27 replies to this topic

[Meterman]

Hi Everyone,

It's almost time to finish the Truss-Tubes for the build project. I have questions about preferably a suitable covering for them. I am concerned that painting aluminum tubes will require upkeep or come off.

What kind of foam tubing would be a good choice? Something as dark and flat in color is the ideal choice.

Thanks

[Oberon]

Painted aluminium tubes are fine and paint works well provided you properly prep (aka do your research and follow instructions). Mine have no visible damage after 12+ years.

iirc procedure was:-

1. clean with scotchguard and water

2. aluminium primer coat

3. paint x 2 coats

4. clear coat

 

…but that was a while ago now, so double check.

On another scope I covered with the aluminium with heat shrink tubing, but it added so much weight I went with paint on the next scope.

[TOMDEY]

The foam pipe insulation has a nice feel to it. Black paint is also good. Apply properly and enjoy. Here's my 29-inch with the foam insulation and my 36-inch with paint. permanently in domes so they don't get banged around and abused like those portable scopes.    Tom

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[Sean Cunneen]

I find paint gets scratched/nicked up. I know a lot of people like pipe insulation because its easy to hold onto in the cold and keeps the tubes from getting dings. Personally I like heat shrink tubing. It's a little more expensive, but it looks great, insulates your skin from the cold metal and doesn't add any bulk. 

[kfiscus]

There's also powder coating to consider.

[Bob4BVM]

A vote for the foam pipe insulation.

Couldn't be easier to apply, just snaps on in seconds, a couple wraps of black elec tape or tie wraps keeps it in place.

Total insulation from the cold trusses.  best protection for the poles too.

In short, the least expensive, best performing solution by long shot IMO.

 

Tried the heat shrink tubing,-  way too heavy, pretty expensive, very distant second to the foam for insulation value, and still frosts up on very cold nights.

 

Just paint is out of the question half the year where i like to observe.

[Psalm19One]

I've used foam in the past and it is nice for handling in the cold, but it gets beat up pretty quickly and is bulky to store eight tubes with foam.

 

On my last couple of builds I have used Rustoleum flat black with primer, holds up well.  Only added about 12 ounces total to my eight 3/4" poles for a 13.1" scope.

 

Paint is cheap, easy to touch up, and slides easily into a 3" ABS pipe storage container, but It is cold to the touch, but is not an issue with a shroud in place and moving the scope by the wood UTA rings.

 

Here's a related thread:

https://www.cloudyni...ape/?p=12724689

[TayM57]

Agree with Psalm19one. I considered foam for my 24" but the bulkiness would have interferred with the shroud. So I went with heat shrink wrap, and it was a good decision. It holds up well, and it looks sleek to boot.

 

You can see my post about the heat shrink wrap HERE.

[TayM57]

[a__l]

Use lightweight and strong carbon. Forget about heavy, dirty aluminum. I have a lot of black anodized aluminum for three telescopes, I actually have four sets. About ~50 meters of tubes. A lot of money was spent on them before. All of it is now in the trash.

 

Carbon is very pleasant to the touch and does not smear your hands.

Edited by a__l, 20 January 2025 - 02:51 AM.

[Dick Jacobson]

Why paint or cover at all? The poles on my 30" are bare aluminum. I see no scattered light even when shining a flashlight on them. As long as they are entirely outside the light path, they should have no effect on the image.

[Bob4BVM]

Why paint or cover at all? The poles on my 30" are bare aluminum. I see no scattered light even when shining a flashlight on them. As long as they are entirely outside the light path, they should have no effect on the image.

OK Dick, you are one tough cookie saying that from Minnesota !  If i didn't have foam on my bare poles where i observe in winter, i'd still be out there with my frozen fingers stuck to the metal poles !  

 

Cheers

Bob

[Don H]

I like pipe foam for my scope trusses. It protects the tubes from dings and keeps them quiet in transit. It insulates them in cold weather, helping to keep dew and frost off the metal and making them easy to touch. I also like the way the foam matches the Ebony Star laminate on the alt bearings. Between my friend and I making scopes, we probably used foam on about 15 or 20 truss scope builds. I store them in a tall narrow box and they never get beat up. Over 20 years mine still look like new. I also find that the foam facilitates sliding the shroud over the poles. Here is my 13" with foam pole covers. 

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[Meterman]

Thanks for all the replies so far. I'm beginning to lean towards painting the tubes. There are actually a couple reasons for this. 

 

I live in a hot, dry climate. Eventually the climate is going to get to the foam and cause it to crumble. 

 

It may not add much weight wise, but it will add to the bulk.

 

I thought about heat shrink tubing but it's not cheap and will also show age and dings after a while. 

 

The tubes are currently bare aluminum. 1.25 inch OD x .054 wall. I have self-etching and camo flat black primer.  I can pickup a can of flat black top coat for durability. If, by chance, I need to do any touch up it will be easy. 

