by Jason Newquist
In late May, I called Discovery about the stock bearing pads on my 10" Premium DHQ telescope. The rep on the phone indicated that he believed the weight-bearing pads on the rocker box trunnions were indeed Teflon, but he wasn't sure. Since I was dissatisfied with the performance of both car wax with silicon and Armor All on the stock pads, so I opted to replace the pads, rather than simply relocate them. A local observing comrade, Albert Highe, who makes (and sells) his own telescopes, generously supplied the materials, workshop, and his expertise.
Albert gave me another option besides full pad replacement. He suggested going to a store that sells plastic furniture pads. They apparently have Teflon coatings which could very simply be applied to cover up the existing original pads. Since we were already at his workshop, I wanted to proceed with the pad replacement, but I thought I'd pass along that idea as a solution that's within reach of many of us who lack the tools, experience, or chutzpah to do a full teflonectomy on our precious scopes.
The procedure we used employed three changes to ease the altitude motion:
Regarding item (1), the original pad material looked and felt like nylon -- but the point is moot. Even if it was a kind of Teflon, the Teflon that we replaced them with was considerably more slick to the touch. You could really feel the difference. And, incidentally, the color is different. The stock pads are a plasticky gray while the Teflon we used were an opaque milky white with a surface sheen.
The dimensions of the pads listed in item (2) were selected to satisfy the ATM rule of thumb which states for every 15 pounds of weight, you want 1 square inch of bearing pad placed around 90 degrees apart. The 4 pads in the dimensions given total 4.5 sq. in. However, the actual surface area is probably closer to exactly 4 sq. in. because we used screws to attach the pads to the base, and the heads of the screws remove a certain amount of surface area from the pads.
Item (3) was recommended by the gentleman from Discovery on the phone during our conversation. He admitted that many customers find the altitude motion stiff, but since many customers like to load the scope up with stuff on the top, they selected a very wide placement.
We left the existing pads in place to use as a guide so we could install the new pads just inside of, and flush with,
them
The Teflon material, after being cut (and milled) to size, was pre-drilled for the length of the screws, as well as with counter sinkers so the head would be safely below the surface of the Teflon
Screw holes were pre-drilled into the rocker box as well, and Albert used brass screws for a nice finish. After attaching the new pads, we removed the old ones. The nail brads Discovery used are really solid! They did not deform in the course of removal. I could have easily re-used those pads, as suggested
Fortunately, the finish of the rocker box was applied BEFORE the pads were, so the finish was unimpaired by removing the pads. Albert brought over some furniture putty sticks and we filled in the holes left by the staples. Looks great.
And the result? I immediately noticed I needed to rebalance the scope - and it surprised me how much I needed to move the bearings upward to balance the scope. When all was said and done, with an average eyepiece in the focuser and a Telrad mounted up top, the bearings were nearly perfectly centered along the metal attachment assemblies mounted to the tube of the scope.
Now that I have some experience with the scope and know how fine you need to move the scope to scan a field, or just barely nudge to keep an object in view, I was able to use this experience to "nudge test" the motion. After the apparent indoor success of the Armor All followed by its failure in the field, I am not going to declare this a success until it's actually used in the field.
Currently, the bearings are "dry"; I'd spent the last several days wiping (with warm soapy water, Windex, and lots of elbow grease) as much of the residual Armor All and car wax from the bearings as I could get, so I could see how the hardware changes affected motion in and of themselves.
Having said all that, though, I have to admit that I can really feel the difference. The nudge test seemed to go very well. Albert says that even with this configuration of pads, a car wax containing silicon might be necessary every month or two for a *really* slick motion. I very well might use it, but I'd like to try it dry first. As soon as pictures are available, and I've tried it out in the field, I'll update my web page and post here, in case anyone's interested in the continuing saga. :-)
After two observing sessions with the scope, the altitude motion issue is the only annoyance I can detect. Overall, I'm very happy. It's true that it's at the limit of my portability, but I find that the "sweat cost" of hauling it down the stairs and squeezing it into the car very much worth it. Am I still in the honeymoon phase? Yes. But my level of enthusiasm in the hobby has never been greater. I think this bodes well.
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Updated on 06/04/2001 11:13:16 PM