Kozo A3 in 1.5" scale - new project

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kvom
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Kozo A3 in 1.5" scale - new project

Post by kvom » Tue Nov 16, 2010 4:29 pm

I have decided to start a build of this loco, hoping to "get r done" in 2 years or less. For a start I have located donor materials for the tender wheels (4140). I plan to purchase the driver castings from Friends Models, and possibly the cylinder castings. I have a few preliminary questions for anyone who has built one:

1) Does it make sense to skip the axle pump and just use an injector? The decision could be put off for the future, but I'd need to make sure to put the eccentric on the axle and potentially drill the mounting holes early on.

2) The shape of the tender makes it difficult to sit on apparently. I am thinking of constructing the tender frame/chassis as per plans, but building a more oblong tender body. Thoughts?

3) Is there any problem in drilling the holes in the spring leaves?

I'm sure other questions will pop up as I proceed.

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kenrinc
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Re: Kozo A3 in 1.5" scale - new project

Post by kenrinc » Tue Nov 16, 2010 4:54 pm

I overbuilt the the axle pump to allow for excess volume. More is better (to a point) as you can always dump it back in the tender. I will have an injector in addition to it.

I think Kozo's fabrication of the tender frame would be overkill in 1.5" scale. Solid CRS for the frame makes no sense and would be put to better use on the engine itself. The tender does not need to be heavy, the engine - yes. I'm just going with angle iron for the frame and a 1/8 sheet for the floor. For the tank I've got a plug I'll be using to do a fiberglass layup of the tank otherwise crs or stainless will work. I'll be eliminating the coal bunker to gain about a gallon of extra water (running propane). Sitting is no problem as the seat is a separate assembly attached by posts at 4 corners. It's been done before. You can build a standard run of the mill tender which gives you the extra water and space but the "charm" of the A3 really shines with a slopeback. Indeed many are drawn to it as it's not something you see everyday. YMMV

Spring leaves are just prehard blued spring steel from McMaster. I drilled them all using a 1/8" carbide spade bit and then milled the slot with an 1/8" carbide mill. They are hard but not that hard. You can also punch them. I didn't try it but I've been told it's possible.

Good luck

Ken-

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Dick_Morris
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Re: Kozo A3 in 1.5" scale - new project

Post by Dick_Morris » Tue Nov 16, 2010 10:51 pm

The decision could be put off for the future, but I'd need to make sure to put the eccentric on the axle and potentially drill the mounting holes early on.
The Stephenson valve gear eccentrics on my CP-173 are split with set screws at 90 degrees giving the final attachment. I don't know why this couldn't work for a pump, although I would probably put dimples in the axle to help the set screws.

kvom
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Re: Kozo A3 in 1.5" scale - new project

Post by kvom » Wed Nov 17, 2010 9:15 am

Is there any reason why 6061 Al couldn't be used for the axles?

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kenrinc
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Re: Kozo A3 in 1.5" scale - new project

Post by kenrinc » Wed Nov 17, 2010 11:32 am

Anything is possible but this engine needs as much weight as possible on the drivers. You may find yourself adding weight when your done. I'd shy away from aluminum for everything with the possible exception of the running gear (7000 series).

Ken-

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Re: Kozo A3 in 1.5" scale - new project

Post by Harold_V » Wed Nov 17, 2010 4:11 pm

kvom wrote:Is there any reason why 6061 Al couldn't be used for the axles?
Aluminum is not known for having good bearing qualities.

Harold
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kvom
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Re: Kozo A3 in 1.5" scale - new project

Post by kvom » Sat Nov 20, 2010 5:17 pm

Well, took the first step today by going to the local steelyard and buying material for the frame and cross members, as well as some round for axles. A friend tells me he can give me enough 4140 round for tender wheels.

kvom
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Re: Kozo A3 in 1.5" scale - new project

Post by kvom » Fri Nov 26, 2010 8:59 am

I made a start by commencing to mill the side frames. Although my BP has a 9x42 table, the effective x-axis travel is about 24", so moving the pieces is needed to machine and drill the entire length. My strategy is to use pair of ground/hardened rods that fit the table slots as a stop to clamp the top edge of the metal against. After milling the pockets for the axle boxes, I have the following questions:

1) How precise do I need to be on the pockets? I don't have any measuring equipment for lengths greater than 6", so I used an edge finder with DRO to measure the pockets and their locations. Seems I made the rear pocket about .002" too wide, and its forward edge .003" too far forward.

