit "B". 
This will make the holes about 1/64"
too small (maybe even closer depending on what that diameter really is... If it's a wire drill, you might just be
only a few thousandths too small, which would be great).

Then carefully use a reamer to enlarge the gear hole until the gear will just barely fit over drillbit "A", spinning but not wobbling.

Do the same to the truckholes, but on ONE end, don't ream it as much.   Now, using care, eye protection, a Dremel cut-off
disk, and patience, cut off the smooth shank part of drillbit "A".  Slip it through the larger truck hole, through the gear, and then press
fit it into the other truck hole which was reamed SLIGHTLY SMALLER, and it should press-fit.   

If the fit isn't tight, a drop of LocTite will do the trick.

I wish I had more close, sharp photos of how that gear and shaft fit together inside that truck, but I really think this will work.

[mmagliaro]

Max and John.

If y’all can make that thing.... I'd like to pay you for about 6.

No can do.  Even though I have a milling machine, cutting threads is a special process and I don't have the
skills or the attachments to do it.  Usually, you would cut threads on a lathe.  I don't think it's worth it.
I think converting the thing to a standard knock-out pin is much easier (see my other post).

[u18b]

Christian, the joint in question is merely a square tube.

But forget it.  Also dump the plastic u-joint cups.

If you REALLY want to do this thing right  (assuming you solve the gear pin/screw situation) is to add a flywheel.

Parts are to Atlas JAPAN (not china) SD7/9
flywheel.
U-joint
Hex nut

[u18b]

Reaming everything out and going to a standard knockout pin is a possibility.

But the complication is that in ALL Kumata locomotives, EVERY part (except the insulated wheels) from the wheels, to the truck frame to the sideframe to the drive gear to the gearbox--- all of it is electrically charged.

Now, on one gearbox, the UN-insulated side (I call it the charged side), that would be no problem since the shell is also charged identically.
By the way, the side Christian has problems with is indeed the uninsulated side.

But on the insulated side, you would now have to insulate the knockout pin from the shell- or you will have a short.

I'm helping a fellow right now who has a sentimental SD40-2 where someone had beaten out the screws and made poor knockout pins.  Loco will not run.

He did as I suggested above and just bought a donor loco for the trucks.

[u18b]

Maybe NWSL could build the threaded non-knockout pin?

-Mark

To me,  "threaded knockout pin"  is an oxymoron.  It is contradictory.
I personally would avoid the term knockout.

It is a headless screw.   Or a screw/pin.
My 2 cents.

[ChristianJDavis1]

Okay, knock-out pin gone. I did not know that that was bad, but I figure something with the threads? Anyway, the knock-out pin is gone, so let us focus on the correct part. The flywheel sounds like a very good idea. Is there a way to get the drive completely seperate (motor, shafts, joints)?

[u18b]

Not sure what you mean.

You mean purchase?

Or break down all the parts.

[ChristianJDavis1]

My apologies. I meant to ask whether or not there was a way to break down the pieces, but I think buying extra pieces would be helpful as well (but definitely more difficult to achieve).

[mmagliaro]

Well, no, the knockout pin is still quite possible.   I didn't realize that the pin had to be insulated
on the side of the frame where the screwhead is.  That is an added complication, yes.  But it's not so bad. 

Chuck the drill rod "pin" into a power drill, and run a diamond file
on it to turn down that end, so there's a shoulder on it, the way the original screw-pin was made
(again, this assumes you don't have a lathe).  You'll need a diamond file because drill rod is very hard.
A running dremel with a cutoff disk held against it will also work.  I have turned down hardened steel
shafts that way before.

Questions:
1.
Can you show a close-up shot of just how that pin sits in that truck frame?  The whole screw is brass, so it must be
insulated very carefully on one side.

2.
Oh... by the way, is that pin brass???  It looks like brass.
If it is, then this knock-out pin could be made of brass, which would be a lot easier to work with.

[spookshow]

To me,  "threaded knockout pin"  is an oxymoron.  It is contradictory.

Yeah, go back and re-read. I said "threaded NON-knockout pin" 

-Mark

[u18b]

Haha. Sorry spook.

I had a bad headache tonight and clearly misread.

[spookshow]

Well, no, the knockout pin is still quite possible.   I didn't realize that the pin had to be insulated
on the side of the frame where the screwhead is.  That is an added complication, yes.  But it's not so bad. 

Max, I think you're confusing Ron's "sides". When he says "left side" and "right side" he's talking about the gearboxes in relation to the motor (as opposed to the sides of the actual gearboxes). Did that make any sense?



In the above picture, the left-side gearbox is not insulated from the chassis, whereas the right-side gearbox is (the right-side gearbox has a plastic gasket between it and the chassis and the screws are isolated from the gearbox by plastic inserts inside the screw holes).

-Mark

[u18b]

Mark is correct. 

What we mean is. The knockout pin (if that's the way some one were to go) would have to have the TIPS prevented from touching the shell on the insulated end. (that's the end with the jumper wire).

So on way to do this is to glue a styrene wall to the SIDES of the gearbox.

Make better sense?

By the way, the screw pin is steel, not brass.

[spookshow]

Mark is correct. 

What we mean is. The knockout pin (if that's the way some one were to go) would have to have the TIPS prevented from touching the shell on the insulated end. (that's the end with the jumper wire).

So on way to do this is to glue a styrene wall to the SIDES of the gearbox.

Not sure that's even an issue...? Unless OP used really long knock-out pins that reached all the way to the shell.

-Mark

[u18b]

Mark  you are sort of correct  the real issue is the loosness of the pin  it cannot float.
When i first began this project, i thought how different the Kumata chassis is. No one makes a brass loco the way they do. It is very distinctive.

But the reason i  Thought that is because i have become so accostomed to the newer split frame mechanism.

Then i realized the Kumata design is practically exactly like almost every plastic frame loco from the late 60s and into the 90s.  The only difference is the fact that we are dealing with almost 100% metal parts. That makes a few things trickier.

For example. In a plastic loco, the knockout pin is held in place by a tight fit in the geartower. The gear is loose on the pin and the pin is held rigidly by the gear tower on the truck.

Here, the screw part is what keeps the pin from sliding around. If you were to do away with the screw function, you idealy might be able to open up the gear hole so it is free and loose on the pin, but yet have the pin fiction tight in the geartower.   Possible.

Bottom line. Unlike plastic locos, the kmt pin is what gets electricity from the wheels to the motor. It MUST make good contact with the gearbox WITHOUT touching the electrified shell.