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20" f/4 Dob build

swamp thing

By swamp thing
in DIY Astronomer

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Wobbly Bob

Wobbly Bob

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Your almost there Steve, I have enjoyed reading your progress with the project. As with Gena,s observatory SGL must have been a great source of inspiration and information.

Looking forward to the the great unvieling.

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swamp thing

swamp thing

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Cheers Bob.

Having SGL on the team is like having another pair of eyes and an extra brain, it's gotta have saved me loads of time and research. The knowledgeable peeps on here are certainly a huge help, wish I'd known about here when I built my 10" all those years back.

Its really nice to get words of encouragement too. Thanks to all for that.

I'm also hoping my build will encourage others to get into ATM, it's a huge thing in the states but here people would rather buy which is a massive shame if you ask me. Homemade stuff is so much more fun, trust me, have a go.

There are plenty tinkering with cameras and building obsy,s on here but sadly too few scope builds.

Ordered the ply for the mirror box today. Still wondering whether to dovetail or mitre the corners. Since finishing the UTA I have been thinking the end grain on the ply actually doesn't look too bad, so I might make a small section dovetailed then see what I think before committing to the box itself.

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umadog

umadog

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I'm also hoping my build will encourage others to get into ATM, it's a huge thing in the states but here people would rather buy which is a massive shame if you ask me. Homemade stuff is so much more fun, trust me, have a go.

Ok, I'll bite! I built a 9" when I was 15 or then re-built it about 3 years later. It's functional but there's plenty I don't like about it. The optics (David Hinds Pyrex: really thick primary!) have been needing to be re-coated for years. They've just been done and I was planning on picking up the mirror when I'm next in London. So I'm toying with the idea of another rebuild. I could get someone like Teeter to build me a structure: his solid tubes are very nice. Or I could do it myself (better this time!) as a learning experience with a view to possibly building a >22" in a few years time. It seems unlikely that I could ever afford to buy a larger premium scope but if the cost savings ar big enough I think I could afford to build. I imagine the money saved gets larger with increasing aperture. What would you estimate the cost of your new build? Would it be significantly less than buying from, say, Webster.

Ordered the ply for the mirror box today. Still wondering whether to dovetail or mitre the corners. Since finishing the UTA I have been thinking the end grain on the ply actually doesn't look too bad, so I might make a small section dovetailed then see what I think before committing to the box itself.

Webster dovetail, and I think it looks pretty good. Teeter does rabbets, which also look good: http://www.teeterstelescopes.com/tenreasons.html

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swamp thing

swamp thing

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I'll have to get back to you on costs Rob I have kept all the receipts for this purpose but they're not with me at the moment.

It might be better to remind me when nearer completion then I can give you a more accurate estimate.

I can tell you it's considerably cheaper than importing a Webster scope though or even buying a Lukehurst one.

The only way I'm gonna resolve the mitre v dovetail debate is to make a coupe of bits up. Dovetail is stronger so I'm swaying that way........at the moment. :dontknow::rolleyes:

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Gina

Gina

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I'd quite like to have a go at making my own scope - maybe I will one day. Trouble is, I don't like spikes in my images and I don't think a refractor would be within my building capabilities :D I suppose a Mak, Mak-Newt or SCT might be possible. Now that would be different from the usual Newt :D

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swamp thing

swamp thing

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The optics I took from an old 'Beacon Hill' telescope Mike. I also used the spider from this, although after the alterations I made to it I may as well have made one from scratch. :grin:

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swamp thing

swamp thing

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There are books to help with building refractors Gina (no excuses :D), it's a lot easier than you think TBH I've had a look and it may well be a future project. :)

http://www.willbell....r-telescope.htm

This also has a section on building a refractor in this book:

http://www.willbell.com/tm/tm2.htm

Reckon it's time for a new Gina's build thread????? :evil6:

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umadog

umadog

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Thanks, Steve. Yeah, I can imagine the cost of importing from the US is high. Not looking forward to the hassle and price tag involved in crating and shipping my D18 when I return to the UK or Europe. There's no hurry at all on the price, but it would be great to see the "shopping list" some time! I still have to read Kreige & Berry (which wasn't even published when I originally built my Dob!).

