Removing dovetail from a SW 180 mak now done

[5ash]

I have looked on the net for info on removing the dovetail on my Skywatcher BD 180 maksutov . Most suggest removing the corrector plate from its cell to gain access. Does any one know why the front can't be removed by removing the 4 retaining screws thus making the process much easier. Surely removing these screws will remove the whole assembly. I'm hoping someone has gone through this process can help me befor I lay Allen keys to screws.
Regards philip :shrug:

[doppler]

Just had a look at my 180mm mak, I would think that the best way would be to remove the 4 screws and take the whole end assembly out complete. I would also mark the tube and corrector assembly position with some masking tape to get it back in exactly the same rotation. If you google cleaning a mak you will probably find more info there.

Just found this on google, (my mak is a gold series and the 4 cell mounting screws don't have nuts on the inside of the cell, just the dovetail so the following would work)

"One thing I'd like to add. When I remove the corector plate, I like to leave it in the housing and remove the housing from the tube. I don't have to worry about how to align the plate because the writing goes in the up position and I also don't have to handle the glass. This seems to work well for the Celestron SCT's."

"Some corrector plate cells are attached using screws with nuts inside the tube. On that type, you cannot remove the corrector in its cell.
Some Maksutovs have their corrector and cell threaded into the tube. This type may be removable in the manner you suggest. But there exists a strong possibility of cross-threading when reinstalling. Careful."

[5ash]

Thanks Rick, I looked in my OTA and can see where the end assembly screws come through the side.similar to a Meade SN . Can't do any harm to remove the 4 screws and see if it comes free. I'd imagine it should , just couldn't figure out why you'd want to remove the corrector from the assembly as suggested by many on the net.
Regards philip

[netwolf]

I also want to do this on my Gold Maksutov the optics seem to be very good on this but I dont like the flimsy dovetail as it also limits me from moving it forward on my Evolution mount to avoid hitting the base near Zenith.

But the task of the removing the front seems daunting.

[doppler]

I find that its best to try and disturb individual optical elements as little as possible to save having collimation issues later, except for newts which are fairly easy to set up again.

[Wavytone]

Having done same with an Intes 7" mak:

1. Although it looks like you could do it leaving the backend attached, the central baffle tube makes it quite hard to do this and not touch the mirror. Best to take the backend off as well.

2. Use tape or similar to make some markers on the tube and the cells to realign both assemblies in the sane orientation as they were originally. If you do this there is every chance the optical alignment will be good after reassembly. It also saves any grief if it turns out the hole spacings are not equal.

Note that like refractors, the rotational orientation of the optical components is extremely important for optimal optical performance. Get this wrong and no amount of tinkering with alignment screws will fix the result.

[Saturnine]

I removed the dovetail from my gold 180 mak several years ago and fitted ota rings and dovetail, there is no great secret to doing it. Remove the 4 small screws that hold the corrector plate cell to the tube and gently pull the cell and plate off without touching the glass if possible. The dovetail is held on by 2 small screws and internal nuts, 4 or 5 mm, just undo the nuts, without touching the mirror and remount the corrector plate, in the same orientation as before removal.
Would recommend covering the 2 small holes of the original dovetail mounting with some pvc tape or something similar.
Removing the corrector plate and cell may ever so slightly, affect the collimation but if the corrector is re-fitted to the same screw alignment there should not be a problem with collimation, which can be tweaked via the 3 sets of screws in the rear.

[doppler]

I would put the little dovetail mount screws back in to fill the holes, looks a bit neater and you know where the screws are if you ever want to replace the original dovetail.

[5ash]

I suppose that opens the question "is it easier to remove the rear cell?" And go from there to remove the bolts.
Philip

[Saturnine]

It is much easier to remove the front corrector plate and cell and yes , putting the 2 screws back in the holes after removing the dovetail is a good idea.

[5ash]

Removed front corrector , removed bolts and dovetail, dusted tube and blew dust off primary and replaced corrector assembly as shown in pictures below.Will now purchase 8" rings , pad them out , then tweak the collimation back to the way it was.Whole process took about 10 minutes even with my knarled arthritic hands.

[netwolf]

excellent work and thanks for the pictures. I am also on the lookout for a good rings solution.

[5ash]

Will post a pic of setup with rings when I get them.
Regards philip

[5ash]

hi Fahim,
got the gso rings and padded them out whole assembly with gso focuser and sw motorfocus attached without finder weighs about10Kg.
here are pics.
regards philip

pS with rings tightened up and dovetail attached is very rigid.

[netwolf]

Thx Philip looks good and much more ridgid then with the dovetail it came with.

[Saturnine]

Hi
Not to sure about the Abelflex as padding, may be a bit spongy to grip effectively, I know this because I worked for the company who manufacture the stuff until I retired last year and handled the stuff regularly. Though, as it is being compressed equally around the diameter, it may be up to the job, I hope it is.
All said and done, you have done a good job removing the old dovetail set up and fitting the dovetail to a pair of rings, a much more satisfactory arrangement as it keeps the ota away from the mount head by a few centimetres and avoids the chance of scratching the paintwork.

Jeff

[5ash]

I was a bit worried by the limited amount of compression of the abflex , however The grip is very good. And on tightening the rings appears rock solid.will have to try it on a mount and see how stable the view is . If I hold onto tscope when mounted I can't feel any give anywhere. Friction between the surfaces is much greater than felt , so adjustment of ring positions is much harder.
Regards philip

[Saturnine]

The best test is, obviously, that there is no movement of the tube in the rings when it is mounted to the EQ. The foam itself will have good grip but my concern is that over time the foam will lose its memory and not have the firm spongy feel that it has now. But if that happens it is easy enough to replace the foam every few years as you have a roll of the stuff.

[5ash]

Thanks for the advice ,I was surprised at how well it gripped and scope holds well on compression of the foam by 4-5 mm. Just tried the scope on a bessor. Eq5 out on my verandah and seems rigid . Views are good with no obvious movement in the rings .looks like collimation has not been affected much.a star test will tell when the rain goes away
Regards philip

[doppler]

I had to pad out some gso rings to fit my 10" skywatcher newt. I used some strips of high density neoprene rubber from Clark Rubber and also found rotating and sliding the tube for balance difficult due to excessive grip, so I got some felt from spotlight and contact glued some strips to the rubber. It slides and rotates easily now but still clamps down tight.

[Wavytone]

Rick another material that works is the adhesive contact used for smartphone screen protectors. This stuff is very tough yet very slippery like teflon.

[5ash]

Mounted the telescope on my NEQ6 out in the observatory ,observed and tracked a bright star. I found that the foam strip in the tube rings was holding the scope rigid and a star test that the ou t of focus images were almost perfectly symmetrical with just an almost imperceptible difference between the central dark spot and the edge on one side.. so all seems well after removing and replacing the front end.
Regards philip:)

[netwolf]

Glad to here it Philip, where did your source the rings and felt?
I see there is a pair of Parallax rings for an RC8 on the classifieds but those things look really beefy and not sure how much weight they would add. While I dont like the look of the GSO rings they are at least much lighter.

[5ash]

Hi Fahim,
They are gso 230mm rings bought from Bintel , they are padded out with the foam strip (abelflex).
Regards philip

[doppler]

Well done , it's always good to see a plan come to fruition. On a side note I came across this quick daylight collimation check for mak telescopes.

http://www.robincasady.com/Astro/collimation/

[5ash]

Thanks for sharing that link, I'm sure other members will appreciate it as well.
Regards philip:)