Just add another layer of felt to the existing liner, with either contact cement or double-sided tape. You may only need to add it to one ring half of each set. If so, do the same ring half on each one or you'll generate some cone error. Thin sheet cork will probably be too thick if you line the entire ring.

Ziggy, that's a lotta work to increase gripping friction ever so slightly... The quick way is a couple of loops of vinyl tape around the tube where the rings clamp. On 3/14/11, ziggy943@xmission.com <ziggy943@xmission.com> wrote:

My suggestion is not to use cork. Rather fix the location of the tube. First get some small tube weights so balance can be maintained for different eyepieces. Find the location where balance is achieved. Note the location of the upper ring. Countersink a ¼" screw into the ring, leaving the head to stick into a hole into the tube. Guaranteed not to slip.

It's a band-aid. That said, if you can live with it, it's a free country. ;o) On 3/15/11, Siegfried Jachmann <ziggy943@xmission.com> wrote:

It's a simple one time fix with items already in hand. It has worked on the Clark for nearly thirty years.

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I disagree. Add slideable tube weights and it's much easier to achieve balance for changing eyepieces or cameras. The friction on the axels will take care of most of that anyway. Only if you add something as heavy as a binoviewer would you have a need for rebalancing. Sliding a tube that size and weight has risk attached to it. It's much bettter to fix the tube in place and slide a tube weight. That is a one man piece of cake operation. You don't give up any longitudinal balance. It can also be done easily with weights attached to a slidable tube ring. Or the way I have it on the Clark. BTW, the original Clark didn't have tube rings. The tube was fastened to the saddle via 4 bolts. The fact that this is up for discussion shows that tube slippage is a problem. In order to tighten the rings enough to stop splippage when pointed vertically you very well could stress the lens cell. A pin would avoid all of that. Quoting Chuck Hards <chuck.hards@gmail.com>:

Why use tube rings and then disable them with a pin? Suddenly you have lost the ability to quickly achieve longitudinal balance if using heavier or lighter than usual accessories. Admittedly, at SPOC we don't really have many (if any) members using the telescopes with any significantly massive instrumentation attached, but the option is nice. With the tube pinned, clamp rings become simply dead weight. May as well just screw the OTA to a saddle and sell the rings.

Properly shimmed (felt) rings cannot be "overtightened" anyway. A set of tube rings is too far away from the lens cell on a long refractor to introduce any unwanted stress to the cell.

On 3/15/11, ziggy943@xmission.com <ziggy943@xmission.com> wrote:

...

What do you mean "a band-aid?" It's a permanent solution. Never worry about slippage. Never overtighten the rings and introduce a pinch to the lens cell.

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FWIW, since I completed the scope in 1988 I've never needed to move the tube in the rings. In fact, when we opened the rings last fall it was the first time they'd been opened since '88. So I'm really not concerned about pinning it in place. If someone does come up with some sort of heavy piece of something to hang on the back we can just do a combination of putting temporary weights in the front and sliding the existing weight further down the declination shaft. patrick On 16 Mar 2011, at 07:46, Chuck Hards wrote:

Why use tube rings and then disable them with a pin? Suddenly you have lost the ability to quickly achieve longitudinal balance if using heavier or lighter than usual accessories. Admittedly, at SPOC we don't really have many (if any) members using the telescopes with any significantly massive instrumentation attached, but the option is nice. With the tube pinned, clamp rings become simply dead weight. May as well just screw the OTA to a saddle and sell the rings.

Properly shimmed (felt) rings cannot be "overtightened" anyway. A set of tube rings is too far away from the lens cell on a long refractor to introduce any unwanted stress to the cell.

Thanks to all who replied. After talking with Bruce we went with a combination of a couple of your suggestions. We used thin sheets of cork between the rings and the tube. That alone is holding the tube well. But just to be safe Bruce is going to follow up on Sieg's suggestion. When I made the rings all those years ago I put a single, unthreaded 5mm hole in both of the top rings. So Bruce is going to pass a drill bit down through those holes and drill holes in the tube. He'll then put pins in the holes. The rings, BTW, turned out really nice. While it's only gold plate, there's something about the look of gold... patrick On 14 Mar 2011, at 14:56, ziggy943@xmission.com wrote:

My suggestion is not to use cork. Rather fix the location of the tube. First get some small tube weights so balance can be maintained for different eyepieces. Find the location where balance is achieved. Note the location of the upper ring. Countersink a ¼" screw into the ring, leaving the head to stick into a hole into the tube. Guaranteed not to slip.

Siegfried