Hello again everyone. Now that most of the shows I attend are over, I've been getting to spend time out in the shop. Regular readers may remember I've wanted to put together a series of 'follow-along' articles on building scale-model engines.
Well, I'm finally in the groove, and the engine I'm starting with is the 1/4-scale 1-1/2 HP Gade available from scale-model engine plans made by Morrison and Marvin Engine Works (previously Morrison and Martin) out of Benton City, Wash. Roland Morrison supplied this model, and it's top notch. I got all the little trinkets and small parts to go with the model, including the spark plug, gears, springs, small bolts and other small items.
After looking over the plans, I decided to start with turning the flywheels. These weighed in at 1 -lb, 1 -oz each before I started and they turned down to 4-1/2 inches, just as the prints indicated. The flywheels are now in primer, and I am still deciding how to paint them and what paint to use. I like red, and Wendel's Notebook calls for Dupont no. 660. This is close to Krylon no. 2118 or Rustoleum Regal Red no. 7765 by Rustoleum (all in spray cans). My local paint shop quoted me $34.89 for a quart of Martin-Senour mix. He won't mix any less, and for this model I only need about 3 ounces, so I will probably use the Krylon spray paint.
Next, I tackled the belt pulley. This took a little thinking, plus trying to remember how I have done them before. My tip on turning a flat-belt pulley is to align the center of the pulley and drill and ream your center first, then make a jig to hold the pulley as you turn the outside to the needed diameter. In this case it was 1.25-inch, with no crown. The pulley is also in primer, and it and the flywheels still need to be broached (3/32 broach). I will do this before the final coat of paint is applied. Total time for this part of the project was less than two hours, and I have figured in my set-up time and turning time.
The next morning I decided to start on the crankshaft, and I have a tip for turning them, also. I built a jig to hold the crank so I can turn the crank throw first. This end is mounted into my lathe and then I use my live center to hold the other end. I center punch a mark in a heavy piece of aluminum and use my dial caliper to mark off the needed throw. In this model it is 0.625-inch. I center bore and tap a 1/4-20 thread into the big end of the crank about 1/2-inch deep and bore a 1/4-inch and a 5/16-inch hole in my jig on my marks to mount in the lathe center for my throw. I use my parting tool to turn the crank to my desired diameter and then the jig is removed from the part.
Now, there are some things you should NOT do. I cut off the excess from the crank and quickly soft-soldered a brass plug between the throws (this helps keep the crank from flexing). I then chucked the crank into my lathe and started to turn it to the needed diameter of 0.312-inch. My distance from the throw to the lathe was set at 2.75 inches and I turned about an inch in length to the diameter needed. I then went to the other end of the crank and started to turn the shaft to my diameter into the throws.
After a few passes, everything was working fine and looked good, so I set the power feed and stood back, when ...OOPS ... I broke the crankshaft.
I have turned probably 15 cranks, and this is the first crankshaft I have ever broken -and it was no one's fault but my own. The crank was not faulty, nor was the lathe.
After standing back and thinking what to do next, I gave some thought to what I had done Basically, I was taking too deep a cut and was power feeding. Also the brass plug I put between the throws was not solidly soldered and fell out of the throws after the crank broke. Bottom line: You should always stay on your toes and never take anything for granted. Now I know better.
I contacted Roland, who graciously supplied me with another crank. I have turned the second crank, and it came out fine. Continue reading about this project in 1-1/2 HP Gade Scale-Model Engine, Part 2. Is this hobby great, or what?
Contact Morrison & Marvin Engine Works at: P.O.Box 555, Benton City, WA 99320; www.morrisonandmarvin.com