The Home Machinist!

Hi,

Just in case it isn't clear how the collection of parts in the pictures fit together, here's a scan of the Roy Johnston design from the June 1986 issue of Modeltec. There were very few dimensions given, but in spite of that, Gerhardt made what looks like an exact copy of Roy's design. The series of 4 Aces articles is very good and runs for more than a year, starting in January 1985.

The second picture of the cross section should answer most questions. Running almost concurrently with the 4 Aces series was one on the full size Big Boy & I'm sure Gerhardt got a lot of his information from that series.

Hope this helps.

Richard Trounce.

Hi,

As you can see from the first picture, the superheaters are now permanently attached to the throttle body assembly with silver soldered bronze flanges and nuts. The superheaters are made from thin wall stainless steel tube and are the "hairpin" style. Its a little finicky to get everything fitted the way it needs to be. The hot header had to be flattened to fit against the throttle body so the smokebox flanges would line up with the cylinder piping flanges and the superheater ends have to be staggered "just right" for them to fit on the two headers.

The next picture shows that assembly in place on the front of the boiler as well as the way the boiler fits on the chassis. The throttle body bolts onto the end of the dry pipe and is sealed with an "O" ring. As you can see, the boiler is copper and is made in cylinders just the way the real thing is built. The superheaters will just fit through between the water tubes in the combustion chamber and they extend to within an inch of the back of the firebox. Anything other than the "hairpin" style simply wouldn't fit.

The third picture shows how I make imitation "chequer plate." Yes, I know it isn't the way the real stuff is, but it looks better than plain sheet for catwalks, etc., especially in 3 1/2" gauge. I learned this trick from Harry Hawkins of TSME. Use a coarse knurl and it doesn't look too bad. The knurling process stretches the top surface of the sheet and distorts it, but it isn't too difficult to straighten it out afterwards. The "C" clamped weights on the clapper box supply enough torque so the knurling tool doesn't ride up on the sheet. The sheet shown in the picture will be big enough and is long enough to make all of the catwalks required for Big Boy. In case anyone is interested, this is one thing you can do with a shaper that you can't do with a milling machine.

This assembly isn't permanent yet, but things are slowly moving along. You can also see the temporary position of the 3 propane burners and the axle pump on the chassis just behind. The cab covers the pump and there is also enough room under it for the automatic boiler pressure control when I get it built.

This shows where things are at the moment.

Richard Trounce.

Wow! Whats the diameter of that boiler!?

_________________
Projects:3/4" scale Southern/CNO&TP Ms-4 & 3/4" scale Juliet
RYPN Username: 10stewi
15 years old and loving the hobby!
- Stuart T. Harrod -

Hi Stuie,

To answer your question, the boiler is 6 3/8" dia. at the firebox and 6" dia. at the front. It is made of copper and weighs 80 lbs. The firebox is 13" long at the top and 13 1/2" long at the bottom and it will be fired with propane. The complete locomotive is going to weigh something over 250 pounds.

If you read this thread from the start, you should have a pretty good idea of all the details. The model is big for 3 1/2" gauge, but then the real Big Boys were big too. Engine and tender together are 8 feet long. As I've said before, the original builder did most of what you see, I'm carrying on and making any changes that are necessary to make it a working model. Its a slow process, but I'm getting there. Don and I were very lucky to acquire this model; as you can see from the pictures, Gerhardt's workmanship is very good.

Thanks for your interest. If you have any further questions, don't hesitate to ask. Welcome to the hobby.

Richard Trounce.

Hi,

Lately I've been spending time making the numberplate for Big Boy. For those of you who may be interested, here's how it was done.

Using the original Union Pacific drawing, I started by drawing the numberplate full size in Anvil1000. I next shrunk the drawing to 1/16th full size (right size for 3 1/2" gauge). After using Anvil to make sure all the lines really intersected, I transferred the drawing to Synergy, the 3D CAD program I have. With Bob Schuppel's help (at Weber Systems) I was able to get Synergy (using a .030" dia. end mill) to generate the "G" code required to cut the inside of the shield (the outside was done with a 3/32" dia. end mill with a separate "G" code program). There are over 900 lines in the finished program.

