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20inch Dobsonian Construction


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Hello again Scopers.  Almost finished scope and First light experience. Ok so Ive push the project almost to the end now. Ive had to lash together my secondary mirror holder for now. Because Im still

Hello Scopers  I managed to get the inside of the secondary cage and the mirror box Flocked. this was fun and tricky. I enjoy a challenge. I varnished all the surfaces to be covered with flock to ensu

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Hello again Scopers

just a small update on the mirror cell. After a few day thing about the fact that my 20 ing mirror is only 40mm think Im probably going for a 27 point mirror cell.

Mainly because thats what this Dave Kriege suggests and it cant hurt putting the extra work in for more support for the mirror. Here is a plan i knocked up this evening. 

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Plans look great and a bit of extra support won't hurt as you say. Better safe than sorry

Did you run it through PLOP too? as it may save a bit of work for you?

Simonfromsussex build used an 18 point K+B cell on his F3.4. I'm not sure if the mirror was the same thickness as I don't think he mentioned it? you'd have to ask him and get  his opinion on how it performs.

Damian

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Mo

Plans look great and a bit of extra support won't hurt as you say. Better safe than sorry

Did you run it through PLOP too? as it may save a bit of work for you?

Simonfromsussex build used an 18 point K+B cell on his F3.4. I'm not sure if the mirror was the same thickness as I don't think he mentioned it? you'd have to ask him and get  his opinion on how it performs.

Damian

morning Damian. What is PLOP?
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Momorning Damian. What is PLOP?

Apologies thought you'd seen it before

PLOP stands for PLate OPtimiser you put in your mirror details and it translate's this into a cell design which is optimum for your mirror. It take's some getting your head around at first but is interesting as you can see graphical representations of the error and flex in your mirror.

Here's the web site if you want a look and download the program

http://www.davidlewistoronto.com/plop/

27 point's will be fine to the K+B design though as it is tried and trusted, but just thought you might want to look at a more modern interpretation as I can see your no stranger to computer programs in the design you've put up

Damian

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Couldn't get PLOP to run on my Mac at the time I designed my mirtor cell.

Mine is a 27pointer too as my 20" is also a thin mirror. The KB design works extremely well with no astigmatism at all.

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Apologies thought you'd seen it before

PLOP stands for PLate OPtimiser you put in your mirror details and it translate's this into a cell design which is optimum for your mirror. It take's some getting your head around at first but is interesting as you can see graphical representations of the error and flex in your mirror.

Here's the web site if you want a look and download the program

http://www.davidlewistoronto.com/plop/

27 point's will be fine to the K+B design though as it is tried and trusted, but just thought you might want to look at a more modern interpretation as I can see your no stranger to computer programs in the design you've put up

Damian

Cheer for that Damian. Its not as simple as 123 but very handy. 

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So it has begun. Ive cut up the still box section and flat bar for the mirror cell and drilled all the holes. Also welding jig made to hold it all square and parallel hopefullying this weekend a friend will kindly do the welding.

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Hello again Scopers

I managed to get some time to make some split blocks and the top truss connectors i took some photos of the split block progress but ran out of time record the progress of the top truss connectors so ive only got photos of them finished.

Cutting the blocks up 

post-5432-0-66847500-1426534143_thumb.jp

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Lots of progress Pete (sorry if I've got that wrong) and lovely looking bits

Just a question

Is there another piece to go on the back of the clamp blocks? or are the bolts going to go right through the rocker box of the scope once they're screwed on the side? Just wondering how they clamp?

Damian

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Lots of progress Pete (sorry if I've got that wrong) and lovely looking bits

Just a question

Is there another piece to go on the back of the clamp blocks? or are the bolts going to go right through the rocker box of the scope once they're screwed on the side? Just wondering how they clamp?

Damian

Hi Damian  

I had a few hours spare this afternoon and managed to get them finished. rather chuft :-)

Yes the quick release will bolts through the Rocker box. I think i will get maximum stability that way. I will either use threaded inserts or Tee nuts through the Plywood wall of the Rocker box. Im going to test to see which is the most stable/strong.  

Pete

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