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How I deforked my 8" LX90

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#1 exmedia

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Posted 15 November 2013 - 08:30 AM

DEFORKING MY MEADE 8" LX90

When I went looking for information on how to defork my LX90 I found quite a lot, but not the step-by-step instructions I was hoping for. So, I decided to document what I did in case it may help someone else.

What follows are the steps I took to remove my 2006 Meade 8” LX90 from its fork mount. Other LX90s may be different, so please take that into account before you set out to modify your own LX90.

It's probably a good idea for you to read through the instructions before beginning. The project isn't really all that hard, but it's good to know what you're getting into. Here's what you'll need:
  • Full set of SAE Allen wrenches (hex key)
  • Phillips head screwdriver
  • Penetrating oil (Liquid Wrench)
Preparation: Place your LX90 in the position shown, using a box or equivalent to support the base. Other positions may be used; this is one that was suggested to me and which worked fine. The goal here is to provide access to the left fork arm (the one without the alt clutch).

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#2 exmedia

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Posted 15 November 2013 - 08:33 AM

There are three screws toward the rear of the OTA. These three screws, along with the ones on the opposite side of the OTA, are all that secure the telescope to the Alt-Az mechanism. Begin by removing all six screws. You will need a 9/64” Allen wrench.

If you’re extremely lucky, the scope tube will now slide out of its trunnion carriers (http://en.wikipedia.org/wiki/Trunnion) and you’ll be done. Be very careful! You can easily scratch the paint. More likely, though, it won’t budge and you’ll need to continue.

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#3 exmedia

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Posted 15 November 2013 - 08:34 AM

This is a view of the inside of the left fork arm. Remove the four screws using a 3/32” Allen wrench.

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#4 exmedia

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Posted 15 November 2013 - 08:35 AM

Next, remove the two Phillips screws at the base of the left fork arm.

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#5 exmedia

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Posted 15 November 2013 - 08:37 AM

Unscrew and remove the knob.

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#6 exmedia

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Posted 15 November 2013 - 08:38 AM

Remove the three, 3/32” Allen screws.

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#7 exmedia

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Posted 15 November 2013 - 08:39 AM

You can now remove the plastic cowling from the left fork arm.

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#8 exmedia

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Posted 15 November 2013 - 08:40 AM

At the base of the left fork arm is an angled plastic plate from which you previously removed the Phillips screws. Grasp and slide this plate out. It may take a little force.

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#9 exmedia

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Posted 15 November 2013 - 08:41 AM

You now have access to the four Allen bolts which hold the fork arm to the base. Loosening these will allow you to spread the fork arm slightly so the OTA may be removed. These are most likely very tight, and may require application of penetrating oil (like Liquid Wrench) to help break them free. Penetrating oil needs to soak in to be effective; it can take up to 24 hours before you'll be able to break loose the bolts. Be careful not to get the penetrating oil anywhere other than around the bolts.

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#10 exmedia

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Posted 15 November 2013 - 08:43 AM

Once the bolts are loose you should be able to spread the left fork arm slightly and slide the OTA from its trunnion carriers. Reverse all the above steps to put the left arm back together. Caution: Any screws you put back into the OTA should be screwed in only to the depth they were before. Any further in may place them in the optical or mirror path.

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#11 exmedia

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Posted 15 November 2013 - 08:44 AM

And here is the final result on a Celestron AVX mount (Frankenscope!). Total weight of the OTA with finder scope, Telrad, ADM ring mounting bar, Vixen dovetail bar, diagonal and eyepiece is 15 lbs. Good luck!

Richard

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#12 psyhiker

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Posted 16 November 2013 - 12:11 AM

Excellent instructions...thanks for posting...

#13 Brian Risley

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Posted 16 November 2013 - 10:08 AM

Only comment I might add since it is an issue with Celestrons is to make sure any screws you put back in the OTA from the mount holder do not go too far in and obstruct the mirror path. Same holds true for any accessory added/removed from the OTA.

Brian
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#14 exmedia

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Posted 16 November 2013 - 11:39 AM

Only comment I might add since it is an issue with Celestrons is to make sure any screws you put back in the OTA from the mount holder do not go too far in and obstruct the mirror path. Same holds true for any accessory added/removed from the OTA.

Brian


Got it. Good point. I made the change.

Richard
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#15 Matthew Ota

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Posted 16 November 2013 - 03:44 PM

Another Frankenscope....
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#16 Dinomonaco

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Posted 04 October 2014 - 10:53 AM

Excellent procedure! Just came across this article because I have an ACF 8" LX90.

Love the OTA , but ready to move it onto a GEM.

thanks.

ps. Wondering if I can sell the fork. Has the GPS module and Audiostar controller.

 

regards,

 

dino


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#17 d33d0gg

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Posted 06 October 2014 - 12:21 PM

I am sure the fork would sell quite easily, as it contains a bunch of goodies!


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#18 BLACKDRAGON

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Posted 26 November 2015 - 07:07 PM

Many thanks for this video as it gave me the basic idea and confidence to de-fork my LX200 12 inch scope.   Knowing what size Allen wrenches I needed for a great help, although I found that in what I thought was my vast and comprehensive collection of Allen Keys I didn't have a 9/64" one!!!!  So I had to send for a set which, thankfully, arrived the next day.   I did unscrew the three screws on either of the scope as advised and, of course, the Telescope didn't budge!!! :gaah:   So I made a mug of Tea, and looked at the base. There were 4 large bolts on either side of the base of each Fork right in the corner. The inner bolts were made awkward by being protected by the base strengthening vanes.   They eventually surrendered to a bit of torque and came loose with an alarming crack!, but they came loose.   Once all 4 bolts were slackened right off the Telescope slid out of the forks easily without any damage or scratches.    The sense of relief was immense and the Telescope is now safely in a large plastic wheeled box and lying on a bed of foam rubber.   The fork needs putting back together and will go up for sale when I've put a dovetail on the scope.    



#19 OzAndrewJ

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Posted 26 November 2015 - 07:19 PM

Just another option if the forks arent too tight.

You can use the quickgrip style F clamps

http://www.bunnings....-clamp_p5860115

to preload the forks thus springing them out far enough to release the OTA.

The ends of many clamps are reversible, ie they can clamp like normal

or push apart :-)

 

Doing this also means you dont affect the orthogonality of the DEC axle

 

Andrew Johansen Melbourne Australia



#20 junomike

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Posted 27 November 2015 - 08:14 AM

Many thanks for this video as it gave me the basic idea and confidence to de-fork my LX200 12 inch scope.   Knowing what size Allen wrenches I needed for a great help, although I found that in what I thought was my vast and comprehensive collection of Allen Keys I didn't have a 9/64" one!!!!  So I had to send for a set which, thankfully, arrived the next day.   I did unscrew the three screws on either of the scope as advised and, of course, the Telescope didn't budge!!! :gaah:   So I made a mug of Tea, and looked at the base. There were 4 large bolts on either side of the base of each Fork right in the corner. The inner bolts were made awkward by being protected by the base strengthening vanes.   They eventually surrendered to a bit of torque and came loose with an alarming crack!, but they came loose.   Once all 4 bolts were slackened right off the Telescope slid out of the forks easily without any damage or scratches.    The sense of relief was immense and the Telescope is now safely in a large plastic wheeled box and lying on a bed of foam rubber.   The fork needs putting back together and will go up for sale when I've put a dovetail on the scope.    

Be sure to update your other thread with pics If possible!

 

Mike




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