 

I'm also going to make a carry bag for the tubes. The bag will also be made to keep the tubes from banging together during transport/setup/breakdown. 

 

Sound like a good plan? 

[triplemon]

Heat shrink tubing.
Not bulky, but not weightless either. Durable, though and reasonably flat/matte.

[TayM57]

Heat shrink tubing.
Not bulky, but not weightless either. Durable, though and reasonably flat/matte.

Agree on all counts, especially durability. The thick heat shrink has amazing durability, and it looks fantastic.

 

Paint on the other hand, would scratch and look ratty after a while.

[TayM57]

Why paint or cover at all? The poles on my 30" are bare aluminum. I see no scattered light even when shining a flashlight on them. As long as they are entirely outside the light path, they should have no effect on the image.

You aren't wrong. I heat shrink wrapped my tubes for a finished look. The aluminum color looks odd with a scope that is 100% veneered with various species of wood.

[Jon Isaacs]

Use lightweight and strong carbon. Forget about heavy, dirty aluminum. I have a lot of black anodized aluminum for three telescopes, I actually have four sets. About ~50 meters of tubes. A lot of money was spent on them before. All of it is now in the trash.

 

Carbon is very pleasant to the touch and does not smear your hands.

 

Well,.

 

- There is nothing dirty about aluminum. Dirty is CFRP, one needs to be careful with the dust when cutting CFRP.  

 

- Aluminum may be a little heavier than Carbon Fiber Reinforced Polymers but it is not brittle so it will not fracture. Ductility is a wonderful material property.  Before I retired, I was in charge of a materials science research laboratory at a major university.  I had a carbon fiber bicycle frame hanging in the lab. The bike had been leaning against a wall but fell over, fracturing the thin tubes. 

 

- Strength is not a concern in truss Dob except if the tubes are clamped.  Then one has to be concerned about brittle fracture.. 

 

As far as the original question:  I have Dobs with painted tubes, covered with pipe insulation and covered with heat shrink.  It all works.. 

 

Jon

Edited by Jon Isaacs, 21 January 2025 - 02:53 AM.

[a__l]

Why paint or cover at all? The poles on my 30" are bare aluminum. I see no scattered light even when shining a flashlight on them. As long as they are entirely outside the light path, they should have no effect on the image.

For some reason, my hands are left with a lot of dirt after touching aluminum. If it is not anodized aluminum. Then this dirt can easily transfer to the glass. And in general, it leaves a feeling of discomfort from dirty hands.

[a__l]

Well,.

 

- There is nothing dirty about aluminum. Dirty is CFRP, one needs to be careful with the dust when cutting CFRP.  

 

- Aluminum may be a little heavier than Carbon Fiber Reinforced Polymers but it is not brittle so it will not fracture. Ductility is a wonderful material property.  Before I retired, I was in charge of a materials science research laboratory at a major university.  I had a carbon fiber bicycle frame hanging in the lab. The bike had been leaning against a wall but fell over, fracturing the thin tubes. 

 

- Strength is not a concern in truss Dob except if the tubes are clamped.  Then one has to be concerned about brittle fracture.. 

 

As far as the original question:  I have Dobs with painted tubes, covered with pipe insulation and covered with heat shrink.  It all works.. 

 

Jon

"little heavier" hm... 2.7 vs 1.7 g/cm3 

Carbon is practically weightless when you take a carbon tube in one hand and an aluminum tube in the other.
The surface of the carbon tube is smooth and silky, aluminum is smears your hands.
If you accidentally step on the tube, you will bend the aluminum too. I don't know of any other ways for a carbon tube for a telescope to burst. These are all horror stories of people who don't use carbon.

 

_________

 

Actually, do a simple experiment, rub your palm with an aluminum tube and see the result.

Edited by a__l, 21 January 2025 - 03:53 AM.

[Oberon]

Thanks for all the replies so far. I'm beginning to lean towards painting the tubes. There are actually a couple reasons for this. 

 

I live in a hot, dry climate. Eventually the climate is going to get to the foam and cause it to crumble. 

 

It may not add much weight wise, but it will add to the bulk.

 

I thought about heat shrink tubing but it's not cheap and will also show age and dings after a while. 

 

The tubes are currently bare aluminum. 1.25 inch OD x .054 wall. I have self-etching and camo flat black primer.  I can pickup a can of flat black top coat for durability. If, by chance, I need to do any touch up it will be easy. 

 

I'm also going to make a carry bag for the tubes. The bag will also be made to keep the tubes from banging together during transport/setup/breakdown. 

 

Sound like a good plan? 

I use a tent pole bag as a carry bag, it even has handles. Its perfect, like its made for the job.



Even if your paint is self etching primer I would rub the poles down with a scotch-brite pad first, then quickly prime. Also a final clear coat (can be satin or gloss) will protect from damage.

