Making a cone from 160mm PVC pipe?

[Barry Burgess]

I am trying to make a cone from 160mm PVC pipe with an ID151mm. I need the bottom opening to the cone to be 59mm with and ID of 50mm. The cone depth has to be 250mm I have a number of programs that will allow you to calculate the sizes for using flat sheet but they are not working with tubes.
Thanks for any help
Barry

 

[OLD]

Draw out flat sheet shape on card put inside pipe trace shape cut out make cone , sounds easy but altering the shape of the plastic pipe may be difficult.

 

[Barry Burgess]

Old many years ago I watched one of those swimming pool fitters do it - he made 4 triangle shaped cuts into the pipe and used a heat gun. With the single cut its more difficult - the heat gun is not a problem - I am trying to figure out the circumference reduction to get the 250mm depth
6" diameter circumference 18.84"
2" " " 6.28"
I am of an age that I have forgot all my university maths but what I was hoping that there was somebody on the forum that does it regularly.

 

[Inspector]

I am trying to make a cone from 160mm PVC pipe with an ID151mm. I need the bottom opening to the cone to be 59mm with and ID of 50mm.

You want to make a 6" to 2" reducer the hard way.

(Pi x OD) - (Pi x ID) = amount of the circumference to be cut.

Have you considered making a 6" plywood plug with a 2" hole drilled into it? Epoxy in a coupling to slip in the smaller pipe/hose if you want it removable.

 

[DaveL]

Barry is trying to make a cone as the air flow is much better than with a step change in diameter. There will be eddies with the step and the dust will tend to be dropped out of the air.

 

[9fingers]

Large radius = 75.5mm
Small radius = 25mm

change in along the cone radius =50.5mm

Length along axis =250mm

Length of cone surface (inside) =sqrt (250^2 + 50.5^2)
=255.05mm

So you need two arcs one length 151*pi and the other 50*pi with difference in radii of 255.05mm

Assuming you draw this out on flat card, the sector angle is 72.34 degrees,
the minor radius is 125.65mm and the major radius is 375.70mm

Cut this out and fit inside your pipe to see where to cut

Does this help Barry?

Bob

 

[johnb]

You just about answered it yourself.

6" diameter circumference = 18.84"
2" diameter circumference = 6.28"

So you need to cut out a total of 12.56" out of the circumference at the narrow end. If you want to do it in four equal isosceles "triangles", they each need to be 3.14" around the circumference. So the angle for each from the centre of the tube is 360*3.14/18.84 = 60 degrees.
So make a cross on one end of the tube and then mark 30 degrees either side of the cross lines. Mark lines all the way down the tube for the original cross. Then put a line round the tube (200mm) when you are happy to cut down to and cut out the "triangles" from the 30 degree marks.

Then get the heat gun out.

Good luck.

 

[Inspector]

PostPosted: Sun Sep 17, 2006 7:06 pm Post subject:
Quote:
I am trying to make a cone from 160mm PVC pipe with an ID151mm. I need the bottom opening to the cone to be 59mm with and ID of 50mm.


You want to make a 6" to 2" reducer the hard way. Wink

(Pi x OD) - (Pi x ID) = amount of the circumference to be cut.

Have you considered making a 6" plywood plug with a 2" hole drilled into it? Epoxy in a coupling to slip in the smaller pipe/hose if you want it removable.

Sorry Barry. Looking back I realised I screwed up my formula. ](*,)

should be: (Pi x OD of large) - (Pi x OD of small) = amount of circumference to be cut

eg: (Pi x 160) - (Pi x 59) = 317.3

 

[Barry Burgess]

Thanks for the replies I will give it a go. Might consider two cuts rather than 4 but I will see how I go I was going to form a wooden plug first using the band saw or on a lathe(which I do not have) to aid with getting the shape right with the heat gun. Thanks again
Barry