AlienFirstClass
Pooh-Bah
Reged: 02/13/09
Posts: 1149
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I recently got several 10" diameter by 72" long cardboard tubes....tube thickness about 3/16".
Would they make a good tube for a scope and if so, what type?
They are NOT sonotubes.
Thanks
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chollman
super member
Reged: 04/24/08
Posts: 134
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They would be good for an 8" F/8 Newtonian or, if cut shorter any focal ratio for an 8" newt. They would need to be primed and painted for protection and a flat black or flocked interior. Charlie
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AlienFirstClass
Pooh-Bah
Reged: 02/13/09
Posts: 1149
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How about solar....does a cardboard tube offer any advantage?
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grendel
sage
Reged: 04/12/09
Posts: 470
Loc: Canterbury, Kent, UK
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telescope mounts
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chollman
super member
Reged: 04/24/08
Posts: 134
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Solar?? Not sure what you mean there.
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Jim Romanski
Pooh-Bah
Reged: 01/02/05
Posts: 1024
Loc: Guilford, Connecticut
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Yes you can build a Dobsonian Sun Telescope
--------------------
Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 592
Loc: UK
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Cardboard might soak up heat and give rise to unwanted tube currents in a solar scope. A cardboard tube can be reinforced by coaiting it with a layer of newspaper bonded with epoxy resin as in GRP manufacture, or glass fibre. The ends of the tube must be fitted with a collar to prevent crumbling and damage by bashing the tube against door posts as you take it out for observing. OK for the beginner.
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John Carruthers
Skiprat
Reged: 02/02/07
Posts: 2382
Loc: Kent, UK
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Quote:
telescope mounts
 
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Jc
ATM 10" F6.1, 1/25th wave spec (max wavefront error +/- 1/12.6 in zone 4 of 6, sodium light )
6" F7 spec
127mm F9.4 Refractor
10 x 50 bin
ETX80 (finder)
Canon 20D
PST
DSI 1
and a curious mind
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Jim Romanski
Pooh-Bah
Reged: 01/02/05
Posts: 1024
Loc: Guilford, Connecticut
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Quote:
Cardboard might soak up heat and give rise to unwanted tube currents in a solar scope.
From the link I provided:
Sonotube. With a Sun Scope, we do not have to worry about "tube currents"
Quote:
The ends of the tube must be fitted with a collar to prevent crumbling and damage by bashing the tube against door posts as you take it out for observing. OK for the beginner.
True but you can use inexpensive materials to do this. Some kind of rubber guard or something from the hardware store.
I've always thought that cardboard tubes are superior to metal tubes in terms of tube currents.
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Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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grendel
sage
Reged: 04/12/09
Posts: 470
Loc: Canterbury, Kent, UK
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cardboard also damps out vibrations a lot quicker
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GaryS
sage
Reged: 10/30/06
Posts: 201
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Quote:
Quote:
The ends of the tube must be fitted with a collar to prevent crumbling and damage by bashing the tube against door posts as you take it out for observing. OK for the beginner.
True but you can use inexpensive materials to do this. Some kind of rubber guard or something from the hardware store.
As it happens, the latest entry in my Telescope Diary deals with this very issue. It's up on my web site.
Quote:
I've always thought that cardboard tubes are superior to metal tubes in terms of tube currents.
They are. Their insulating quality helps keep heat from the observer's body from getting into the light path too.
Regards,
Gary
--------------------
Sky & Telescope Contributing Editor
SkyNews Columnist & Blogger
www.GarySeronik.com
A place for stargazing enthusiasts.
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rboe
Reged: 03/16/02
Posts: 47555
Loc: Phx, AZ
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Cardboard has a few drawbacks you have to watch out for - like soaking up moisture like a sponge. Epoxy will not block moisture; fibreglass boat owners found this out the hardway and some owners of the Quickie homebuilt airplane paid a high price for this hidden feature.
But it can be managed if you are aware of it.
Does not have the strength of metal so torquing down spiders and such needs to be done carefully.
Once built they can be just a wee bit on the heavy side (once set up I think a heavy scope is easier to use so this is a good thing. But transport makes this a bad thing for us older guys with damaged backs).
But hey, the material is cheap and typically strong enough for a very serviceable scope.
I have some very strong tubes from wide format printer paper sitting in the shop thinking they may make good tripod legs or truss parts. Still scratching the noodle over just how to use them.
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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AlienFirstClass
Pooh-Bah
Reged: 02/13/09
Posts: 1149
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So what is the recommended SIMPLE approach to preventing moisture from penetrating a cardboard tube?
