DIY Dob build

[Astralstroll]

Probably a difficult question to ansqwer, but just how difficult would it be to build a large Dob from scratch? I have seen that there is a lot of information available, but what level of skill would be required?

Dave.

[Moonshane]

I am not a joiner but have the luxury of a father in law who is and he helps me/teaches/shouts at me when struggling. however if you are a competent diyer and have a jigsaw, drill and preferably a router then you'd be OK to do it. I have a few DIY threads and it's a rewarding, sometimes frustrating yet enjoyable exercise. you'll definitely go wrong at some point, learn from it and adapt your design. you'll wish you'd done some things differently at the end but it's part of the process. make no mistake it's hard work but well worth it and when someone compliments your work it makes you feel a bit proud of yourself. if you need any help then just ask.

[Joseki]

Hi, I don't think it's too hard if you take your time. If you're happy cutting wood and joining sections together (no dovetails required!), drilling, sanding and using a router (if you want circles) then I don't think you'd have a problem. If you want you can then (like I've done) buy the focuser, spider and mirror cell and still just about call it a self built scope. If you have more skills and tools you can make those too. There's a lot of information on the internet but buying

https://www.willbell.com/tm/dobtel.htm

or

http://www.willbell....nTelescopes.htm

is probably a good idea.

[8kids]

It will be dependant on your level skill. Are you a practical person? Good with tools and able to follow plans? What type of Dob are you thinking of? I have made a mount for my Newtonian scope, mainly because I couldn't afford an eq-6 mount. That was a very simple design mainly stolen from Moonshane above. If your thinking of a Truss Dob that will require more work but if tackled correctly not impossible for a practical diyer.

Moonshane has an ongoing thread at the moment for his 10" portable Truss Dob, do a search for it.

[JamesF]

I'd say if you're competent at DIY then given a set of mirrors you'd have no trouble making a dob. Making the mirrors yourself probably wouldn't be that difficult either, but there are fewer people to ask for help

James

[Astrobits]

Depends on what you mean by "big Dob" and "from scratch".

It would be necessary to know what tools/skills you have, or have access to, and what your ambitions are before I could comment on your question.

Personally I have made all the components of my 16" Dob apart from commissioning a piece of rolled galvanised sheet steel for the secondary cage from a local dust extraction company. By all the components I am including: Both mirrors, Finderscope made from a binocular objective, novel finderscope mount, Focusser ( crayford inspired with slow speed knob), novel Secondary holder and of course the tube and mount assembly.

I am near Burnham-on-Sea so you could always pop down from Bristol and have a look at my scope.

Nigel

[Moonshane]

good points by Nigel. I assumed (perhaps wrongly) that you'd be buying the glass ready done and puld but the tricky bits (focuser and maybe spider).

[LeeB]

As above really they are easy to make and require minimum skill if you take it a step at a time, my latest one has a home made lazy susan base with 150 1/2inch bearings and is a pleasure to use. You will not regret trying and with care the end result is as good if not better than you can buy (without spending a fortune that is)

[Ajohn]

I have made 2 telescopes one from scratch and another a dob based round bought mirrors. This book has a lot in it about telescopes in general especially if you are making one yourself. It's free now too.

https://ia600706.us....eATelescope.pdf

It's based round full thickness mirrors which are rather hard to get these days and more complex mirror cells are used instead. Personally I think the alt az set up the book describes is a step up from a dob but ideally needs access to a lathe or having a few parts made by some one else. The tube could be converted to a skeleton design easily enough. Some parts made and some bought etc.

The dob I built was a 10in F6.2. One piece mirror box plus tube all in ply wood and cut with a jig saw and a straight edge to make sure joints came up straight. Screws and wood glue were used apart from the tube plus careful measurement. The tube was hexagonal made up with strips cut up with the saw blade at the correct angle and just glued together. Worked well but I didn't get the tube ends square to it's axis which made life difficult using the scope. It would go into a hex hole in the mirror box so that it could be trued up if I made one again. The 2ndry was just carried on a bar across the tube so it could be collimated by moving one end around. Nuts inside and outside of each side of the tube,

I sold a pack down one recently. 11in F4.2. Made by some one else. I offered it for sale on here some time ago. No takers despite it being well known design. I still have some photo's that show how it went together. As it is it needs a dark site.

I

It all fits in the mirror box apart from the poles.

This one is mainly aimed at low power work - starfields. The 2ndry height is adjustable so that it could also be used for moon or maybe planet photo's. The idea is to only use a 2ndry that is relatively small. Moved further away from the mirror a larger field can be covered visually without enough focal plain clearance for a camera. The poles are landing net sticks from a fishing tackle shop. There are 2 blocks fixed in each corner of the mirror box to locate them. The 2ndry is carried in an oval shaped short tube that just extends past the centre line of the scope with enough room to carry it. No diffraction spikes this way - much like curved vanes. The discs that make up the mirror box bearings are mounted in slots so that the balance can be altered. It really needs a roll up say foam tube made for it to keep out stray light but as this isn't really my thing I didn't bother making one. It also should have another stay running from the 2ndry holder wooden plate down to the side of the mirror box but was ok as is. Also possible to add one each side. For a fixed rigid set up that's what I would do anyway. The main stray light problem was the 2ndry holder part. It needs to be longer, mirror box too really.

