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Leg Dia. Stability

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7 replies to this topic

#1 Seahag

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Posted 21 October 2019 - 02:17 PM

I have never owned a tripod with 2" dia. ss tubular  legs but have read about greater stability over 1.75" legs which is what I own. The 2" tripods I have seen advertised are about 27" in height at lowest settings, mine at 34"and just right for seated viewing. Is there anything to be gained by increasing leg diameter if it is necessary to raise the mount? 



#2 wrvond

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Posted 21 October 2019 - 03:18 PM

I would say "no". However, while I haven't measured the legs on my CG-5 mounts, I'm pretty sure they're more than 27" tall fully retracted. I only extend one or two legs enough to level the mount.

 

IMG 1942
 
The Sky_Watcher sits atop a 16" tripod pier extension.
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#3 Jon Isaacs

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Posted 21 October 2019 - 03:46 PM

I have never owned a tripod with 2" dia. ss tubular  legs but have read about greater stability over 1.75" legs which is what I own. The 2" tripods I have seen advertised are about 27" in height at lowest settings, mine at 34"and just right for seated viewing. Is there anything to be gained by increasing leg diameter if it is necessary to raise the mount? 

 

The tripod with the larger diameter legs will be stiffer, more rigid. The lower legs are also involved so the stiffer lower legs also play into it.  The stiffness of a tube in bending is a function of the 3rd or 4th power of the diameter so the 2 inch legs could be`50%-70% stiffer.

 

Jon



#4 Seahag

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Posted 21 October 2019 - 03:47 PM

Thanks for replying, I was contemplating the purchase of one locally  for use with a larger alt mount and 6" f/10 refractor arriving soon but I was thinking build a pier or buy a larger tripod. At my age I couldn't  move it around much anyway.


Edited by Seahag, 21 October 2019 - 03:55 PM.


#5 vtornado

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Posted 21 October 2019 - 05:07 PM

I have the SVP mount head and tripod with two inch steel legs.

I was able to mount a 6 inch f/8 refractor, and a 8 inch f/5 reflector on this mount.

Both scopes were at the limit of this setup.   I did not figure out if the mount head or the

tripod was the limiting factor.

 

The tripod is not that heavy,  most of the weight is in the EQ head and counter weights.

With the scope, tripod, CWs, mount head, finder, diagonal,  no way you are going to

move the setup to tree dodge, without partially disassembling it.

 

I think I read that the flexure of a tube is proportional the cube of the diameter.

So a 2 inch is 50% more stable than a 1.75 inch.  Whatever that means???

And I'm unsure how the tube wall thickness plays into the equation too.


Edited by vtornado, 21 October 2019 - 05:13 PM.


#6 wrvond

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Posted 21 October 2019 - 05:12 PM

I just measured one of the legs on my CG-5 (2" tube), it's 32.5" from the bolt at the top to the foot at the bottom. They're all folded up and strapped down in the camper right now, so I can't tell you how tall they are when spread.



#7 Seahag

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Posted 21 October 2019 - 05:37 PM

Thanks, the permanent pier set up would require me to build two, one for home and one for the farm. If I can get the  height out of a 2" tripod then problem solved. I will look for a taller tripod for now but I am getting shorter.


Edited by Seahag, 21 October 2019 - 05:40 PM.


#8 Jon Isaacs

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Posted 21 October 2019 - 05:44 PM

I have the SVP mount head and tripod with two inch steel legs.

I was able to mount a 6 inch f/8 refractor, and a 8 inch f/5 reflector on this mount.

Both scopes were at the limit of this setup.   I did not figure out if the mount head or the

tripod was the limiting factor.

 

The tripod is not that heavy,  most of the weight is in the EQ head and counter weights.

With the scope, tripod, CWs, mount head, finder, diagonal,  no way you are going to

move the setup to tree dodge, without partially disassembling it.

 

I think I read that the flexure of a tube is proportional the cube of the diameter.

So a 2 inch is 50% more stable than a 1.75 inch.  Whatever that means???

And I'm unsure how the tube wall thickness plays into the equation too.

 

If the tube wall is of constant thickness, then it's the third power.  If the wall thickness increases proportionally, then it's the fourth power.

 

But there are many factors involved, the lower leg design, the connectors, the bracing are a few. My experience is that the 2 inch tripods are a good deal stiffer than the 1.75" tripods.

 

Jon




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