High-Speed Sanding Lathe
for Large Tubes and Airframes

The biggest pain related to fiberglassing airframes is sanding them smooth. I've spent hours on this task and was never satisfied with the results. Then, using a few spare parts and about an hour of work, I created a tool that cuts sanding time dramatically and improves the final results even more.

The concept is similar to another tool I had made earlier, the Airframe Tube Fiberglassing Rotisserie Stand, only with these modifications the airframe rotates faster -- about 700 rpm. In essence it is a lathe for big stuff, and once mounted on it the tube practically sands itelf. All I have to do is wrap a length of sandpaper around it and watch it spin.

I had originally planned to build a better stand that would also be more portable, but at this stage I just reused the Rotisserie Stand and mounted new components on it. The rotisserie mountings are still in place, but my next project is to experiment with a variable speed control. If I can get satisfactory results I will get rid of the rotisserie motor altogether.

The instructions for the construction of the Rotisserie Stand are available HERE so I won't repeat them on this page; but here are the parts I used for the addition of a high-speed sanding function:

1 Salvaged Air Conditioner Motor w/ 1-inch pulley (7800 rpm) 1 6-foot length 0.5-inch Steel Square Tubing, 1 6-inch length 0.25-inch Steel Square Rod 4 Bearings(1.5-inch external diameter x 0.75-inch internal diameter) 2 1-foot lengths of 1/2-inch copper repair fitting 4 1.25 x 1.5 PCV threaded male coupler 4 1.25 PVC cap 2 3-inch lengths of 1.25-inch PVC 1 Pulley (11-inch w/ 3/4-inch shaft diameter 1 shaft stop w/ set screw, 3/4-inch shaft diameter 2 hitch pins

My pal Brett McFarland started this project by giving me a salvaged air conditioner motor. I found the bearings at Ace Hardware. To mount the bearing I bought the PVC fittings and bored 1.5-inch holes in the end caps. I also bored a 2-inch hole in the frame of my Rotisserie Stand, through which the male couplers were mounted end-to-end using a 3-inch section of PVC to hold them together. Then I put the bearings in the caps and tightened them onto the threaded couplers.

My next problem was like fitting a square peg in a round hole -- literally -- since I had selected a square shaft to mount the airframes as they will keep the airframes from slipping on the shaft. 1/2-inch copper pipe coupling fits neatly inside the bearing, and the 1/2-inch square tubing fits inside the copper coupling -- so the square shaft is inserted inside this coupling material at all points that mate with the round holes. Home Depot sells it in lengths of 12 inches (also called Repair Pipe), which works perfectly for this application.

I wanted to be able to remove the copper tube from the shaft end opposite the pulley, so I slit the tube lengthwise using a Dremel tool with a cut-off wheel. The copper tube slides on and off easily, but it still has enough friction to hold it in place.

The pulley assembly is a little more complicated. I cut off a 10-inch length of the 1/2-inch square tubing, and using a hammer drove it inside a 9-inch section of copper coupling. This leaves one end with 1-inch of the square tube exposed. Into this esposed end, half of the 6-inch long 1/4" square rod is inserted and a 1/16-inch hole drilled for a hitch pin. The pulley was mounted on the other end of the 10-inch shaft. The shaft of the pulley assembly was then inserted into the bearing assembly and secured in place with a shaft stop.

The exposed rod is inserted into the longer section of square tubing, and is also held in place with a hitch pin. This makes the shaft disassemble easily at this joint when mounting or unmounting an airframe on the stand. The 1/4-inch square rod also fits into the rotisserie motor, so the shaft can be moved back and forth without removing the airframe from the shaft.