Whirligig Blade Hub Construction
Whirligig Blade Hub for Tubular Blade Arms and Bearings
These are the two blade hubs for Whirligig #33. First I cut a 2 1/4″(5.72cm) x 2 1/4″ block from 3/4″(1.91cm) thick African mahogany stock. (Honduran mahogany is not currently available here, but African mahogany is a good substitute suitible for outdoor applications.) The 2 1/4″(5.72cm) dimension will become the diameter of the round hub.
First I find the mid points on the four sides of the block where I drill on a drill press 3/16″ (.48cm) diameter holes 3/4″(1.91cm) deep. I will use 3/16″(.48cm) diameter brass tube for the arms. (Since making this entry, I have switched to using 1/4″(.64cm) diameter, heavy walled brass tube for the arms, so the holes would be 1/4″(.64cm) diameter. Check your local hobby store for the brass rods and tubes. You can order directly from K&S. )
Next I drill a pilot hole through the center of the large face.
Next, using a 5/8″(1.59cm) diameter spade bit, which I have slightly narrowed with a file to give a better fit with the bearing, I drill a hole 3/16″(.48cm) deep on both sides of the block. These holes will receive the bearings, which has a 5/8″(1.59cm) OD, 1/4″(.64cm) ID and is 3/16″(.48cm) thick. (These bearings are the heart of the whirligig. If the hub is made with care and the arms balanced, the bearings will allow the whirligig blades to move in the lightest air. The bearings are made in China and Japan. I get them from Motion Industries, and they cost less than $4(US). The product number is “77 R 4 BRG.” There is a version of this bearing that has a protective dust shield, but the shield produces a lot of friction and the bearing doesn’t work nearly as well. There is also a stainless steel version, which is very expensive and unnecessary.
Whirligig Blade Hubs with Bearings and Brass Rod Shaft after Cutting to a Disk
Using a General beam circle cutter, I cut 2 1/4″(5.72cm) disks from the blocks. The through hole left from the spade bit is less than 1/4″(.64cm) in diameter, so that 1/4″(.64cm) diameter bit on the circle cutter will center itself in the hole. Of course the work has to be clamped firmly in place on the drill press. The maximum safe speed for the cutter is 500 rpm.
Next, using a brad point drill, I enlarge the center hole to 3/8″(.95cm) to give clearance for the brass rod axle. This hole doesn’t need to be exactly in the center, but must allow the hub to turn on the axle without rubbing.
Next, I mark where the 3/32″(.24cm) retaining pin holes will be, in this case 1/2″(1.27cm) from the edge of the block and 5/8″(1.6cm) deep. These holes don’t need to go all the way through the block, but they can, depending on the design. (Since making this entry I have switched to 1/8″(.32cm) diameter retaining pins. Leave at least 1/4″(.64cm) showing so that the pin can be pulled out easily with a pair of pliers.) The exposed pins add to the “action” of the whirligig hub and blades. Insert the brass tubes blade arms in their holes and drill the retaining pin hole and the arm at the same time. Insert the pin to make sure it fits snugly. Mark the arm and the hole it goes in so that you can match up them up later. It’s not possible to drill the holes precisely enough so that any arm can go in any hole.
If these operations are done with care, the two bearings, one on each side of the hub, will be parallel and in line. Actually, the 1/4″(.64cm) diameter axle will not fit through the bearing without first being milled a little. I clamp the axle rod in a drill press. While the rod is turning at low speed, sand a little off the rod with medium sandpaper. The rod should fit snugly through the bearing. There are several ways to hold the bearings in place. In most cases I use chrome plated collars avialable from available from Du-Bro.
