All image credits: Steve Richards
- The ‘Construction’ zip folder is available here
- The ‘Assembly’ zip folder is available here
Constructing the building blocks
The dimensions of our design are based on a 10-inch Newtonian reflector but you can work out what size components you need for any Newtonian with an aperture of 8 inches or more using the ‘Calculations’ spreadsheet in the ‘Construction’ zip folder available at the link above.
The mount is made from 18mm plywood, which has great strength and warp resistance.
We chose to use cheaper ‘Far Eastern’ plywood and give it a painted finish.
Alternatively, you could opt for a natural wood finish if you use the more expensive Birch plywood; this wood has a nicer grain, with fewer knots and blemishes, which gives a better result when varnishing.
Apart from a plunge router, you only need standard tools and sundries.
A full list is included in the ‘Construction’ zip folder.
Power tools – A plunge router for cutting the circular components of the mount; hand drill with 1.5mm and 2mm bits to make pilot holes.
Tape measure and pencil – Accurate measurements are essential for making sure that the mount assembles to a tight tolerance.
Telescope – This project assumes that you own or are going to acquire a Newtonian reflector tube with an 8-inch or greater aperture, as well as suitable tube rings and a pair of dovetail bars.
Wood – External-quality 18mm plywood is ideal for this project as it is strong and warp resistant; make the router jig out of 3mm MDF.
Tools – A standard crosshead screwdriver is needed for much of the assembly; Allen keys and spanners are required for some of the retaining bolts.
Paint or varnish – To give the mount protection from night-time moisture to prolong its life. Make sure the product you use is intended for outdoor use.
Tape measure, protractor and pencil – For accurately marking out the positions of the various components.
Adhesives – Both PVA wood glue and epoxy resin are needed.
To begin the build, enter the nine dimensions required in the yellow boxes of our Calculations spreadsheet.
This generates the sizes for the wooden parts you need in the blue boxes.
Transfer these figures to a diagram similar to the ‘Cutting Template’ in the ‘Construction’ zip folder (allowing an extra margin for the altitude bearing wheels – see Step 3) and ask your timber merchant to cut the sheet for you.
You should end up with six pieces: two equal squares for the base board and rocker box base, one short rectangle for the rocker box front, one long rectangle (we’ll use this to make the box’s sides) and two larger squares for the altitude-bearing wheels.
Note that the ‘Tube to Altitude Bearing Ratio’ in the Calculations spreadsheet defines how large the altitude-bearing wheels will be.
Anywhere between 1.5x and 1.8x is fine, with larger wheels resulting in smoother operation.
Creating a jig
The figures produced in the red boxes in the Calculations spreadsheet are to help you make a circle-cutting jig for use with the plunge router.
This jig is vital to turning the square altitude-bearing wheel ‘blanks’ into circles.
First, cut a piece of 3mm MDF board to the dimensions given in Step 2, then mark and drill 2mm holes in the jig at positions ‘a’ to ‘e’, as indicated by the numbers in the red boxes.
Note that these positions are measured from the inner edge of the router bit.
Replace the router’s foot with this jig, then push a 2mm round nail through position ‘a’.
Place one blank on the table, mark its centre, then drill a small pilot hole.
Place the router and jig on the board, then tap the nail into the pilot hole.
Start the router and plunge it down by just 3mm, then lock it and slowly rotate it around the nail in a complete circle.
Plunge it down a further 3mm and cut a deeper circle.
Continue until you have cut through the full thickness of the board, then repeat for the second blank.
You now have two circles.
Follow one of the lines passing through the centre and mark the one- and three-quarter points; drill pilot holes on them.
Then cut two holes in each wheel, with the pilot holes at the centre and the nail in the jig at position ‘c’.
Keep the two best cut-out discs for use as ‘retainers’ later on.
Altitude-bearing wheel complete, we need to make the sides of the rocker box.
Mark the centre of the side panel sheet (the long rectangle), drill a pilot hole, then move the nail in the router jig to position ‘b’ and cut out another circle.
This time the circle will be incomplete, leaving you with two rocker box sides with one scalloped edge.
Mark the centre of each side and use the router to cut out further circles using position ‘e’.
Finally, cut a rectangular piece of ply 50mm deep by the width of the rocker box base for use as a brace.
This How to originally appeared in the December 2014 and January 2015 issues of BBC Sky at Night Magazine.