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furrysocks
member


Reged: 01/24/13

DIY 8.5" f/7.6 binoscope - in progress
      #5643742 - 01/26/13 03:04 AM Attachment (33 downloads)

Hi, folks - first post and pretty new to astronomy.

I picked up a pair of mirrors and flats for £100 and have set about making a binoscope.

The OTAs will he a hybrid of the following two designs:
- Toshimi Taki's 8 inch newt
- Robert Royce's 8 inch open truss newt

I using 3mm hardboard (masonite) for the walls, 9mm laminate MDF for baffles/ribs, 18mm MDF for the external rings and 1/2"x1/2"x1/16" aluminium channel for the struts. The tubes will be wrapped in polyester tissue and resin, and the external rings attached with pins and then resin.

Yes - heavy. Assembled, each OTA will weight in the region of 11-12kg.

I'm planning to make my own helical crayford focuser(s) from ply, skateboard bearings and PVC waste pipe.

It started off as a minimum-cost build, but I've made a few concessions since starting the build. I am making it up as I go along.





Making slow progress, but having fun doing it. I'm currently just under half way with the resin and have only one external ring cut - yet to attach. In the meantime I've got a 3" f/4.6 dobs and a cheap ruby pair of 10x50s with which to look up.

Hope you like it!

Best,
Matt.


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Rutilus
Carpal Tunnel


Reged: 12/17/10

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5643751 - 01/26/13 03:13 AM

Welcome.

Looks like a great project you have there.


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astrobeast1
super member


Reged: 09/28/10

Loc: leicester england
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: Rutilus]
      #5644102 - 01/26/13 10:21 AM Attachment (36 downloads)

warm welcome Furrysocks -what country are you in? --supercool my man--what is the reason for your bino build as opposed to a mono-if you don,t mind saying ?

you belong to a pretty rare breed !that,s for sure .

do keep the pics coming

look,s like you are very handy with tools too.

I count your tubes as 12 sided -is that correct ?--that would make it a Dodecagon shape - wow!

I,ve made a sixteen sided (hexadecagon) bino-scope with 25 inch mirror,s -be interesting watching your build.


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: astrobeast1]
      #5644480 - 01/26/13 02:14 PM

Cheers, guys.

Beast - I saw your scope in another thread earlier today. What a MONSTER!!! Very nice - what a thing to build!!!

I got two mirrors and two flats - originally, I was just going to make one - single dodecagon tube like Taki's, 1.6-1.7m long. When I mocked up a small 5 inch tube to check the size of the internal baffles, it looked quite good, so I worked out that I could get all the tubes I needed out of one 8'x4' sheet of hardboard if I went for an open truss. The laminate MDF is an old kitchen wallboard and the 18mm MDF is leftover.

I found Robert Royce's page and liked the principle of open truss (better cooling, less surface area to the wind, etc...) and the Serrurier design (stays collimated or thereabouts, despite strut sag). So I decided on a hybrid and have used his dimensions for the length of the tubes, despite being a bit larger diameter.

I used £1-shop high strength adhesive to put the tubes together (in sub-zero), and they were very fragile. I then decided to use polyester resin and tissue to make then stronger. The external rings will help them hold shape, and Royce's method of shaping the aluminium channel at the end and designing the external ring profile to allow them to sit flat appealed to me - no brackets or ball joints or whatever...

In summary, somewhat unsuitable materials, little regard for weight, an ever changing plan (scope creep?!) and a tendency to neglect household chores a couple of evenings a week.

It's nice to find a use for the 100 spring clamps I bought a few years ago! Broke one bandsaw blade so far, and struggling to keep on top of the dust in the workshop at the moment.

Looked through an 8" dobs for the first time, at a Stargazing Live event earlier this month. I hesitated, thinking it would be nice to look through my own first but reasoned about what Jupiter was going to look like first and then took a look. Whatever - hasn't put me off.

I doubt I'm going to go straight for the binoscope. I'll make a mount for one (possibly this on - http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2570652/page... Can't afford the diagonals and extra eyepieces yet. DIY focuser might be a bit hit and miss, but not going to pay for two shop-bought ones yet, either. The secondaries have been recoated and should be with me next week. One primary should be serviceable - the other less so. Want to look through them first though, maybe a season or two, before I stump up £150-£200 to get them recoated too.

Blah, blah... Off to warm up the curing cupboard and stipple some more resin onto some more tubes...

PS. I'm in Scotland.


