Equatorial Platform Design Compromises on this Build

These instructions on building an equatorial platform simplify a very complex design process. One of the main compromises is that I have omitted the calculation of the centre of balance. As such, this assumes that the Dobsonian telescope to be mounted is a conventional 200mm or 250mm f5 type design. It also requires that the telescope is always weight balanced between the mirror end and the eyepiece end. I have not tested this with heavy 2” eyepieces - be very careful if you intend to do this. If you choose to follow these instructions, you do so entirely at your own risk.

The telescope is held on the platform by recesses on the top board. Make sure you are confident that this is sufficient for your latitude or come up with some other way of fixing it to the top board.

These instructions grossly simplify the work of others and have not been endorsed by them. I am particularly indebted to Reiner Vogel and would recommend that you visit his comprehensive website:

http://www.reinervogel.net/index_e.html?/Plattform/plattform_VNS_e.html

I also studied and benefitted from he solutions of Moonshane on Stargazers Lounge:

https://stargazerslounge.com

and finally, Nick Hill suggested using an EQ1 motor rather than designing your own.

Potential modifications can include attaching a compass, attaching a bubble level, amongst others.

Prerequisite Components

• Plywood 1m x 1m x 20mm (Do not use chipboard due to dampness warping) • Aluminium Block: 40mm x 20mm x 100mm • Aluminium Angle: 50mm x 50mm x 3mm - al least 150mm length • Aluminium Sheet: 200mm x 200mm x 5mm • Furniture Adjustable Feet with T Nuts • 8mm Pillow Bearings x 4 • 8mm steel rod 150mm length • EQ1 Motor (ideally with a drive shaft at the lower end) • M20 Bolt 70mm, M20 Nut, M20 washers x 2 • M4 screws 25mm long, washers and nuts • Assorted wood screws

1

Section 1

Top Board Cutting

Use a right angled set square for this.

a. Draw a centreline and measure 540mm this is the top and bottom of your basic shapeb. At the top and bottom, draw lines at 90o from it.c. Measure in both directions from your centrelined. Join the top and bottom edges.e. Cut the wood to this shape.

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50mm

245mm

540mm

Top Board

f. Measure 122mm each way from the bottom centrelineg. Using a protractor, Draw a line from these points at 20o

h. Cut alone the lines.

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50mm

122mm

540mm

20o

122mm

20o

Section 2.

Bottom Board Cutting

a. Place your top board onto another piece of board.b. Draw around your top board to get the basic shape for the bottom board

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540mm

20o angle line

Bottom Board

c. Extend the outer line by 160mm to give the A shaped. Measure across 120mm at right anglese. Draw a parallel line back to the 20o angle line f. This gives you the basic A shape for the baseg. Optional: You can cut out an triangle in the centre to make the whole thing lighter.

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120mm

160mm 160mm

120mm

Optional cut out

Section 3.

Preparing the Aluminium Arcs

a. Select the template for the curve that best matches your latitude here: http://www.reinervogel.net/index_e.html?/Plattform/plattform_VNS_e.html

b. Print off that page.c. Trace it onto the 5mm aluminium sheet and make a series of straight cuts (marked

red) and then file the waste away - aluminium is relatively easy to work with. The aluminium is so thin that you just cut it at right angles.

6

Section 4.

Southern Pivot

Top Board

a. Take a piece of 20mm depth aluminium block.b. Drill through two fixing holes for wood screwsc. Drill a shallow 20mm hole in the centre of the block - about 5mm depthd. ream and widen out the edge of the hole with a file or edge of a screwdriver to create

a sort of crater

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25mm

Southern Pivot

Bottom Board

a. Drill a hole on the centreline to admit a M20 boltb. Put a wide washer on the bolt and insert it through from the bottom. Put another

washer above and secure with a nut, above.c. The bolt now needs cutting to achieve (at least) a 50mm gap when it is in the crater on

the top board. It is essential that this gap is even along the length of the board. The bolt tip needs rounding with a file to allow it to pivot in the crater. (See below)

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25mm

25mm

50mm 50mm

Section 5.

Adjustable Levelling Feet

Bottom Board

a. Drill three holes on the bottom board as shown below to admit M10 boltsb. Obtain 3 adjustable furniture feet as shown below (Google Image search is easiest

way to source these).c. Insert bolt into underside of hole and hammer the T-Nut into the bottom board

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60mm

20mm

40mm

20mm

40mm

Section 6.

Dob Feet Recesses

Top Board

d. Place the top board on the floor with the southern pivot block underneath.e. Place your dob base on the board with one foot on the centre line.f. Move the dob base back until the other two feet are just behind the aluminium arc

segments.g. Mark around the dob feet with a pencil.h. Select a drill with the same diameter as the dob feet and apply tape to your drill to

mark 5mm depth.i. Carefully drill a shallow hole to accept each of the dob feet.j. Tip: Mark the edge of your dob base turntable clearly to indicate the position of one of

the feet - this will help you align the turntable when lowering it onto the board.

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Section 7.

Pillow Bearings

Bottom Board

a. Cut two pieces of 8mm steel rod at 60mm and 70mm length.b. Slacken the grub screws on two of the pillow bearings and insert the 60mm rod - to

form a roller bearing. tighten the grub screws. c. Repeat with the second roller bearing but leave 10mm of rod protruding from one of

the bearings. This will form the drive shaft attachment for the EQ1 motor shaft.d. There seem to be two designs of EQ1 motor. The main difference is one type has the

motor shaft coming out of the back of the box towards the bottom. The other type has it at the top. I was lucky enough to get a Meade box with the bottom shaft design. If you have the other type, you may have to either mount it on its side or upside down to align it with the pillow bearing shaft and maintain a 50mm gap between the upper and lower boards.

e. Even with the bottom design, I found that I had to put a 10mm thick wooden block under my pillow bearings to allow the shaft to line up with the height of the EQ1 motor shaft. You should check this. (See also Mounting the EQ1 Motor)

f. Before fixing the pillow bearings to the bottom board, check that the top board sits on the structure with an even gap along the length of the board. If not, you may have to adjust the length of the southern pivot bolt until the gap is even and at least 50mm.

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50mm 50mm

70mm Drive

Section 8.

Attaching the Arc Segments

Top Board

a. Drill a hole on both aluminium arc segments to admit an M4 bolt (i).b. Insert 25mm length bolts into the holes and secure with nuts. These are stops to

prevent the arc coming off the bearing assembly at the end of their travel.c. The arc should be mounted on the top board using 25mm x 25mm aluminium angle-

piece with M4 bolts.d. The arc should be mounted on the top board with the inner edge aligned with the start

of the 20o angle (Point A) on the board. The upper edge of the arc should be aligned parallel with the top of the board.

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Inner Edge

(i) M4 Stop bolt

Upper Edge

20o angle Point A Stop

Bolt

Arc

The arc segments should look something like this.

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Section 9.

Attaching the EQ1 Motor

a. There are two types of EQ1 Motor designs with the drive shaft at the top or bottom of the design. See below. If you have the top drive type, you will have to invert it to achieve alignment with the pillow bearing shaft and maintain a 50mm gap between top and bottom boards.

b. Both types come with a right angled fixing attachment. You will need to match this up to an aluminium angle piece fixed to the board. These can be fixed together with an M4 bolt and nut.

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50mm 50mm

EQ1

Attach