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

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Benjamin Maggi
Posts: 1093
Joined: Wed Apr 25, 2007 10:38 pm
Location: Albany, NY

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

Post by Benjamin Maggi » Thu May 03, 2018 1:35 pm

Um... yes it does! I guess that makes it my 6th year anniversary!
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

nabob
Posts: 9
Joined: Sun Dec 23, 2012 9:13 pm
Location: iowa

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

Post by nabob » Thu May 03, 2018 6:00 pm

Time really does fly when you are having fun; keep it up. Best wishes, Bob

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Benjamin Maggi
Posts: 1093
Joined: Wed Apr 25, 2007 10:38 pm
Location: Albany, NY

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

Post by Benjamin Maggi » Thu May 24, 2018 7:34 am

We installed the side rods (sometimes referred to as coupling rods) on the chassis again and rotated the wheels to see where there was some binding. They turned over nearly perfectly, but there was some slight binding in one or two areas that went away once the nuts on the ends which held everything together were tightened up. In the future I should probably put some threadlocker on them to prevent them from working loose while running the locomotive.

The next step was the leading crankpins, which only have the side rods (“coupling rods”) bolted around them. I had machined them slightly longer in the back and as a result they stuck out of the wheel’s rear face. Less than a 1/32, it came off quick in the lathe. Then, the wheel’s crankpin hole was cleaned as was all surfaces of the crank pin. Some Loctite #680 was applied to the shaft of the crank pin and it was inserted and swirled around the hole to distribute the adhesive, and it was left to cure. I inserted a piece of paper behind the axle box and the thrust washer so that if any Loctite oozed out it wouldn’t bind the two together. The other wheel got the same treatment, and the job was done.

I decided to work on the Return Cranks next. Because this is Hackworth valve gear, all of the motion is on the outside and admittedly it doesn’t look as neat as Walschaerts valve gear. But, it is a lot simpler than inside Stephenson valve gear and easily accessible, which is important to me. Because there was going to be a bit of machining involved, I went with hot rolled over cold rolled as I didn’t want to deal with deflection. I laid everything out on some ¼” thick steel I had on hand. However, it had a bow in it from the so it was first passed back and forth on the belt sander to remove the hump in the middle. It was pretty simple layout work, and a circle tracing template came in handy. Drilling out the holes resulted in me losing some 1/16” drill bits in the process. Cheap steel I would imagine. A large belt sander took care of rounding the ends.
Return Crank layout.jpg
Return Crank layout.jpg (15.75 KiB) Viewed 404 times
The slot was a bit tricky. Jack Buckler’s book instructed not to use a mill to completely make it because it would be too large for a 5” engine. Instead, he suggested milling most of the way through from the back and finishing the slot by using a hacksaw to break through the final 1/32” or so. Instead, I drilled a 5/64” hole at one end of the slot and there was already a 3/8” hole on the other end so we used a hacksaw to carefully connect the two. We later discovered that the slot was too narrow to get a good clamping action, and I used a Dremel tool and a thin file to open it up a bit.
Return Crank layout 2.jpg
Return Crank layout 2.jpg (18.39 KiB) Viewed 404 times
To provide for the area where the return crank clamps onto the end of the driving crank pin, a small flat spot was milled on one side and then a hole was drilled through #28. The bottom portion of the hole on the lower side of the slot was drilled #36 and then tapped 6-32, which allowed a 6-32 SHCS to be passed through from the top and tightened. The ends of the driving crank pins were discovered to be slightly tapered, so I corrected that. I then used an expanding reamer to open up the 3/8” diameter hole in each of the return cranks to just slip onto the ends of the driving crank pin. Once that was done, we put the return cranks in a vice and tightened them at the slot a little bit. After that, they clamped tightly but it of course will need to be drilled and pinned later on after adjusting the valve gear.
Machining Return Crank tightening bolt location.jpg
Machining Return Crank tightening bolt location.jpg (23.77 KiB) Viewed 404 times
The hole at the other end of the return crank has the return crank pin pass through it, and it was designed to have a “T” shaped crank pin pressed into a recess from the back. We decided to skip the “T” profile and just have it as a straight pin made from some stainless steel stock which will be Loctited in place. While I saw various methods for retaining the cranks and vibrating levers on the pins, most involved drilled a hole through the front (visible) end of the crank pin and then using some sort of bent wire that looked pretty ugly. So, I instead cut slots in the ends of the pin to fit c-clips. A specially ground tool my friend had made cut the slots real quick. I actually cut slots on both ends of the pin, and when it comes time to Loctite them into the return cranks I will push the pin snug against the ring on the rear and later mill it away once the glue cures.
Return Crank on Crank Pin.jpg
Return Crank on Crank Pin.jpg (22.78 KiB) Viewed 404 times
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

User avatar
Benjamin Maggi
Posts: 1093
Joined: Wed Apr 25, 2007 10:38 pm
Location: Albany, NY

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

Post by Benjamin Maggi » Thu May 24, 2018 7:43 am

I purchased some cold rolled steel and laid out the parts, using one straight edge from the stock for each side and angling the other one in the middle of the bar. The hole which rotates around the return crank pin has a bronze pushing pressed in and then reamed. One side of the lever was first cut on the band saw and then milled down to the scribed line. There is also a slot that the extension rod connects to, and that slot is supposed to be perpendicular to the vibrating lever.
Vibrating lever layout.jpg
Vibrating lever layout.jpg (22.33 KiB) Viewed 403 times
While I think I laid it out perfectly with squares and such, it isn’t critical as long as the slot is wide enough for the full movement of the extension rod without binding. There are probably a lot more scientific ways to clamp the vibrating lever in the mill vice and then machine the slot, but I went with the easy one. I took a piece of wood and drilled two holes along its centerline and then bolted the lever onto the wood. This held the piece perfectly centered in the vice, and milling the recess slot was then easy. Beyond that, it wasn’t a difficult part to make.

Once I put everything together so far (the driving crank pin, return crank, return crank pin, vibrating lever, and the retaining c-clips) I couldn’t help but push the pieces around and around! One thing I have found useful is to search the internet and especially the company Station Road Steam's "Archives" (https://www.stationroadsteam.com/archive/) to look at pictures of other Sweet Pea and Sweet William engines. There is a tremendous amount of differences in how each person has built his engine, including such things as fittings and joinery techniques. I sometimes print out pictures of various pieces I am working on and keep them as a reference. That explains the picture of the green engine behind my valve gear parts.
Valve gear and picture.jpg
Valve gear and picture.jpg (26.35 KiB) Viewed 403 times
It isn’t much, but it is getting closer to being able to run on air!
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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