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What material for a portable pier tube

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17 replies to this topic

#1 JeffB

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Posted 11 January 2020 - 04:05 AM

Hi

 

I'm planning to make one which would be left outside all year and would like your thoughts what material to

use.

 

It will need to be portable as I need to move it from one place to where I will be observing so cannot be

over heavy.

 

I can get hold of 4" or 6" platic drain pipe cheaply, which I thought I could cap the bottom and fill with  

sand, but not sure as it will be outside and plastic expands quite a lot

 

At the moment I'm considering getting 120mm dia aluminum from Ebay

 

Thanks Jeff



#2 clivemilne

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Posted 11 January 2020 - 04:23 AM

 Hot dipped galvanized steel would be my recommendation.

 

Not pretty, but strong and best bang for your $ by an order of magnitude.

 

Also, be aware that the material is less important than the design/geometry.


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#3 Astrojensen

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Posted 11 January 2020 - 04:37 AM

How tall is it going to be? A 6" PVC tube is going to be pretty soft and flexible, if tall. It's also going to be a LOT heavier than you thought it would be, if you fill it with sand. A 6" tube, 4 feet long can contain 75lbs of sand... (approximately)

 

I would also recommend steel, as it's both strong, stiff and cheap. 

 

 

Clear skies!
Thomas, Denmark



#4 Stevegeo

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Posted 11 January 2020 - 04:42 AM

Depending on the size and weight of your scope a post from Lowes or Home depot  4 by 4 set into a pier block which is over 100 lbs would work nicely for most refractor and small reflectors  up to 4 or 5 in. 

The blocks have a 4 by 4 hole in them for the post and a simple wood wedge pounded inbetween will secure it solid.

 

I have  two set up in my yard, one with the pier block and post , the other a post in concrete that was poured in a cut off plastic drum.. this one is  solid enough for my C8 on a GEM. Used 2 1/2 bags of concrete @ 60 lbs each.

 A pier plate on top lagged down and all set to go.

 

 

Stevegeo Area3751 observatory otisco lake.. NY  


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#5 Jon Isaacs

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Posted 11 January 2020 - 05:21 AM

Being an engineering type, my first question is , how big is the scope and the mount?

 

A steel tube and an aluminum tube of the same diameter and weight will be equally rigid. 

 

Jon


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#6 m. allan noah

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Posted 11 January 2020 - 08:15 AM

Being an engineering type, my first question is , how big is the scope and the mount?

 

A steel tube and an aluminum tube of the same diameter and weight will be equally rigid. 

 

Jon

...but one of them will cost 3 times as much :)


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#7 dmcnally

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Posted 11 January 2020 - 08:41 AM

Being an engineering type, my first question is , how big is the scope and the mount?

 

A steel tube and an aluminum tube of the same diameter and weight will be equally rigid. 

 

Jon

 

 

...but one of them will cost 3 times as much smile.gif

Correct, sort of.  Steel weighs 3 times as much as aluminum.  When it's priced by the lbs, like at my local metal supply yard, it ends up costing the same.

 

Clear skies,

Dave



#8 polaraligned

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Posted 11 January 2020 - 10:24 AM

Correct, sort of.  Steel weighs 3 times as much as aluminum.  When it's priced by the lbs, like at my local metal supply yard, it ends up costing the same.

 

Clear skies,

Dave

The aluminum will be approximately triple the price for the same rigidity of tube.  Example, a 100# steel tube will be approx $100, 100# aluminum tube will be approx $300.  My pricing is just rough as there are many variables on the purchase, but for the most part aluminum is running about $3 per pound and steel under $1 per pound. 


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#9 dmcnally

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Posted 11 January 2020 - 10:47 AM

The aluminum will be approximately triple the price for the same rigidity of tube.  Example, a 100# steel tube will be approx $100, 100# aluminum tube will be approx $300.  My pricing is just rough as there are many variables on the purchase, but for the most part aluminum is running about $3 per pound and steel under $1 per pound. 

You're still missing the point.   Tubes with the same dimensions will cost the same.  Alluminum is 1/3 the weight and costs 3 times as much.  1/3 * 3 = 1.

 

Clear skies,

Dave



#10 polaraligned

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Posted 11 January 2020 - 01:54 PM

You're still missing the point.   Tubes with the same dimensions will cost the same.  Alluminum is 1/3 the weight and costs 3 times as much.  1/3 * 3 = 1.

 

Clear skies,

Dave

I don't think so, because you need 3x the mass for aluminum to equal the same rigidity as the steel tube (assuming same OD).  Stiffness is what we are after here, right?  So no matter how you slice it, you need either to go to a larger diameter, or a heavier walled aluminum tube to be the equal of steel.   Same OD and ID of aluminum vs steel tube, and the steel is far stiffer.  For economy, steel wins easily. 


Edited by polaraligned, 11 January 2020 - 01:56 PM.


