What is the diameter of the hanger bar in the final phase of the competition?

[Jr2d]

What is the diameter of the hanger bar in the final phase of the robotics competition?

[Palacio2312]

In the field drawings says 1 ¼"

[Jr2d]

Thank you

[plusparth]

Be careful — it says schedule 40 1-1/4” pipe. These pipes are measured by their inner diameter, meaning the inner diameter is 1.25”. The same paragraph lists the outer diameter as 1.66”.

[Palacio2312]

Thanks for clarifying

[David_Lame]

@plusparth

Be careful — it says schedule 40 1-1/4” pipe. These pipes are measured by their inner diameter,

The weird thing is, they aren’t measured by their inner diameter.

Yes, we’re finishing the robot, and hadn’t hung yet, and had just finished the field element, and so we go to hang, and…not much success, because the hook was made for a 1 1/4 inch pipe.

At first, we reacted by thinking that we had purchased the wrong pipe, because the mentor who bought the pipe wasn’t there, so we blamed him, of course. This pipe was 1.66". However, we weren’t too quick to blame him. That was just a preliminary assessment. Out comes the rule book, and we read the “Outer diameter 1.66 inches” line. Oops.

Well, we still had calipers in hand, so we just had to satisfy our curiosity, so we measured the inner diameter. 1.38 inches.

Well now this is just too weird. So, off to google, and look up “Schedule 40 pipe”, and on the table it says that 1 1/4 inch schedule 40 pipe has an outer diameter of 1.66 inches, and an inner diameter of 1.38 inches.

I’m sure that must make sense to someone. Does anyone have a clue why someone would call something 1 1/4 inch pipe when none of the dimensions happens to be 1 1/4 inches. This is even weirder than figuring out the width of a 2x4. Either way, we need a new hook.

And some repairs. It didn’t land gently.

[GeeTwo]

@David_Lame

oes anyone have a clue why someone would call something 1 1/4 inch pipe when none of the dimensions happens to be 1 1/4 inches.

Because schedule 80 pipe has the same outside dimensions so it can use the same fittings. It’s inside diameter is something much closer to 1.25".

Added: 1.278"
https://www.metals4uonline.com/PipeSchedule10,40,80Specifications

[EricH]

@David_Lame

Yes, we’re finishing the robot, and hadn’t hung yet, and had just finished the field element, and so we go to hang, and…not much success, because the hook was made for a 1 1/4 inch pipe.

At first, we reacted by thinking that we had purchased the wrong pipe, because the mentor who bought the pipe wasn’t there, so we blamed him, of course. This pipe was 1.66". However, we weren’t too quick to blame him. That was just a preliminary assessment. Out comes the rule book, and we read the “Outer diameter 1.66 inches” line. Oops.

Our students did the same thing. They redid the hook.

[MrForbes]

1.66" outside diameter.

1 1/4" is a pipe size, NOT a dimension.

[David_Lame]

@GeeTwo

Because schedule 80 pipe has the same outside dimensions so it can use the same fittings. It’s inside diameter is something much closer to 1.25".

So it has the same outer diameter as some other piece of pipe that has an inner diameter that is also not 1 1/4 inches, but is closer.

Well that seems fairly obvious.

Actually, I’m just being facetious. I can see why the size of the fittings might matter, but as the applications changed, the walls got thinner. So the new 1 1/4 inch pipe could fit in exactly the same space as the old 1 1/4 inch pipe, but had a larger capacity because the walls didn’t need to be as think in a “schedule 40” application. The difference between 1.25 and 1.278 was probably a slight change as precision of manufacturing got higher, but it still fit in the same space as an old pipe.

And then a robotics team didn’t read the stuff in parentheses, and tried to hang off a 1 1/4 pipe with a 1 1/2 inch hook, thinking that made sense.

[GeeTwo]

Yeah. The general rule is that “pipe” and “conduit” and terms that refer to passing things through the passage inside the tube refer to a nominal inside diameter. Tube, and architectural tube (as, IIRC were referenced in the 2014 pyramid) refer to the nominal outside diameter.

Nominal: of or referring to a name. (not necessarily an actual measurement; for example, a “2x4” is actually much closer to 1.5" x 3.5".) LIterally, it means “that’s what we call it”.