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5646595 - 01/27/13 06:15 PM Attachment (40 downloads)

I've finished applying resin/tissue to the six tubes. One has a test coat of reddish paint, one has an external ring.

After putting the last tube in the curing cupboard, I left the workshop. About 30 minutes later, I thought to pop back in and take this photo. About to put the last tube back in the cupboard to finish curing it and I noticed one of the ends of the ribs (they're in 1/3rds) and one of the side panels had separated badly. With a few spring clamps I got the rib flush again but a 1/2" wide section of tissue lifted up on the outside which extended about half the length of the tube. I slit it with a blade and used a small brush to put the somewhat jellyfied left-over resin under the tissue. Over this I put a bit of black bin bag, and a caul clamp made from a couple of bits of hardboard. Close one!

Carry on...

Edited by furrysocks (01/27/13 06:24 PM)


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astrobeast1
super member


Reged: 09/28/10

Loc: leicester england
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5647368 - 01/28/13 02:50 AM

Very nice , my kilted friend.--I strengthened the joint's by gluing fibreglass joint tape on the inside of the tube, but your's is stronger being on the outside-- so better .

regards Dan


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: astrobeast1]
      #5647398 - 01/28/13 04:04 AM

With the first one that I put together, I pressed bamboo skewers into the adhesive squeeze-out on the inside, figured it would give me two more surfaces for the resin to act on, but I decided it was 'overkill' and 'ugly' so didn't bother - kinda wish I had, for all the weight it would have added. Humidity has played a part - making the adhesive soften and the hardboard warp badly when a joint fails.

These are heavy tubes. Not heavy like 9mm ply, mind! With less than half of that red one painted, I can close my eyes and feel the weight of the paint even.

What do you reckon... are my external rings going to hold up being pinned from the inside and flooding the "gap" with resin? I'm concerned about the middle tube, lower ring, where the primary mirror tube is going to hang from. Don't want a mirror to end up on the deck.


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astrobeast1
super member


Reged: 09/28/10

Loc: leicester england
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5648513 - 01/28/13 03:35 PM Attachment (29 downloads)

Hi Furry ,
take a look at my scope internals


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: astrobeast1]
      #5648548 - 01/28/13 03:53 PM

I read in your build thread that you'd lapped and screwed the ribs - I didn't. That's been the biggest problem, when the not-quite-but-jointed-ribs separate - ie they don't hold the round, which is why the external rings are essential (for me).

What weight are each of your tubes, then?


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astrobeast1
super member


Reged: 09/28/10

Loc: leicester england
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: astrobeast1]
      #5648642 - 01/28/13 04:31 PM

the 50mm wide tape was adhered using just brushed on PVA glue-wished I,d used something stronger on reflection afterwards-but pva has excellent adhesion to plywood in thin coats, and I,ve laid inside painting it black = no parting so far --different story though trying to calk cracks with pva ,it is too brittle .my board edges were angle cut at 17 degrees for a tight fit
too be fair I have made the tubes with 8 foot strips of 9mm ply -so the lengths are one piece and there are external rings to hold the tubes together as the exterior is painted on bare ply for smoothness.
Regarding your tubes --external rings at the ends of each piece would def. prevent parting but it might look a bit cumbersome to your eyes.this is all assumed the tape you used rips easily (per your concern) -if it don't and the skin envolopes the complete tube externally whallah! I would do a test and try force the boards outwards to see if they will part ,
By the way --what tape did you use ??

I nailed two 1/12 inch pins through the exterior each board into each ring at an angle .
so your external rings are unlikely to move.
The shape we are employing is amazingly strong for rigidity's sake -but do that test and satify yourself before continuing --my scope is fully loaded -weight wise with dummy granite mirror,s inside at mo ,and on swirling it around I hear no audible creak's -surprisingly .just mine!

my criteria is always test twice now ==taking it all apart afterwards is very punishing to the soul--when you had slight doubts or incomplete confidence to begin with.

so in summing =if you don,t wish too see more rings but need to strengthen more then buy fibreglass matting and resin the whole tubes externally --if the wind blows it off a high precapice - it will bounce right back intact , less the glass of course.lol
hope this helps.
dan


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astrobeast1
super member


Reged: 09/28/10

Loc: leicester england
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: astrobeast1]
      #5648688 - 01/28/13 04:52 PM

Laminate profile is used widely in most industries , and is extremely strong ( plywood for instance is also able to take flexure really well)
I would def double up your internal rings =laminate /overlap screw and glue --that would boost your confidence no end

my tube weight /--never weighed them but they feel like around 65-75 kilos when handling .
Weight is no prob's at all if the balance maths have been attended to. note the huge lump,s of metal and gas they violently chuck into space nearly all leave verticaly.==balance ==critical term for ATMer's

Dan


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: astrobeast1]
      #5648731 - 01/28/13 05:10 PM

Hehe - I thought you'd be lying in there! I just had to roll my sleeve up - all mine are black inside now, 20 year old matt blackboard paint.