#11 JeffB

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Posted 11 January 2020 - 02:30 PM

Thanks everyone for the information. 

 

The mount will be carrying a 102 F7 refractor with a porta mount so nothing too heavy.

 

Not sure on the height yet but will base it on sitting down while observing, so should not be too high

 

For the legs I was planning on using slotted channel drilled and bolted to the tube

 

Based on all the comments I'm thinking steel seems the best bet



#12 izar187

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Posted 11 January 2020 - 04:07 PM

There is a lot of different ways to do this.

Wood, sealed properly, works.

Solid treated pine, or perhaps marine grade ply.

 

Permanent observing stations, of the right shape, work IME.

So one just has to carry the ota and mount head around the property, and not the head to ground structure.

 

I would not vote for sand filled pipe of any kind, for portable movement, unless it was on at least two wheels.

To tip back and roll around the yard.

 

Possibly the most portable movable pier, is a short as possible pier section, that allows a 360 near/at zenith,

on top of a tall enough tripod, to put your focuser at your best position.

 

My pier projects have been mostly steel, for short tube newts so with focusers on top, and honestly.... heavy.

Last one being made to mount up to a 20 lb ota, and for disassembly, assembly and setup right beside vehicle.

No carry with scope on top at all.

 

For carry about, I would investigate wood, for this circumstance. 


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#13 Stevegeo

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Posted 11 January 2020 - 04:55 PM

How about keeping it simple ...

Another suggestion .. car rim ( with tire) welded or bolted pipe through the center , fill tire with water .. there you have a heavy base, and vibration damping ... and I may add CHEAP... 

 

 I used this method for many other projects ... from portable lighting ( farm) , fencing, umbrella stand outside sun, 

Tool holder( with hooks) ... 

 

Stevegeo Area3751  observatory  otisco  lake. 



#14 dmcnally

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Posted 11 January 2020 - 06:32 PM

I don't think so, because you need 3x the mass for aluminum to equal the same rigidity as the steel tube (assuming same OD).  Stiffness is what we are after here, right?  So no matter how you slice it, you need either to go to a larger diameter, or a heavier walled aluminum tube to be the equal of steel.   Same OD and ID of aluminum vs steel tube, and the steel is far stiffer.  For economy, steel wins easily. 

 

https://www.reddit.c...ngle_passenger/

 

YMMV


Edited by dmcnally, 11 January 2020 - 06:33 PM.


#15 Pinbout

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Posted 12 January 2020 - 09:16 AM

 

The mount will be carrying a 102 F7 refractor with a porta mount so nothing too heavy.

 

its pretty funny listening to all the arguements about steel vs alum. and not knowing what your putting on the pier. lol.gif lol.gif lol.gif

 

but I don't get portable, but you'll leave it outside all the time... some of those nice wood tripods would be great for that rig. carry it out seperately.


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#16 Jon Isaacs

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Posted 12 January 2020 - 09:33 AM

You're still missing the point.   Tubes with the same dimensions will cost the same.  Alluminum is 1/3 the weight and costs 3 times as much.  1/3 * 3 = 1.

 

Clear skies,

Dave

Dave:

 

This is what i wrote:

 

"A steel tube and an aluminum tube of the same diameter and weight will be equally rigid."

 

The Young's modulus of aluminum is 1/3 that of steel. The density of aluminum is 1/3 that of steel. 

 

What this means is that a steel tube that has the same outer diameter will be about as stiff as an aluminum tube with a wall 3 times as thick.  Both will weigh about the same.

 

Aluminum costs about 3 times what steel costs.

 

 

its pretty funny listening to all the arguements about steel vs alum. and not knowing what your putting on the pier. lol.gif lol.gif lol.gif

 

but I don't get portable, but you'll leave it outside all the time... some of those nice wood tripods would be great for that rig. carry it out seperately.

 

Yes.. tripods will be lighter and easier to move. They offer a wide base so the don't depend on gravity for stability.  This just might be the stiffest tripod ever used to support a Portamount.

 

5560437-NP-101 Portamount Houston Fearless CN.jpg

 

Ymmv

 

Jon


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#17 TxStars

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Posted 15 January 2020 - 10:37 PM

Dont forget about checking your local recyclers for a good deal.

Steel vs Al if left outside I would look for Al unless you can find some stainless.



#18 MikiSJ

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Posted 15 January 2020 - 10:53 PM

If you want to stay with plastic then Schedule 80 PVC comes in 4", 5" and 6" diameters but you may need to but a 20' length. Schedule 80 PVC is very strong and considering what you want to use the pipe for will be more than satisfactory.

 

A 6" x 20' length will run around $100. If you know an electrical contractor (commercial) there may be a scrap laying around. I would lay in 3" or 4" Sched 80 underground for PG&E to run the house drops - so you know it will stand up to what you want to do.




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