Might give you some ideas but I would ask myself is the Texereau design harder to make - no not really, probably easier actually. I think there is a picture of an equatorial mount version of it in the book - even better. The main aspect of that one is the over all way it's done - the tube could take all sorts of forms.

The book is also one of the best for mirror making. Some would argue about only polishing mirror down and I extended the tests a bit. The tester works very well and is suitable for an F6 mirror. No doubt if some one asked about further details separately there would be replies. If some one wants a real 1/10 wave error mirror making it yourself is probably the only option.

John

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The date on the shots was when I offered it on here by the way. It sold for more but still a lot less than what the bits would cost especially the mirror.

[DonRemus]

I am not a joiner but have the luxury of a father in law who is and he helps me/teaches/shouts at me when struggling. however if you are a competent diyer and have a jigsaw, drill and preferably a router then you'd be OK to do it. I have a few DIY threads and it's a rewarding, sometimes frustrating yet enjoyable exercise. you'll definitely go wrong at some point, learn from it and adapt your design. you'll wish you'd done some things differently at the end but it's part of the process. make no mistake it's hard work but well worth it and when someone compliments your work it makes you feel a bit proud of yourself. if you need any help then just ask.

What sort of cost are we talking about if you buy these bits and do the rest diy?

[Ajohn]

I'm not sure if B&Q still do the powerpro range but the jigsaw and routers in that range were fairly good really. Bosch tend to make decent items like that as well at reasonable prices. I would think a 1/4in / 6mm router would be big enough. The B&Q router table if you feel the need for one isn't too good but is as I would put it usable with some care and did come with a rather large router.

If you want to make the mirror yourself the best uk source is probably this one

http://www.galvoptic.../telescope1.htm

The tester that Texereau describes works well and could be made from all sorts of materials but brass would be best for the slit. I once tried grinding a pyrex blank with a plate glass tool. It took a hell of a lot of coarse grit because the pyrex is so hard. Not sure about borosilicate in that respect. It's possible to buy large quantities of some sizes of grit off ebay intended for jet blasting etc. Last time I looked it would ideally be coarser for rough grinding but a supplier might be able to get something coarser.

There used to be a UK web site that listed things like spiders and holders for the 2ndry mirror and focusers and a number of other things such as mirror cells fairly cheaply but I have lost the link. If anyone knows of a UK source for that sort of thing I would appreciate a link. How much of that sort of thing you can make depends on how far you want to go and in some ways the tools you have. Most people buy the focuser. It's not out of the question to make a spider and 2ndry mirror support with a hand drill, hacksaw and a file plus some taps for threading holes.

The telescope Texereau describes is pretty sound and I would reckon could easily be stretched to 10 or 12in.

The tools and bits for the scope probably work out dearer than buying a scope but the tools can always be used for something else and then there is the fun of the challenge.

John

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[Moonshane]

What sort of cost are we talking about if you buy these bits and do the rest diy?

it depends on what you buy really. I agree with AJohn that Bosch are good tools and not too expensive

http://www.amazon.co.uk/dp/B001E4EJ5S/?tag=hydra0b-21&hvadid=9550946949&ref=asc_df_B001E4EJ5S

http://www.amazon.co.uk/Bosch-PST-Watt-Compact-Jigsaw/dp/B003UES794/ref=sr_1_1?s=diy&ie=UTF8&qid=1358165499&sr=1-1

I'd strongly recommend 18mm and 12mm birch ply up to 12" scopes. about £50 per sheet.

then you'd need to factor in the mirror costs, truss poles, glue, fixings etc. it's not a cheaper option on the whole but you end up with a far more rewarding and strong system.

[Ajohn]

If some one isn't a joiner I would seriously consider a small circular hand saw, straight edge and a square as well. Then some clamps are needed to hold the straight edge in place and square straight edges are just a matter of careful measurement and positioning of the straight edge. Silverline produce straight edges to just over 8ft long but somebody may have to get one in to order. Makita did do an excellent small diy circular saw. Not sure if they still do. When using a saw like that on ply it's important to set the depth so that it just cuts through it. When cutting sheet etc the timber breaks near the end of the cut sometimes even if you have some one about to hold it. The answer to that is clamp some suitable strips of timber under the piece being cut. The saw only goes a little way through that so the piece doesn't break off.