Finally…consider a snazzy colour. Doesn’t have to be black! I love my two tone metallic…

 

 

 

[Jon Isaacs]

"little heavier" hm... 2.7 vs 1.7 g/cm3 

Carbon is practically weightless when you take a carbon tube in one hand and an aluminum tube in the other.
The surface of the carbon tube is smooth and silky, aluminum is smears your hands.
If you accidentally step on the tube, you will bend the aluminum too. I don't know of any other ways for a carbon tube for a telescope to burst. These are all horror stories of people who don't use carbon.

 

_________

 

Actually, do a simple experiment, rub your palm with an aluminum tube and see the result.

 

I know a fair amount about CFRP.. In our research group, we tested thousands of CFRP coupons to failure.  We had a project with Spirit-Aerosystems to develop in-situ health monitoring systems for their CFRP aircraft structures. Spirit-aero manufacturers things like fuselage sections for Boeing and Airbus.   

 

The problem with CFRP is that it is brittle and internal damage cannot be easily seen.  In a commercial aircraft, it's a big problem and the planes have to inspected using NDT, I believe mostly ultrasound. 

 

https://en.wikipedia...rit_AeroSystems

 

A little heavier. I just weighed the a 50 inch long, 1.25 inch OD tube with a 1/16" wall.  That included the shrink wrap.  1.2 lbs.  The local metal supplier carries 1.25 inch in black anodized, those tubes would weigh 1.1 lbs.  A CFRP tube of identical dimensions would weigh 0.7lbs so the savings would be 3.2 lbs and in terms of balance, 1.6 lbs.

 

The aluminum tube will not bend if I accidentally step on it or jump on it. I just did that test, stood on it with one foot, it is very strong.. I wouldn't want to jump on a CFRP tube with my 225 lbs. 

 

The problem with CFRP is that it is brittle and if the surface is nicked or damaged, that is a stress riser and a crack can run. One has to be very careful transporting it.   

 

I don't see much reason to spend the money when the weight savings is minimal and the aluminum is more forgiving.  

 

Jon

 

P.S.: I have no problems with aluminum and my hands.  Aluminum naturally forms a hard oxide layer.. 

Edited by Jon Isaacs, 21 January 2025 - 06:16 AM.

[Sincos]

Was once a press operator in an aluminium plant and have made miles and miles of extruded poles . Paint or cover with insulation are not the only options,  There is also anodized aluminium that you can have etched in a multitude of colours much like Oberon did in their above post . Personalized my telescope when going with tubes made to hold carpet in place on stairways and matching the colour scheme of the telescope . What type of wood did you use and did you paint or stain it ?

 Good Luck and Clear Skies

 

 

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[Meterman]

I use a tent pole bag as a carry bag, it even has handles. Its perfect, like its made for the job.



Even if your paint is self etching primer I would rub the poles down with a scotch-brite pad first, then quickly prime. Also a final clear coat (can be satin or gloss) will protect from damage.

Finally…consider a snazzy colour. Doesn’t have to be black! I love my two tone metallic…

 

 

 

 

Thanks for the reply. 

 

I haven't done anything with the tubes, yet. The only part I have done is make the upper end attachment. It's been quite cold here in Southern New Mexico but that won't last. 

 

I have to mount the secondary and focuser to the upper cage and finish the upper tube clamps. Once that's done it's time to find the balance point and cut the tubes. 

 

Once the tubes are cut they'll be cleaned, get a scotchbrite rub down, and painted. Wooden parts are Baltic Birch, but finish hasn't been applied yet. Probably just clear urethane for a finish. I have a couple scrap pieces I can experiment possible staining on. 

 

Currently the mirror box weighs about 43 lbs., give or take, and the upper cage will be around 8 to 9 lbs. Not sure yet if I'll need to add weight to the bottom or not. 

 

Build Progress is here.

https://www.cloudyni...build-progress/

[triplemon]

For some reason, my hands are left with a lot of dirt after touching aluminum. If it is not anodized aluminum. Then this dirt can easily transfer to the glass. And in general, it leaves a feeling of discomfort from dirty hands.

That is not dirt, but aluminum oxide. Untreated bare aluminum when handled does that to your hands. If you ever handled a currency with aluminum coins, you'd know vey well.

 

That is also the reason why aluminum usually gets anodized or painted. But anodizing itself creates a moderately shiny surface, as aluminum oxide is a glass like substance.. Even dying the anodization black will not do anything to fix that shinyness, as that process embeds the color pigments in cavities deep in the initially quite porous oxide, before these pores are sealed to trap the dye particles in there permanently. So while anodizing is by far the most durable and hardest (much harder than aluminum itself) option - wrt optical reflections its just so-so at best.

Edited by triplemon, 21 January 2025 - 11:53 AM.