Making a Pacific scale model
Lester Bowman's plans for the cam made a complicated machining project much simpler.
By Roland M. Morrison
Most of you will remember Lester Bowman from his articles in Gas Engine Magazine on “Little Sam,” the exquisite scale replica of a 4 HP Samson web-spoke. Others know Lester as a California engine collector who is very knowledgeable about early engines, especially the Samson. In either event, once Lester finished “Little Sam” he and I knew there had to be another replica of a rare California engine. Thanks to Buzz Stetler, I had Pacific Engine Co. factory blueprints and several pages of dimensioned sketches I made from his Pacific. And after Lester studied them, he agreed the world needs a scale Pacific.
The Pacific is an elegant 19th century upright engine made in San Francisco with beautiful lines and cast lettering on the base. It is a gearless 4-cycle engine where the cam roller is moved sideways by a crossover cam so it will alternately lift and miss the exhaust valve. Although this cam was obviously made by the old machinists, it presents a challenge to a home shop.
Model maker Dale Petty, Pasco, Wash., made a crossover cam on a vertical milling machine by plunge cutting as he rotated the blank. He would index the blank a couple degrees, move the axis a few thousandths of a degree and plunge with an end mill to a preset depth. Dale learned the secret to success was to unplug the phone and lock the shop door.
I was looking for someone with a 4-axis CNC lathe or at least a CNC with live tooling when Lester, not realizing the job was impossible, sent me a picture of the cam he made.
His tooling and setup is so simple I still don’t believe it. Lester used an Atlas mill with a vertical head and a rotisserie motor to rotate the cam blank. A handmade face cam moves a spring-loaded shaft back and forth to cut the crossover groove. The result is an exact scale replica of the Pacific cam.
With this ingenuity and Lester’s determination for perfection we can be sure this scale Pacific will be a jewel like “Little Sam” when it’s finished.
Roland M. Morrison is co-proprietor of Morrison and Marvin Engine Works. Contact him at P.O. Box 555 Benton City, WA 99320 • firstname.lastname@example.org