Rocker Box and Ground Board

My grandfather helped with most of the woodwork. He has decades of experience on a huge range of different projects. Naturally he was a source of great ideas and tricks to help craft the scope. It was he who suggested using the band saw for cutting the Formica. This was far easier than using a router as Kriege suggests and gave me much better cuts. He also helped when I was having trouble with some of the cuts on the 1" thick wood I made. The saw was creating rough edges on the bottom of the board. When I showed him he gave me this trick of applying masking tape to the underside of the cut, and that trick completely solved the problem.

If that wasn't enough, he also had access to a great shop with tools we could use. Probably the most wonderful feature of the shop was the table saw that was perfectly square. After years of building wobbly, slightly misaligned joints, it was a true joy to have cuts that went together perfectly for this project. The photo shows Grandpa setting up the drill press to cut the feet for the baseboard.

Birch veneer was then applied around the edges of the wood to hide the fact that plywood was used in construction. The veneer I bought at OWL had an adhesive backing that allowed it to be ironed on. After digging my iron out of the far depths of the closet, I discovered that it worked best when I got it nice and hot. Applying a lot of pressure seemed to help as well. Generally I would heat the veneer to put it in place. I then trimmed it with a utility knife. I then reheated the veneer so it got quite hot and pressed very firmly. My sign that it was ready was when the glue began to seep out the sides a tiny bit. By getting things good and hot I was also able to slide the veneer around a little if necessary at the expense of burning my fingers a bit.

Next step was to apply the Ebony Star Formica to the rocker bottom. I think Kriege recommends doing this later so the Formica will cover the dry wall screws he uses in the rocker box. Since Norm Abrams poisoned my brain, I choose to use "biscuits" instead of screws. I had assumed that my bottle of contact cement would be a lifetime supply. So I was surprised to see that I used almost the whole thing up just getting the Formica on the bottom. I need to buy a second bottle to put the Formica on the side bearings.

Once the Formica was in place, I went ahead and drilled the center hole in the bottom of the rocker box. This turned out to be tricky. This was because the board is so big that there wasn't enough clearance in the drill press for the drill bit to reach the center of the board. This was true of not just the drill press in Grandpa's shop, but also with all three(!) drill presses Del has. To get around this I bought one of those cheesy attachments for a drill to turn an ordinary hand drill into a pseudo drill press. I figured that I would never be able to get it truly vertical, but it would be squarer than I could do free hand. I believe that the squareness of this hole affects the accuracy of the digital setting circles, so the less error the better.

The pseudo drill press worked about as well as I expected it would. The bigger problem turned out to be my aging cordless hand drill. Even with the cord plugged in, it could only go for about 5 min before it needed another half hour of charging. As a result it took over three hours to get the hole drilled. The photo was taken during one of many of these long breaks.

I picked up a center pivot kit from AstroSystems. It has nice things like a bushing and a t-nut to screw the bolt into. So with the holes drilled I glued in place the bushing and t-nut for the center bolt.

Biscuits were the next order of business. I cut the biscuit notches with Grandpa in his shop. I wish I had made a phony box with biscuits before making my joints. I did one test cut, figured I knew what I was doing and then started in on my work. Here are the mistakes I made, cringe as needed:

• My biscuit cutter has an adjustable setting for where on the edge of the board the cut will be made. I didn't lock down the guide and as a result, my cuts crept up until my third cut was no longer inside the edges. Instead it was a notch in the face of the board.
• Some edges are just too short to hold even a small biscuit. I never should have bothered to make those biscuit cuts.
• The switch of my biscuit cutter is on the bottom of the tool. At one point I unplugged the tool and moved it to a new work area. When I plugged the tool back in, I realized that the tool was resting on its switch which was propped up by a piece of scrap wood. Needless to say, the tool suddenly turning itself on surprised me.
• The sawdust bag on the tool fills up fast. Be sure to check it fairly often even if it isn't looking like it is full.

I then glued together the rocker box with biscuits. This went well, but I probably used too much glue. Normally I wouldn't have cared, but since I was doing this on my kitchen counter I didn't enjoy seeing glue drip all over the counter, dishwasher and floor. There are times when there are advantages to being a single guy living alone. While the glue was out, I attached the feet on the baseboard.

The Teflon was then added to the baseboard and the sides of the rocker box. I trimmed the Teflon with a band saw while the Teflon was screwed into the wood. This probably wasn't the best solution as I had a tendency to nick the wood with the band saw blade. The nicks came out with a bit of sanding though, so I don't see that as a big deal. It was nice to see that I could sand the rough edges of the Teflon as well.

I did a lot of sanding to the rocker box, baseboard and side bearings. They had all gotten quite dirty during construction. Plus there were problems like extra contact cement that dripped all over the side bearings.

Varnishing is something I don't do very often. So I learned the hard way about drips. I was smart enough though to remove the Teflon and to cover the Formica with tape. I also covered the pivot bolt hardware with tape. This kept most of the varnish off those. After drying a day, the extra varnish from drips or where the tape was hadn't dried completely. So I could use my fingernail to scrape a little of it off as it somehow got under the tape or formed a ridge where the tape was.

A minor setback occurred when I went to bolt the ground board to the rocker box. Turns out the triangle I made for the ground board was too big. I needed to cut an inch and a half off all around. This meant that the feet for the ground board had to be trashed and new ones cut. It also meant that I had to apply new veneer and revarnish the new edges.

During the trial assembly for first light, one last problem was revealed. It turned out that one of the bolt heads in the mirror cell didn't clear the rocker box. So I cut a small notch in the side of the rocker box about 1/2" tall and 1" wide. This provided just enough clearance for the mirror cell to clear.

On page 122 of the October 2003 issue of Sky and Telescope magazine there was an article titled "Better Dobsonian Bearings" by Martin Lewis. While I was fairly happy with the Teflon/Ebony Star combination, there were times when the bearings stuck a bit and so I was open to trying an alternative. Lewis suggests replacing Teflon with perfluoroalkoxy fluorocarbon or "PFA". So I bought a 1/4" thick chunk. It cut easily on Del's band saw and drill press. So there was no problem installing it in time to try it out at Astrofest 2003.

The jury on PFA is still out, but my initial reaction is one of slight disappointment. When the scope has been moving around a lot recently, the bearings are perfect. There is hardly any extra force needed to get the scope moving compared to the force needed to keep it moving. Once the scope sits still for a minute or two though the bearings get "sticky" again. I may be missing the key aspect of the improvement though. That improvement is that with Teflon, I was never able to train my hand to push the telescope just hard enough to move it a tiny bit at high power. With PFA though, I feel like I was able to learn to move the telescope without having what I was looking at fly out of the field of view of my eyepiece.

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Last updated 1/12/06