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LBSC's Netta in 3-1/2" gauge

Drawing errors in LO-90 sheet 2

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John Fielding09/12/2012 09:04:26
235 forum posts
15 photos

After a long lay off I have finally gotten around to finish my Netta, started in the 1970s! I have the original Percival Marshall plans plus all the ME copies for this era

I have the frames erected as well as the cylinders machined, slide bars and brackets, internal valve gear all made and fitted etc. The outstanding parts are the valve eccentric rods and other bits and pieces. Y'day I made the valve and pump eccentrics and came to fit them on the driving axle. The frame stay directly behind the driving axle is fouling the eccentric straps. With the eccentrics on back dead centre the frame stay is about 5/8" too far forward. Obviously it cannot be moved backwards as it would then foul the front of the firebox, so something else needs to be done to correct this problem.

Another error I found is the size of the lubricator eccentric on the leading axle. This is never going to fit as its strap fouls the pump directly behind it, or the valve chests on either side of it.

I know that LBSC never built this loco, he admits as such in his notes. If he had he no doubt would have discovered these problems.

The frame stay is fairly easy to correct, discard the original item and fit two 1/4" round pieces drilled and tapped to stiffen the frame in this area, similarr to the Gauge 0 & 1 versions. One can use the bottom hole of the pattern of 4 holes and the top one can be 3/16" down from the top of the frame on the same vertical line, which is 7/8" behind the driving axle. The lubricator eccentric if made to the dimensions on the drawing, even without the strap is a serious problem as it fouls the water pump no matter where on the leading axle it is positioned. I omitted the stub and drilled the hole for the grub screw the same as the valve eccentrics, but this still left too little clearance. The largest eccentric it is possible to fit is only 3/4" over the flanges with about 1/8" throw and a minimum thickness strap.

The lubricator eccentric can be discarded and the lubricator driven off one of the slide valves rod, or the water pump ram pin, which would have been a better idea as the works are a bit crowded in this area of the frames.

Another problem I came across regards the balance weights on the wheels. The castings I had (bought from Reeves all those years ago) has the same protrusion as the web for the crank pins. This presented a problem with it fouling the coupling rods on the leading and second axle. I milled this down to just over the thickness of the wheel tyre, you can't turn it down as the tool would cut into the crank pins boss! The trailing wheel balance weights can be left as cast as there is no danger of it fouling, the driving wheels also can be reduced a bit for the same reason.

Bruce Voelkerding25/12/2012 16:28:25
32 forum posts

I am building my Netta with LBSC drawings and castings from Reeves. However, I am making slight detail changes here and there, hopefully to mke it a bit better. I did not care for the cylinder angle shown on LBSC's drawings, I am leaning towards making it 3 degrees.

I discovered the issue with the Wheel counterweighta as I began to face them and I heard a second click in the interrupted cut as I began to face the hub. My solution was the same as John's, I milled the weights to size. I took the opportunity to reduce the counterweight and hub on the leading axle by 1/32" per side.

As a side note, I machined the wheels on the usual "turned in place" stub mandrel with threaded end. Since all the wheel bores were within .0005" (all made at the same time with the same process), I decided to do one operation per wheel per mounting, i.e. I rough turned all the ODs one after the other, I then finish faced the wheels one after the other, etc. It did mean mounting and dis-mounting the wheels many times, but as I have no quick-change tool holder. The oerations were executed very fast as I was not constantly re-adjusting the tool or measuring size. My old SouthBend lathe is very repeatable. All eight wheels were finish turned in ~10 hours tops.

I do not understand the Frame Stretcher problem dimension. It does foul the Eccentric Rods and I assume that is the reason for the large opening in it. On sheet 2, middle of the drawing, it shows a dimension of 1" from the axle centerline to the face of the Stay. It seems like you erected the Stay backwards, although with the Reeves Hornblocks, that would not fit without maching more off the back face.

I am coming to a point where I have two questions:

1. is there an error with the Eccentric Rods ? Their centers are shown as 5 1/8", but they are attached to a loco style Expansion Link which has a 5 1/4" radius. Although I have a couple of books on Valve Gears, none state explicitly that the radii should be identical. I note they are the same for LBSC's Maisie.

2. Crosshead clearance: the locomotive centerline to cylinder centerline is 1 7/16" + 1/8" + 1 1/16" = 2 5/8". Minus half the Crosshead thickness gives 2 5/8 - 7/32 = 2.406". Compare this to the leading Coupled Wheel 1.641 + .500 +.188 + .062 = 2.391" or .015" clearance per side. Since the wheel face to bearing face clearance is 1/64" per side, this would indicate the clearance could drop to zero when rounding curves which would allow the CrankPin or leadoing Coupling Rod clicking the CrossHead. I am addind clearance to my model. Any comments ?


Bruce Voelkerding26/12/2012 14:43:25
32 forum posts

No one has an answer regarding the question " should the radius of a locomotive type Expansion Link equal the length of the Eccentric Rods" from my email above ? I would appreciate any comments.


mick H26/12/2012 15:35:54
744 forum posts
21 photos

Bruce...according to Greenly you are correct in saying that the radius of the expansion link should equal the length of the eccentric rod.

Seasons greetings....Mick

Derek Drover26/12/2012 21:26:30
86 forum posts

I have a Netta in storage since last summer, so I cant comment on the above questions, but I would suggest NOT plumbing the axle pump in the tender as shown by LBSC. The gauze pickup is shown standing vertically, but once the water level drops to the top of the gauze all it sucks in is air.. plumb it laying horizontally on the bottom of the tender and you have ample water supply.

NEtta's a great loco.. very capable puller (although not the fastest).. mine runs best on smaller coal.

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