A friend is a crafter who wants to paint designs, logos, and sayings onto stainless steel drinking cups and asked me to make a cuptisserie for her. It uses the motor from an outdoor grill to spin four cups at about 10 rpm so she can get a smooth continuous application all the way around each cup. The photo shows my finished project. (It is resting on a circular saw to table saw conversion I built. That is the steel plate in the upper left part of the photo.)
I like to weld things when possible, but that can create special problems. This Instructable will use some drawings to show how to build your own cuptisserie without welding.
Here is a brief explanation of what I did. A rotisserie motor from a store that sells outdoor grills is mounted so it stays in place, but can also flop around a little like these motors tend to do. It is mounted with the sides sloping at about 45 degrees to provide more room for the user's hands. (My friend explained she sometimes needs to remove a cup on its sleeve for touch-up painting. Each spindle has a sleeve of 1/2" PVC pipe that locks onto the steel spindle, but unlocks easily.)
I made a hollow core in four little 5" foam footballs. These slide onto the end of the spindles and mount the cups to be painted. The cups slip onto the footballs and compress them a little for a fit.
I did not use the square shaft that comes with the rotisserie kit, but made a square end on a round shaft to fit into the motor drive socket. A plywood disc about 4" in diameter fits onto this round shaft and has a round rubber belt for an Oreck vacuum cleaner in a groove around it. This disc and rubber belt use friction to drive two other wooden discs connected to shafts.
YouTube has a number of videos showing various designs for home-built cuptisseries. One commercial version solves the problem of power transmission to other spindles by using a separate motor for each spindle. A four spindle machine lists for almost $400.
Step 1: Steel Shafting
I recently gained access to an old Atlas metal lathe. The internal diameter of 1/2" PVC is really just a little more than 9/16" and not anything standard. I had part of an old grass catcher from a lawnmower that was round and about 5/8" in diameter. I was able to cut two pieces about 13" long each from the grass catcher attachment. I was able to turn them down to a diameter that nicely slips into the PVC.
No Lathe Workaround: Use 1/2" steel rod for the shafting. (See the second graphic.) Later, when ready to assemble the cuptisserie, wrap four turns of plastic electrical tape around the 1/2" steel rod to make a smooth fit with the PVC. See the third photo.
Step 2: Motor Drive Wheel
See the first photo. I turned some 5/8" shaft from the grass catcher down to 3/8" and ground flats on it by hand to make an end 5/16" square. The square end fits into the socket on the rotisserie motor.
See the second photo. I drilled a 3/16" hole through the round portion and inserted a tension pin. Make a 4" disc with a lathe or a hole saw. Drill a hole in the disc to fit the round shaft. Slide the disc on and mark the location of the tension pin. I used a Dremel tool to make a recess for the tension pin so the disc's rotation is locked to that of the shaft. Note: If you are using a 1/2" shaft rather than 5/8" as I did, you might want to use 1/8" tension pins. Drilling 3/16" out of a 1/2" shaft does not leave much strength where the hole is made. A 1/8" tension pin will likely be quite adequate.
See the third photo. In this situation I added a second hole for a second tension pin set at 90 degrees to the first one. This pin locks the disc firmly against the first tension pin in its inlet. (On the two driven discs I used a similar arrangement, except that there is no second tension pin. Instead, I placed a screw into the plywood at each end of the tension pin. The heads overlapped the ends of the tension pin and keep the discs in place. I also put a generous amount of JB Weld into the inlets and let it harden around the tension pins. Those driven wheels are very firmly attached to the shafts.)
See the fourth photo. I made a groove around the circumference of each wooden wheel with a depth of about 1/3 the diameter of the round rubber belt. The grooves keep the rubber belt on the drive wheel and aligned with the driven wheels. I had the luxury of a lathe for this. Grooves could be done by hand with a rat tail wood file. Try to make the grooves consistent.
Step 3: Bearings
I used steel spacers from the hardware department of a big box home improvement store for bearings. I bought them a little long and cut their length in half to economize. They are smooth inside and will work fine for something that turns only 10 rpm.
