Measuring Tool

[Hitch]

If you put a fixed (one end, obviously )arm across the legs, you could add a series of marks that line up with the other leg, to correspond with the most common pipe sizes for reference...
Further from the pivot, the more accurate..but longer it needs to be...a sort of bit like these

 

[Hitch]

Heres what I mean

 

[Pete.]

I was going to suggest similar. If you make the scale curved and set it the right distance from the pivot (the curve radius) you can use a linear scale too.

 

[Sidewinder]

You can't use a Pi "tape" with spiral wound, only longitudinally seamed.
Even then it's not accurate.
Mind, if it is spiral wound it's rubbish anyway and wants ripping out and replacing with LS.
So a calliper is a better option, however, you MUST know the material thickness to verify the ID which is what the LEV calcs are based on, if it is LEV for COSHH you are looking at.
Remember, also, if you are making decisions, recommendations or requirements on the duct under COSHH, as a business then you need to CYA IYKWIM.
Insurance, qualifications, competence, experience etc.

 

[Parm]

Heres what I mean

Hitch, this is exactly what I had in mind, I've got some ally kicking around but not enough to make curved legs so it's gonna be a bit like he drawing I posted earlier. Ally is around 5x 30 mm and about 500mm long.

Is there any specific reason the legs are curved?

Oh and I have an idea for an In built measuring scale

 

[Pete.]

Legs must have a curve otherwise they would never touch the opposite sides of a circle.

 

[Parm]

Legs must have a curve otherwise they would never touch the opposite sides of a circle.

Not quite sure I understand that!!

 

[Pete.]

Calipers have to bend around the curve of the circle or they won't touch on the diameter. Crappy sketch shows it more clearly.

 

[Parm]

Calipers have to bend around the curve of the circle or they won't touch on the diameter. Crappy sketch shows it more clearly.

View attachment 66765

Ah, ok Got it now !

My simple plan was to attach some points on the end. You can see them in my realy crappy sketch somewhere in this thread

 

[Maker]

I just had an even simpler idea: A big framing square.

Provided the legs are longer than the radius, where the pipe contacts the leg of the square, the measurement will be the radius. Does that make sense or do I need a crappy sketch?

 

[Parm]

I just had an even simpler idea: A big framing square.

Provided the legs are longer than the radius, where the pipe contacts the leg of the square, the measurement will be the radius. Does that make sense or do I need a crappy sketch?

I think that's the simplest idea so far, to develop your idea further it could be calibrated to read of diameter

Take a bow that man !!

 

[Maker]

to develop your idea further it could be calibrated to read of diameter

No, just double it, it's not hard, stop trying to make things complicated.

 

[Wedg1e]

You can't use a Pi "tape" with spiral wound, only longitudinally seamed.
Even then it's not accurate.
Mind, if it is spiral wound it's rubbish anyway and wants ripping out and replacing with LS.

You cab get spirally-welded oil pipeline as well, for reasons nobody's ever explained to me.
It's a bu99er to inspect with our long-range ultrasonic kit, first the weld prevents a ring of probes from clamping down properly and then the return echos are just gibberish and noise.

 

[Migmac]

Get a set of tree calipers, there not expensive