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Bent CGEM Alignment Pin


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Ever since I got my new mount, I’ve been having an extraordinary laborious time turning my Azimuth knobs and I’m starting to think I figured out why. Call me crazy but I think I have a bent alignment peg…would you agree? I’ve never owned a mount like this so I’m suspecting it shouldn’t be like this correct? It’s takes outrageous effort to turn these knobs and the mount doesn’t even seem to turn much if at all anyway. It’s also causing all kinds of scraping in the metal of the peg itself.

I’m happy to get another one so would you think the one I attached is the right one? Didn’t know if there was a difference between the CGEM and CGEM II pins.

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I have no idea what that part is or what it is for, but speaking as a former mechanical engineer, it is definitely bent and you should get a replacement or straighten it AND find out how it got bent in the first place.  Probably excessive force has been applied. Speculating here, but maybe something was done up tight that needed to be slacked off to let some part swivel?

Maybe time to have a local expert have a look at it?

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Posted (edited)
2 hours ago, Cosmic Geoff said:

I have no idea what that part is or what it is for, but speaking as a former mechanical engineer, it is definitely bent and you should get a replacement or straighten it AND find out how it got bent in the first place.  Probably excessive force has been applied. Speculating here, but maybe something was done up tight that needed to be slacked off to let some part swivel?

Maybe time to have a local expert have a look at it?

This peg protrudes up from the tripod base and it’s where the mount housing sits so that you can adjust the position of the azimuth knobs which are basically long screws, one on each side of the mount and those control the movement of the mount for polar alignment purposes. It actually came this way and I didn’t think anything of it until I learned what it was for, which took a few weeks. By that time there was no way to really prove it was shipped like that so I’m stuck with it. I’m gonna order a replacement but in the meantime I popped some WD40 on it and it’s gotten *slightly* better.

Edited by Maideneer
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If it was mine I'd have a go at straightening that pin. It's hard to see how you could make it worse so long as you do not burr the thread. Or, if Celestron are out of stock, a local machine shop could make a replacement from a piece of steel bar.

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13 minutes ago, Cosmic Geoff said:

If it was mine I'd have a go at straightening that pin. It's hard to see how you could make it worse so long as you do not burr the thread. Or, if Celestron are out of stock, a local machine shop could make a replacement from a piece of steel bar.

I actually ordered one just a few minutes ago.  Since I didn't exactly think it through that much and tried to fix on impulse, I actually did make the threading a bit worse since I stuck it in a bench vise and tried to bend it back to no avail.  I managed to screw it back into the tripod since it wasn't totally destroyed and then put oil on it.  But a new, unbent one is on it's way thank goodness.

Good advice though, I should look up what local machine shops are around here since I never really needed one before, it's just handy information just in case.

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May seem a daft point, but the screw holding the mount down to the tripod may need slackening first before the mount is moved in azimuth using the adjusting screws. Otherwise a lot of force could be exerted on the pin, causing it to bend. Apologies if you have been doing this.

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3 minutes ago, bobro said:

May seem a daft point, but the screw holding the mount down to the tripod may need slackening first before the mount is moved in azimuth using the adjusting screws. Otherwise a lot of force could be exerted on the pin, causing it to bend. Apologies if you have been doing this.

I'll make sure to do that with the new pin, but unfortunately as I said...this current pin was shipped like that so not much I could have done. But to avoid any future malfunctions, I'll be sure and put that into practice going forward.

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1 hour ago, Maideneer said:

I actually ordered one just a few minutes ago.  Since I didn't exactly think it through that much and tried to fix on impulse, I actually did make the threading a bit worse since I stuck it in a bench vise and tried to bend it back to no avail.  I managed to screw it back into the tripod since it wasn't totally destroyed and then put oil on it.  But a new, unbent one is on it's way thank goodness.

Good advice though, I should look up what local machine shops are around here since I never really needed one before, it's just handy information just in case.

That pin looks like it's been hit with a hammer, but it only provides a fixed point against which the azimuth knobs can push while doing polar alignment. Even bent, I would not expect it make turning the azimuth knobs difficult unless it was pressing against the side of the mount. If that's the case you might want to experiment with a quarter or half turn of the pin to see if having the 'lean' of the pin a different direction helps.

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1 minute ago, Shimrod said:

That pin looks like it's been hit with a hammer, but it only provides a fixed point against which the azimuth knobs can push while doing polar alignment. Even bent, I would not expect it make turning the azimuth knobs difficult unless it was pressing against the side of the mount. If that's the case you might want to experiment with a quarter or half turn of the pin to see if having the 'lean' of the pin a different direction helps.

It's an extremely difficult turn for whatever reason.  The added WD40 helps some but it's almost like the endpoints of the screws are digging in to the pin head so much so that there are indentations now.  IMO it's just a weird system of making adjustments.  Everything else is virtually automated nowadays, not sure why this mechanism can't be computerized and controlled without all of these physical parts.  RA/DEC are computerized already, there's nothing stopping them from updating this too.

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32 minutes ago, Maideneer said:

Everything else is virtually automated nowadays, not sure why this mechanism can't be computerized and controlled without all of these physical parts.  RA/DEC are computerized already, there's nothing stopping them from updating this too.

As an engineer, I think the sensible solution would be to engineer the mount so that the manual method works properly (as it does on my EQ-5 mount).  Some of these CGEM mounts will be installed in an observatory where the adjustment will only be done once. 🙂

I agree that the adjustments required on an equatorial mount for imaging are time-consuming and fiddly but I doubt that either the manufacturers or the end users have the funds to pay for a fundamental hi-tech redesign.

The CPC925 (which would be excellent for planetary imaging) sidesteps this issue by being an alt-azimuth mount which does not require polar alignment at all. 🙂

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When I had an EQ6 in my observatory, I used a simple pier head and I just had a bolt with the head sawn off as the ‘stop’ for the Azimuth adjustment and this worked just as well as the square pin that was part of the original tripod/mount setup so you could always use that as a fall-back. I think @bobro may have the solution to further issues as this is often forgotten in the race to polar align!

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