Last updated on
4/11/
2006

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Balance Weights You Can Make
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Here are directions for making an extra balance weight for a U2K, and also for a Losmandy Counterweight Bar (on any SCT):

Celestron Ultima2000
For a Celestron U2K scope (which includes a factory-provided counterweight bar) you can make an additional counterweight for less than $10 in parts from your local hardware store. With the Celestron Dew Cap/Lens Shade installed, this counterweight can achieve static balance for heavy 2” eyepieces or a CCD camera, flip mirror, and focus motor on my scope (click here for a photo of this), which is as much equipment as you are likely to hang on your rear cell.  Note that this will not achieve dynamic balance for a rich-field scope or camera mounted atop the scope - you need a 2D counterweight system for that - see the Balancing an SCT page for more information on dynamic balance.

The secret to making this additional weight is that the large counterweight supplied by Celestron for the U2K is threaded to accept additional weights, and it is a 10-24 screw thread (not the more common 10-32 thread). My counterweight is shown here, threaded onto the Celestron weight.  Click on any of the the thumbnails to view a larger image.

What you need to make this weight is a 10-24 machine screw 2 inches long, 22 fender washers 2” in diameter, two fender washers with a #10 hole, a 10-24 nut,  a #10 lockwasher, and a 10-24 acorn nut. Fender washers are thin, wide washers with a much smaller hole in the center (for their diameter) than normal washers. The 2” diameter matches the diameter of the Celestron weight, which makes for a clean-looking result that will trick your friends into thinking you really have your act together. My local Ace Hardware has them and I live in a town of only 10,000 people.

The 2” fender washers have a center hole larger than the #10 screw, so put one of the two smaller fender washers (that have a #10 hole) onto the 2” screw, then the 22 washers that are 2” in diameter, then the second small washer, then the lockwasher and the 10-24 nut. 

Tighten it firmly and you should have about 3/8” of the screw sticking out, to be threaded onto the Celestron weight when you need to add more weight.  I use the acorn nut to protect the threaded end when I’m not using it and it’s rolling around in my accessory case (a plastic toolbox from Sears).

If you use the above specs - a 2” screw with 22 washers - you’ll get a weight that’s about 1.5 times the original Celestron weight.  Obviously you can add even more weight with a longer screw and more washers, but at that point I’d consider making a second, smaller one to mount at the top front of the scope, to maintain dynamic balance along the scope’s central axis.  Also, if you make it longer you need to be sure to position it so it doesn’t strike the scope’s mounting base when the scope is moved to the stowed (down-stop) position.

Losmandy Counterweight Bar
Losmandy doesn’t sell a small counterweight to fit their two-dimensional counterweight system - they seem to be assuming that you will always have a heavy object attached to the top of your scope.  If there are times when this is not the case for you and all you need to balance is a heavy eyepiece, you will need to make a small counterweight just like the one described above, but with a different center bolt.

The sliding “adapter” (indicated by the red arrow in the photo on the left) on the Losmandy counterweight bar is tapped to accept the threaded rod on which the counterweights mount; this is a ½”-13 rod.  So purchase a 3” long ½”-13 bolt, a ½”-13 nut, 25 fender washers 2” in diameter with a ½” center hole, and a small tube of “LocTite” (a liquid which after drying keeps nuts from vibrating loose on bolts). The LocTite is easier to use, in this case, than a ½” lock washer.
Assemble the parts as shown in the photo on the right.  When you are comfortable that everything fits together well, back off the nut, apply a little LocTite to the threads where the nut will end up when tight, and tighten it snug.

There is one additional step.  In the Losmandy counterweight system, the bolt itself tightens against a recessed slot in the dovetail bar to lock the weight in place. You need to taper the end of your new counterweight’s bolt so it fits up into the slot. If you don’t, over time it will really mar the edges of the slot.  You can taper the bolt by turning it against a belt sander or grinder, or file it by hand.  It should look like the photo above on the right (click on that photo for a larger image), where the end tapers down to less than ¼” in diameter.  Note that over time this counterweight will still scratch the bar inside the recessed slot, at the locations you where tighten it.  Losmandy avoids this problem by drilling a hole in the end of the threaded rod they provide, and inserting a non-marring (rubber?) insert.

Finally, you can mask the exposed threads and spray the counterweight black to match the Losmandy counterweight bar. This counterweight weighs about 1.3 lb. and on my scope it does achieve both static and dynamic balance with my eyepieces, Baader prism diagonal, and Telrad.


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