The problem I had was that I welded them in place on angle iron. I was careful to have the shaft inside each bearing and running through its mate to keep them in alignment while welding. But, when welds cool things move. A couple of times I had to bend and twist to keep the shaft from binding inside the bearing because things moved when the welds cooled.
For something that turns at 10 rpm, a properly fitting hole drilled through wood and lubricated with some motor oil that soaks into the wood will do fine and last a long time. (My father had a grain combine that used oil impregnated wooden bearings on two crankshafts and turned very fast. He cut a lot of grain around our neighborhood. Those bearings were greased everyday and replaced after a season or two when they had worn a little loose, but they worked just fine.) See the second graphic. It is a wooden box with holes drilled through both sides at the same time for proper alignment. One side is screwed on and can be removed to insert the shafts and driven wheels. The holes fit the metal shafts. (In this wooden box that is a mount for the spindle shafts and driven wheels, the holes are 7" apart on center. That allows plenty of room for cups to be near to each other and for an operator's hand to remove one cup for touch-up painting. Leave enough space for the driven wheels, too.)
Step 4: Motor Mount
I made two of these mounts for the drive wheel and rotisserie motor from angle iron. The pieces are welded together. They are screwed to the plywood base.
See the second graphic. A piece of bent rod welded to one of the supports keeps the rotisserie motor from falling away from the supports and the shaft of the drive wheel. It fits loosely enough that the motor can flex a little while remaining on the square end of the driveshaft.
The third graphic shows a wooden version of the basic motor mount shown in the first two graphics. 1 x 2 could be used.
I was surprised to discover the rotisserie motor does not always turn the same direction. Sometimes it starts clockwise, but sometimes counterclockwise. I had planned to let the corner of the motor rest on the plywood base, but needed something more positive. I made a support to hold the corner of the motor. See the fourth graphic. If you are using wooden construction without welding, the fifth graphic shows a piece for securing the motor.
Step 5: Spindle Release
PVC pipe slides onto each steel shaft to make the spindles easily removable while in motion. The 3/16" rod in the photo would be a bit shorter, would be in a hole drilled into the 1/2" steel shafts, and would be a tension pin. (See my earlier caution about drilling 3/16" out of a 1/2" shaft. 1/8" tension pins might be better for preserving as much strength in the 1/2" shaft as possible.) I drilled holes at the corners of the pattern and cut between them with a cutting disc on a Dremel tool. The cutting disc was worn so its diameter was less than usual.
The user grasps the PVC between the cup and the tension pin, pushes inward toward the box that mounts the shafts, twist about 1/4 turn, and pulls the PVC spindle off of the axle..
Step 6: Putting It Together
The base should cover the area below the four spindles and a little more to catch paint drips. I used a piece of 3/4" plywood 13" x 29".
Screw the two supports for the motor and driveshaft to the base near its center. (If you ever need to replace the motor or the vacuum cleaner belt, remove the forward driveshaft mount [two screws], slide the driveshaft out of the remaining mount, slide the motor sideways.) Mount the piece that holds a corner of the motor in place.
Mount the driven wheels and spindles shafts in the box for the driven wheels. Use washers as necessary to keep the driven wheels centered between the sides of the box. Drill a hole through the 1/2" spindle rods about 1 1/2" from the outside of the box and drive a tension pin in that sticks out of the rod on one side only. Mount the whole assembly above the drive wheel. See the second graphic. It pivots on its support. (This support could easily be made from wood.) Leave the screws fastening the support to the base a half of a turn or so loose. Add an extension spring with a couple of pounds of pull between the other end of the box and the base to pull the driven wheels down onto the drive wheel. (See the wooden motor bearing support from two steps back. This support for the bearing box could also be wooden and made very similarly.)
Add tape around the spindle rods for a close fit with the PVC pipe so it slides on and off easily, but is not loose.
Add foam footballs or part of a foam noodle for swimming to hold the cup. I cored the foam footballs by making a jagged edge on the end of a piece of 1/2" steel electrical conduit and twisting it into the end of the footballs. See the third photo. It works best if half of the core is cut from one side and the other half from the other side.