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My 10" Dob build

JamesF

By JamesF
in DIY Astronomer

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JamesF

JamesF

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Quite some months ago I picked up a 10" mirror set with a view to building my own dob and it's sat in its box under my desk ever since, waiting for me to get around to doing something with it -- mostly sorting out a tube. As luck would have it, a 10" flextube tube (without optics) came up recently and I decided that as it would move the build on I'd have it. The tube arrived without a base or or the bearings, so my build ended up being reduced to making new bearings and building the rocker box. I also needed to make some "caps" for the OTA to keep dust out.

I dealt with the caps first, having discovered that a couple of lids off some empty paint containers fitted rather well. I cut some thin ply circles that would just fit inside the OTA and glued them to the inside of the lids and fitted a couple of wooden cupboard knobs that I had lying about.

I intended to follow Berry and Kriege's "small dob" build instructions for the bearings and rocker box, but a flextube dob creates a few awkward problems with the truss tubes and there wasn't really a sane way to make a box for the tube to fit inside. Instead I made up some wooden mounts cut to match the circumference of the tube and lined with felt. These I fixed to small wooden discs aligned to suit the existing mount holes and those in turn I fitted to 18" diameter semi-circular bearings. The rocker box itself is fairly standard B&K design, but I have a lazy susan bearing on the ground board with three PTFE bearings on the outer edge of the board, the two being held together with a 12mm bolt fixed to the bottom board using a half nut I made by sawing a standard size nut in half. This means the bolt is stationary with respect to the ground board and I can fit a digital angle gauge later.

The ground board itself has three height-adjustable feet allowing about 40mm of adjustment. I wanted to allow this much because there's very little level ground here.

The OTA was finished off with an optical finder made from a 50mm binocular optic and a focuser purchased from FLO's "clearance".

I've quickly tested the optics and they seem fine, though it still awaits first light. I want to add a digital setting circle system using the GemRed angle gauge and need to find a nice way to add the logo. The lids could do with painting, too. They make me think of a biscuit barrel at the moment :) The top one doesn't fully close the upper cage as there's a gap between the two parts of the tube when the OTA is closed up, but it does stop anything being dropped onto the secondary when it isn't in use. I've not added an eyepiece shelf yet. I'm still pondering on what I'm going to do there. I might also see if I can add a handle for carrying the OTA.

I needed a number of new nuts and bolts for mounting the mirror cell, focuser and bearings, all of which I purchased from ebay because I could get them in small numbers at reasonable prices. I chose stainless steel because I prefer it to the plated or black options.

I'm very happy with the alt movement. It's smooth, can be done with one finger and has enough rigidity that it won't move in the breeze. I'm not so sure about the az motion. It grabs ever so slightly and I wonder if the ply isn't very fractionally out of true. It doesn't feel so bad that I want to take it apart just yet though, just a bit uneven. Movement is still a one-finger operation nonetheless.

Anyhow, here it is:

IMG_0074.jpg

James

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wrinkly

wrinkly

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Good job but please have pity on us much less talented individuals.

That's the good thing about astronomy, it's mainly done at night, my neighbour can't see the messed up mods that I'm looking through. :grin:

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swamp thing

swamp thing

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Nice job James.

Great fun building your own kit isn't it?

:D Haha tell me about it. I got myself an extraction system a few years back for this very reason.

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JamesF

JamesF

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Nice job James.

Great fun building your own kit isn't it?

It is. I enjoyed the process and learnt quite a bit along the way. Hopefully I can get out and use it a bit more and then tweak the things that need sorting.

James

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JamesF

JamesF

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The base is 50cm diameter. I'm not sure how that compares with the standard Skywatcher dobs and the Lightbridges. The feet I used are ones I picked up from ebay. They're plastic feet about 50mm wide, with an M10 50mm screw thread. They screw into "T" nuts on the bottoms of the wooden blocks on the ground board and seem fairly stable thus far.

James

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JamesF

JamesF

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We'll see how it goes. I'm not desperate for an EQ mount at the moment. Part of my reason for wanting a dob was to get away from the whole EQ mount thing for at least some of my observing. I'm quite happy using a GEM, but sometimes it's nice just to have an uppy-downy-lefty-righty type mount :)

James

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JamesF

JamesF

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The construction is mainly painted 12mm and 18mm ply. The exceptions are the small pieces that fit to the scope and the braces for the sides which are softwood. I prefer to cut small/narrow parts out of solid wood rather than ply unless it's really good quality ply. The semi-circular bearings (18mm ply) have some edging strip left over from installing the kitchen worktop glued to the edge and the rocker box has 40mm lengths of 3mm PTFE sheet nailed to the top edge, one at either end of the curved edge for the edging strip to run on.

James

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fwm891

fwm891

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it's nice just to have an uppy-downy-lefty-righty type mount :)

James

Know the feeling but then once you've done the uppy-downy-lefty-righty things its nice to just view for a few minutes at least and you don't get the nudge vibrations

Enjoy that's the main thing

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JamesF

JamesF

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Know the feeling but then once you've done the uppy-downy-lefty-righty things its nice to just view for a few minutes at least and you don't get the nudge vibrations

Enjoy that's the main thing

They'll always be enjoyed :)

We shall see what happens. I can understand now the attraction of a large aperture newt and I don't imagine this will be my last :)

James

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Beulah

Beulah

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The construction is mainly painted 12mm and 18mm ply. The exceptions are the small pieces that fit to the scope and the braces for the sides which are softwood. I prefer to cut small/narrow parts out of solid wood rather than ply unless it's really good quality ply. The semi-circular bearings (18mm ply) have some edging strip left over from installing the kitchen worktop glued to the edge and the rocker box has 40mm lengths of 3mm PTFE sheet nailed to the top edge, one at either end of the curved edge for the edging strip to run on.

James

Thanks for your reply. :)

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