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rboeAdministrator

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Re: Round Wooden Tubes? new [Re: Dane Lance]
      #4231591 - 12/06/10 08:47 AM

For our purposes, visual use for the most part, wood is just fine. Sure it will move but if you assemble the staves with some care the movement will be even so you won't have stress cracks and it won't affect focus as the movement is quite slow over time.

All in all it works rather well; just don't leave it out in the weather.

I agree, you can't really seal up wood against moisture but a good finish will keep gross changes in moisture abosorbtion from happening and that is all you really need.


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ColoHank
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Re: Round Wooden Tubes? new [Re: Dane Lance]
      #4232068 - 12/06/10 01:30 PM Attachment (49 downloads)

Quote:

I can only think of one question here...why on earth would you want to make the tube for a telescope out of a material so susceptible to movement with changes in humidity?







Wood movements induced by changes in humidity are far more pronounced radially (from pith to cambium) and tangentially (across-the-grain) than they are longitudinally (along-the-grain). Thus, a scope tube made of properly cured, more stable woods like mahogany, walnut or cherry would likely exhibit only modest changes in length in response to seasonal or other variations in ambient humidity. Such change could be easily compensated for by the scope's focus mechanism. Composite construction, where the tube is built-up of numerous staves (carefully selected for grain attributes) rather than produced by simply boring a hole through a log, also promotes stability because, with careful grain selection, each stave's tendency to shrink, swell or warp is subordinate to the whole assembly, and undesirable movements cancel one another out. I've attached a picture of the wood-tubed Merz und Mahler scope, with Fraunhofer objective, which has been in regular service at the Cincinnati Observatory for almost 170 years. It's not only functional, but also a thing of beauty.

Edited by ColoHank (12/06/10 09:57 PM)


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tim53
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Re: Round Wooden Tubes? new [Re: ColoHank]
      #4232440 - 12/06/10 04:22 PM

That's the bottom line, as to the real reason why most of us who used wood do so.

It's downright purdy!

I wish I could afford the quantity of African Blackwood it would take to make my next OTA. I've made pens of that stuff, and it's got the most amazingly deep purple-black tight grain!

-Tim.


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rboeAdministrator

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Re: Round Wooden Tubes? new [Re: tim53]
      #4232562 - 12/06/10 05:14 PM

http://www.woodworkerssource.com/blackwood_african.html

Hard to shop on line due to defects, should really shop in person but the price runs about $80-$85 per board foot.

For folks that may not know, a board foot is 1" thick by 12" by 12".

Sounds pricey (it is) but when you do small projects you won't need that much and can splurge a bit. You probably would not want to floor your house in it - but a small refractor might be just the ticket.

I'd have more concerns about machining it.


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PhotoGazer
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Re: Round Wooden Tubes? new [Re: tim53]
      #4233040 - 12/06/10 08:56 PM

Wow, That scope at the Cincinatti Observatory is beautiful. I feel that wood is a good choice for an optical tube. Sure it swells and moves a little, but very little. Would it be the best choice to a scope that is doing imaging constantly? Probably not. But most of us are talking visual use here, and as everyone knows, we are ALWAYS! fiddling with the focuser. Inaccuracies would be nearly non-existent. Attention to grain and runout would be a good idea for assembling the most stable tube, but not extremely critical. I think well made wood OTA's are functional as well as beautiful. Just look at Normand Fullums' work to see what wood can do with a scope.

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PhotoGazer
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Re: Round Wooden Tubes? new [Re: rboe]
      #4233061 - 12/06/10 09:02 PM

Quote:

http://www.woodworkerssource.com/blackwood_african.html

Hard to shop on line due to defects, should really shop in person but the price runs about $80-$85 per board foot.

For folks that may not know, a board foot is 1" thick by 12" by 12".

Sounds pricey (it is) but when you do small projects you won't need that much and can splurge a bit. You probably would not want to floor your house in it - but a small refractor might be just the ticket.

I'd have more concerns about machining it.




Yeah, but African Blackwood is a rare exotic, and difficult to find in decent lengths and widths. Besides that, at $85 a board foot, you can get carbon fiber tubes, and maybe even honeycomb carbon fiber. If I had a choice of African Blackwood for a scope, or Carbon Fiber for the same price or less, I am going with the Carbon Fiber.


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tim53
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Re: Round Wooden Tubes? new [Re: PhotoGazer]
      #4233255 - 12/06/10 10:43 PM

Quote:

Wow, That scope at the Cincinatti Observatory is beautiful. I feel that wood is a good choice for an optical tube. Sure it swells and moves a little, but very little. Would it be the best choice to a scope that is doing imaging constantly? Probably not. But most of us are talking visual use here, and as everyone knows, we are ALWAYS! fiddling with the focuser. Inaccuracies would be nearly non-existent. Attention to grain and runout would be a good idea for assembling the most stable tube, but not extremely critical. I think well made wood OTA's are functional as well as beautiful. Just look at Normand Fullums' work to see what wood can do with a scope.




