Help - Declination axis not moving on mount

djbunting · #1 28-04-2011, 10:26 PM

Hi Guys,

Long time reader first time registrator and poster. However i do apologise in advance for the lack of correct terminology

Ive had this 9in scope for years. I thought id pull it out and start looking at the sky again.

This evening while trying to chase Saturn around i realised why it'd been sitting in my shed for so many years. The declination axis is jammed and I am unable to aim the scope effectively.

I have attached a couple of photo's to attempt to explain the issue.

When i rotate the dec axis knob(?) The part with the white arrows (below) moves and the part above it (hose clamped to scope) remains stationary. Whereas it should be the other way around. It doesnt seem to matter how hard i tighten the lock bolt(? under left arrow head)

http://i5.photobucket.com/albums/y19.../DSC_06552.jpg

There is an access cover in line with the right asc axis that reveals the shaft which should rotate when dec axis knob is turned. This seems to be attached( threaded ) to the couterweight mounting pictured below. There seems to be two notches in the couterweight mount that i would have thought would allow me to remove the counterweight mount and access the dec axis shaft however i am unable to unscrew this.

http://i5.photobucket.com/albums/y19.../DSC_06572.jpg

I recall several years ago emptying a can of WD40 into various holes and hitting with hammers mallots and pulling as hard as i can to get the dec axis moving and to remove the scope mount ( bit hose clamped to scope ). Also tried a angle grinder spanner to remove the counterweight mount to no avail.
The mount itself seems to be of cast aluminium so i have been so far unwilling to put it in a vise and really force it into submission.

If anyone could suggest a more elegant way of achieving the desired result please let me know.

Kind Regards,

Drew

ps Saturn still looked good though

ZeroID (Brent) · #2 29-04-2011, 10:04 AM

Hate to say it but I suspect the shaft and mount casting have corroded into one lump internally and even if you get them apart they will never really work properly. Rust and alum oxides hydroxides can be pretty bad partners.
Unless you can strip it all down and rebuild I'd suggest buying a new stand or making a dob base for the scope. Easier in the long run.

djbunting · #3 30-04-2011, 10:44 AM

Thank you very much for your reply ZeroID.

After further inspection there doesnt seem to be much corrosion or oxidization anywhere on the mount. It is however possible that at the very top of the dec axis shaft there may be some corrosion, I cant quite see in there.

Being a tight arse and not wanting to spend any money what would be the actual procedure to pull this thing apart?

Kind Regards,

Drew

asimov (John) · #4 30-04-2011, 11:01 AM

Certainly fixable I'd say. Sounds like it probably has bushes rather than roller bearings, but it's hard to say. As far as a procedure for actually pulling it apart, I'd say it's a case of following ones nose. I've never seen this mount before but if you can somehow find out the manufacturer name & a model # it would certainly assist you in tracking down any info. (if any) on it etc.

In the trade we use heat to unseize things. If you are not the DIY kind, I'd suggest taking it to a friend in the know, or a quick visit to an engineering/welding shop should have it apart in no time.

G'luck.

mikerr (Michael) · #5 30-04-2011, 03:08 PM

Drew, I have the identical mount that came with my 6" Newtonian. I purchased the setup secondhand from Astro Optical Supplies in Crow's Nest North Sydney in about 1980.

I just went and dug the mount out in the shed. Mine still turns OK

Have you removed the round black cap shown uppermost in your second photo? It allows you to look inside that T housing and is opposite the hidden end of the RA axis. With a torch you can see the top and bottom of the Dec shaft inside the housing which may or may not help. Maybe get some penetrating oil in there.

The bottom line is that I think you need to get the correct Pin Spanner on the bottom nut/thing that you already mentioned and hold the casting which the tube assembly is sitting in. I am assuming that we are dealing with a Right Hand thread. That is, Lefty loosey/Righty tighty!

If you can undo that thing a couple of threads then you might be able to
gently tap on it and drive the shaft up a little and loosen it.

To get the correct Pin Spanner, you might try Astro Optics,Bintel or a Bicycle shop in Melbourne. Maybe Astro or Bintel would do the service for you.

I hope this all makes sense because it is not always easy to visualise what someone else is writing. I know what I mean

Rgds

Michael

djbunting · #6 30-04-2011, 06:43 PM

Hi guys thanks for the input.

Mike you are right. The old box the tube came in has Astro Optics written on it. It seems the last person to pull it apart and put it back together has just done it up too tight.

With a lot of kero and some brute force i managed to unscrew the counter balance mount buy standing on the wooden tripod (laid flat out) and turning the tube shoulder as hard as i could.

There was a lot of old gluey, near solid, grease everywhere. There are 2 grub screws in that bottom counter balance mount. The mount doesnt need to be screwed tight. The grub screws hold the mount on the shaft. Ill post a couple of photo's later which may explain better and help someone else in the future.

I have now managed to clean all the old grease up and lightly sanded all of the surfaces with 1200# wet dry so they are smooth again. Ive got my lithium grease ready to go.

Will post photo's shortly

Thanks for help

Regards,

Drew

ZeroID (Brent) · #7 01-05-2011, 08:52 AM

Hey, well done !! A bit of persverance and application of good old brute force solves lots of things when applied correctly.

jenchris (Jennifer) · #8 01-05-2011, 10:24 AM

Cool fitting!
Dunking/soaking in boiling kero was going to be my solution -
If you're machining aluminium, you use Kero as a coolant as it soaks into the metal a few microns. Hence my thought.
Overtightened machinery irks me - I get right up the tyre fitters for overdoing my nuts. How am I supposed to change a wheel when they've used a rattle gun on them?

Astroman (Andrew Wall) · #9 01-05-2011, 10:36 AM

Glad to see you made some headway, nothing worse than a mount that wont let you move...

Quote:

Originally Posted by jenchris

Overtightened machinery irks me - I get right up the tyre fitters for overdoing my nuts. How am I supposed to change a wheel when they've used a rattle gun on them?

They can do what they do to my car, leave them hand tight