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Jim's Dob.

jbk44

By jbk44
in DIY Astronomer

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jbk44

jbk44

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Well now I have a new hobby that is totally dependant on clear night sky’s I thought it best to have something to do during the cloudy nights and bright days. I’ll start building a 12" truss dob (one to fit in my car) this weekend, but to how long this will take me to finish I really don’t know. So between work and social life I’ll try to enjoy learning the fine art of swearing and breaking things until I get this scope done.

I'd rather finish the scope then show you all, but I'm hoping when I'll need help I can ask here... or you'll just tell me.

Here are a couple of pic's of what will become the housing around the primary mirror.

R1.jpg

R2.jpg

Here’ is some lightly figured American cherry that has been equalizing for a few weeks inside, this will surround the mirror.

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Here is the donor... I'm going to miss my chair dob. :)

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Beulah

Beulah

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I laughed when I saw your Lazy-dob! Ingenuity at its finest!! :)

Good luck with your build, I hope it goes well. :( I did think of making a coopered OTA made of Black Walnut - would look stunning but would be SO heavy.

Must admit, that figured cherry is making me drool a little, I do so love wood...

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jbk44

jbk44

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I know that seat mount is a silly but it works!

I know what you mean about a coopered OTA made of black walnut, it's funny because I'll be using black walnut in this build as i love the stuff so much, also I've just had some brass delived that I'll use also. If you take another look a the pic of the cherry you'll see a bit of the black walnut table i made a few years back.

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jbk44

jbk44

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Hi, this link may help, has lots of further links -

Stellafane: Build a Dobsonian Telescope

And this book is brilliant The Dobsonian Telescope: A Practical Manual for Building Large Aperture Telescopes: Amazon.co.uk: David Kriege, Richard Berry: Books

All the best with the build, please let us know how it goes.

Regards, Ed.

Brilliant just the sort of info I'm looking for. Thanks.

Well as for how it's going I'll have a few cad drawings printed 1:1 tomorrow and start to make a few templates. I've got a few days off this week so I'll do my best.

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jbk44

jbk44

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I’ve always been a bit stupid but good at misunderstanding the obvious.:D

I managed to get a couple of things done today. First off was to stick the 1:1 scale drawing on the mdf, and after cutting that one it was used as a template for the other. I was not going to use mdf at all (I hate the stuff), but after thinking about it for a while I thought why not? Its very stable when kept dry and it will be painted and then flocked so I’m sure it will be just fine. Also this is my first scope and I don’t really want to spend too much on it because knowing me as soon as I finish it I’ll learn from the experience and want to start a better more detailed scope.

4.jpg

Just about to clean up the edges with a router.

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Cutting the center out with a circle jig. Tip is to make the hole a little small and on the last pass screw the router 1 or 2mm wider on your jig so you get a nice clean edge if the material is too deep to cut in one pass.

I counter sank and screwed down the mdf onto the 2x1 below it (avoiding the path of the cutter) then clamped the 2x1 to the table. On the last pass I held the outer ring in place with a couple of clamps to stop it moving and freaking me out.

6.jpg

There will be thin peice of birch ply to help support the mdf that will have threaded inserts in position to fix the telescope base thingie from the inside rather than the outside as on the original telescope.

7.jpg

Think I'll get the black thingie sandblasted and powder coated, its a bit rough.

8.jpg

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jbk44

jbk44

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You have made a great start :D and your workshop looks much more organised than mine.........in fact in comparison, mine is more of a disorganised heap :)

Regards, Ed.

Well the pic's are zoomed in, if i were to zoom out...

Just getting my work space sorted again, after moving house a few years ago. I'll zoom out a bit when I'm happy.

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jbk44

jbk44

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Hi - good start - nice to see pictures of the process. What thickness MDF are you using? 12 or 18mm? I'm looking forward to following this thread. Thanks. Ed

Thank you.

I'm using 18mm for the braces that hold the timber around the mirror. I have amended the hight of the box from 250mm, the box is smaller in height. These braces will be more than strong enough at 18mm.

I'll be back at it again tomorrow, it will be a day of making jig's and if i get the 75 degree router bit i ordered I'll start the getting the box together.

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  • 5 weeks later...
jbk44

jbk44

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Well I’ve managed to get back out in the garage and get a little more work done on the build. It’s been a busy crazy time at work and a few busy weekends away has kept my dob in the background but with my fingers crossed I’ll get a little more done this weekend. Here’s a few pic’s of what I have managed to get done before work during this week.

After cutting out the 75 degree angle on the cherry and checking the fit a few times i used the ratchet straps while gluing.

IMG_0090.jpg

Really happy with the result, the fit was spot on.

IMG_0095.jpg

I will be routing a channel and putting in a decorative strip where each peice of wood joins (hard to type what i mean but you'll get the idea). Here is the jig i will use to hold the router guide.

IMG_0094.jpg

Jig in place.

IMG_0093.jpg

Here's a few of the decorative strips that i have made, using american walnut and some veneer that was hanging around.

IMG_0092.jpg

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spaceboy

spaceboy

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Sorry JBK but your going to have to bin that MDF. ( I also hate the stuff )

You are doing such a good job it seems such a shame that MDF has found it's way into the project. I used MDF once and I swore never again. Not a bad material to work with but it so let me down once the slightest bit of moist air got in contact with it.

One think to consider if getting anything powder coated is it will add to the overall dimensions by around 2-3 mm.

That is going to be one sweet scope once finished :)

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jbk44

jbk44

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Spaceboy yeah i hate MDF, but this is going to made from free timber or scraps that i have. I really don't want to spend any money on the first go and as i said as soon as I've made this I'll make a more detailed version that i really will keep for a life time.

The mdf is going to be sealed and then covered with yachting varnish and then covered with a thin layer of birch ply and that ply will also have a waterproof covering of yachting varnish too, i think that will be fine as this scope will only be out on good nights and have to cope with a little dew. Also the flocking i have is plastic backed.

I do however wish that i had the money to buy 20mm birch ply, and as i have a terrible allergy to MDF too i have regrets. The jigs I've made will be kept and will make the next version very easy to build so i don't really care about the time i take on the first one. I guess this is a learning curve and a way of getting back into woodwork as I've been away from it for a several years.

Thanks for your input, all that you said has been on my mind for a while.

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