I image with my wood scopes all the time!

-Tim


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rboeAdministrator

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Re: Round Wooden Tubes? new [Re: tim53]
      #4233809 - 12/07/10 09:58 AM

When it comes to material choices logic may or may not enter into it. Sometimes we say we're gonna use X, price and logic be damned. You and I would choose something else (and I'm pretty sure they would not be the same thing).

Tim; did you post pics of your completed wood scopes yet? Could you pop in one or two here?


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PhotoGazer
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Re: Round Wooden Tubes? new [Re: rboe]
      #4253271 - 12/16/10 09:05 PM

I hope to put up some pics soon of the wood round tubes that I am making and the system I am using to make them. Hopefully, they will possibly jog some new ideas. Anyone else doing anything along this line right now. BTW, I am ramping back the time in the shop until after the holidays.

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Pinbout
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Re: Round Wooden Tubes? new [Re: cloudmagnet]
      #4253364 - 12/16/10 09:44 PM

Never thought about that type of joint. Thanks for sharing.

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tim53
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Re: Round Wooden Tubes? new [Re: Pinbout]
      #4253536 - 12/16/10 11:15 PM Attachment (56 downloads)

Ron:

Here's one of my 10" f/6, in a 9-sided chinese mahogany 1/4" plywood tube (edit, this pic is more recent, and shows the current backplate/cell):

Edited by tim53 (12/16/10 11:28 PM)


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tim53
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Re: Round Wooden Tubes? new [Re: tim53]
      #4253554 - 12/16/10 11:21 PM Attachment (45 downloads)

Here's my 12.5" f/23 Cass (Mirrors by Ed Beck) in a 1/4" Teak plywood tube with poplar corners and 3/4" Birch plywood backplate (rest of cell is Novak):

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tim53
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Re: Round Wooden Tubes? new [Re: tim53]
      #4253576 - 12/16/10 11:37 PM Attachment (61 downloads)

Here's me and my 6" f/15 Jaegers in walnut plywood tube, at Mt Pinos classics star party in August 2009. The blue thing piggyback is a 6" f/5 Jaegers in a blue anodized aluminum tube.

The tube for the f/15 worried me a bit, because the plywood has an MDF core. But it's doing okay!


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plyscope
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Reged: 11/23/06

Loc: Perth, West Australia
Re: Round Wooden Tubes? new [Re: tim53]
      #4253762 - 12/17/10 02:08 AM

You do good work Tim. The wood tubes look great on the Tak green mounts.

Andy


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rboeAdministrator

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Re: Round Wooden Tubes? new [Re: plyscope]
      #4253995 - 12/17/10 08:57 AM

Holy Moly Tim! Some very nice work there.

Have you considered making a wood version of the telerad - then gutting the plastic one for its' parts?


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astroneil
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Re: Round Wooden Tubes? new [Re: rboe]
      #4254054 - 12/17/10 09:40 AM

Wood is good. Thanks to all for posting some incredible pictures of their wooden scopes.

Regards,

Neil.


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tim53
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Re: Round Wooden Tubes? new [Re: rboe]
      #4254965 - 12/17/10 05:59 PM

Quote:

Holy Moly Tim! Some very nice work there.

Have you considered making a wood version of the telerad - then gutting the plastic one for its' parts?




Funny you should ask! I haven't done this, but I've been thinking about making veneer inserts for the sides where they're recessed inside that ridge edge?

-Tim.


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tim53
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Re: Round Wooden Tubes? new [Re: tim53]
      #4254982 - 12/17/10 06:06 PM Attachment (57 downloads)

Here's my 8" f/6 Springfield Newtonian, built in 1981. For this one, I used a sheet of 1/4" Indian Rosewood plywood. I remember thinking it was awfully expensive, at $48 for a 4x8 sheet. I doubt you can buy it anymore, and if you could, it'd be a heckuva lot more expensive!

-Tim.


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StarStuff1
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Re: Round Wooden Tubes? new [Re: rboe]
      #4255132 - 12/17/10 07:29 PM Attachment (53 downloads)

Quote:

Holy Moly Tim! Some very nice work there.

Have you considered making a wood version of the telerad - then gutting the plastic one for its' parts?




Here is a wooden "Telrad" on top of a "Schmidt and Wesson Cassegrain". I built this as a prop for an astronomy skit about 15 years ago. The Telrad is full size you can sorta get the idea of the size of the "scope". Nothing is functional.

BTW, beautful scopes, Tim!


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PhotoGazer
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Re: Round Wooden Tubes? new [Re: StarStuff1]
      #4255363 - 12/17/10 10:00 PM

I think all of those scopes are beautiful. I hope my work stands up to those nice pieces. I was wondering about the rings I would use, but I noticed Tim made some beefy looking custom rings on the scope, with some Losmandy "D" mounting plates. That answers some of my questions. Tim, are those rings from plywood or solid wood?

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