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How hard is it to build a telescope?


gooseholla
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Hello all,

Looking for some advice really. I am about to inherit some money and was going to buy a new telescope, maybe 16" dobsonian. However, I am thinking a. this is my hobby, I therefore want something good. b. I want to do this for life, therefore I don't mind the initial cost being higher if it saves buying 2 or 3 scopes until I get one that's right. So, part of me got thinking into buying a good telescope that is relatively portable and easy to setup. Then part of me got thinking, why don't I save the c. £2k it would cost for someone to build one (price of optics not included in this), and build one myself. I am thinking this way I could make a decent 18 or 20 inch telescope for c. £3k for mirrors, and say £1k for materials.
 

I built a mount for my current scope and if I asked say B + Q to cut most of the wood, it wouldn't cost anything then I could simply trim and finish as necessary. So while I am sure I could make a couple of wooden boxes and a groundboard my major concern comes in 1. A spider and secondary mirror support. 2. The main mirror support system 3. Getting the length between mirrors right.

So really I'm thinking, how hard is it for someone with basic tools, a few handheld power tools to make all these complicated bits work precisely? I have read a few threads on here and like what I see and the telescope part doesn't look too complex to make, if you mark accurately and take your time. Like I say, it is the more important intricate bits that worry me - I don't want a nice new secondary smashing, or primary falling out because of dodgy handywork! Nor do I want it so that you can never get the thing in collimation.
 

Thanks for any advice.
 

John

 

Edited by gooseholla
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Whether or not something is hard to do is up to the doer but if you want to build your own then take a look here:

http://www.rfroyce.com/

I think that this is wonderful :

http://www.rfroyce.com/ultimate%20newtonian.htm

Design your own:

http://www.dalekeller.net/ATM/newtonians/newtsoft/newtsoft.htm

I think that the Ultimate Newtonian would be an excellent instrument. Well worth having a go at.

Jeremy.

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Making a basic Dobsonian is fairly easy with simple hand tools. I have made more than one as have others on this forum.. You can get bits made ( spiders, secondary holders etc. ) fairly easily or purchase ready made components as necessary.

In your position I would purchase all the tools I needed to make my own with the proviso that you have the room to do the work and keep the tools for future use. 

It is probable that having made your first telescope you will eventually discover that improvements can be made and you will embark on a second telescope build ( and a third, fourth ? ).

SGL is here to help.

Go for it.

Nigel

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Agree with Nigel! You can make a decent scope with just a jigsaw and a drill (preferably get a router too). There is a lot of personal satisfaction in making your own telescope. The nice thing is that if something doesn't work out quite the way it should, you can fix it easily. 

There are a lot of designs on the Web which can give you inspiration, but your personal circumstances will dictate the type of scope you want (small/large, transportability, available storage space, weight...etc).

From my experience, I made a 16" ultralight 1st time round, which worked well as a home-based scope, but was difficult to transport and keep the secondary protected. The truss poles were too long to easily fit in my car, so I rebuilt it in a more conventional manner and it is now my dark-site scope. 

good luck with your build!

Scott

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It is not really that hard to do. Just a case of taking your time and being accurate.  I would not sweat over the spider and secondary holder too much. Just have a look at the various build threads on here to see that there are so many ways to go about it. Having built a couple now, and just about to start another, I would  thoroughly encourage you to have a go.

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Hello John,

I'd say its as difficult or easy as you want to make it. Someone with basic tools and a bit of skill can do it and there are loads of designs out there to take ideas from.

Having already done the mount for your current scope you're not a stranger to wood working by the looks of it. 

All depends on which design you chose and how you want it to work and then look? Having space to do things is a real bonus. My garage is 12ft wide by 18ft long and I can say its a struggle with an 8ft by 4ft sheet of 18mm ply. Getting it cut at your local timber yard is a good idea if you're limited for space and transport.

As Alan says, have a go, it is highly satisfying and there are plenty of people on here willing to help.

Damian

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Hello thanks for all the replies so far.

I have sat and sketched some rough dimensions and think that for size and weight an 18" will be my limit. I am interested in a truss type dob. 

