"Catherine", a USA "Sweet Pea" engine build

[Benjamin Maggi]

After a bit more work both eccentrics were finished. To get the straps to fit cleanly onto the eccentrics themselves a bit of final adjustment with a file on the eccentric was necessary. This not only cleaned up the sides of the groove but also put a nice finish on them. With the strap pieces bolted up, they just rotate around without binding. And, as I have been told, they will wear in and get looser over time. For my purposes in using them as a water pump it should be fine. Small holes were drilled at the top to allow for oiling.

[Benjamin Maggi]

Drilling the off-set hole for the axle should have been a simple thing. Once the eccentrics were put in the 4-jaw chuck and adjusted to run true, the holes were center-drilled and then opened up. I decided to use axle stock that was 1.375" in diameter instead of the 1" as called for in the plans, but I didn't adjust the location of the axle hole in the eccentric. As the diameter of the bottom of the groove is 1.25" and the axle hole is off-set the center of the eccentric by 3/8", it means that there is only 3/16" between the axle and the bottom of the groove. I hope this is okay. Since the eccentric itself shouldn't wear very much I won't worry about it.

During machining of the second eccentric the center-drill bound up in drilling for the off-set and cracked, causing a bit of a scare. After using pliers to extract the remains, we used another one and it too bound. Cutting fluid was used, we checked our speed and it was okay, so I don't know why it happened. They are made out of C12L14 which should have machined fine. However, eventually we got through.

The holes were then bored to proper size.

Still to do is drill the two holes used to secure them to the axles. These will be drilled at 90-degrees and threaded, and grub screws (perhaps 2 per hole to prevent them from backing out over time) installed.

[Benjamin Maggi]

The drivers on the engine are supposed to be "disc" style, or very plain. While it is true that some Bagnall engines had spoked drivers, their appearance wasn't what I was looking for on my engine. Thus, when it came to finding suitable drive wheel astings for the engine I ran into a wall. The raw castings are available from the UK, but including shipping they were close to $400 for just the four wheels. That would have crashed my budget. One local source here in the USA for Sweet William castings is Model Steam Railways, a small supplier who only has select castings available for the engine. (http://modelsteamrailways.webs.com/) His products looked good, but to get the drivers I needed to buy a set that included the pony wheels, axle box castings, and brake shoes. I didn't need any of those parts, so I passed.

I inquired in the Marketplace section (http://www.chaski.org/homemachinist/vie ... 30&t=92798) to see if people knew of something similar but no such luck. Many helpful people responded but they all recommended spoked wheels. I admit, for a while I nearly went down that road.

Then, I decided that it was my engine, possibly the only engine I will ever build, and I wanted to do it right. The possibility of getting spoked wheels now and replacing the entire wheel/axle assembly with disc drivers later down the road was intriguing but not very practical.

So, I started investigating having them custom made. While making a pattern myself didn't seem scary, (either wood, or using a 3d-printer), the possible extended time frame led me to instead have someone custom machine them on a CNC machine. A couple of forum members here gave me estimates, and I was in business! I specifically wanted to do all of the tread turning myself, and only wanted the front profile of the wheel and counterweight milled. To me, turning wheels is exciting and though a CNC could do it more consistent I wanted the pleasure of making them. Thus, it was agreed that I would purchase blanks of 7" diameter steel, face them on both sides to 1" thickness, and then mail them to be machined. When they came back, I would turn the treads and flanges.

After talking with the local steel shop, 1" thick slices of HR 1045 steel nominally 7" in diameter were ordered. Those may seem excessively thick it is a scaled down narrow gauge engine. (Just what scale... I am still trying to figure out!) Though I specified minus-0.0" for the thickness requirement, I picked them up after work on the day of a snowstorm and didn't wait to check with a measuring device. I probably should have, though I doubt they would have recut them right then and there anyway. And, I needed them soon. So, they actually turned out a little too thin (0.960") instead of 1" it won't affect the project in any meaningful way. They are still much thicker than the IBLS standards.

The discs were then faced to uniform thickness on the lathe. The outer edges were not turned to final dimensions now, in case during shipment they got dinged or otherwise damaged.

[Benjamin Maggi]

To get the new steel discs ready to ship I went to the local office supply store and purchased some reinforced filament tape. I wrote with a permanent marker my address on all four pieces, in case one should become separated mid-transit. The, they were paired up with cardboard between them and tape together in 8 different places. Then, the two pairs were put into the box and the corners were taken up with cardboard and old shop towels. I finished by taping every corner and joint of the box, multiple times. I used the whole roll! But, the package arrived safely.

[Benjamin Maggi]

While the steel was away being machined on the CNC, my friend took a couple of pictures. First, I drew up my own plans for what I wanted the wheels to look like. This original sketch was based on pictures of the castings available for 7.25" gauge and 5" gauge, and pictures of some finished machined wheels. I had to guess as to some dimensions like the cosmetic side holes' diameter and how deep the step was from the crank area to the thinnest part of the wheel, but I made sure not to get it too thin. Since the wheels started off at 1" thick, I could have a bit of relief milled down and still keep the thickness of the wheel safe.

Then, with my sketch in hand my friend converted it to CAD. I checked his numbers, we adjusted it a little to compensate for the blanks being a little less than 1" thick, and off he went. The first picture shows what the part looked like on his computer. To me, it looks like an egg.

Then, the next pictures show the wheels being cut and the final product.

[Benjamin Maggi]

The wheels arrived back from the shop with a ½" diameter center axle hole, and we used this hole to center the wheels on the lathe. Each blank was held in a four-jaw chuck, and in the tailstock was mounted a ½" diameter steel rod. The tailstock was advanced toward the wheel and the wheel was adjusted until it was centered to the rod. Then, the four jaws were tightened well. Then, the jaws were tightened up.

