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Engineery Types: Tube/Pipe Sleeve

300sniper

300sniper

Gun Plumber
Joined
May 20, 2020
Member Number
695
Messages
428
Loc
Greenwood, CA
So I’ve got some 2-3/8 x .154 A500 fence/railing posts I want to extend. The extension is going to be about 8’ tall and I want them removable.

Plan is to turn some solid bar so it is a slip fit in the existing post and a press fit into the extension with some plug welds. I want the joint as rigid as possible, while still being removable.

Question is: what’s the minimum amount of the solid bar that needs to slip into the existing posts for maximum strength?

Yes, I over think everything….



IMG_8062.jpeg
 
I think the rule of 3's would apply. 2.375x3=7.125 so 14 1/4" sleeve would be robust enough. For what you're doing I'd grab some thicker wall tubing to turn down instead of the solid stock or drill the solid since tube is stronger than solid.
 
Maybe drill/tap the slip fit tube side for some set screws?
 
Slip fit tube. but tolerancing can be an issue. if it gets tweaked at all you're screwed, if you cant set it all down evenly at once, you're screwed. Id use square receiver tubing in the ground and 2" square tube with round welded inside it. Use what's already available instead of making custom stuff. Tolerancing is already there. Bending moment is going to be the same no matter what, right where the slip fit ends.

Oh, bottom bending moment. 6" should be enough for 2" tube. longer for less wobble but you can tack it or shove a wedge in the square stuff to reduce movement
 
Engineery type answer: the minimum length of solid bar needed to maximize the strength of the tube it slides into is equal the length of the tube it is sliding into. Any longer then the tube and it will not provide any additional support. Any shorter then the tube and there are still potential strength gains :flipoff2:
 
DWT said:
Strength is in surface area. If it wasn't there would be no need for gun drilled axle shafts.
Click to expand...
Are you saying that removing material from the center of a round piece of material makes the part stronger? If that is what you're saying, it is incorrect.

The strength is largely in the outer diameter, and the reason they gun drill shafts is to reduce the rotational mass, not make the shaft have a higher overall strength.
 
Not much to add except to say, make sure you cap the extensions. It rains there at some point does it not.

How tall are the existing fence posts?
 
DWT said:
Strength is in surface area. If it wasn't there would be no need for gun drilled axle shafts.
Click to expand...
Hollow axles and driveshafts are made because they are lighter, not stronger.
Stress is proportional to distance from centerline. The center of a solid shaft has a marginal contribution to strength, so it can be removed for the weight savings.

shafted.jpg
 
welndmn said:
Is it supporting anything, or is the extension just holding 8' more of fence pipe?
Click to expand...
It's honestly just going to have some 3/32" cable between two of them 36' apart that some cafe lights will attach to (but it drives me crazy looking at other people's cafe light supports and they're all leaning/bending).
 
300sniper said:
So I’ve got some 2-3/8 x .154 A500 fence/railing posts I want to extend. The extension is going to be about 8’ tall and I want them removable.

Plan is to turn some solid bar so it is a slip fit in the existing post and a press fit into the extension with some plug welds. I want the joint as rigid as possible, while still being removable.

Question is: what’s the minimum amount of the solid bar that needs to slip into the existing posts for maximum strength?

Yes, I over think everything….



IMG_8062.jpeg
Click to expand...
I think I'd try to find some butt weld hammer unions.
Solid connection infinitely removable.
 
How about you get a larger diameter pipe for an outside sleeve? Weld it to the removable piece. It would be easier to slip over then inside the fence post, and you could make it a little loose and put a bolt through it. Would be easier to remove than trying to wiggle it out of the inside after it rusts.

Or fab a super sized set of these
Interlocking Chromoly Bungs Tube Connectors Roll Cage 1-3/4" x(.095 Wall) Amazon.com
 
that sounds like 2" Sch 40 pipe

Try sticking a piece of 1 1/2" Sch 40 pipe inside of it and see how it fits.

We commonly use a 6" long by 2" Sch 40 pipe as an embedded socket to drop a 1 1/2" post into for flags around pools. these flags are sometimes 82' long and held up by a cable.

another option would be to weld some flanges to the pipes to be able to unbolt and remove them
 
jeepnmatt said:
that sounds like 2" Sch 40 pipe

Try sticking a piece of 1 1/2" Sch 40 pipe inside of it and see how it fits.

We commonly use a 6" long by 2" Sch 40 pipe as an embedded socket to drop a 1 1/2" post into for flags around pools. these flags are sometimes 82' long and held up by a cable.

another option would be to weld some flanges to the pipes to be able to unbolt and remove them
Click to expand...
1-1/2" pipe is way too lose in it.
 
BDK said:
How about you get a larger diameter pipe for an outside sleeve? Weld it to the removable piece. It would be easier to slip over then inside the fence post, and you could make it a little loose and put a bolt through it. Would be easier to remove than trying to wiggle it out of the inside after it rusts.

Or fab a super sized set of these
Interlocking Chromoly Bungs Tube Connectors Roll Cage 1-3/4" x(.095 Wall) Amazon.com
Click to expand...
X2 on the larger pipe for a sleeve. I've done that before.
 
if you mill a slot in the slug to avoid the seam you can probably get a much better slip fit in there
might still be something you're going to need to torch apart though
 
why not make two slugs and thread them together, you're always doing that nice threading stuff
female on the lower one and male on the upper one
would be a much less wobbly fit than a slip fit inside pipe

if you're using the cnc you could go real fancy and go with tapered threads like the drill stem guys always use, but really straight thread wouldn't be terrible
 
[486] said:
if you mill a slot in the slug to avoid the seam you can probably get a much better slip fit in there
might still be something you're going to need to torch apart though
Click to expand...
That was the plan.

If I ever do need to get it apart and it's stuck, I can figure a way to use a bottle jack to getter out.
 
^
Weld a nut into one tube end and a bolt in the other.

Socket head bolt head the size of the tube id would make it easy.
 
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