I used surface tissue and polyester resin (3% hardener) round the entire OD. It's not a structural tissue and the excess tears very easily. They say polyester resin doesn't adhere well to wood, or itself - this is in the context of boat building - how much that matters for me is debatable. I had thought I might pin the hardboard to the ribs from the outside.

The shape requirement for the external rings is all about geometry. The way Royce determined the shape for his outer rings was to attach the top and bottom tubes with trusses either side of the four "cardinal points" of his round top and bottom tubes and by taking the tangent to those attachment points, working out where the other end of the truss should be fixed, on the middle tube. The reason this is important is that he's using U-channel and keeping the end tabs flat (or co-planar).

In doing the same, if I attached two trusses to a single side panel and extend out that "tangent", I'd end up with a square which is what he (and I) are trying to avoid. Attaching the trusses either side of a vertex where two panels meet, extending that out without increasing the distance between the truss and the tube outer wall, I'd be attaching small triangles to 4 faces on the next tube, which would give no additional rigidity to the shape, which I had convinced myself that I needed. This is where external rings come in - to afford me that rigidity - in doing so, they also raise the truss attachment points proud of the tube wall, giving me meat into which I can screw the threaded inserts.

The current template for my external rings has 3/4" all round, with four corners extended to give me the attachment points on the middle tube. I am already thinking that I could reduce this to 1/2" to make them look less cumbersome, but given my reservations about the inherent strength of the tubes without being "clamped" around the OD, I'm not going to go without any rings at this stage. Nor am I about to test one of the tubes to destruction!!

That said, you have got me thinking. There is an argument for buying thicker, structural polyester matting and re-coating in order to dispense with the rings. I've got about 300 grams invested in each external ring, perhaps 200-odd if I were to go down to 1/2" width, which is a lot of weight against which to offset the second mat layer. The small triangular wedges to then make up the required shape (as described above - coplanar truss tabs, tangents and all that), rather than a full ring, could be screwed from the inside and matted onto the tube with a few strips of mat - they would not then shift. Adequate rigidity all round (note: the threaded inserts for attaching the trusses for the top and bottom tubes would require additional 'meat' on the inside of the tube, instead).

But then I've already attached one ring... but only one...



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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5648873 - 01/28/13 06:10 PM

I may get rid of the rings...

Edit: Surface tissue is 30gsm and not at all what I should have used in the first place. I may go for 300gsm chopped strand mat and another coat of resin - 0.75 square meters plus resin at 2.25:1 is about another 0.75kg for the job, plus my wee MDF corners. Compared to 1.5kg for a full complement of ugly external rings... The only critical point is the wee triangle corners but I'm sure I can get those solid (either screws or bolt, plus mat strip and resin).

Edited by furrysocks (01/28/13 06:57 PM)


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astrobeast1
super member


Reged: 09/28/10

Loc: leicester england
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5649686 - 01/29/13 04:08 AM Attachment (28 downloads)

Ok then what about the internal rings --are you doubling up ?
as to the external rings-you could substitute for a thin brass/copper aluminium metal strip, nicely shaped and perhaps 50mm wide--this would make the tube edges more than strong enough without needing any rings and fixing the truss tubes easier -just a thought. all this feeds the learning curve and you never know quite what will suffice until you test it .
BTW I never meant for you test the tube too violently -just apply reasonable enough force to see if there is a parting of material-it wouldn,t have to move much to let you know.
I was able to drill 6mm bolts through my rings at the mirror end x16 to take the shear weight of the mirors and cells ,otherwise mine would have fallen apart .
have fun Dan


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: astrobeast1]
      #5649713 - 01/29/13 05:29 AM

Cheers, Dan.

Lots to think about and great to have your input challenging my ideas, so I'll keep pushing my thoughts on here. It's what I get for making it up as I go along, and using new materials and processes all the while - fighting the learning curve.


What I'm (currently) planning to do, more or less in order...

- take a small hacksaw blade, stanley knife and files to each of the rib butt joints and clean them up.

- fill those gaps with a wee dob of some epoxy putty I have and shape/smooth it nicely after 5 minutes setting up - that will give me the continuous 360 degree internal structure that I don't yet have - just a few grams in total.

