[mental4astro (Alexander)]

Hi all.

Finished a little project for a school's telescope my wife teaches at & I'ld like to share it for those of you who may have the same scope, even if you have limited tools & skills.

Scenario: 4.5" scope on an equatorial mount belonging to a school. It had not been used in the years my wife has been at this school, mainly because nobody knows how to use it, & the eq. mount scared anyone who thought of using it.

My solution: Give it a new dobsonian mount.

The 4.5" scope is probably one of the most common first telescopes bought. However, most come with an equatorial mount, which is usually wobbly & intimidating & frustrating to use, especially as a first telescope.

This dob mount is inexpensive & easy to make. All the hardware can be found at a local hardware store, except for the teflon bearings (more on this later), and the larger hardware stores can cut the pieces for you. You can cut the pieces yourself to save money if you have at least a saw. A jigsaw makes it quicker & helps with the altitude bearing cut-out. You can also use a coping saw to cut out the bearing face, which is cheaper than buying or hiring a jigsaw just for this cut.

Because this scope & mount set-up is quite light, teflon is not necessary to use for the bearings. A PVC end cap can be cut up to obtain the bearing material. It will be nearly as smooth in action as using teflon, & much cheaper. Teflon can be obtained through specialist plastic suppliers listed in the yellow pages. 3mm thick sheet with the size cut to 15mm x 15mm is sufficient (you will need 7 such pieces). You can drill the hole through it, but don't forget to counter sink it for the screw head to remain tucked away.

Here I used two sheets of melamine shelving, 445mm x 1200mm. Ply wood of 12mm or 15mm can also be used. Just make sure that the bearing surface in contact with the teflon on the azimuth bearing is textured laminate like on the melamine board. Smooth, shiny laminate does not work quite as well.

For the altitube bearings I used two 100mm PVC flanges screwed onto the scope craddle.

The craddle is oversized to the tude diameter by no more than 1mm either side. This will allow the use of thin foam to line the craddle to hold the tude in place without crushing the scope. It should be firm enough to allow the craddle to side up or down the tude, just, but with some effort. If too loose, well, the tube will be unstable. This tiny amount of play will allow the tube to be balanced in the rocker box, so that it stays put no matter were the tube is pointed. Once the balance is sorted, either tighten the craddle a little more, or insert a small strip of double sided foam tape between the tube & craddle.

I hope this has served to inspire some of you to dust off your 4.5" scopes & give them a new lease on life.