ETX TECHNICAL TIPS Last updated: 12 August 2005

Model 884 tripod tune up

Sent:	Thursday, August 11, 2005 05:04:54
From:	Terry Godfrey (terry.godfrey@materials.oxford.ac.uk)
I have owned an ETX125 supplied with the 884 tripod for a couple of
years and have always been disappointed with the tripod due to excessive
play in the tilting plate axis, excessive play in the latitude adjusting
bar clamp and the lack of fine tuning when setting HOME in Polar mode.

I recently dismantled the tripod into its component parts and saw ways
to improve all these faults - things that Meade could and should have
done at the manufacturing stage. The remedies outlined below should only
be considered by ETX owners who have access to a metal working lathe and
an electric pillar drill. Do not be tempted to drill holes with a
hand-held drill! The Tilt Stage Axis: Meade relies on passing an M8
screw (8mm metric thread which actually has an outside diameter of
typically 7.8mm) through oversize clearance holes (typically 8.5mm
diameter)in the Tilt plate and Base plate of the tripod. It is hardly
surprising that the tilt axis is sloppy. Tightening the self locking
nuts is not the answer as this will not prevent axial slop BUT will
increase wear on the relatively soft aluminium alloy plates. Also having
the sharp screw threads rubbing on the plates' mounting holes is also
poor design.

Solution:
1)I enlarged the holes in the Tilt and Base plates to 11.0mm diameter.
NOTE: It is essential to firmly clamp the component, making sure the
hole to be enlarged is perfectly at right-angles and CENTRED on the
drill. I would recommend running the drill at high speed and using
intermediate sized drills i.e. 9.5 and 10.5mm rather than drilling out
in one bite.

2) I discarded the 25mm long M8 set screws supplied by Meade in favour
of 25mm M8 bolts with a smooth shank of 15mm length and a threaded
portion of 10mm length which is all that is needed to secure the
components. I re-used the Meade washers and self locking nuts.

3) I machined a couple of brass sleeves 12mm long (one for each bolt)
such that the outside diameter was a smooth sliding fit in the new holes
of the tilt and base plates and the inner diameter was a similar sliding
fit over the smooth shank of the bolts.

4) When the Tilt Stage is reassembled (a little grease should coat the
sleeves' surfaces) , the result is silky smooth with no axial slop. The
self locking nuts should be tightened sufficiently to prevent end float
of the bolts and NOT rub on the plates.

The Latitude Clamp bar:
When dismantling the tripod components I was staggered to find that
Meade had wrapped Sellotape around the clamp bar to "improve" the fit in
the tripod base plate.

With the Sellotape removed and the clamp bar reassembled in the tripod
base, there was unacceptable movement of the latitude bar with the Clamp
bar fully tightened (hence Meade's solution with the Sellotape!).

Solution:
I had no choice but to machine a new Clamp bar with an external diameter
to produce a sliding fit in the tripod base (after first cleaning paint
out of the holes!).

Fine Tuning Latitude Adjustment for Polar mode (see photograph):
Even if your 884 Tripod does not suffer from any of the defects that
mine used to,  being able to fine tune your local latitude when setting
HOME in Polar mode is easily attained with a modification so simple I
don't know why Meade hasn't already incorporated it (perhaps they have -
my tripod is 2 years old).





1) Remove the Latitude bar from the tripod by first unscrewing the cross
bar at the upper end that supports the scope in Alt-Azimuth setup and
then slacken the clamp bar.

2) The diameter of Meade's Latitude bar is just right for cutting an M10
 thread (metric thread 10mm diameter) on the lower portion. It is not
necessary to thread the entire length of the Latitude bar - just
sufficient for your observing latitudes. The design of the Set knob (see
below) allows for you to see your local latitude as engraved by Meade on
the bar. This allows for a speedy but rough setting. For example: my
latitude is approx. 50 and the threaded portion extends to approximately
35.

3) A Set knob is machined for the Latitude bar. I chose a diameter of
20mm by 20mm tall internally threaded M10 and extended the top for a
further 20mm with an outside diameter of 14mm chamfered at the top face.
The inside diameter of this section being 10.5mm  (i.e clearance - not
threaded).

When setting HOME in Polar mode, it is not necessary to clamp the
Latitude bar - the weight of the scope will ensure a positive contact
with the Set knob allowing fine alterations to be made. When adjustments
are complete, lock the Altitude bar with the Clamp bar.

Regards

Terry Godfrey
Oxford, UK

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