Joe Bauer's Celestron 9.25 Fine Adjust Focuser
Here's a fine adjust focuser idea that Joe Bauer came up with. Joe provided
me the vernier speed
reducer along with a set of detailed drawings and I provided the machine
work. Great idea Joe !
The focuser uses a very small Vernier speed reducer that has a
6 to 1 reduction.
The large focuser knob ( coarse adjust ) turns the focuser shaft
at a 1 to 1 ratio.
The smaller knob ( fine adjust ) turns the focuser shaft at the 6 to
1 ratio.
Parts Breakdown
Fine adjust focus knob, coarse adjust knob, vernier, adapter ring ,
shaft adapter
Parts Description
Fine adjust knob: Radio Shack part # 274-424A (1" OD aluminum knurled knob x 1/4" ID)
Coarse adjust knob: 2-1/4" od x 3/4"
& 1-3/4" id . Turned and knurled on a metal lathe. The id
recess was formed using a boring bar with the od held in the
lathe
chuck.
Vernier speed reducer: The vernier units are
$9.95(US) each; item VD61, from the bottom of
this page: Click here
The manufacturer's page is here:
Oren Elliott Products
Note: the vernier needs
to have the dial flange to work for the focuser unit.
Adapter ring: 1-5/8" od x 5/8" & 1-1/8" id aluminum turned on metal lathe.
Shaft adapter: Turned from 3/4" od stainless
steel on metal lathe. ( aluminum would work also )
Reduces from 1/2" id to 1/4" od.
large portion: 3/4" od x 3/4" & 1/2" id
small portion: 1/4" od x ???" one edge flattened
The Vernier speed reducer is very stiff "out of the box". A lot
of this is due to the grease used.
Six small tabs around the od of the vernier can be bent to adjust the
pressure. I also went ahead
and disassembled , cleaned and re greased. After this movement
was very smooth.
Fine adjust focus knob, coarse adjust knob, vernier, adapter ring ,
shaft adapter
Fine adjust focus knob, coarse adjust knob, vernier, adapter ring ,
shaft adapter
The adapter ring is notched to allow for access to the shaft adapter
mounting screw.
Back view.
The two mounting holes in the adapter ring are threaded.
Vernier mounted to adapter ring.
The threaded mounting holes will allow the mounting screws to
be marked from the top side.
Coarse adjust focus knob
Rear view
Completed Focuser
Front view.
The information provided can hopefully help with building your
own focuser or having one built.
I would really like to build one for everyone who ask but at this time
I just have too
many projects going on at once.
Thanks & good luck,
Steve
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