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Construction II


Rocker Box & Ground Board

The rocker has a lot of parts that mate to other parts --- curves to cut to match the bearings, thick sides to support the entire mass of the superstructure, and the azimuth bearing mount to the groundboard. All this adds up to making it a reasonably complicated part to make and get right!

The first task was to make the baseboard of the rocker box. Kriege and Berry suggest bonding plywood plates by putting your car up on top of them. I don't have a place where I trusted I wouldn't get some rock or grit mashed up into the plywood, so I used clamps and huge numbers of astronomy books. :-)

rocker thumb rocker thumb rocker thumb rocker thumb

The sides of the rocker box mesh with the side bearings, so have to be cut to the same curve. I set up a jig for my router to make a large, constant radius curve. I cut each layer of the side boards, then glued them together.

rocker thumb rocker thumb rocker thumb
rocker thumb rocker thumb rocker thumb

The bottom of the baseboard is covered with an entire piece of formica for the azimuth bearing. Since Ebony Star laminate is no longer available, I had to choose a new laminate to work with. Lots of debate has been had on this matter online, and several people have done qualitative tests. I did some qualitative (sliding laminate on teflon pinched between my fingers) and some quantitative tests (measuring the force to start motion for loaded teflon on different formica) and settled on Formica 909-42 Sparkle Finish for my bearing surfaces. The piece is contact cemented to the baseboard, and I used my router to put a beveled edge all the way around to help keep it from lifting up.

rocker thumb rocker thumb rocker thumb
rocker thumb rocker thumb rocker thumb

Since the sides of the rocker box aren't fully linked together over long surfaces (like in the mirror box) and since the rocker carries all the mass of the full scope, I worry a lot about making sure it is structurally strong enough. I used large lag bolts, screwed up from the bottom of the baseboard into the rocker sides. I also don't want to ever have to take the vertical parts of the rocker off for some reason (who knows!), so I don't just cover up the lag bolt heads with formica; I drill through the formica and leave them exposed, but countersunk.

rocker thumb rocker thumb rocker thumb
rocker thumb rocker thumb rocker thumb

The end boards of the rocker are glued and screwed into the rocker sides.

rocker thumb rocker thumb rocker thumb
rocker thumb rocker thumb

The ground board is mounted through the center of the rocker box base. It is sized so the outer teflon pads will touch formica just inside of the line of bolts used to mount the sides of the rocker to the base. I use an Astrosystems pivot kit.

rocker thumb rocker thumb rocker thumb

To keep the groundboard up off the ground and protect it against wear and tear, I replicate what I did with Equinox. First, I make feet out of two pieces of plywood laminated together (cutouts from my side bearings). I attach to these metal angle plates used to attach legs to furniture. The metal plate provides a hard interface with the ground that can easily be replaced if it shows too much wear and tear.

rocker thumb rocker thumb rocker thumb
rocker thumb rocker thumb rocker thumb

Becasue the bearings are so large, at low altitudes the mirror box is completely clear of the rocker box. This means that the bearings can wander side-to-side, and the entire scope could fall off of the rocker! To counter this, the mirror box is slightly wider than it normally would be. I built two riders and mounted them at the lowest part of the rocker box arc. They cross the lip of the rocker side of the bearing, and provide a face for the bearing to butt up against, preventing it from wandering off.

rocker thumb rocker thumb rocker thumb
rocker thumb rocker thumb rocker thumb


[ Mariner Home | Introduction | Optics | Plans | Final |
Construction I | Construction II | Construction III | Construction IV ]
Click images to embiggen them!
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Last Updated: 25 September 2012