projecting a triangle for template for cutting pipe?

[bigegg]

I have a project...
I want to cut some pieces of pipe into a particular shape.

Imagine a piece of 12" diameter pipe.
Cut a 2" slice off one side so that it's now a "C" shaped curved plate - with a height of 12", and a width of 10"

I want to cut the pipe into 30deg sectors so that when they are welded together, I end up with an oblate spheroid shape - 20" diameter, 12"high - sort of a 12-sided tangerine.

I can't work out how to project the shape onto the cylinder to make a template?

It should be easy to do in inventor, but it's not - there is an add-on which might work, but it's £££

 

[Wendelspanswick]

Isn't it just 30° slices?
360 ÷ 12

Take your longitudinal slice out if your pipe with a cutting disc then sit the pipe on the bandsaw and set the fence at 15° (to give you 30° inclusive) I think.

 

[Wendelspanswick]

Edit:
Doing it the above way wastes a lot of pipe, if you slice the pipe on the bandsaw first, moving it through 180° after each slice and pushing enough through that the cut lines meet at 10" from the fence.

 

[zeppelin builder]

Edit:
Doing it the above way wastes a lot of pipe, if you slice the pipe on the bandsaw first, moving it through 180° after each slice and pushing enough through that the cut lines meet at 10" from the fence.

look up hortonsphere like large lpg tanks used in refinery

 

[bigegg]

Isn't it just 30° slices?
360 ÷ 12

Take your longitudinal slice out if your pipe with a cutting disc then sit the pipe on the bandsaw and set the fence at 15° (to give you 30° inclusive) I think.

Should have pointed out, my bandsaw is too small to cut the pipe.
Hence the need for a template.

 

[smashweld]

If you cut a hole bit bigger than 12” diameter (so you can rotate a bit) in a stiff sheet you could pit the pipe in the hole and have a flat pen/scribe flat on the surface of the sheet with the point of the pen on the pipe...bit fiddly, need to keep the pipe and sheet in place whilst marking
Could even make a wedge shape with 2 sheets (with the hole in each, coming to a point 2” from the edge of the hole...if that makes sense!) then line up the point with the edge of the pipe.

I’m wondering now if there’s an easier way

 

[smashweld]

Pipe wrap thing would work too but need to get the proper shape first...then line it up with a straight line on the pipe, wrap it round and mark...only way I know to do that is to have it cut first, then draw round it...which prob doesn't help!

 

[MoreWellie]

find someone local with a bigger bandsaw?

 

[Maker]

Is this what you're going for?

There's a dimple but not a hole all the way through (The radius of the curve is smaller than the radius of the pipe)?

 

[MoreWellie]

been scratching my head and I think this is right

you need a piece of paper 2 inches by 27.6062878 inches and then mark the centre of each side and draw lines between each long side centre and each short side centre and then cut them off

the bit that is making me head scratch is whether these lines should be straight or curved, currently I am thinking they should be curved and the radius should be a big number. I have asked the mrs to do it but she is busy at the moment, if she comes up with a figure I will let you know

 

[Seadog]

You can use this method for generating the template.

 

[zeppelin builder]

curv o mark gadget is what you need
mark tdc of pipe attach gadget set angle drag arm with chalk holder round pipe

 

[bigegg]

Is this what you're going for?
View attachment 138232
There's a dimple but not a hole all the way through (The radius of the curve is smaller than the radius of the pipe)?

Yes.
Like that.

 

[bigegg]

You can use this method for generating the template.

Yeah.
I get that bit...

I'm really regretting selling the two copies of "caxtons sheet metalworking" now.

 

[bigegg]

curv o mark gadget is what you need
mark tdc of pipe attach gadget set angle drag arm with chalk holder round pipe

I like that...
I'm going to adapt a laser line marker to do it.
Suspend it above the pipe, turn to 15deg, mark the line in chalk, turn 15deg the other way.
Cut the first triangle out of the pipe, then use that as the template.

 

[Maker]

Yes.
Like that.

Use this (OD=12", angle=150), draw a line down the length of the tube to align the template, cut it so the fat end of the wedge is 5.17" and 12 pieces will fit together with a 10" radius to form that shape (A spindle torus).

 

[daedalusminos]

In inventor can you not flatten a surface? That would be the way I'd generate a template...but it would be so much easier just to cut it into 30° segments using a fixed saw. To save material, cut the pipe first then chop of the 2inch section

 

[bigegg]

@Maker Perfect. Ta very much

 

[bigegg]

In inventor can you not flatten a surface? That would be the way I'd generate a template...

Not without buying a plugin for mucho quido