I wouldn't be adverse to using 10mm or 12mm ordinary exterior grade ply. It just means a bit more elbow grease - stain as wanted - exterior grade varnish - sand with soapy water after a couple of coats - clean off and varnish again. Repeat until happy. I have made furniture like that which my wife and everybody else is happy with. I did route up some mahogany mouldings for the edge though, Or use paint it if that's the sort of finish you want.

B&Q stores will also cut sheets up for people. Sizes wont be precise and that is where a router is handy. Say it was the sides of a mirror box. Assemble it with say a couple of mm sticking out from two of the sides and then remove the excess with a router cutter with a ball race on the end. These are for trimming things flush.

A straight edge can also be used to guide a router. My 1st straight edge was a length of the strip that adjustable shelves fit onto - B&Q again but it's a bit narrow to clamp in place without the clamps getting in the way. When I made the hexagonal scope tube it was a piece of very straight timber that was lying around. Hard to find these days. I used a jig saw for that but taking a little more care to keep the saw up against the straight edge a circular saw will do a better job.

All sorts of things can be done with the basic bits and pieces. I wanted a pair of timber garage doors a few years ago. Bought some 19mm exterior ply. Cut to size with a circular saw and straight edge. Cut a strip to provide an overlap where the doors meet and strips to reinforce the doors in line with the hinges. Made up one door and fitted it and then carefully measured up and made the other. Glued up and screwed from the inside so that none showed on the outside and the only other tools I used was a metal working file to take the burr of the edges and a bit of sandpaper and a drill to drill the holes for the screws - rather important. Time 2 to 3 hrs. It probably took that time to paint them. I cut the full sized ply sheets up balanced on a do it all work mate - 2 would be a good idea really and used pieces of lathes to support the piece being cut off. If the 2nd door had come out too big I would have used a router to trim some off using the straight edge again. That door had to be slightly out of square due to the brick work being out.

There is an old saying relating to this area - measure twice and cut once. There is a lot of truth in it. The usual reason is miss reading a tape or not remembering the size correctly or getting some sums wrong.

Jig saw or circular saw - I just accepted what was said but I think I know which of the 2 I would prefer if just one tool was bought,

John

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[Moonshane]

as always there's more than one way to crack a nut, skin a cat etc.

[furrysocks]

I'm building two 8.5" f/7.6 newt scopes at the moment - eventually forming a binoscope. I was going to build a simple dobsonian mount for one of them - may still do - but one thing I would say is that you should decide what you want to get out of it and plan accordingly. There are many designs around, some of which are more portable than others. I'm favouring a double open truss design by Robert Royce, as the focal lengths of my mirrors is up around 1.6m.

I'm one for jumping in feet first, before I've thought it all through - it's making for an interesting build. There has already been a bit of 'scope creep' along the way, in terms of materials, design, effort, cost, etc...

To give you an idea of cost, here's how mine breaks down...

- 2nd hand mirrors £100

- mirror re-coating £150 (?est... won't do the primaries for a good few months yet - they should be just about good enough)

- wood £30

- adhesive/resin £40

- aluminium £40

- misc bits (bearings, tape, hardware, etc...) £20

- EPs (£100)

- focusers (self-made)

- mirror cells (self-made)

I've kept that list rough - some stuff I have lying around, I'll have stuff left over, I'll have missed some things off that list. However, in my case, I'm ending up with a binoscope, which would probably cost me £800 or more new, and I'll end up spending well over half that. My wife will think I'm crazy when I eventually let on that I've started.

Good luck, look forward to seeing what you decide.

Matt.

[furrysocks]

Meant to say... I reckon I'm handy enough but not by trade - have a lot of tools and can use most of them. I'm making mistakes and taking wrong turns every step of the way. If you've enough confidence and the perseverance to right a wrong rather than throwing in the towel, you'll make it through a build no bother. The right tools sometimes make or break a job, though for most things a few hand tools and the ability to accurately repeat cuts will suffice.

[Astralstroll]

Very many thanks to everybody for the encouraging and informative messages. I think I have some serious pondering to do now! Wish me luck.

Dave.

[8kids]

Good luck Dave.

[furrysocks]

Best of luck! How large are you thinking of going, given that you have a 10" already??

[Astralstroll]

Am kicking myself for not buying a 12" straignt away, so am pondering a 16", which I think is about the maximum realistic size for transportability and mirror price. If I won the lottery I would dearly like to buy a handbuilt 16" from Sumerian Optics or similar. In the maantime I can gather tools and dream.

Dave.

[Ajohn]

What F ratio for a 12 or 16in or even a 14in. I'm curious?

A decent 12in blank that will still need PLOP for working out the support will run to over £270. A plate glass 25mm thick 300mm blank is a mere £50 but plate is dubious at that size really. The prices of low expansion blanks tends to jump up above 10in - only £70 for one of those. The way the finished mirrors work out is usually much worse but you can buy a modestly accurate 12in mirror for a bit under £500 at F5

John

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