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Post by boomboom on Jun 5, 2014 20:58:46 GMT -5
I have started on a Tangent Arm for the Gaunt mount and my 6" f12 refractor. As mentioned in the RA setting circle thread this is what I chose to fit to this scope. Jim Sapp has a very nice design that I'm adapting. Here is his idea… and Jim's cylinder block…
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Post by boomboom on Jun 5, 2014 21:06:21 GMT -5
So far here is my cylinder block... The aluminium bracket is 150mm wide, it needs a couple of brass bushes and knobs. Here is a better photo with the brass cylinder showing...only took three attempts to get the block right! Next the arm that the block is attached to. The hard part is going to be getting it to clamp around the mount, but I have a few ideas!
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Post by Mike on Jun 6, 2014 15:58:09 GMT -5
I have a few pictures of arms used in the past as I almost needed one. You want me to post them for ideas?
Mike
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Post by boomboom on Jun 6, 2014 17:44:59 GMT -5
Thanks Mike, that would be great! The more the merrier…it takes a while for me to sort things out in the grey matter, but I get there eventually. Like Jim Sapp's version mine will have to be attached to the mount. Matt
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Post by boomboom on Jun 8, 2014 18:45:40 GMT -5
Here is an enlarged etching from a newspaper article about the mount. Interesting to see the simple tangent arm used on the Dec, and the RA gear. I assumed that the RA would have been a 360º….not so! And the newspaper article too from 1877. It's nearly impossible to read. When I get a chance I'll try and redo it.
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Post by Mike on Jun 9, 2014 11:40:22 GMT -5
I may have misunderstood "tangent arm." I thought you were talking about a connection rod between the end of the scope tube near the objective down to the mount.
Mike
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Post by astromanuk on Jun 9, 2014 12:56:11 GMT -5
I may have misunderstood "tangent arm." I thought you were talking about a connection rod between the end of the scope tube near the objective down to the mount. Mike That would be a Hargreaves strut. The tangent arm is an excellent solution for fine declination adjustment. I had one on an old 4" Cooke and although 100+ years old it worked perfectly.
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Post by Mike on Jun 9, 2014 13:48:04 GMT -5
Yes Yes Yes a Hargreaves Strut. Sorry
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Post by boomboom on Jun 9, 2014 17:42:32 GMT -5
Yes tangent arm is a good way for the dec adjustment. Is this a scope you still have Ian? Love to see a photo if at all possible. I've only just worked out how to take a screen shot and enlarge it….so admitting I'm a computer idiot, I am pleased to see the etching as a close up, revealing a few details that were a bit of a mystery to me. From what I gather there is only one or two other mounts still in existence from this era in Oz. Everything I do, I intend to be reversible, and this tangent arm fits that brief perfectly. The RA is coming together too…all theoretical at the moment Matt
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Post by boomboom on Jun 20, 2014 1:22:19 GMT -5
Here is a pdf of the newspaper article if anyone is interested. issue643.pdf (723.83 KB)
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Post by boomboom on Sept 15, 2014 22:46:32 GMT -5
With the RA all but complete it's on with the Tangent arm for Declination control. Out with the jigsaw to cut out the shape. It's long as this is hand control at the eyepiece end. That's all so far...more to come
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Post by boomboom on Sept 24, 2014 1:52:40 GMT -5
More cutting grinding filing drilling and tapping of aluminium and this is progress so far. From the front, two aluminium blocks 40x80mm will be cut in half and be part of the clamping mechanism controlled with two rods. At the eyepiece end the cylinder block. All that is left to do is to put in the threaded rod along with nuts bushes and a home made 50mm knob to operate it....nearly there Thought I would paint it black....any other ideas? Not to sure about leaving it natural aluminium but it would save a bit of work! Matt
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Post by boomboom on Sept 24, 2014 1:56:47 GMT -5
Oops missed one photo. This is the threaded rod holder....should give an idea of what it's all about.
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Post by boomboom on Oct 4, 2014 2:56:05 GMT -5
Currently undergoing version II as there is too much slop with the long arm on this version! No surprise rerally...what would atming be without a bit of trial and error. The new version will be shorter and possibly completley different. TBC Matt
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Post by boomboom on Oct 13, 2014 21:35:48 GMT -5
OK here is version !! of the Tangent arm....and does it work? You bet. Really thrilled how this has turned out so a few details and photos. A view from the back. The arm is much shorter, I removed half of it as it sagged under its own weight. The other solution was to extend a new arm out the front of the scope and attach a small counterweight for balance but this scope and mount is heavy enough so I went the short route. A view from the front. The four clamping blocks which clamps around the mount with the help of some thing Cork for grip. A view of the blocks with compression spring. Continued ...
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