Android & Arduino Controlled Projector Screen

Step 10: Prepare the Rod

Since attaching the screen to the rod is done in a later step the modifications to the rod here are simple but not necessarily easy. You need two holes, one on each end, in the center the rod. One of these holds the grommet that interfaces with the pot, the other slip fits with the motor shaft. Finally a set screw holds the motor in place. I recommend not cutting the rod down to size yet if it is longer than you need. This will give you a chance or two to try again if you mess up.

There are several methods you can use for finding the center of the dowel. I tried using calipers set to the radius, using a square to find diametrical lines, and finally settled on using a compass. If you have a better or different method please post it for others to see.

1. Cut a small disk off the end of the rod. The raw end of my rod was not very smooth which made marking hard.
2. Find the radius of the rod. Don't go off of what the lumber yard said, it most likely is not that size. My rod had slight bulges at two points so I tried to pick a decent average radius.
3. Set your compass to the radius and make sure it is tight enough it won't slip.
4. Place the point of the compass as close to the edge of the rod as possible and then sweep a mark across the area the center should be. Avoid placing the point on any irregularities or bulges.
5. Repeat Step 4 at a point that will create a near perpendicular mark with the first. If you want more confirmation you have found the center, repeat again from a third position.
6. You can check how close your center is by placing the point of the compass on the center mark and sweeping a full circle. Don't worry about minor variations, the grommet will absorb those.

Once you have found the center it's time to drill a hole for the grommet. Use the center punch on the point were the compass markings cross. Now begin drilling out the hole starting a little larger then the center punch and working your way up to the outside diameter, or just under it if you have the right size bit, of one of the grommets. The hole does not need to be deep, no deeper than the full length of the shaft that will go into it. This will allow you to cut off the end a couple of times if you aren't happy with the grommet hole without having to adjust the screen size. Secure the grommet in place with epoxy, being careful to keep the center hole clear of excess.

With one side done move to the other repeating the steps above. The two exceptions are: cut the rod to length first ( the width of the screen plus leave an inch or two on each side, maybe more in case of mistakes), and drill the hole to the exact size of the motor shaft.

Finally to make sure the motors rotation is transferred to the rod it is secured with a set screw. Drill a hole, just smaller than the thread size of the screw, on a center line through to the axial hole you have already drilled. This position of the hole is a little tricky, to close to the edge and the threads will split the wood. To far away from the edge and the screw won't seat completely on the shaft. With a clearance hole drilled, use the set screw to cut threads, or if you have a tap use that of course. When cutting the threads, run the screw backwards and forwards as you go, don't just run it all the way down. You will get much nicer threads if you do this.