Marking angles on tube ?

[sardine]

I have a 12 " piece of 1.5 " od tube and I need to mark out a lengthwise slot 25 degrees from a centre line how do I do it ?

Ideal would be a measurement I could make on the OD of the tube with a paper template.

Forget any calculations as I'm number illiterate.

 

[James1979]

If you've got a printer there are a few free pipe template websites out there.

There was a really good one I can't remember now but quick Google found this one: https://www.blocklayer.com/pipe-miter.aspx

There are plenty of others but principle is the same

 

[brightspark]

have u protractor mark the tube with marking blue or a black felt tip clamp the pipe down to something flat .scribe a line with the edge of protractor at 90 degrees then alter it to 25 degrees and scribe again that should get u the off center marking more than likely

 

[mdr]

Sounds like you need to calculate the "length of arc" for a 1.5" pipe with 25 degrees. Maybe...

https://www.omnicalculator.com/math/arc-length



Test it first! I offer no guarantees!

Edit/Update:

Here's another site with a diagram at the top: https://1728.org/radians.htm

Sounds complicated but you can plug in numbers, get a length and measure round the pipe with a flexible tape or something cut exactly to length.

 

[Morrisman]

Theres a simple way to mark out and cut a piece of paper to wrap round you tube to mark it, but I can't remember how to do it.

 

[James1979]

Theres a simple way to mark out and cut a piece of paper to wrap round you tube to mark it, but I can't remember how to do it.

Me either! That's why I linked the above i was shown it years ago. I think the fabrication series on YouTube covered it in one of his videos too?

 

[Agroshield]

Theres a simple way to mark out and cut a piece of paper to wrap round you tube to mark it

Wrap paper around tube and mark overlap. Lay paper flat on table. Lay ruler diagonally on paper with zero aligned with one edge and a convenient measurement aligned with the other edge. Mark off as required (if you need 180 degrees, mark at halfway measurement; 120 degrees mark at 1/3 measurement, etc.). Pick convenient measurement to suit divisions or angle required.

In the OP's case, the circumference is approx. 120mm so he should make his band, lie it flat on table, align ruler diagonally on zero and 144mm and mark it at 10mm. When wrapped back around the pipe, it will give the 25 degrees (25 degrees is 25/360 of the girth or 5/72 or 10/144).

 

[8ob]

Wrap paper around tube and mark overlap. Lay paper flat on table. Lay ruler diagonally on paper with zero aligned with one edge and a convenient measurement aligned with the other edge. Mark off as required (if you need 180 degrees, mark at halfway measurement; 120 degrees mark at 1/3 measurement, etc.). Pick convenient measurement to suit divisions or angle required.

In the OP's case, the circumference is approx. 120mm so he should make his band, lie it flat on table, align ruler diagonally on zero and 144mm and mark it at 10mm. When wrapped back around the pipe, it will give the 25 degrees (25 degrees is 25/360 of the girth or 5/72 or 10/144).

The the way I have interpreted the question from our fishy friend is he merely wants to mark a tube lengthways 25 degrees off the tube centreline ( as in parallel ). I have got it at tube circ of 120mm divided by 360 = .333333333333333 x 25 = 8.3mm off centreline (ish)

Bob

 

[mdr]

The the way I have interpreted the question from our fishy friend is he merely wants to mark a tube lengthways 25 degrees off the tube centreline ( as in parallel ). I have got it at tube circ of 120mm divided by 360 = .333333333333333 x 25 = 8.3mm off centreline (ish)

Bob

Yep, that's how I read the question.

 

[Country Joe]

The the way I have interpreted the question from our fishy friend is he merely wants to mark a tube lengthways 25 degrees off the tube centreline ( as in parallel )

That's the impression I got, not just coping the tube end.

The program that used to be linked to on here, years ago was the "Tube Miter Program", which allows you to input the diameter, thickness, angle, etc.
It only works on Windows, though.

All the Best,
CJ

P.S. :- I realise that reads back a bit strangely:-

I first establish that this isn't what you want, as you're trying to do something completely different.

And then, "here's the thing referred to earlier - that you don't actually need" - and a link to it, too!

 

[hotponyshoes]

The pi/r/squared calculation thing will give you the circumference of the tube (4.71" or something?)
Mark out a strip that wide on short of paper and draw it out on that.

This is the sort of thing I find my 3d printer useful for.
Draw up a sketch of what you want (slot size/position etc) and I will have a go at printing a template sleeve that you can slide over the tube.

If its alloy tube you can make the printed slot oversized and use a guided router bit to make the cut out. Or you could just fit the sleeve, pen/spray paint to mark the tube, remove, drill/grinder most of the slot, refit the sleeve and use as a guide to finish off with a file.

 

[MBB]

circumference of the tube is 1.5"x pi= 4.172" Divide by 360 then x 25 will give you the distance in inches which would be .327" from the slot centre line, more or less what 8ob said but in inches.

 

[Onoff]

Get a bit of 3/4" (19.05mm) ply and a bit of "8mm" ply or plate. Place tube on flat surface - tape it down if you want. Holding the 3/4" ply against the tube and scribing it will give you the centre - green line. Lay the 8mm bit on top of the 3/4" and scribe another line - red line. It'll be 25deg off the first.

How accurate has this got to be?

Putting a bit of a chamfer on the 8mm plate would get where you scribe against nearer to the tube face.

 

[Agroshield]

The the way I have interpreted the question from our fishy friend is he merely wants to mark a tube lengthways 25 degrees off the tube centreline ( as in parallel ). I have got it at tube circ of 120mm divided by 360 = .333333333333333 x 25 = 8.3mm off centreline

That is correct. But it is far easier to measure 10mm on a slanted 144mm than to guess at 8.3mm or 0.327".

It is the classic carpenter's way of dividing by proportion where you do not need any established system of measurement units.

You could even do (a simplified version of) it without any tape measure at all. Make your wrap. Take another piece of paper longer than the wrap and put equally spaced marks along it (use the width of your thumb). Line up the zero and eight mark and mark every second one and you have quartered your pipe.

 

[Mark 2]

I'm not sure I understand the question but if said tube is cut length ways then it will ping open surely.

 

[sardine]

Get a bit of 3/4" (19.05mm) ply and a bit of "8mm" ply or plate. Place tube on flat surface - tape it down if you want. Holding the 3/4" ply against the tube and scribing it will give you the centre - green line. Lay the 8mm bit on top of the 3/4" and scribe another line - red line. It'll be 25deg off the first.

How accurate has this got to be?

Putting a bit of a chamfer on the 8mm plate would get where you scribe against nearer to the tube face.

View attachment 229008

This ^^^^

 

[bigegg]

If you don't need it mega accurate, then marking opposite sides will give you 180°
Half the distance is 90°
Again is 45°
Then halved again is 22.5°. Near enough?