Introduction: Upgrade Your Small Telescope/Spotter to a Tabletop Dobsonian/Alt-Az Telescope
Author's note: This Instructable was written and published by our Making and Tinkering Programs Manager, who's personal Instructable account we co-opted. He is now publishing personal Instructables over at member ID MechaNickW.
This Instructable details making a mount to repurpose a spotting scope or small telescope that would normally mount on a tripod or equatorial mount onto a small alt-az or dobsonian mount. I'm very much into astronomy and telescopes, and have a keen interest in altitude/azimuth (alt-az) mounts. They are functional, dead simple, reliable, sturdy, cheap, and can be made out of a variety of woods with simple tools. I made my first telescope with not much more than a $2 corded drill and a jigsaw, and chose this style - I've been in love with it since!
If you have a small spotting scope or maksutov telescope (up to ~4" in mirror diameter and short, about 18" long at most), follow along to upgrade it to a tabletop telescope mount that is easy to make and even easier to use! I find this a helpful upgrade to a telescope to make it more user-friendly, especially for kids. I created this project for my nieces (three of them aged 8-18) and they love it. I based the design parameters off this telescope's mount, which is regularly used as a checkout telescope for libraries around the country.
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- Small spotting scope or telescope. I used a vintage Celestron C90 from the 80s, which is a 4" Maksutov style telescope.
- Sheet of 3/4" plywood - I prefer baltic birch for the look and sturdiness, but use what you have!
- Thick wooden cake plate/board for the base, (you can use plywood for this, but the cake plate is thicker and heavier). About 14" in diameter, anything 12"-18" would also work - too much bigger gets unwieldy.
- Three hockey pucks or rubber feet
- Scrap of countertop laminate
- A few pieces of teflon or furniture glides
- Aluminum or steel stock, ~2" wide by 6" long
- 2x 3/8" bolt about 2.5 - 3" long plus washers and nylok nut
- Wood screws (about 1" long but might vary depending on your wood, etc)
- Sandpaper (sander is helpful but not necessary)
- Drill and assorted drill bits
- Circular saw
- Disc sander or drill drum sander attachment (optional)
- Wood varnish and paintbrush
- Brads/small headed nails
- Nail set or brad nailer (optional)
- Leather (optional)
- Pliobond or similar rubber cement
- Trammel points or a piece of string and a wood screw
- Marking pencil
- Wood glue
- 2" hole saw
- 3/8" tap
Step 1: Measure Up Your Design and Mark on Plywood
I loosely based this design off two things: the aforementioned Orion Starblast telescope, and a wooden cake plate I found kicking around in my garage. The cake plate was about 1-1/2" thick by 14". To create this design you really only need to cut four different pieces out of the plywood (three if you use the cake plate as a base):
- A circle for the ground board, which is what the whole thing sits on.
- A circle of the same diameter as above for the base board, which the mount attaches to.
- A large "fin" to extend up from the base board to where the telescope mounts.
- A support piece for the fin so it doesn't flop around or break.
That's really it! Like I said, simple. For your base and ground boards, consider your own telescope's parameters. Mine was about 12" long by about 5" in diameter, and not very heavy - I'd say 4 pounds. Do you have a small newtonian that needs some extra height on the fin and a bigger base to support it? Are you using a very small spotting scope? For reference, here are some measurements that I used:
- The ground and base board were both about 14" in diameter.
- The fin was a little over 12" wide by 13.5" tall
- The fin support was about 9" tall by 4" wide.
To draw your circles on the plywood, use trammel points or just a screw, pencil and a piece of string. Put the screw at the center of your circle and measure out to half the diameter you would like, then tie off a pencil and scribe the circle. Remember that the radius of a circle is half its diameter, so if you want 14", you'll need to measure 7" from the center.
For the fin piece, I honestly freehanded it. I took a piece of butcher paper and drew the shape I thought looked nicest, then cut it out and traced on the wood. I only did this because I'm terrible at drawing and didn't want to mess up a bunch of times on the wood.
For the fin support, one side needs to be a right angle, so use the corner of the wood and draw a half-round shape about 9" tall by 4" wide.
Step 2: Cut and Sand Plywood
Now it's time to cut your pieces out. I like to use a jigsaw with a higher tpi blade (like 14 tpi) for smoother control when cutting around a radius. Take your time here, the closer you get your circles and fin to the shape you want when using the jigsaw, the less work you have to do sanding. Clamp your work (always a good safety practice) so that it's easier to cut it out.
Once the pieces are cut, you'll want to sand the edges. I routed them down so that they were rounded, but this isn't necessary - just make sure the edges aren't too sharp, and smooth them with like 180 grit sandpaper to start, then work up to 320 to make them smoother.
A note on the base board and ground board - if you want a really nice, clean circle and it's hard to cut it with the jigsaw, you can do as above. This makes it looks aesthetically appealing, but is not a necessary step so don't sweat it if you don't have a disc sander or access to one. Just mount (one of them at a time!) on a board with a screw through a small hole (3/16" or 1/4") the center, and clamp that board to your disc sander table. Make sure the board can spin freely, and work it against the disc sander so that the sander spins it. This takes some time and be patient (and careful), but with practice you can make each of these boards almost a perfect circle. We'll be drilling a hole through the middle anyways, so don't worry about adding a hole in the middle. If you have a drum sander attachment for your drill, you can do this same work but it takes more time and patience.
