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Last updated: 16 February 2012

Sent:	Monday, February 13, 2012 20:27:30
From:	Mark Stewart (
Pictures referenced are found here:

The instruction here are not the best. I did not think to take
pictures until I was half done and I did not write this until months
after I did it. If I can find a cheap (or free) base I will take a
video of how to do it.

Materials List
should be less than $30

2 1 1/4" sch 40 pipe coupler
1 1 1/4" to 3/4" sch 40 pipe bushing
2 20mm ID x 42mm OD x 12mm Ball Bearing
1 20mm ID x 35mm OD x 2mm Needle Roller Thrust Bearing
2 20mm ID x 35mm OD x 1mm Thrust Washers
1 25mm ID x 42mm OD x 1mm Thrust Washer
1 1/4" x 2" galvanized pipe nipple
3 Allen Head grub Screws (can be any convient size and thread)
1 14mm ID x 20MM OD x 22mm Bronze sleeve Bearing
1 5/16 x 3" course thread bolt
Electrical Tape
Hot melt glue

Tools Used

Utility knife (box cutter)
hacksaw (used a sawsall but hand saw will work)
belt sander
tap sized for grup screws
drill bit sized for tap
A cheap rotary stone may be nice for cleaning up in hard to reach
places and flat sanding disc for drill may be needed.

Remove by prying the cover on the bottom of the base.
Remove lever used to tighten EA clutch
Unscrew the bolt take it all the way out You may have to hold the
bottom clutch nut from turning.
Unscrew the castle style plastic nut
Seperate the top from the bottom
Remove the 3 screws holding the upper clutch and remove
Mark the worm gear for up

The upper section was tackled first. The tube from the base has to be
cut off. I cut it off the thickness of the bearing (12mm), plus the
thickness of the thrust bearing assembly (1mm+1mm+2mm=4mm, for a total
of 16mm (see pic 1). It not really critical that it is exact as it can
be adjusted later. I took the upper clutch part (mine was yellow and
has the 3 screws that attaches it to the base) and sanded down the
"fins" on it so the 1.25" coupler would fit over it. The assembly if
formed by the coupler being cut off to fit 12mm above the cut off base
tube previously cut when all the down on the upper clutch part (see
pic 2). The 1 1/4" to 3/4" sch 40 pipe bushing fits over the upper
clutch part and the top of it is sanded to fit even with the tube
previously cut. It will mean cutting off some of the top of the upper
clutch part to be even with the base tube. You can cut and sand until
the parts fit as shown with 12mm left for the bearing to fit in after
the pipe coupler sits down on the base of the upper clutch. (see pic 3
and pic4) I glued mine in place but you can put the small screws up
through the bottom of the yellow upper clutch into the pipe coupler
(see pic 5) but be sure they are slightly counter sunk because the
gear slides along here when the clutch is loose. Test your assembly by
sliding a 20mm ID x 35mm OD x 1mm Thrust Washers onto the upper part
ot the base (metal stem) (see pic 6), then the thrust bearing (see pic
7), then a final washer. Take your clutch assembly with bearing in
place and slide over the upper base stem against the thrust bearing
washer. Put the ra gear against the clutch assembly and see how the
gears mesh. You can sand the inside of where the roller bearing
sitswith a disc sander than fits in a drill, or add 1mm washers for
spacers. I had to add a washer for my worm gear to be centered in the
worm (see pic8). Now drill holes for grub screws at 60 degree
intervals around the clutch assembly as shown and tap. I made sure I
drilled through both the pipe couple and pipe bushing to allow for
extra threads but it really isn't that important (see pic 4). The grub
screws attach the clutch assembly to the base tube, replacing the
small screws originally used. Just don't over tighten as you could
crush the tube and they don't have to be real tight anyway. Here is
how the assembly looks without the worm gear in place (see pic21)

Next is the lower bearing. The fins in the base where the plastic
castle nut was were cut off and sanded smooth (see pic9 and pic10). A
pipe coupler was sanded with a taper to fit in the area. It was cut to
be about 16mm tall (see pic11 and pic13). The clutch fingers are
dropped in (see pic12). Then the thrust bearing with washer on top
(see pic14 and pic15). The roller bearing is placed on top of this
(see pic 16).

Now the shaft has to be extended. Tap the center of the upper part of
the base stem to fit the 1/4" pipe nipple (see pic17). Put the white
clutch disc that the clutch fingers press against on the base, place
the worm gear with your up marks up, make sure your thrust bearing and
washers are in place, along with the upper clutch/bearing assembly,
and slide the lower base over the upper base stem. Mark the pipe
nipple even with the bottom of the bearing. Slide the bottom off and
cut the pipe nipple a little shorter than your mark (see pic18). Take
the Bronze sleeve bushing and sand it to fit the clutch nut (see pic19
and pic20). it is going to take the place of the original plastic
clutch nut and the roller bearing will ride on this.

Now assemble the bottom base back onto the upper base. Slide the
bronze bushing over the pipe nipple and inside the roller bearing.
Mine was just a little tight against the pipe nipple so I sanded the
pipe nipple a little but left not too much as it needs to be a little
tight. If you sand it too much you will need to glue it to the pipe
nipple shaft for the clutch to work properly. Take the bolt and drop
it in the hole in the upper base and screw the round clutch with the
holes in it onto the bolt. Tighten the bolt to slide the bronze
bushing in. When the clutch starts to work (the bottom base starts to
not turn freely) stop. Unscrew the bolt a couple of turns and mark the
bottom of the bolt (see pic20). Cut the bolt off at your mark. Now
reassemble but don't tighten the bolt enough to engage the clutch yet.
Rotate the base and make sure it tracks level with the upper base.
Mine did not so I straitened it out and then used hot melt glue to
glue the lower bearing's pipe coupler to the bottom base. As I rotated
the botom section the space between the bottom and top was not even
but the closer spot was always in the same place. In other words the
bottom base was not parellel to the upper part (it came this way from
the factory), so i took the opportunity to fix this issue. It made the
gotos better as a result.

Reassemble and adjust the clutch bolt so the clutch lever will both
engage the clutch when tight but be free when loose. The clutch always
has a little drag but I leave mine engaged all the time and only use
the motors for moving the unit. if you leave the gear off when
assembling you can see how free the unit now opperates (see pic21).
The base and forks are still flexible but the tracking is much
improved. The scope will now operate in polar mode. The whole
operation is easier than it sounds and took an afternoon once the
parts were selected and sourced.

How the clutch works now; the bolt is turned, the bronze bushing keeps
the round holed nut from turning which leads to the bolt tightening.
The tightening bolt pulls the round nut aganst the roller bearing. The
roller bearing presses against the thrust bearing which the pushes up
against the clutch fingers. The roller bearing must be left to slide
up and down in the pipe coupler retainer and not glued in place
although the upper bearing can be glued in place if desired. I used
tape on mine to make it easier to assemble and disassemble.

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