- re-mat/resin the back of each joint, maybe nestle a short length of bamboo skewer in behind each joint first, for fun - a few tens of grams more.

- skew-pin short finishing nails through each hardboard face into the existing ribs. That's just belt and braces, but only a few grams - why not.

- add at least one additional baffle/rib in the top tube anyway, just above the focuser hole, but this won't be 'doubling up'. Given the length of the middle tube (14") and the fact I'll likely be adding mounting rings to here, I should probably add 2 more internal ribs there, too. Budget 100g per rib, all in.

- chock out the external geometric profile on the middle tube, top and bottom ends of it, each with 4 double-thickness MDF triangles (36mm thick, 75mm wide - width of one side panel, just under 18mm tall) - basically extending the line of the panels either side of it to meet at a point, resulting in the irregular octagon seen in one of the pictures above but without the additional thickness all round - just the 4 points. Budget maybe 50-100g.

- fire a screw or two into these wedges from inside, lay a strip of mat over the top of them, extending off to the adjacent faces. Grams.

- fit similar wedges on the inside of the bottom end of the top tube and the top end of the bottom tube, to give meat for the threaded inserts. Budget another 50-100 grams

- make one full ring to terminate the trusses from the top tube, matching the irregular octagon shape of the top face of the middle tube - making the scope split in two. Provide a way of bolting the top half to the bottom half. Budget 250 grams.

- give it all a good hard sanding, trying not to break them.

- re-mat/resin the lot (probably fit the external triangles on the middle tubes at this point, while wet, giving a layer of wet mat under them - clamp and add screw when cured, probably unnecessary)

- drill for and fit the threaded inserts for truss attachment

- sand and paint

- design, build and fit mirror holders, focuser and finder

- weigh and calculate truss lengths

- cut and fit trusses


If I'd used a heavier mat in the first place, one coat would have been enough but the tissue is so thin and brittle that I wouldn't trust it under a knock to provide any more rigidity than the structural support afforded by the ribs. Another layer of 'proper' mat may well - I read some canoes are made from just two layers of 300gsm. So I think I'm set on the second layer of resin/mat. Budget around 750g per OTA if using 300gsm, but offset against removing up to 1.5kg in the external rings.

If I am set on another layer of mat/resin then, I'm going to have the rigidity I need in the round with minimal additional work needed on the internal ribs, and am happy I can add the meat needed for the threaded inserts. I think that's it - not going to need 'straps' of metal around the edges or anything like that, though I've seen folk do that and it can look really nice. I think I just need wood, mat and resin

Perhaps one could get a better finish with a bit more thought/patience/etc... but for a hybrid of the polygonal tube and Serrurier truss designs, it's getting on to be not bad at all I think.

Thanks for prompting me to ditch the rings. It's going to be a few weeks, yet...


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5649749 - 01/29/13 06:35 AM

Rather than buying more mat - I've got bulk rolls of nappy liner tissue - significantly stronger than the surface tissue. I'm in two minds as to whether the existing tissue/resin layer is strong enough and erring on the side of caution, I'm saying it's not.

However, another layer of "anything" is going to improve it. I'll measure the nappy liners and work out the gsm... trying desperately to get back to the cost-cutting principles with which I started this build...

Edit: no heavier than the surface tissue - approximately 25-30gsm but stronger. I may test a little later.

Edited by furrysocks (01/29/13 06:43 AM)


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m. allan noah
scholastic sledgehammer


Reged: 08/14/09

Loc: Virginia, USA
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5649824 - 01/29/13 08:10 AM

Cost cutting? Old cotton bedsheets are quite strong...

allan


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: m. allan noah]
      #5649835 - 01/29/13 08:19 AM

Quote:

Cost cutting? Old cotton bedsheets are quite strong...

allan



Hah! Heavier though, I bet.


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astrobeast1
super member


Reged: 09/28/10

Loc: leicester england
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5650606 - 01/29/13 03:37 PM

Hey resin impregnated nappy liners sound,s rather humorous, but they are really strong -- I,ve used them when the kids were young , clever idea that !
will remember that one .

keep us posted --with pics too

Dan


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress [Re: astrobeast1]
      #5650643 - 01/29/13 04:06 PM

The fibres in the purpose-made tissue and longer and while the liners are strong, they do tear. I did a test which may have been compromised by poorly measured or mixed resin, but it wasn't very good. I'll probably order some 225gsm or lighter CSM and go with that. I can play with nappy liners on some other project...

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