To cut a handle into the fin (I highly recommend this), use a 2" hole saw to drill a hole at the top and bottom of where you want the handle, then cut out the remainder in between with a jigsaw. I didn't measure this - just used my hand as a rough reference.
Step 3: Assemble!!
Once you've sanded your four pieces down, assemble them as above. Attach in the following manner:
- The large fin attaches to the base board - I used 3x 1" screws. Countersink them a bit if you are able, if not, make sure they are about 3" from the very edge of the base board.
- Attach the fin support to the base board and the fin. This kind of makes a "plus" shape, as viewed from the top or bottom. Screw through the back of the fin as shown here - again, countersink the screws a bit so they are flush, or use pan head screws.
- Clamp the base board and ground board together so that they are perfectly matched up, and drill a 3/8" hole through the center. The base board spins freely over the ground board, kind of like a lazy susan, so these pieces are NOT glued together.
A bit of wood glue at these joints is helpful for strength. If gluing, allow to dry overnight.
Step 4: Make the Bearing System on Ground Board
Set the top part with the fin aside for a minute. If gluing, let that part dry overnight while doing this bit. Take the ground board, and attach three pieces of teflon about 1/8" thick by 1" square to the top part. These will be sandwiched in between the two boards, and the top part with the telescope will rotate around on these bearings. I like to take a protractor and measure 120 degrees in between each piece so they are exactly spaced around the center, but it honestly doesn't matter - eyeball it if necessary, close is good enough. They should be attached about 2-3" from the edge. I like to use stainless brads and a nail set/punch. It's important that your nail is recessed a bit into these piece, so use a nail set, brad nailer, punch, etc. to achieve this. Put two nails into each piece. If you're using nail-on furniture glides, you might be able to get away with just nailing them into the ground board instead of using the teflon and brads - YMMV.
To finish off our ground board, you have some options. I laminated the bottom to keep it from getting wet in damp grass, etc. but that's not necessary - you can just seal it with polyurethane. I also like to recess the bottom of the center bolt a bit, but again this is unnecessary.
Take your thick rubber feet or hockey pucks and screw them to the bottom of the ground board. If using hockey pucks, countersink the screws with a pilot hole bit and try to use stainless hardware so it doesn't rust. I had these rubber feet so used them, but honestly prefer hockey pucks as feet for telescopes - they work well to damp the vibrations from the ground and are cheap! They are also easy to drill and shape, and are very durable.
Step 5: Make the Bearing System on Base Board
Take your fin/base board piece and flip it so you can work on the bottom. Add a piece of smooth countertop laminate that is just smaller than the base board in diameter. I like to use Pliobond rubber cement here, but other adhesives are fine. I did this step before attaching the fin on the top, but you can do it after and in some ways that's better so you cover the screw holes. Allow to cure as per manufacturer's guidelines with your adhesive.
Step 6: Seal to Finish Wood
Take your favorite polyurethane (I like Varathane, but use what's handy) and seal up your wood. Be sure not to get any on the laminate or teflon pads! Use 3 coats or more, telescopes can get dewy late at night and that will ruin or warp the wood. Allow to dry between coats - read and follow the guidelines on your product.
Step 7: Make the Altitude Bearing and Mount Telescope
Now for the part that you can experiment around with depending on your telescope. I had a chunk of aluminum that worked well for this part, but steel is fine too. I drilled some holes to mount it to the base of the telescope where it would normally mount, then drilled a series of them and tapped them for a 3/8" bolt. I did a series because you'll need to balance your telescope around this pivot so it doesn't flop around, this allows for you to mount in a number of different configurations to achieve this.
So, on one side you have the telescope, which is attached to the piece of metal. In between that metal and the fin is a piece of plastic - I used teflon, but some nylon or a scrap of milk jug would work too. 1/8" thick is nice, but thin pieces will work okay, they might not be as smooth. On the other side of the fin is a knob, use this to adjust the friction of the telescope altitude bearing. You want it to move smoothly, but not fall down or flop around when you let it go. Put a washer in between the knob and the fin. All of this hardware is 3/8" and available at most hardware stores in the fasteners section.
Step 8: Finishing Touches and Assembly
I decided I wanted to go for a bit of a steampunk look, and happened to have this leather piece that had pouches in it which fit my eyepieces. To attach to the handle, I just used the Pliobond rubber cement (from the step attaching the laminate), wrapped it around with some glue between the layers, and clamped so that it stayed in place. For the pouches, I did the same and added a couple of brad nails like I used for the teflon. This is all unnecessary, but made it look pretty cool!
To finish off your telescope, mount the top fin part and base board to the ground board by putting a bolt, washer on top and bottom, and nut through the middle. Tighten this nut until you can move the base board around over the ground board without too much friction, and no slop. This will wear in so may need adjustment. I like to use a nylok nut here so it doesn't come loose.
Step 9: Use It!
You've successfully made your mount and modified your telescope to be more useful and functional. Now get outside and use it! These are great plopped on top of a picnic table or folding table. To look up and down (altitude), move the telescope up and down. Spin it around (azimuth) to move across the sky. Clear skies!
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