Telescope Equatorial Mount part 2

In the previous post I described the equatorial head I’d made for my telescope mount.  Now I’m going to cover the tripod.  First, I needed to figure out how large the tripod needs to be.  To do this I measured the highest and lowest points the eyepiece would be from the floor with my scope in the equatorial head clamped to a bench.  Then I measured the height of my eye while I was bent over in the sitting position.  From here I figured how how much I need to raise the eyepiece at the lowest point to get it to a comfortable position.  This resulted in me needing a tripod that lifted the equatorial mount 46″ from the ground.

I looked around for designs of wooden tripods and came across a design I liked in a book called “Build Your Own Telescope” by Richard Berry.  The book covers several telescope builds and one of them was for a tripod mounted 6″ refractor.  I used the design as a jumping off point to make my own design.  In the book, each leg was held at an angle of 75 degree from the ground which results in me needing roughly 48″ long legs.  In the book, each tripod leg is an I beam made up of three pieces of wood.  I decided to go with a C channel shaped beam still made up of three pieces.  The legs start wide at the top and then taper to a point at the bottom in the book.  I liked this element and went with it.  I laid out the design for the wed of the C channel on the pieces of wood and then cut them out on the band saw.

EQ2_1

The band saw doesn’t leave a smooth surface on the edges of the pieces.  A hand plane makes quick work of smoothing the sides.

EQ2_2

The flanges on my C channel legs are made of a 1×4 ripped in half on the table saw.  To make sure both pieces were the same width, I ran all the pieces back through the saw after setting the fence to the width of the thinnest piece.

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To attach the flanges to the web I drilled holes every six inches for screws.  I also drilled the hole for the bolt that the leg will pivot on.

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The pieces were glued, clamped, and the screwed together.  I clamped sections, inserted screws and then moved down the line leading the way with clamps.

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On the pointed ends of the legs, clamping is a must to bend the wood to the shape.  The web at the location for the last hole isn’t thick enough to be screwed into.  Instead I bolted the pieces together.  It’s not coming apart now.

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To connect all the legs together I borrowed another idea from the book.  My hub consists of two pieces of 3/4″ plywood in the shape shown below.  I started with a 10″ diameter circle and then laid everything out with a straight edge and protractor.  It’s always good to shade the areas you want to cut as it is tough to add material back.

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Off to the band saw for more cutting.  I freehand cut all the pieces because I planned to clean them up on the sander.

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Here’s the two pieces clamped up while the glue sets.  After the glue dried the inside edges of the piece was sanded.EQ2_9

To go on top of my hub I cut out a 10″ diameter circle.  All the parts were center drilled, glued, and then temporarily bolted together so I could sand them as one piece.

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To attach the legs I held them in the extended position pushed up against the top of the hub.  This way the legs will jam tightly when opened to increase the stability of the tripod.  I marked the location for the bolt holes by drilling shallowly into the hub with the legs in this position.  I finished the holes using the drill press.  I drilled down halfway on one side and flipped the piece over to drill the other half of the hole.  This way, if your drilling isn’t perfect the problem is inside the piece where it can be fixed as opposed to being off when you exit the other side of the piece you’re drilling.

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Here’s everything together.  To attach the head to the tripod I drilled a 3/8″ hole and bolted the two together.  A wing nut on the bolt allows me to move the head around in azimuth.

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The tripod was very stable but when lifted the feet would come together as expected.  To fix this I added a spreader in between the legs.  I thought about it for a little bit and decided I’d add braces attached to each leg that would meet in the middle.  I recalled a joint in a book I have around here called the Triple Lap joint that would be perfect.  Here’s the one I made.

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How do three pieces of wood occupy the same space?  Here are the piece separated for a better view.

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I installed the spreader using hinges and put a bolt through it to hold it closed.  The joint is meant to be stacked vertically.  Swinging the arms together on an arc causes results in them not coming together smoothly.  I think I’ll need to remove a little material to solve this problem sometime soon.  But it does come together nicely.

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Here’s an underside view on one of the spreader arms.  The end of the arm is cut at a 15 degree angle to jam up against the legs.  EQ2_16

The spreader can be disassembled allowing the legs to collapse for storage.  EQ2_16a

Finally, the pic you’ve been waiting for.  This is the setup currently.  I’m still testing so I haven’t finished any of the pieces.  No finish means I haven’t put felt in the rings so I’m using a towel to take up the space.

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I put it all on the bathroom scale and measured the weight of all the pieces.  Currently the tripod weighs 16.4 lbs, the equatorial head weighs 11.6 lbs, the scope with diagonal and finder weighs 7.6lbs, and the counterweight is 7.5 lbs.  Summed this results in about 43 lbs.  I have given thought to making new legs with material taken out of the webs to reduce weight.  I think I could lighten it some but I don’t want to decrease its rigidity.  Currently, it may be on the heavy side but it is solid as a rock.

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6 Responses to Telescope Equatorial Mount part 2

  1. schwitters57 says:

    It’s a beautiful mount.

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