Below is one possible way to remove and re-install a Meade secondary.

Place two stacks of books on the table and lay a clean towel over them.
Obtain a small hex wrench ( Allen wrench ).
Make an index mark with a black marking pen if desired.
Remove the screws from the correcting plate retaining ring.
With a clean towel place the correcting plate with the secondary mirror facing down between the books.
Cover the tube with foil or plastic wrap.
Remove the three secondary adjustment screws.  The secondary will fall onto the towel.
Wrap the secondary in a small clean towel for shipment via U S Mail.
Retain the parts for reinstallation.

The tricky part of re-installation is reinstalling the secondary in its well without touching the 
       easily damaged new coating.
If possible find someone with steady hands to help.  
And you will need a small mirror, possibly a mechanics adjustable mirror and a clean 'Q' tip.
Holding the correcting plate and the secondary with clean towels insert the secondary sideways
       back against its center fulcrum pin.  Then tilt the plate so the secondary is facing up.
One hex screw should be on the long end of the hex wrench.
Have your helper hold the correcting plate with the clean towel and you gently rotate the secondary
       on its fulcrum pin using the 'Q' tip.   Looking in the mirror on the table watch through one
       of the adjustment screw holes until the tapped hole in the secondary plate lines up.  
       Then start the first screw.
The remaining two screws are then relatively easy.
Re-install the correcting plate into the telescope with the index marks aligned, if present.
Remove eyepiece and right angle adapter from tube bottom if present.
Put a solid color towel over the top of the tube with a light behind it and look into the bottom of the tube.
When you are relaxed and have some time adjust the three adjustment screws until when looking through
the center of the bottom of the tube all the mirrors and reflections of mirrors appear to be concentric.
To get the adjustment screws snug with the optics in alignment will take some patience.
While doing the adjustment be sure not to loosen the adjustment screws too far or the secondary will fall onto the primary.

For a more detailed collimation method using an artificial star refer to 'Sky and Telescope'
February 2018, page 28.


Disassembly of a common type of diagonal mirror cell
Use caution when working on these cells.
Often the diagonal has been pressed into the paint for many years.
Only a small amount of pressure will pull a flake chip off the diagonal.
We soaked this assembly in mineral spirits paint thinner
for a few minutes to soften the paint and lubricate.
After disassembly the parts can be cleaned with 70 percent rubbing ( isopropyl ) alcohol or
reagent grade methanol.
After cleaning with methanol.
Re-coated diagonal, diagonal cell and cotton from a vitamin bottle.

Re-attaching secondary to backing plate

We no longer remove the secondary from the aluminum back plate during re-coating unless there is some unusual reason for doing so.

If a mirror is attached to a metal back plate the adhesive can be softened by soaking overnight in regular paint thinner.  Then slip the edge of a utility knife blade between mirror and back plate to gently separate them.  Often you can cut the sealant without soaking. Or otherwise slip the blade of a hacksaw between mirror and wood back plate to saw the sealant.  Keep metal tools away from the mirror face.

De-coating without separating the diagonal is often possible.

de-coating an attached diagonal

Separating a mirror from its backing plate.
It may not be possible to separate the mirror from its backing plate if the customer did not space the mirror off
the backing plate or if some type of super epoxy was used instead of the elastomer. (Silicon sealant or similar.)
With the wood backing shown it will not be possible to coat the mirror attached to the backing
because it will not be possible to attain the required vacuum for coating.  More 'how to'.

Separation of Mirror from backing



When gluing mirrors to their mirror cell be sure to allow the sealant to cure overnight.
More info

This summer (2019) we noticed that our favorite sealant, GE 100 percent silicon which releases the acetic acid smell as it cures is no longer available.
So advise doing a test of your sealant/adhesive/elastomer and allow to cure overnight. If it's still sticky the next day it's probably not usable for attaching mirrors.
RTV means Room Temperature Vulcanizing.
Room temperature should be at least 70 degrees F for at least 24 hours.

We have seen various other satisfactory elastomers used for attaching mirrors.
We just completed testing XtraBond250 (white) and XtraBond150 (clear). We spaced plate glass away from a plywood mirror backing disk with six nickels in three places. After waiting two days we forcibly twisted the glass horizontally to break the bond. The bond failed at the adhesive/plywood interface. We then sanded the three former attachment points with course sandpaper and cleaned with methanol (alcohol) and after it dried rubbed sealant into the roughened area with our finger before pressing the plate glass back as it was before. Waiting another two days we found the attachment to be satisfactory. Over time the sealant continues to cure.
(January 2022)



Update, November 2020


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