12 replies to this topic

[Astro_In_Tampa]

I have an Apertura AD12 and I can twist down on the tension knobs as hard as I can, but the scope still moves up and down with the slightest touch. It will hold it's place marginally in some of the range of motion, from vertical to straight up, but in probably 25% of that range of motion, there is virtually no tension keeping the OTA in place.

 

Is there something I can do or make or use or buy to torque that OTA down more? Maybe some aftermarket upgrade that I can buy?

 

Or is there an adjustment that I can tweak to make it stay in place better??

 

Appreciate any help you can offer.

 

Rick

Attached Thumbnails

• 

Edited by Astro_In_Tampa, 20 November 2023 - 11:03 PM.

[TOMDEY]

Unfortunately, I don't have one in hand to troubleshoot --- but foolishly-designed bearings are common on alt-az mounts, especially the bargain priced ones, but sometimes even on otherwise expensive premium offerings. I see there's a balance-trim adjustment built in there, but that's not necessarily a panacea. Have you tried tweaking that fore-aft degree of freedom?    Tom

 

Having to torque the heck out of friction clutches just means that something is terribly wrong with the design or build. The yoke on my Vixen Optics BT126SS-A was like that --- so bad that I sold it off cheap, explaining to the buyer that it had various optical and mechanical issues.

[Inkie]

See if a wrap or two of dental floss will tighten things up a bit.  Wrap it around the axle and see if that works.

[CrazyPanda]

I've seen reports of the clutches on these dobs being too loose even after fully tightening them down.

 

The way they work is they have a nylon split sleeve on the inside. When you tighten the knob, it pushes the sleeve inward against an aperture and ramps on the sleeve force it closed and force it to tighten down on the shaft.

 

You can see an example of this in third picture of the second post in this thread: https://www.cloudyni...altaz-bearings/

 

However, it sounds like it's not able to be pushed in hard enough, so there's a possibility that an extra washer is needed to allow the tension knob to push the sleeve harder which will force it to get tighter.

 

Here's a topic I found where someone had a similar problem and modified their AD12 to improve the clutching capability of their altitude tension knobs: https://www.cloudyni...ification-r2415

[NicasDream]

I have an AD 12 and mine is really stiff honestly, how high or low do you have the bearings mounted?

[Astro_In_Tampa]

I have an AD 12 and mine is really stiff honestly, how high or low do you have the bearings mounted?

I have it set right at 0 like in the picture. The balance seems fine for 75% of the 90 degree field of travel. But if you are in that 25% range and you adjust the scope, it drops down when you let go of it. I simply can't tighten it any harder. I suppose I could drop it down some and see if that gets it to hold its head up. It just seems to me that if I have it wrenched down as hard as I can, it should really take some doing to move the scope at all from ANY point along its up and down path. 

 

But I'll try dropping it down a bit and see how that works.

[Astro_In_Tampa]

Thanks for the replies guys. I'll try dropping it down some and see if that helps. If not, I guess I'll take the clutches apart and really create a mess for myself!

[NicasDream]

I have mine set from the 6th line from the top and if I tighten it all the way it's super stiff

But I also made a base out of wood I leave outside so I don't have to carry out the original base every time and the one I made has more play to it but still really stiff it just moves at first because it's made by me XD

[Neanderthal]

I think the altitude bearing system on these is better suited to the 6" and 8" Dobs. The bearings on our AD8 operated very nicely, with very little tension. I always put the Dob away with the bearings completely loosened. There's a teflon bushing in that assembly that I think can be damaged by repeated over-clamping. In operation, I set the far-side tension just enough to barely hold the scope in position, then used the near-side tension to "set" the altitude. If you are having to tighten both sides completely, study your balance point for starters. Try balancing the system with a mid-weight EP. If you are using EP's that are drastically different in weight, it's going to be harder to achieve balance, i.e. going from a 31mm Nagler to a 9mm Plossl, lol.

[sevenofnine]

You may need to resort to magnetic weights that slide along the belly of the scope. The weights really take stress off the clutch so you only have to tighten it a little bit to balance the scope as you change eyepieces. Good luck!   

[Neanderthal]

Sorry, I forgot to mention, I did have some weights for the AD8 that attached where the collimation locking screws went. One could do something similar for any Dob.

 

[Echolight]

Bungee cord...

 

....that just starts to get tension on it before the last 25%.

 

 

Edited by Echolight, 25 November 2023 - 11:07 PM.

[Jon Isaacs]

You may need to resort to magnetic weights that slide along the belly of the scope. The weights really take stress off the clutch so you only have to tighten it a little bit to balance the scope as you change eyepieces. Good luck!   

 

 

Added tension should not be used to keep the scope from dropping or rising, that messes with the tracking.

 

Magnetic weights properly positioned solve the problem without compromising tracking.

 

I use the 150 lb capacity Harbor Freight lifting magnets. They weigh 2 lbs and cost about $10.

 

 

Jon