a deck would get us up off the cold ground
Pier Design
We tried out a pier designed by Mark Kaye made out of four 2x4's with sand in the middle
to dampen vibration.
Parts List
One pier:
four 2"x4" x 8' regular (non-pressure treated)
#8 by 2.5" wood screws
carpenters glue
one bag dry sand
two bags of readymix concrete (just add water)
Deck:
x10 5/4"x6"x10' pressure treated decking
x2 2"x6"x10' pressure treated (long outside support)
x1 2"x6"x10' pressure treated (short outside support)
x4 2"x4"x10' pressure treated (short inside supports)
Mount:
1'x2'x 3/4" plywood
Supplies needed:
drill, robertson screwdriver, concrete mixer, level
The Assembly
The Pier
- Predrill pilot holes for the screws into a 2x4. Put glue down along the edge and
put two pieces of 2x4 together into an "L" shape. Screws should be no more than 12" apart.
- Repeat for the last two 2x4's. You now have two assemblies of two 2x4's.
- Put the two assemblies together with glue and screws as above. Let dry
- Dig a hole on the pier spot below the frost line or down to bedrock. We went down about 28" to
solid rock.
- Put the pier in the ground and mix up the first bag of readymix concrete.
Pour it in the hole around the pier and tamp it down with a spare 2x4.
Mix the second bag (as many as necessary) and fill up the hole to just
below the surface (so you can cover it up with dirt, grass or sod and not
have to worry about the lawnmower). Tamp it down to release air bubbles.
Use the level to insure perpendicularness and tamp concrete to suit.
This stuff hardens within 20 minutes. Cover and leave to cure overnight.
That went so well that we went off and gathered the materials for the second pier
and the deck, and within a short time, the second pier was in.
The Deck
We used pressure treated wood, 1.25"x6"x10' decking
The trick here is to ensure that the deck does not come into contact with the piers
and you can notice the 2x4 supports grouped close to the piers and the decking
cutouts around the piers.
The mount
The last step was to assemble the mount.
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- A suitable height was determined by measuring the primary observer's height
and the estimated height of the telescope with mount. The pier was cut off
to that height using a skill saw along all four sides.
- scrap 2x4's were then mounted around the pier to create a larger top surface, making
sure that they are level
- fill the pier with dry sand. It doesn't take all that much, maybe 1/2 bag
or so. Our sand was wet and we had to spread it out and let it dry first.
- Two circles of plywood are cut out, approx 12" in diameter (or whatever size
your largest dinner plate is). Drill 1/4" holes through the centre of both circles.
We mounted a 1/4 x 20 3" bolt from the bottom up,
gluing it in place on the bottom so it doesn't turn.
Glue and screw the first circle onto the 2x4's.
- The second layer is meant to fit overtop of the bolt and move around until
the most accurate polar alignment can be made, then it is permanently screwed
into the first bottom circle.
- With our particular metal mount, the tightening knobs extend below the bottom
surface of the metal mount itself, so we had to make another circle, smaller than the others, to place
the metal mount on. We measured to suit, drilled a 1/4" hole in the centre as well
and mounted the small circle to the top larger circle.
- With the 2nd large circle still "loose" on the platform, we then placed the metal mount
on top, used a large washer and a wingnut to tighten the entire assembly
together
- That night we polar aligned the best we could, tested it again the next night
and finally secured the second circle to the first one with three more screws.
- The telescope and metal mount came off and the whole thing was varathaned
several times, with some decoration (stenciled stars) put in first.
After the fact
The piers and deck have survived the winter and we actually got out and used
them quite often. The decking does need some kind of anti-slip treatment,
especially in the ice and snow.2003 July 15: We found some sticky antiskid tape in a local hardware store
after months of looking. We've been using a heavy guage plastic bag that fits over the mount and
pier and is secured with bungie cords. The plastic has not survived the winter too well
so we are looking for a better, heavier-duty UV resistant kind of cover, possibly the
alumnized mylar/tarp material.
2003 September 03: Extended the deck from 5'x10' to 8'x10' in preparation
to cover it with a metal shed that will be used as an observatory.
back yard,
but tripods are most always inferior to piers, especially if
you want to polar align an equatorial scope.
