ETX TECHNICAL TIPS Last updated: 11 April 2004

Meade Electronic Focuser

Date: 4/8/04, 08:25
From: Niall Saunders (niall@njs101.com)
I have just completed the repair of a Meade Focuser for another visitor
to Mike's ETX site - and during the process I have managed to fine a
supplier for most (but not all) of the gears inside these units.

However, none of the gears are 'standard', ex-stock - but I have been
able to take 'stock' items and modify them on my lathe to do the job.

If you are looking for the gear to fit the focuser shaft on an ETX-105,
the following details apply

Gear Overall Diameter = 24.0 mm
Gear PCD = 23.0 mm
No. of teeth = 46
Gear MOD value = 0.5
Gear Thickness = 2.0 mm
Gear Boss Thickness = 5.0 mm
Overall Gear Thickness = 7.0 mm
Gear Boss Diameter = 10.0 mm
Gear Bore Diameter = 5.0 mm

For anyone looking for the same gear to fit an ETX-125, all of the above
details apply,
EXCEPT
Gear Bore Diameter = 4.0 mm (the ETX-125 has a NARROWER focusing shaft)

I can source these gears made out of DELRIN (a high-grade plastic, equal
to - if not better than - the other plastic gears in the focusing unit),
rather than Brass, as is used for the original Meade component. However,
the replacement gears are NOT identical, in the following measurements:-
Gear Boss Diameter = 12.0 mm (this is NOT critical, it will just give
'extra meat' for a locking screw to bite into). Gear Thickness = 4.0 mm
(this is NOT critical - it may work perfectly well using this 'stock'
item, but could easily be lathed, or filed (sandpapered) down to the
appropriate thickness (remember, it is an easily machined and worked
'plastic' gear).

Also, the gears are supplied WITHOUT a tapped hole for the locking
'grub' screw. This could easily be drilled and tapped for any suitable,
and available 'small' screw - it does NOT need to be a 'grub' screw as
such (a short 'slotted' screw would serve exactly the same purpose).

Finally these spur gears are supplied with a 4.0 mm Gear bore diameter -
so easily suit both ETX scopes (just drill out to 5.0 mm when adapting
to the ETX-105).

These gears COST ME the hefty amount of UK GB £5.68 (plus 17.5% VAT) -
however the MINIMUM postage charge from the supplier (to cover
occasional 'small' orders) is UK GB £8.00 (!!!!!!) - so, you would be
looking at UK GB £14.00 for me to send you a 'raw' item, and I would
charge you UK GB £20.00 for the 'finished' item - the extra just to
cover my time.

As far as the mounting screw is concerned - this is identical for BOTH
Meade focusers (to suit ETX-105/125). This is an 'imperial' item and is
size 6, UNC, with a 32 TPI 'thread pitch' (usually quoted as UNC 6-32).
It is a HEX HEAD CAP bolt, with a 1.500 inch thread length, taking a
7/32" AF Allen Hex Key.

I have attached several images pertinent to the two Meade Electronic
Focusers I have here (one for my ETX-125, and one that I have been
repairing for Nick Howes' ETX-105) - Mike, if you feel others might
benefit, please feel free to publish these.











In the case of Nick's ETX-105 focuser, I found that there was NO grease
on any of the gears, and that the intermediate gear between the output
of the drive motor and the long brass idler gear, had split - although
this was the case 'as delivered' to Nick - but he could not easily get
it repaired under warranty - simply because it had been purchased 'new'
from a dealer in the USA. Nick said that there were NO FRAGMENTS of the
broken gear in the case or packaging - again, this seems to be
reminiscent of poor quality control at Meade (or at Meade's
Taiwanese/Chinese manufacturers). In Nick's case I not only had to
source a replacement gear, but this had an 'oversize' Gear Bore, which
required an 'oversize' shaft for it to rotate on - and I had to use the
Lathe to run these up.

What also is quite important is WHERE the spur gear is fitted on the
actual Scope shaft - on the ETX-105 there is a groove cut into the focus
shaft, and the drive gear grub screw should locate in this groove when
tightened. On the ETX-125 there is no such groove, and (as far as I can
determine) the drive gear should be fitted such that the 'boss' faces
the main body of the telescope - NOT the gear teeth themselves).

Hope this is of some use to all concerned.

Cheers,
Niall Saunders
(ETX-105, ETX-125 and LXD55 8"SCT owner)
NJS Technical Services
Aberdeen, SCOTLAND

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