I've been looking at primary mirror cells people have made or purchased and I took inspiration from a design which had 6 triangles, with 3 bits of I assume felt on each edge, and 3 wooden tubes with circles on top to stop the mirror falling out. Also, it had two posts with what looked like a piano wire tightened up holding the mirror. Now, presumably each set of triangles needs a bolt to collimate, and they should be 120 degrees apart, but how far from the centre of the mirror should they be? Does it make much of difference where they are along the diameter of the mirror? As for how to make the collimation system sturdy, any suggestions welcome.

For the secondary, some aluminium or steel rulers are what people seem to purchase, painted flat black. I assume a central part made of wood is okay, with the bottom cut at an angle for the mirror to be stuck to. However, I am worried that over time, the collimation bolts will make indents in the wood, making it harder and harder to collimate. Therefore,  small sheet of metal on top of the wood would be advisable?

Are the truss tubes steel or aluminium? I have heard that 1.25" is used, but what thickness walls, or does it not really matter? Of course it needs to be light, but also sturdy!

I am thinking of getting a router, but I may just end up main the top octagonal or even square, as there seems less to go wrong that way! I know a woodworker, so I may get him to route me any circles, and especially the altitude bearings.

The cost of an 18" 1/10th mirror is about £2- 2.5k, a decent focuser £300, and I can see wood and metals being another £300+ easily (I still have a large bit of 18mm ply left, and might cannibalise my mount to make the ground board and box - after all, it only involves cutting the sides down!).

Regards

John  

 

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A fair few questions there John, from the top....

I think the cell you are referring to is the one in this thread http://stargazerslounge.com/topic/224241-22-f338-diy-scope-build/ A nice simple design that works well. The spacings and size of the triangles is quite important to get optimum performance out of your mirror. Have a look at this http://www.davidlewistoronto.com/plop/ By entering a few figures, iy will design you the perfect layout of rear mirror support points.

I would probably not use solid wood as such, but Birch ply is fine for the secondary assembly. Coat the angle with epoxy resin and allow to harden before using silicon to attach secondary mirror. Yep, a metal washer/disc underneath the collimation bolts saves wear and retains accuracy.

Truss tubes are usually ali, but can be carbon fibre if you are feeling particularly flush. The "normal" rule is the fattest tube with the thinnest wall for max stiffness. As you can see in Damians  excellent build, this is not always the case. An awful lot depends on method of upper and lower clamping. Rigidity is King. Neglect at your peril with this area.

A router will allow you to make a more polished job of your scope for sure. The mirror is a big wedge of money, so you may as well dress it up in some fine attire :wink:  Take some time to practice with the router though, and do not try to cut too much in one pass. They can grab suddenly and eat soft fleshy bits :eek:

Use Birch ply, it is the best grade for this purpose. More expensive than normal exterior ply, but so much more rigid and far higher quality.

A good book to get and for many, "the bible" of classic dobs is this http://www.obsessiontelescopes.com/publications/index.php

Best advice would be to finalise what it is you are wanting from your scope before you start cutting anything. Amazing how many times your mind changes when you sit down to plan it out.

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Hi rusty,

Thanks for the reply. Yup I have that book on order already, waiting for it to arrive. That was the primary mirror cell I was thinking of. I like the design of it and it seems rock solid. I believe that they are metal in that build, but would wood be okay, or get someone to cut me some metal triangles the right shape?

Is there a certain angle the wood has to be for the secondary, say 45 degrees?

John

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You could use ply triangles I guess, but with 6mm ali plate being so cheap and fairly easy to cut with a jigsaw, I would not bother.

Correct, 45 degs is what you are after.

I think you will find that a read of the book will make it all much clearer. The classic "ladder" type mirror cell that it shows, is a tried and tested design that just works. Full instructions in the book on how to set it all up.

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Thanks. If this goes ahead may be stealing some ideas from the scope you built with Simon!

Still debating focal length wondering if someone can confirm my rough calculations before I do some scale drawings of a design. 

18" F4.5 is c. 2m, and the F4 is 1.8m. Now, assuming that the secondary mirror sits something like 200- 250mm in the centre of the scope, that means, the eyepiece height would be a respectable 1.6m or so from ground height at F4, as focal length includes the length between focuser and secondary doesn't it? F 4.5, though probably produce less coma, would need a step at the zenith, being some 1.8m off the floor? Obviously also depending how high the ground board and boxes are etc.

Regards

John

 

Edited by gooseholla
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Think Alan has more or less summed it up with that reply.

Just to add another book which I found very useful to build a different design

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

It is a good reference from the writer who is physically challenged and explains different design goals so well worth a read if a little dry in places.

