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GX250 Overhaul

Milamber

By Milamber
in DIY Astronomer

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Milamber

Milamber

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Some time ago I acquired an Orion GX250 f/4.8 Newtonian OTA in a trade and, to cut a long (long, long) story short, it finally hit the house about 10 days ago... that's when the astonishment began...

As you may have read in my for sale ad for a 10" mirror, the Orion "mirror cell" used in the GX was a little on the Heath-Robinson side - consisting as it did of a lump of aluminium glued to the back of the mirror and a few bolts screwed into or onto it through the back plate...

OO-original.jpg

Clearly, this was not going to remain a viable method of either holding the mirror or collimating it - something had to be done and, strapped for time, I decided that the SW cell could be pressed into service if it was altered somewhat. So, using the original Orion back plate I machined some fan holes, did away with the original mounting points, added some more and generally opened up the cell to let more air circulate...

250-cell-rear.jpg

Then it was a simple case of redrilling and tapping the SW cell to a sensible thread (M8 actually), fitting it all together, spring-loading the whole thing to make collimation a bit easier and there you go...

250-cell-inside.jpg

The OO mirror is the same size as the SW one at 250mm - both oddly *not* 254mm so not 10" at all - so it fits snugly into the SW cell and even sits a bit high, which is good for me if I ever want to drop a camera into the scope at some point in the furure. Also in the future I will make some proper hand knobs for the collimation adjustment. I really will. Needless to say, the reason for doing all this is the mirror itself, an excellent lump of glass that has been lovingly rubbed away to it's current figure and performs well, it just is a pity the rest of the scope was below expectations. (Don't get me started on the "rings", the split tube, etc.)

I suspect that now this scope is pretty much operational then I really will have to get the PM-1 sorted at long last, they were made for each other I think.

Arthur

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Milamber

Milamber

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Few more pics then...

Mirror in the cell - no, that dirt is on the window, not the mirror!

mirror-in-cell.jpg

Here's the secondary, not a vast improvement to look at but spring-loaded and the stainless thumb-bolts are better than the dusty Philips screws that were galvanised and dropping crud all over the primary ;)

I hope my focus with the scope is better than my focus with the camera... :icon_rolleyes:

secondary.jpg

Finally, the beastie itself - note Crayford focuser and the OO rings that for the life of me I cannot figure why the mounting hole spacing is 1 1/2"... no chance of fitting these rings to a standard Vixen dovetail (that's an MM-3D one fitted).

OTA.jpg

Next stop, a mount!

Arthur

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Milamber

Milamber

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Fancy pm'ing where you got those nice bolts from in pic 2 of the 2ndry ??:) :)

Karlo

They came from out of the third draw down on the right... same bolts I use for the guidescope rings actually (M6 stainless 50mm full thread with a nylon tap-on thumbgrip tapped on!). Want some?

Thats nice Arth, fancy selling it?;)

Alan:)

I think I'd at least need to use it a few times - else people might start calling me Alan...:icon_rolleyes:

Arthur

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davew

davew

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As the owner of a similar scope, I'm going to watch your thread very carefully and see how a " Real " engineer does things. You seem to have the luxury of glue. My primary is held together with a range of plastic screws.

One thing I have noticed with use is that the tube rings and plate are not up to the job. As the mount swings the tube flops quite badly. Do a meridian flip and a clunk can be heard. "Go to" becomes, "Go near if you're lucky".

Good luck.

Dave

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Milamber

Milamber

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Arm a bit better today, still in a bad mood though :icon_rolleyes:

Final pics of the wee beastie on the HEQ5 that should actually be under the WASP rig but is moonlighting (see what I did there?) with the Orion for now...

gx5.jpg

gx4.jpg

gx3.jpg

gx2.jpg

gx1.jpg

Arthur

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NickH

NickH

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Beautiful restoration job on that GX Arthur..

I told the guys here about the low cost option for "WASP" for amateurs.. They could not believe that amateurs could do this kind of thing..

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