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Gina

Gina

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There are books to help with building refractors Gina (no excuses :D), it's a lot easier than you think TBH I've had a look and it may well be a future project. :)

http://www.willbell....r-telescope.htm

This also has a section on building a refractor in this book:

http://www.willbell.com/tm/tm2.htm

Reckon it's time for a new Gina's build thread????? :evil6:

ha ha :D Thank you for the links - I'll take a look :) I have a couple of projects to finish first but as I have this dreadful tendency to start new projects before finishing what I've got... :D

Maybe there might be no need for me to add... I rather like making something different from the usual :D

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angusb1

angusb1

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Ordered the ply for the mirror box today. Still wondering whether to dovetail or mitre the corners. Since finishing the UTA I have been thinking the end grain on the ply actually doesn't look too bad, so I might make a small section dovetailed then see what I think before committing to the box itself.

Hi Steve, what type of ply did you go for for the mirror box? On the dovetail vs mitre question have you considered finger joints aka box joints? I thought about dovetails but thought they would not be well suited to ply as the angles might cause the ply to break off at the edges of the cuts for the joints. Finger joints are like dovetails but with straight rather than angled edges so you still get the strength from the large contact area. I am finishing the jig to cut mine on a router table but they can be done on a table saw as well. Shout if you want the plans for the jig.

Project is looking really nice btw

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swamp thing

swamp thing

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Yeah I have given finger joints some consideration. I shall see how the dovetail experiment pans out.

The birch ply I'm using is pretty nice to work with (for a ply anyway) it machines very nicely. I'm impressed by how nicely it joints TBH (ply is normally ghastly stuff), in fact this was the only reason I'm considering dovetailing. As normally this is a non starter with ply woods.

If dovetailing is a problem then I may well finger joint it. We shall see. :)

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swamp thing

swamp thing

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They are a nice looking joint for sure.

I used them in an interior I built for an overland camper a while back. They did look nice.

Thats what I enjoy about box and cabinet making, so many different techniques to try and play around with.

Might knock up a shaker box for the UTA, I quite fancy that. :)

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Tinker1947

Tinker1947

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This is very interesting how joint wise this is coming along, so a question, has anybody built this sort of thing out of the plastic angle they make double glazing from, and the joints there are just angles welded together and i would imagine a very light weight structure that's quite solid, of course they might be a reason why i=this is a bad idea ....??

Another type of joint i have used is a Locking Mitre Joint, made on a Router table the grain of the wood can be made to follow round if as in this picture there would be just one joint where the grain doesn't match...

Copyofyew190303b.jpg

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umadog

umadog

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Steve, you are a very bad man. Your thread has resulted in me purchasing a router and resuming my "woodworking", with a view to learning to make stuff that doesn't look like gonads. Am going to start with this: http://www.all-wood-working-plans.com/oak-mailbox.html to learn to make dado joints and to finish things carefully. I'm going to do it in plywood, though. From what I can tell, finished lumber comes in thick pieces and I have no way to split it. May investigate the local cabinet shop at some point.

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swamp thing

swamp thing

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:D yeah sorry about that, there is a lot of waffle. :D All that's left is the "easy" bit, the mirror and rocker boxes. Oh and cutting trusses etc.

Very nice box. This type of joint is indeed under consideration too. :)

Not sure about working with plastice myself. Was never much of a model maker, they all tended to look like just a mess of melted plastic when I finished them as a kid :D

:D Bad? You mean good. Wood work is great fun. You just needed reminding.

We do get laminated wood here that can be purchased in thin sheets of varying thickness it's very nice stuff indeed but I wasn't sure on wether it would be suitable for a Dob, so opted for birch ply instead. Veneered MDF is also very nicely finished I have used this many times but it's only for interior work.

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swamp thing

swamp thing

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No, sorry, that's my bad grammar again. :D

I've still to make the mirror box and the rocker box. The mirror is already finished. Although it could use a recoat but I will wait until the scope is up n running first.

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Naemeth

Naemeth

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No, sorry, that's my bad grammar again. :D

I've still to make the mirror box and the rocker box. The mirror is already finished. Although it could use a recoat but I will wait until the scope is up n running first.

Must be a huge expense to recoat a whole 20" mirror.

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