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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

OHHHHHHHHHHH

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Thanks Pete

I'm a bit ignorant on the traditional style dob construction as I've never made one.

Nice looking wooden bandsaw in the back ground never seen one like that before

Damian

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Thanks Pete

I'm a bit ignorant on the traditional style dob construction as I've never made one.

Nice looking wooden bandsaw in the back ground never seen one like that before

Damian

Cheers Damian 

Thats a homemade bandsaw. very powerful 2 horsepower motor in it. cuts like a dream. Got the design from a guy on youtube. Matthias Wandel. he's a hero of mine hahaha

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Another update. Had a delivery of 2 sheets of 15mm BB grade Birch Plywood today. Face veneers are very nice on one side and good on the other, Which im very happy about as in the past it has been a bit hit or miss with alot of repair patches on both sides but this ply has no repairs.

So i think I have all i need now. Yipppppyyyyy!  

I got all the aluminium triangles cut on the bandsaw for the mirror cell today and my new Pipe cutter turned up so i got the 1.25 inch poles cut for the secondary cage. The pipe cutter is fantastic. takes about 10-15 rotations round the pole till it pops apart with a nice bevel on both cut ends. it leaves a bur on the inside of the pole. but theres a deburring tool on the top of the pipe cutter. 

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Woo lots of bits and looking very smart Pete.

Pipe cutters are nice bits of kit and leave a nice square end on the cut.

I'm waiting for better weather to order my birch ply as I don't want to leave it stood in the garage and risk Mildew on it.

Great pic's and update

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Woo lots of bits and looking very smart Pete.

Pipe cutters are nice bits of kit and leave a nice square end on the cut.

I'm waiting for better weather to order my birch ply as I don't want to leave it stood in the garage and risk Mildew on it.

Great pic's and update

Cheers Damian

Good idea about the plywood storage. Indeed that would be a waste of money. Birch plywood isnt cheap.

Pete 

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Hi again Steve 

I had the impression all connections between all the triangles are loose to rock to there balancing point in the KB design. Thats the way im making this one, fully floating on every access.  

In this image ive just put the bolts through the joins to show how its layed out.  

Pete

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When I assembled mine initially (via KB spec) it didnt seem to offer enough float for my liking, so I spaced it a little more, just to be certain.

Probably overkill but it works very nicely indeed. I'm not saying it's needed though. :)

See what you think Pete.

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Looks very nice Pete and coming along quickly.

Are you going to use a classic sling support for the side

Hi Damian 

Thanks mate. its nothing compered to your guys that grind. Thats amazingly accurate stuff. I admire any one that takes on such a thing.

I am indeed going for the classic sling support.  Have you any suggestions or thoughts on that?

Pete  

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Hi Damian

Thanks mate. its nothing compered to your guys that grind. Thats amazingly accurate stuff. I admire any one that takes on such a thing.

I am indeed going for the classic sling support. Have you any suggestions or thoughts on that?

Pete

It's worked for many years and sticks with the K+B design your doing, many a good scope has come out of it.

Plenty of people with experience to advise too not as though you need it by the looks of the workmanship you've already graced SGL with already.

Looking forward to seeing it come on.

As for mirror making it's a lesson in patience, frustration and lunacy for my first attempt will be a lot more relaxing to get back to playing about with wood and ally

Damian ;-)

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It's worked for many years and sticks with the K+B design your doing, many a good scope has come out of it.

Plenty of people with experience to advise too not as though you need it by the looks of the workmanship you've already graced SGL with already.

Looking forward to seeing it come on.

As for mirror making it's a lesson in patience, frustration and lunacy for my first attempt will be a lot more relaxing to get back to playing about with wood and ally

Damian ;-)

Ive toyed with the idea of grinding my own mirrors. but never saw it through. Instead I just saved my pennies for a long time for a quality mirror from a known mirror maker . I took the easy way out. hehehe. i look forward to seeing how your mirror comes out and the final scope build. 

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Ive toyed with the idea of grinding my own mirrors. but never saw it through. Instead I just saved my pennies for a long time for a quality mirror from a known mirror maker . I took the easy way out. hehehe. i look forward to seeing how your mirror comes out and the final scope build.

Sensible option as it's no difference in cost just the thrill of doing it

Be good to one day see them together on a viewing session one from the teacher and one from the student ;-)

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Hi again Scopers

So I thought its time to center spot my Primary mirror. In regards to collimation I normally use the Baadar mark 3 Laser collimator but on the odd occasion ive found myself with dead batteries and trying to do it with an old 31.7mm/1.25inch camera film case with a 2mm hole drilled out the center to get some kind of alignment, as a emergency  backup. I thought to myself best get a cheshire or some sort of collimator that does the job to the degree of accuracy required for a large Dobsonian. After searching awhile i stumbles upon the CATSEYE collimation system which includes the centring hotspot and Centring Template and a choice of Collimators. I went for the Catseye Infinity XL Autocollimator as i found it going for offer on FLOs website. The template has 4 holes in the center that i first stick a piece of sellotape over the top and then place the hot spot on a table and align the template over the hotspot and press the template so the sellotape sticks through the holes of the template to the top side of the hotspot. Then carefully peeling of the paper back of the hotspot. I had to do this several times as it was a little tricky as the hotspot would tend to come off with the paper backing. Then i aligned the template on top of the primary mirror and with the rubber end of a pencil pressed the hotspot down until the hot spot had stuck in place . :-)

Template on mirror with hotspot  

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Hotspot stuck in place 

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Catseye Infinity XL Autocollimator

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Don't worry about it Pete as they're all the right way up in space ;-)

You can edit the posts although I think you'd have to delete the photo and attach it again then have a look in the preview to see if it's the right way up

That's a lovely mirror (drool)

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