The axle holes were opened up with a ¾" drill, then a 31/32" drill, and then the hole were bored just under 1" diameter. A 1" diameter reamer brought the hole to final size. While searching for a 1" reamer I checked the online marketplace here and a pretty interesting discussion ensued. (http://www.chaski.org/homemachinist/vie ... 18&t=96305). Always check multiple forums, as you never know where you can glean important information.

I admit, sheepishly, that I originally purchased the wrong size reamer. I tried to order it through Grizzly but they were backordered (they did send me an email in April quoting a specific day in September that they were receiving more stock- how in the world could they know that I wonder?) so I went with Enco and in my haste I ordered the wrong one. Instead of a 1.0" reamer I ordered a 0.1" reamer. The prices were similar and I never caught the mistake. It wasn't until weeks later when I went to take it to the shop that I realized the package was much too small to hold a 1" diameter tool and that is when I felt really stupid!

Next, each wheel was installed on a faceplate chucked in the lathe with a 1" pin sticking out of the center. The faceplate was just under 7" in diameter, the dimension of the wheel on the flange, which meant that over-zealous turning would not only result in an undersized wheel but also cut into the plate. The faceplate had a bolt installed on the front which fit into one of the cosmetic counterweight holes and this bolt drove the wheel around. Each wheel then was turned to the final diameter.

[Benjamin Maggi]

Due to the set-up in the lathe the front edge of the wheel could be broken over with a file, but the rear edge was blocked by the faceplate and thus resulted in sharp edges. I cut myself several times, which taught me that in the future perhaps a smaller diameter clamping plate with more clearance would be a good idea.

Then, more lathe work involved cutting away the treads using a specially shaped bit. The wheels were mounted as before but for extra stability the tailstock was slid forward with a live center mounted. A piece of pipe was put on the center and pressed into the face of the wheel, thus supporting it from the front. Taking about 0.040" off at a time, it was advanced into the wheel until it reached the flange area. A stop on the lathe track prevented accidently removing too much metal. The chips came off hot and blue, but the lathe was up to the challenge. We made sure to cut the treads with a 2.5 degree taper angle.

There were a ton of chips after the 4 wheels were finished. I couldn't believe how many there were, or their volume. The lathe had to frequently have the chipped hauled out with a small crow bar to clear the lower bin.

[Benjamin Maggi]

The flanges were done with a profile tool from the late Bob Holder, which worked really well as long as the lathe was set to turn at a slow speed and copious amounts of oil were used. I know that people have used files to do this but I highly recommend a committed cutting tool. It made the process very easy and consistent. Some remaining file work cleaned up the front edges, smoothed over the back, and blended in the tread with the flange.

[Benjamin Maggi]

The wheels finally were drilled to final size for their crankpins. Using a rotary table on the mill, each wheel was bolted to the rotary table which had a 1" diameter rod in the center. The mill table was shifted sideways to account for the throw of the wheel (in this case, 1.5") and a pin inserted into the existing crankpin hole helped us align the mill head. The table was then locked except for up and down travel. Each wheel could then be bolted to the rotary table, drilled 23/32" diameter, and reamed out 0.75" diameter.

[Benjamin Maggi]

The crank pins are next, and I have been pondering these for a while. Originally, the Sweet Pea designed called for marine style drive and connecting rods with the ends separate pieces that would bolt around the pins. Thus, any incorrect machining of the rods could be corrected by filing or shimming the rods. I didn't particularly care for the appearance of the round cross-section marine rods and wanted to build conventional, one-piece (not counting any bearings) rods. These would slip over the crank pins and somehow be retained.

This meant that redesigning the crank pins was in order. Whereas the original had grooves cut into the pins that the rods rode on, the new pins would need some sort of retainer at the end to keep the rods from sliding off. Again, the community here provided me a wealth of information (http://www.chaski.org/homemachinist/vie ... =8&t=95312). After looking at crank pins used for Allen Models' mogul, Little Engines' 0-6-0 switcher, and Kozo's A3, I decided to base mine off of the LE design.

The next issue was what type of steel I should use. Originally I was going to use 1045 but changed my mind and decided to go with something a bit harder. I won't be using any type of roller or needle bearings on the rods so I don't need a hardened surface, I still would rather the rods wear more than the pins. Drill rod sounded great but my local steel shop couldn't sell me anything less than 3,' and I didn't want or need that much. After a call to the forums here (http://www.chaski.org/homemachinist/vie ... =8&t=96360), I settled on 4140 cold-drawn annealed steel.

[xo18thfa]

Where did you get the plans for this loco??

Thanks, Bob

[Benjamin Maggi]

The plans are available from several sources. The engine was originally a 5" gauge engine, and written up in a book by designer Jack Buckler called Build Your Own Steam Locomotive: Constructing Sweet Pea.
http://www.teepublishing.co.uk/books/bu ... sweet-pea/
The book is similar to one of Kozo's books in that it takes a beginner through the steps of building the engine.

Blackgates Engineering in Britain sells plans and castings for the engine. For the 7.25" gauge engine, there are 6 sheets of plans (including one for a marine-style boiler) plus an optional 7th sheet for a steel firetube boiler, and an optional sheet for a ride-on tender. In America, the plans are also available from ModelSteamRailways
http://modelsteamrailways.webs.com/
I don't know if he buys them from Blackgates Engineering and resells them, or if he redrew them in CAD. I ordered mine from Blackgates.

So, there are at least 3 sources that I know of, though to be fair the book will only work for plans for a 5" gauge engine.