2) How critical is the pocket spacing between front and rear? I'm assuming the axle boxes need to be a little loose in the pockets to allow the suspension to flex. I machined the front pockets to have the 11" separation shown in the plans, as opposed to the distance shown from the rear datum.

The book's plans don't have a lot of tolerances given, and as a newby builder I'm a bit nervous. That said, the frame material isn't that expensive, and I could redo them if needed. However, I'm not sure I'd be any better the second time around. These are the only machined pieces too big for my CNC mill for cases where extra precision might be called for.

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Re: Kozo A3 in 1.5" scale - new project

Post by jessebanning » Fri Nov 26, 2010 11:38 am

We had our frames water-jet cut and just did a little clean up machining. If you clamp/bolt the frames together and machine them both at the same time, this will ensure the two side frames are the same. Being a few thousands on the heavy side will not hurt anything. Just keep in mind, the more tolerance you add all adds up. a few here a few there pretty soon you have .020-.030.
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Harlock
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Re: Kozo A3 in 1.5" scale - new project

Post by Harlock » Fri Nov 26, 2010 2:38 pm

Machine them together as Jesse suggests. Then if they're off from the plans, they're both off from the plans equally. There shouldn't a lot of play, only a little bit. A lot of play in the boxes will cause too much play for the valve gear and everything will bang around. The other issue is that the pockets will affect the spacing of the holes in the rods, but the final dimensions for that are measured in-situ after everything else is done, to account for all the error buildup.

In short, it's ok if things are off from plan, but they must be equally off on both sides if you want your wheels perpendicular with the track and perpendicular with the cylinders, rods, pushrods, etc so everything runs true and does not bind or prematurely wear out the gear. This is the one part of the model where its important to have things as accurate as possible.
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kvom
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Re: Kozo A3 in 1.5" scale - new project

Post by kvom » Fri Nov 26, 2010 6:22 pm

I did mill the pockets with the frames bolted together as you say, so that part should be OK. I was thinking that I would make the axle boxes wider if needed to remove slop.

kvom
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Re: Kozo A3 in 1.5" scale - new project

Post by kvom » Mon Nov 29, 2010 8:39 pm

Some progress. I finished the side frames apart from the cutout for the Tee, which I will do on the CNC mill. These were the largest pieces of metal I've machined so far in my young career. I also prepared the stock for the front and rear bumpers from some 1.5x1.5 CRS, so hopefully I can try to assemble the frame in the next week or so. I took advantage of the Enco double offer (free shipping + 15%) to order some more material incl. stainless bar for the fire grate, so that may be next job after the frame. I've also ordered the driver castings from Friend's Models.

Today I score a 3' piece of mystery steel rod 1.25" in diameter. It machined really nicely on the lathe, so I decided to turn a part down to .875 for one of the axles. So now my questions for the experts are:

1) Assuming I'll use green Loctite to secure the drivers, I'm assuming the axle diameter needs to be about .001 smaller than the driver bore. Correct?

2) I have difficulty measuring diameters of round stock on the lathe. Digital calipers seem not to be that accurate, and I'm not comfortable with a micrometer. What I've been doing is setting a mic to what I think the diameter might be and seeing if it slips over the piece, adjusting until it does. Anything wrong with doing it this way.

3) With the smaller model engines I've built, I would just fit a shaft to a hole rather than measuring. I assume this would be OK for loco driver/axle fitment as well. If this is the right approach, then I would want to turn the axle shaft to a few thousands above the target bore, and then fit each end separately. So I left my trial axle at .880 leaving .005 for "fettling".

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