Thanks
Quote:
Cardboard has a few drawbacks you have to watch out for - like soaking up moisture like a sponge. Epoxy will not block moisture; fibreglass boat owners found this out the hardway and some owners of the Quickie homebuilt airplane paid a high price for this hidden feature.
But it can be managed if you are aware of it.
Does not have the strength of metal so torquing down spiders and such needs to be done carefully.
Once built they can be just a wee bit on the heavy side (once set up I think a heavy scope is easier to use so this is a good thing. But transport makes this a bad thing for us older guys with damaged backs).
But hey, the material is cheap and typically strong enough for a very serviceable scope.
I have some very strong tubes from wide format printer paper sitting in the shop thinking they may make good tripod legs or truss parts. Still scratching the noodle over just how to use them.
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grendel
sage
Reged: 04/12/09
Posts: 470
Loc: Canterbury, Kent, UK
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paint inside and out, I have cardboard tube telescopes and mounts, and they are just sprayed with car primer and white car paint.
grendel
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AlienFirstClass
Pooh-Bah
Reged: 02/13/09
Posts: 1149
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How about polyurethane...it really tough on wood floors.
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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 964
Loc: Waco, TX
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Is there anything fun one could do with a 6' tube with 52mm ID?
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Coulter Odyssey 13.1" split-tube
Coulter Odyssey 8"
Home-made 7.8" F/4 dobsonian travel scope
Home-made 68mm F/5.3 achro (typically used as finder on 13.1")
Skymaster 15x70
BPTs4 8x30
32mm Plossl, 30mm GSO SV, 30mm Rini, 27mm Kellner, 13mm Hyperion, 6mm TMB/BO Planetary, Owl 2X Barlow
Palm TX with AstroInfo and RescoViewer
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rboe
Reged: 03/16/02
Posts: 47555
Loc: Phx, AZ
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Moisture should not be a problem even with epoxy as long as you keep the dew off and don't let it sit in water. A bit of car wax on top of the finish when you're done.
I'd still go the epoxy route since it will some strength to it (didn't mean to come across so down on epoxy and the water thing!) and is fairly easy to work with.
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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hwhall
sage
Reged: 09/22/08
Posts: 267
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Would liquid plyurethane like Varathane work well for stiffening and waterproofing, I wonder?
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 592
Loc: UK
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Collar stiffening on the ends as a buffer from bashing can be cheap and cheerful if you rove several thicknesses of DUCK tape around the outside of each end. Spiders and mirror cells can be attached to a separate band made from aluminium that slides inside the ends and glued , this will add exra stiffening. I made a three inch refractor out of a three and a half inch cardboard tube with a 3/16" wall thickness, and painted with a good enamel paint, this is one of my grab and go scopes, and takes a lot of hard usage, the tube is still in very good condition.
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John Carruthers
Skiprat
Reged: 02/02/07
Posts: 2382
Loc: Kent, UK
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Quote:
Is there anything fun one could do with a 6' tube with 52mm ID?
Galileo scope? 
--------------------
Jc
ATM 10" F6.1, 1/25th wave spec (max wavefront error +/- 1/12.6 in zone 4 of 6, sodium light )
6" F7 spec
127mm F9.4 Refractor
10 x 50 bin
ETX80 (finder)
Canon 20D
PST
DSI 1
and a curious mind
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 592
Loc: UK
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Here is a pic of the three inch refractor knocked up out of a cardboard tube with plastic drainpipe end fittings and a push pull Crayford. The scope is mounted on a high tech cutting edge universal mounting, the breaking loading of the string was carefully worked out. It shows that a lot can be done with good quality cardboard. How about a five inch mirror for the 6 inch tube.
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grendel
sage
Reged: 04/12/09
Posts: 470
Loc: Canterbury, Kent, UK
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Quote:
Is there anything fun one could do with a 6' tube with 52mm ID?
you could make a taller mount than these:-
Grendel
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 592
Loc: UK
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That is  really cool.
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grendel
sage
Reged: 04/12/09
Posts: 470
Loc: Canterbury, Kent, UK
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The tubes were from rolls of printer paper from the drawing Office I manage, the bearings were the PVC end caps from the tubes, there is a big bolt through the middle and washers, they are slick enough to make a good bearing with just about the right amount of friction.
Grendel
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AlienFirstClass
Pooh-Bah
Reged: 02/13/09
Posts: 1149
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Quote:
The tubes were from rolls of printer paper from the drawing Office I manage, the bearings were the PVC end caps from the tubes, there is a big bolt through the middle and washers, they are slick enough to make a good bearing with just about the right amount of friction.
