Story and photos by Paul Adams, EAA Chapter 675 President
In Part 1 of this series, we made a 75-pound blank, and in Part 2 we made a propeller duplicating machine. Now it’s time to merge those two topics together and use the duplicating machine to turn the 75-pound blank into a finished propeller. This activity actually started before we moved the machine and blank to my garage; the selected place to make lots of chips and I’ll also add, make some dust. While we were assembling the duplicator at Dave’s workshop we performed some alterations to the blank. First was drilling the nine holes in the hub for the eight bolt holes and center hole.
To drill the holes, we took the blank to Ray Robinson’s workshop. Due to the 4 1/8-inch-thick hub, the length to diameter ratio of the holes required some very accurate drilling. Ray’s shop has an excellent drill for that purpose. Thanks, Ray! Job done including the eight 3/8-inch bolt holes and the 2 ¾-inch center hole. A new Forester bit was purchased for the center hole. The hub of the pattern was used as our drill guide for the eight bolt holes.
The other change at Dave’s to the blank involved trimming some excess wood from the blank so we could avoid having to remove this excess wood with the routing operation. Remember the key word is BIG! To do this we decided to use Dave’s band saw. But holding the 75-pound blank in the band saw appeared to be a daunting task. So, Dave came up with a rather clever solution.
He took the bottom of his shop roll-around chair and used it as a rolling base, then added a platform on top which held the big, heavy blank at the same height as the band saw table. Worked great! Especially when Dave’s neighbor came over and lent us a hand. Job done again.
Everything was then moved to my garage for the matching operation. The pattern and blank were placed in the duplicator, aligned, and the routing process was started.
The routing process was performed on both sides and on each end. As needed, I would swap blank ends and/or reverse the pattern each time, routing the rough shape of the propeller into a section of the blank. Due to the amount of wood to be removed, I would first start with deeper cuts then revert to thinner passes as I got to the finished dimension. Each side took many passes and the resetting of the stylus to assure accurate removal of wood.
Before removing the blank, I would sand the area that had just been routed to a rough finish.
At the end of this phase I was left with two things. One, a nicely roughed in propeller and two, a bunch of chips. Two wheelbarrows full of chips! BIG prop! And it’s good to live in the country. I checked online and fresh chips are not good mulch, so out in the field they went along with the chips from the planing process. A big pile! The prop was now weighing about 19 pounds, so from the routing process alone there was more than 50 pounds of chips! And no friends with a hamster! Humpf‼ This routing and rough sanding took two weeks and more than 50 hours. Yep, from 75 pounds down to 19 pounds!
The duplicator does not do the hub area, and due to the concern for chipping with the cherry wood, I did not route the final part of the leading and trailing edges. Dave came over and he and I cleaned these areas up by practicing some of our sculpting skills. A reciprocating drum sander helped a lot also. No more chips but a lot of sanding dust. Next came the varnishing process. Back to Dave’s workshop and some rattle cans of Helmsman spray varnish. In fact, nine coats total with sanding between every third coat.
The resulting finish at Dave’s shop wasn’t to Dave’s and my liking. There was some roughness where the annual growth rings were separated by a wide margin, and the other lighter part of the growth rings had a slight depression. So back to my house for more sanding. As it turns out, the varnish Dave and I had applied hardened the entire affected growth ring area and it made sanding and smoothing go better. A decision was then made to not use rattle cans of Helmsman varnish. I also felt the finish we had applied was too shiny. A study of some pictures of antique aircraft and their propellers helped confirm that feeling.
So a move from glossy to semigloss was decided upon. I consulted with Beth Grumstrup who is an excellent wood finisher. The resulting conversation with Beth was, should we spray or wipe. Yep, I said wipe. Beth was aware of a varnishing technique where the varnish was applied in a thinned condition many times by wiping the varnish on with a cloth. With the awkward shape of the big propeller and the issues of overspray and handling, the wiping technique was thought of as a possible good solution. Plus, the prop didn’t fit in the spray booth, BIG prop! Time now for a test. Below is a picture of the test panel and in the background the awaiting propeller sanded and ready for varnishing using the wiping technique.
Beth spent a few hours with the wiping technique, applying nine coats on the top surface and eight coats to the bottom surface. As painstaking and slow as it was, Beth did an awesome job.
Here are two pictures, the one of the pattern at the start from part 1 and the second, the finished propeller. It is ready for mounting on the refurbished Pheasant.
When I first responded to John Hopkins, I intended for this prop making to be just my project. But as the project was scoped, it became very obvious this was bigger than just me and my small workshop. And I must say, I am glad as it turned out to be a Chapter 675 project. Thanks go out to Bruce, Dave, Ray, and Beth! What fun it was! For those interested, it took a total of 247 hours of joint, fun-filled effort. I think I’ll volunteer myself (us) again!
