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I cannot find an (affordable) OTA material anywhere!

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#1 Novem

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Posted 13 February 2019 - 11:07 PM

I am in the planning stages for the construction of a 12.5-inch Dobsonian and I cannot find any material for the OTA that is under $100. Fourteen-inch Sonotube is scarce, and no hardware stores within a reasonable distance carry it; PVC is heavy and more expensive than gold; 14" OD phenolic tubing is only available from a German vendor and will cost over $200 for the material and shipping; I don't possess good enough woodworking skills to create a good, durable cylinder; I haven't found any aluminum tubes; and carbon fiber is beyond my wildest dreams. I have called plastic and paper companies, emailed countless hardware stores, and searched online for a month now and have found nothing. It would be unfortunate to have to downgrade to a 10-inch mirror because of a lack of tubes.

If anyone has dealt with this problem and knows of any leads or alternatives, please let me know.



#2 hamishbarker

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Posted 13 February 2019 - 11:12 PM

Galvanised sheet steel duct is usually pretty cheap. Only slightly heavier than aluminium because it can be thinner gauge and if unpainted has similarly low emissivity so less tube currents than plastic.

Find a local aircon or heating duct supplier. What's your location?

#3 kfiscus

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Posted 13 February 2019 - 11:15 PM

Welcome.  Where do you live?  (General location- no specifics needed.)  I have an empty steel tube from a 12" f/5 GSO dob for FREE.  Even if you and I are too far apart (I live in southern Minnesota), someone else nearer you might have something similar.  There are lots of people that have converted solid-tube dobs to truss-tube units.  Good luck.


Edited by kfiscus, 13 February 2019 - 11:22 PM.

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#4 Conaxian

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Posted 13 February 2019 - 11:17 PM

I don't know the total cost but it could be done in fiberglass.

Here's a page where they describe the basic process..

https://www.instruct...s-and-carbon-f/



#5 starcanoe

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Posted 13 February 2019 - 11:18 PM

Make a square wooden tube. Get the thinnest plywood you can find. Luan panels are pretty darn thin and cheap. Run 3/4 by 1 1/2 pine wood stringers in the corners. Throw some  thicker plywood panels with circular cutouts in the front end, one near where the bearings will mount, and one towards the back that the mirror cell can attach too.

 

Very light, cheap, will look good stained and varnished, and the flat sides make mounting the bearings to side a piece of cake.


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#6 hamishbarker

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Posted 13 February 2019 - 11:23 PM

Even in new zealand where building products are about 3x us prices i paid $28 for a 10" dia x 48 long duct. For the big 24" ducts for my big dob i paid about $150 per 48" length for custom manufacture. But forsure if you are in usa it should be much cheaper.

You will need to stiffen it where loads are applied at the mirror box top and bottom. Options could include plywood rings or squares with cutouts, or if you can find a close size, alloy bike rims or similar around the outside, perhaps secure with pop rivets. Or just make the box beefy and screw the tube to the four sides at entry and base above the tailgate.

#7 hamishbarker

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Posted 13 February 2019 - 11:25 PM

At 12" truss construction is possibly getting more attractive bulk and weight wise. But if i had a 12" mirror on hand i would whip up the tube type quickly and use it while working on truss at leisure.

#8 hamishbarker

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Posted 13 February 2019 - 11:27 PM

Make a square wooden tube. Get the thinnest plywood you can find. Luan panels are pretty darn thin and cheap. Run 3/4 by 1 1/2 pine wood stringers in the corners. Throw some thicker plywood panels with circular cutouts in the front end, one near where the bearings will mount, and one towards the back that the mirror cell can attach too.

Very light, cheap, will look good stained and varnished, and the flat sides make mounting the bearings to side a piece of cake.


I second this. Also great retro style points and less likely to get reported for owning an unlicensed mortar...

#9 gregj888

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Posted 13 February 2019 - 11:29 PM

Sonotube, concrete forms are generally available from a mason's or concrete supply.  I've gotten 22" or larger (for a sono-sub).  Generally available by the foot but check out the odds and ends bin, those are often discounted.

 

If you have a surplus metals outlet, you may be able to find aluminum sheet than can be rolled into a tube.  You'll probably have to fasten with a strip of material, glue and screws.

 

Wood as mentioned...


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#10 17.5Dob

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Posted 13 February 2019 - 11:31 PM

"Sonotube" is a brand name and costs several times more than "round cardboard concrete forms"

For the tube on my 17.5" , I used the generic cardboard tubing at 1/2 the price of Sonotube


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#11 Oregon-raybender

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Posted 14 February 2019 - 01:23 AM

Before I knew about Sonotubes I built a square tube using 1/8 plywood, square ends with 2x4's and mounting area. Sometimes you make good with what's at hand for the dream. Don't give up just yet. Can you give us your general area, within 25 miles is fine. Many heads may can be put to work and find something for you. I attached what I found.