Grendel
Great idea!
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AlienFirstClass
Pooh-Bah
Reged: 02/13/09
Posts: 1149
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While we are on the subject of cardboard tubes, where are good sources for cardboard tubes that are NOT Sonotubes?
Thanks
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chollman
super member
Reged: 04/24/08
Posts: 134
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Protostar.
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grendel
sage
Reged: 04/12/09
Posts: 470
Loc: Canterbury, Kent, UK
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Any Drawing Office will have them coming out of their ears (up to about 3" diameter)
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Pedestal
Post Laureate
Reged: 03/11/06
Posts: 3998
Loc: Smoggy Bottom, Baytown,Texas
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Quote:
While we are on the subject of cardboard tubes, where are good sources for cardboard tubes that are NOT Sonotubes?
Thanks
Mailing/shipping tubes.
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Hubert
---------------------------------
www.smoggybottom.org
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 592
Loc: UK
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Postal tubes are good and solid, My three inch refractor is made from one of them...recommended. Adapting used items to make scopes is the mark of a true "telescope nut" as a "TN"myself I used to haunt rubbish tips for usable cast off items which ended up as finished scopes, oil drums bed angle irons, ditched plywood you name it.
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StarStuff1
Pooh-Bah
Reged: 04/01/07
Posts: 1135
Loc: South of the Mason-Dixon Line
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Recently I started rebuilding a 25 year old 8-in f/4.1. The concrete form tube made of cardboard had a 1/8th-in thick wall and was 48 inches long.
Since I only needed 32 inches or so of the tube I cut off the excess and cut this piece into rings. These rings were glued to the inside of the tube to reinforce it in critical areas such as where the focuser and mirror support bolts attached.
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Tools that make objects very far away appear much closer than they actually are.
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StarStuff1
Pooh-Bah
Reged: 04/01/07
Posts: 1135
Loc: South of the Mason-Dixon Line
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Of course I also used plywood end rings to stiffen and protect the cardboard edge. I cut rings out of plywood. The tube now is very rigid and still light.
Even though this was a sonotube the thin wall was not a problem. The inner reinforcing rings not only stiffen the tube they also act as light baffles.
The scope is almost finished.
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Tools that make objects very far away appear much closer than they actually are.
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ed_turco
super member
Reged: 08/29/09
Posts: 102
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Cardboard is wonderful material. If you give it a good soaking in shellac and follow it up with a few extra coats, it will last a lifetime. I've had some tubes last longer than 25 years. One 6" I had for travel to total solar eclipses and it survived ten trips worth of airline baggage handlers! Yazoo Mills of New Oxford, PA has an excellent selection for smaller sized telescopes. Cheap too!
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 592
Loc: UK
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Nice scope, as you say a lot can be done with cardboard, not only tubes. Stiffening with shellac or any hard varnish works wonders, but be warned, if you make it too stiff it will be weakened, and a slight bending stress will result in a crack, I had an excperience with leather, I soaked it in paraffin wax to try it out as a local polisher, and it promptly snapped when I tried to bend it.
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grendel
sage
Reged: 04/12/09
Posts: 470
Loc: Canterbury, Kent, UK
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John thats how they used to make cuir Boille leather armour:-
http://www.dagorhir.com/HowTo/cbgryml.htm
its very hard and strong and resistant to a blow, but becomes totally inflexible, a bit like an old time fibreglass substitute.
The trick is to form it to the shape you want before the wax hardens. I have used it in the past to create hardened infill panels when making viking helmets. I had a wooden hatters head mould I used to form it round. so in theory it could be used to make telescope tubes, but probably not reccomended for warm climes.
Grendel
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 592
Loc: UK
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Grendel,thats very interesting, thanks for that gem of information. Leather finger polishers for very bad zones was a good idea until tried, nope! it dont work.
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Jim Romanski
Pooh-Bah
Reged: 01/02/05
Posts: 1024
Loc: Guilford, Connecticut
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Oh yea...one more thing that cardboard tubes are good for...you can sleep in them:
Excerpt from...
A friend jokes: "John eats pitch & sleeps in a tube."
Dobson: Well of course we do, you know, we do sleep in the telescopes. We sleep in the 24-incher all the time when it's not set up. It take two people end to end, unless they're more than six feet. And the record for sleeping in the 24-incher is eight weeks. Gerard had to sleep eight weeks there when the bus broke down.
Comment: Every summer Dobson, crew & telescopes travel from Public Park to Public Park in a beat up old yellow van with "San Francisco Sidewalk Astronomers" painted on the sides.
--------------------
Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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