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Which Sonotube best for Telescope tube?

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#1 Bryan JR

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Posted 26 March 2014 - 12:50 AM

I've wanted to mount my 12" mirror in a smaller diameter tube.
Just discovered my Menards sells over sized tube on order at reasonable prices.

http://www.menards.c... x 12' Sonotube

Which one-commercial or standard-is best for a telescope tube? Or does anyone know the advantages vs. disadvantages for each? Anyone know wall thicknesses?

Thanks in advance

#2 Pinbout

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Posted 26 March 2014 - 06:49 AM

which has a 3/8" wall thickness?

#3 roscoe

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Posted 26 March 2014 - 06:58 AM

The 'commercial' is the thicker stuff, as far as I know.

From what I have seen, all the big boxes sell the thinner version, which is ok for being buried, but I wouldn't go more than a foot or so unsupported with it. If needed, a 2x4 frame around one will keep it from tipping or warping, but by the time you put the time and money into supporting a cheap one, you might as well drive another 20 minutes and spend another $20....

Masonry supply houses and many 'local' lumber yards sell the better-grade stuff.

The clue here is to look in the parking lot....if there are more pickups than cars, that's where the pros shop, that's where the pro-grade supplies are.....
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#4 Chuck Hards

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Posted 26 March 2014 - 07:14 AM

If you live in a metro area, there may be concrete supply stores that specialize in all things concrete, including tube forms. They will have the heavy-walled stuff, and often the prices are competitive with the big box home centers. You may even be able to get the type with an unwaxed interior, making flocking or blacking-out much easier.

#5 cheapersleeper

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Posted 26 March 2014 - 08:04 AM

I live in an area of high pickup truck density, I went to a store that specializes in structural steel and concrete stuff, I had to buy 14' to get 14" and it is only a bit thicker than the big box stores. My experience is markedly different from what all of you are describing. Good glued end rings stiffen them up a lot and a couple of internal ones would really help.

B

#6 Alan French

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Posted 26 March 2014 - 09:54 AM

Either type, but especially the thin-walled version, greatly benefits from some good, stiff end rings. (On the back, the interior cell back can provide the stiffness.)

With the brand name "Sonotube," the interior wax layer is easy to strip out.

Leave the wax layer on the outside, and cover it with cloth. Easy and looks great.

Clear skies, Alan

#7 Chuck Hards

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Posted 26 March 2014 - 10:03 AM

I have to admit that I now only use such tubes as disposable mandrels for laying-up fiberglass tubes. But they still have their use as an economic means to and end.

#8 MikeMcCaskey

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Posted 26 March 2014 - 10:31 AM

I visited one of the concrete stores here in Wichita, they sell tubes in 16 foot hanks and wouldn't consider cutting one. They didn't have any scraps either. Something to consider, maybe the local astronomy club would go in on a long section. :penny: :penny:

#9 Chuck Hards

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Posted 26 March 2014 - 10:42 AM

My local concrete supply store has a nice saw especially for cutting these tubes, and happily cuts them to any length needed. The cut is remarkably square. You do have to buy the entire 14-foot length, however.

#10 Alan French

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Posted 26 March 2014 - 10:42 AM

I usually bought a 16 foot length, cut it so I could load it into the car, and either saved or sold the unused section. They're also great for making kitty condos, which I've done, and our house rabbits enjoyed them as "tunnels."

Clear skies, Alan

#11 Jeff Morgan

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Posted 26 March 2014 - 11:23 AM

With the brand name "Sonotube," the interior wax layer is easy to strip out.


How is this done?

#12 Alan French

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Posted 26 March 2014 - 11:33 AM

I always just grabbed and pulled up an end and thin layer of tube and peeled. If the end I started with didn't work, I just started at the other end. Never had any trouble with getting it to work, although you need to take some care when you get far down the tube. Once you get past half way you can continue in the same direction, but from working at the other end of the tube.

Clear skies, Alan

#13 Pinbout

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Posted 26 March 2014 - 03:38 PM

i get my tubes from shapeunlimited.com

they have no wax...just have to stay with their stock sizes.

also...

http://www.aitwood.c...D=10&Section... Fiberboard Cylinders

they also carry real wood tubes, around $380 for a 14" dia.

#14 Bryan JR

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Posted 26 March 2014 - 10:55 PM

I'd prefer the thinner tube, and yes, I'm planning an internal ring primary mirror mount for one end and a strip glued inside at the focuser end.

My present tube is a 15" diameter 1/8" wall aluminum-I'm aiming for a smaller and lighter, possibly rotatable, OTA.

The heavier duty sonotube would be ok, if I knew it wouldn't cancel out weight savings or be appreciably harder to cut.

I'm in a rural area, so Menards is best, cheapest source for me. Thanks again for all the info.

#15 cheapersleeper

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Posted 27 March 2014 - 06:08 AM

Bryan JR, those tubes really need end rings. If you are a good craftsman you could make them really small out of plywood, but my 14" tube needed a glued ring on the sky end and was glued to a flange/plate thing on the other. Without those supports, those tubes are too flimsy.

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#16 Chuck Hards

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Posted 27 March 2014 - 07:17 AM

The biggest problem with unsupported cardboard tubes, from my experience, is sag at the spider attachment points. Any tension on the vanes at all, and the walls start to cave-in. Internal stiffening at that point is just as important as the tube ends.

#17 Dr. Woo

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Posted 28 March 2014 - 03:36 PM

I sanded and wrapped a Home Depot thin wall tube with Carbon Fiber. It's way strong now and still very light at 10 lbs for a 12" tube for my 10" Starfinder

#18 cheapersleeper

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Posted 28 March 2014 - 07:55 PM

We need pics and a description, Dr..

B

#19 Alan French

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Posted 28 March 2014 - 08:27 PM

Here's the simple approach. A 14.5" f/6 in a 16" Sonotube. The wax was left on the outside and the tube was covered with cloth. It comes apart just above the cradle, with a kinematic arrangement of contact points and latches to hold it together. The shield slides off - although that needs some work.

Clear skies, Alan

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#20 Pinbout

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Posted 28 March 2014 - 08:42 PM

How long ago did you make that.

#21 Dr. Woo

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Posted 28 March 2014 - 08:46 PM

We need pics and a description, Dr..

B

i'll see if I can't get something together sometime this weekend. It's really not rocket science, but it can be messy in a bad way if you aren't careful with protecting stuff and yourself from drips and spills

#22 Alan French

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Posted 28 March 2014 - 09:24 PM

It was a long time ago. Based on a long equation I wrote in Mathcad to check the balance point, it must have been 1993.

Clear skies, Alan

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