 

Starry Nightswaytogo.gif

 

https://www.spiralpa...ubes-s/1825.htm

 

https://www.mailing-...board-tubes.php

 

https://www.sakrete.com/where-to-buy

 

https://www.homedepo...92204/202092152



#12 mconnelley

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Posted 14 February 2019 - 04:09 AM

Hello:

  

  I like the idea of just using sheets of plywood to make a square tube.  It won't look very elegant, but it won't matter in the dark.  You could also make a truss tube wood for the top ring and mirror box, and wood poles.  Broomstick handles would probably be ok.  If you find larger wood poles, maybe like the handle of a shovel, you could try a parallel-pole "truss".    

 

  It wasn't a 12", but I once made a telescope on a stick.  I wanted to test a lens on a star, so I strapped it to one end of a 2x6, then screwed a focuser to the other end of the plank, and viola!  I mention this as an example of doing something super quick, very cheap, and unconventional but it worked well enough.  

Cheers

Mike



#13 xrayvizhen

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Posted 14 February 2019 - 08:47 AM

14" Quikrete form tube is about ten bucks at Lowes. They're not on the shelf, it's a special order. Here's the link to the 16" which IS on the shelf.


Edited by xrayvizhen, 14 February 2019 - 08:48 AM.


#14 roscoe

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Posted 14 February 2019 - 09:32 AM

Real sonotube is more expensive, but it is also thicker and sturdier.  As suggested above, check masonry supply houses.

 

For you long-tube folks, it also comes 10' long.



#15 Ian Robinson

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Posted 14 February 2019 - 10:12 AM

Sheet metal worker , have them get hold of some Colorbond profileless sheet (used to clad the outside walls of houses) , form a tube and either rivet the seam or solder it.

 

Job done , very cheap.

 

Or do what I did, visit a building site and look at the offcuts they have throw in the skip to go to the tip, if there is a length of stormwater pipe or concrete forming tube (steel or cardboard) offcut the right length , visit the foreman's humpy near the main gate and ask if you can have it. Chances are they'll tell you to help yourself to anything the skip you want.

I scored a 6 ft length of PVC stormwater pipe 316mm OD , that way that become my 10" f4.66 OTA , cost me $0.00.  Bit small for your project but there was also a few offcuts of PVC pipe that looked about 16" OD in the same skip , I wish I'd grabbed one when I had the chance , would likely have been handy for making a concrete pier , I went back later to get one of the bigger pvc tube offcuts but the skip was empty.


Edited by Ian Robinson, 14 February 2019 - 10:27 AM.


#16 catalogman

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Posted 14 February 2019 - 10:37 AM

The OP could request a price quote from here:

 

https://www.yazoomil...tube-packaging/

 

--catalogman



#17 Pinbout

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Posted 14 February 2019 - 12:23 PM

www.shapesunlimited.com has plenty of tubes, but you have to pic their stock sizes...

 

but yeah about $100


Edited by Pinbout, 14 February 2019 - 12:23 PM.


#18 astrojim1

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Posted 14 February 2019 - 05:39 PM

Take the tip on the quickrete (sonotube).  Very affordable, and the best material you can use for a  Newtonian.  Painted it on the outside to protect it from weather.  Paint it black on the inside.  KISS keep it simple.  You will never regret it.



#19 Pierre Lemay

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Posted 14 February 2019 - 05:44 PM

14" OD phenolic tubing is only available from a German vendor and will cost over $200 for the material and shipping

 

 Can you give us your general area, within 25 miles is fine. Many heads may can be put to work and find something for you.

According to the quote above, the OP seems from somewhere in Europe (Germany?). If so, Home Depot and Lowes will not be of much help. He would need a European source.


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#20 roscoe

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Posted 14 February 2019 - 09:31 PM

Good observation, Pierre! 

 

I'm guessing that cardboard concrete forms are available in Europe, but I've been known to guess wrong before.



#21 Pinbout

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Posted 14 February 2019 - 09:50 PM

he needs to state where he’s from



#22 Oregon-raybender

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Posted Yesterday, 04:19 PM

Here are a few in Germany

 

Starry Nightswaytogo.gif

 

https://www.h-bau.de...work/rapidobat/

 

https://www.weig-pac.../products/tubes

 

https://www.ecta.info/


Edited by Oregon-raybender, Yesterday, 04:19 PM.


#23 careysub

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Posted Yesterday, 06:29 PM

I like the square tube idea as most anyone can make that work, cheap.

 

The suggestion of building a laminate tube is also a reasonable option.

But the problem is not that it is not readily doable, but once you get all the supplies together you are bound to go over $100.




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