I can only talk from the experience of building one scope with two more being in the pipelines. I have found it enjoyable and fulfilling up to now.

If you are confident in your abilities then go to town, as I did.

Don't worry about getting it wrong we all do. Measure twice,cut once if you have the enthusiasm to do it give it your best shot.Taught to me by the best mentor I've ever had.Dad

We're here to help so ask as many question's as you like

Damian

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The base of my scope took two attempts to get it square, then was modified another two or three times to make it more refined! I was rushing a bit though, as I wanted a mount to use with my scope. I won't be rushing this time, as I have all the time in the world at the moment. Plus, investing £40 in a bit of plywood is a lot different to a few grand in a telescope! The problem last time in my maths was all over the place, leading to some interesting cuts! Must of been having a bad week!!

I am leaning towards building as the scope I want to buy is £1700 and a 16"... but there seem to be a few problems with it, though fixable, and the mirror quality is unknown. This way I get a known quality mirror. Not sure what difference 18" over 16" would make, but I'd have a good scope for life. And I am sure that if I need to sell it, I will see most of my money back - as long as it is built good. £1500 more for a good 18" has got to be worth it.

I am sure that with my neighbour's help, woodworking friend ( he builds stuff for a living) and the help on here I'd be able to make a functional and semi-pleasing scope. Anyway, black paint and woodfiller covers all sins!

John

Edited by gooseholla
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Well F3.9, F4 all the same really, give or take 20mm! I am thinking of going faster as 1. More portable 2. More practical. A coma corrector will be added into the price, although since I am going to be observing galaxies and nebulae that can wait a while. Good thing about waiting for a mirror to come, or building is you can afford to take it slow, get it right and spend slowly.

I measured up my shed today and confirmed 18" is the limit for getting it through the door. Now I have to work out which mirror I want at 18". Oldham Optical is slightly more expensive than John Nichol - it is a 1/10 instead of a 1/8, but it doesn't have hilux coating. I am thinking, on the average UK night, it is better to have a decent coating to reflect what is there rather than having a mirror whose resolution you can only use once in a blue moon? Therefore a J Nichol mirror would be better I think. Any other mirror makes out there. OO don't list an 18", although they would be more expensive, looking at the prices for 16 and 20.
 

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+1 for Nichol optic.

John is a great guy and a pleasure to know and you'll get a service second to none.

I would not be where I am with the mirror I'm making if not for him. There are plenty with his mirrors on here.

Damian

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+ another for John. Top bloke and superlative mirror wizard!

Agree with that! John has a wealth of knowledge and experience and is generous in sharing it. Can't go wrong there. 

If budget is tight, I saw a 16" aluminised mirror on another forum for £400. It's a collection so perhaps worth a look so you could do a quick qualitative test before you buy with a ronchi? (I don't know the chap, but pm me if interested and I'll send you the link).  It could be hit/miss in terms of quality, but at the worst case, it's still a bargain as the cost of having it refigured by a pro would still make it comparably cheaper.  Or...if you're looking for some additional DIY fun... you could refigure yourself  :grin:

Whatever your choice, I'm looking forward to following your build. 

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Money is not an issue, per se. Obviously I would like to keep the costs down as far as possible, but I am not going to skimp on essentials. I have estimated £3 - 3.2k for this 18" scope build, making  2" of glass some £1.6k more than the telescope I was looking to buy! But it would have a better mirror and focuser. Although, really, would 18" do anything more for me on the average night than a 16"? 

I am still considering all the options and may well still purchase the 16" scope.

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After reading the Kriege and Berry chapter on mirror cells, I believe that I could make one using the dimensions and bolt all the metal pieces to some plywood, which could then be marked to have a few holes cut in to allow air flow and fans to cool. Although all this talk of inches, especially for bolts and drill holes is giving me a headache!

So, the options would be:

1. An 18" F4 John Nichol mirror, focal length of 1828mm, with Moonlight focuser, telrad and truss poles c.£3k total build and a lot of work and learning.

2. Or a 16" F/4.5 mirror would knock £600 off the price in mirror alone.

3. Or an Explore Scientific 16" dobsonian  f/4.5, £1.6k and ready to go, give or take the odd 'fix' on arrival.

Hmmmm. Decisions! Still not sold that there would be much advantage to an 18" over 16", so may settle for 16"?

John

 

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