The Secondary Spider
Making a 4.25 Inch Dobsonian
Reflector Telescope
Purpose
The Spider is a contraption to hold
the secondary mirror in place, and allow its adjustment. Like other components such as the focuser and
the mirror cell, you can purchase a ready made spider on-line. The version I made is nicely adjustable
with thumb screws, but because it is relatively small to fit in the 5 inch
tube, in order to fabricate it I needed
to use a milling machine. This is not
a machine for the faint of heart. I
built a previous version using just wood.
This one was made from plastic.
The design is almost identical to the mirror cell except for size. There are two cylindrical parts that are
connected by three bolts. The mirror
side needs to be cut at a 45 degree angle for the mirror. The mirror is attached with silicon
caulk. The connection to the tube is
made with long bolt threads, cut with a hack saw.
Assembled View
Disassembled View