While Synergy has EMC and EMC2 post processors, the code Synergy generates includes "M" codes which the Sherline machine can't use, so they are edited out. It also puts in the proper offset for the cutter diameter you are going to use. I printed out the code and then entered and tested it step by step.

The Sherline "Front End" gives error messages if the code isn't right so you can debug it in "Backplot" before running the machine. In Backplot, G0 (high speed) codes are green, G1 (straight line) codes are black, G2 (curve to the right) codes are red and G3 (curve to the left) codes are blue.

As you can see from the middle picture, I'm using the Sherline CNC mill system, but I've rebuilt the mill into a much bigger, sturdier unit which works much better. As you can also see, I still have to do the "Z" axis, but that's on my "To Do" list. By the way, the shield is just a little over an inch tall and about .9" wide!

Just another small step. Its great when you are finally finished with the code and the machine actually works!

Richard Trounce.

Hi,

Here's a little better picture of the finished shield. Still not quite in focus, but at least you can see how deep the letters are cut into the shield. You can also see some of the tracks left by the cutter. After having the sharp edges smoothed in the acid, it should look pretty good.

As you may be able to tell, I'm pleased by the result, but that's just me.

Richard Trounce.

Nice job. I recently purchased a 3/64" (.046) EM to use in engraving a builder plate. Hope it works as well, given that my mill doesn't really have the RPMs it really needs for this type of job.

Hi kvom,

Don't worry, the little Sherline spindle doesn't spin as fast as it should either and it works OK. What is probably more important is that your machine is solid with no possible movement. Solid carbide deflects less, but is definitely more brittle.

While the original Sherline mill was OK, especially when you consider what you get for your money, my rebuild is much stiffer with no possible movement on the X & Y axes, since they are both 1" dia. Thomson shafts on support rails with 5/8" dia. machine tool quality ball screws. The shafts and ball screws are both sealed. When I do the Z axis the same way, the machine will be even better.

I run the cutter as fast as the Sherline spindle can go and use a feed of .6"/min. which is slow, but works OK. For the cutter size, I know the spindle speed should be at least 15 thousand rpm., but slower speeds work as long as the feed rate is reduced proportionately. It takes 55 minutes to make one pass, but I find that watching the machine work is fascinating and anyway, I have to be there to vacuum out the chips so the cutter won't recut them and possibly break. There is no way in the world you could write that code manually! Theoretically, a faster rpm. would allow for faster feed rates, but I don't want to push the machine too far, mainly because of the cutters.

I'm not sure, but I think the solid carbide end mills can break from fatigue. I've had two break on me after running for a while, a 3/32" one on the Dart number plate several years ago and one of the .030" ones on this shield. They always break where the flutes join the shank (a stress concentrator). It is also possible that they may have been inadvertently subjected to greater stress than they could take, I don't know. An end mill with a shorter flute length would be better, but that's what I can get from KBC. KBC has them in .005" increments down to .010," with 4 flutes and end cutting.

Hope this helps.

Richard Trounce.

Hi,

As you can see from the picture, the number plate is now finished and mounted on the front of the locomotive. It even looks like it belongs there! For anyone who might want to know how it was done, I spray painted several coats of black on both sides of the plate until there were no light spots. Next I got a spray can of automotive white from Canadian Tire, sprayed a light coat on cereal box cardboard and pressed the shield into the wet paint. It took several tries to get the white on all the lettering, but I'm pleased with the way it turned out.

Now I'm starting to design the headlight housing. It has to be big enough to fit the flashlight bits and pieces I'm using, so shape and size have to change slightly to accommodate the parts. For all this finicky stuff, having access to all 2900 of the Big Boy drawings is essential. You get to see exactly how the real thing was built. The headlight sits above and behind the numberplate. As you can also see from the picture, there is still an awful lot left to do on the locomotive.

I've also been working on the "Z" axis for the little mill and an indexing headstock for the same machine. When I finally get the ball screw & nut I'll be able to finish off the "Z" axis and then I'll be able to use the machine again. The indexing headstock will also add to the versatility of the machine.

Like Don, I often have two or 3 things on the go at the same time. That's it for the moment.

Richard Trounce.