# Making 22 Inches Dobsonian Telescope Body Under 100\$

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### Things required

• 1 inch steel plate 4mm thick,
• 1 inch aluminium square pipes for strutts,square steel pipe 5 mm for body,
• plywood,
• wooden blocks,
• basic welding and carpentery instuments,

### Teacher Notes

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## Step 1: MAKING OF ALTITUDE BEARING.

MATERIALS REQUIRED FOR ALTITUDE BEARING

Can use altitude bearing- more than diameter of the glass preferably 1.5 to 1.8 times .

Make 32 inches semi-circle with 1inch thick steel plate. Give support to the bearing in three equal side of circle. Make two altitude bearing. please see image

## Step 2: BASE FOR PRIMARY MIRROR

Base square with steel pipes of 25inches.

1. Divide it into 4 parts by dividing it into 2/3 & 1/3 respectively (refer diagram)
2. now, weld a sphere made out of door handle at the centre of square for support of primary mirror cell.
3. mirror cell should have a similar size cup for balancing of mirror.
4. drill four corresponding 1/4 holes in base plate and mirror cell.
5. cut head of 1/4 nuts of 3 inch and weld at edge of square.

## Step 3: MAKING OF UPPER OPTICAL ASSEMBLY

1. Take two rings of 24inch in diameter(1 inch width) and joint them in parallel by giving support of 3 aluminium bar (1 feet x 1 cm).
2. secondary holder attachment to be done on upper ring.
3. 6 inch plate is weld at centre of upper ring by using 3 aluminium bar placed at equal distances.
4. secondary mirror holder : Drill 4 holes in plate(one at center & 3 in equilateral sides).

## Step 4: STRUTTS

1. Take 1 inch square aluminium pipe and insert wooden plate inside for stability.
2. Height is calculated according to the focal length of mirror.
3. Drill ¼ size holes at edge of the pipe for connecting upper and lower optical assembly
4. Weld 2.5 inches steel rod at edges of upper and lower optical assembly for strutts attachment.

## Step 5: PRIMARY MIRROR CELL.

• base wooden 25 inches circle in diameter is used
• in the center of wooden plywood attach a metal cup of the size of the sphere which is on the base square with support and secure properly with metal plates so that weight is distributed properly
• drill four holes in the base square corresponding to the base plate of mirror cell
• place 5 inch 1/4th nut at the corresponding holes made on the woooden base. this helps in collumianting the primary mirror by putting springs in the nut. weight of my mirror is 30kgs & difficult to colluminate such mirrors.
• central balancing of mirror helps & gives less pressure on spring making it easy for the mirror to be tilt & colluminated.

## Step 6: ROCKER BOX

place 2 wooden blocks apart at a distance of 25mm+4mm ( 4mm for the easy movement of the altitude bearing(in my case) 9 inches

make a notch on the wooden block of the size of altitude bearing.

place teflon pads on all four wooden blocks

take a similar size base plate for rotation movement of azimuth

put a teflon on centre. as my assembly is heavy i required more teflon pads

nylon pads were drilled at the base

Participated in the
Space Contest 2016

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## 3 Discussions

Thanks for your inquiry. Glass blank has been made by fusing three plate glass of 19mm in furnace. it work well with no optical issues. could make 4 such blanks of 2 no of 16 and 2 no of 22 inches.