Formula

[kraits]

i need to cut some plate to fit into a pipe but it has to taper down therefore no longer remaining round, anyone know a formula to do this? ive already thought about making a template by trial and error with a weetbix box.no doubt i was shown how in trade school but i was probably too busy smoking pot and don't remember.

[RayG]

Hi Kraits,

Not sure exactly what you want, are you making an angled flange, or are you fitting something inside a pipe?

Have a look at this, see if it's what you are looking for... Digital Pipe Fitter software: make pipe cutting templates | Digital Pipe Fitter (http://digitalpipefitter.com/)

If it's fitting an angled plate inside a pipe, just cut a piece of pipe at the angle you want, and then trace the shape directly onto a template.

Regards
Ray

[kraits]

its for the inside of a 600mm pipe so, i can't afford to go cutting it to the desired angle then rewelding it, it has to have two sections of plate welded inside angling in for ash to land on and fall into a tray.

[Dave J]

There was one posted up on HSM forum a while back, I don't think it's the one Ray posted, but I could be wrong.

Dave

[RayG]

Hi Kraits,

Ok, I see what you want to do. The shape you want is an ellipse.

Like this... (from Ellipse -- from Wolfram MathWorld (http://mathworld.wolfram.com/Ellipse.html) )



http://mathworld.wolfram.com/images/eps-gif/EllipseBipolar_700.gif


You can draw an ellipse with a piece of string, anchored at the focal points F1 F2 and a piece of chalk at the edge. Put a screw at each of the focal points and run the string around the screws.

The minor axis will be the inside diameter of the 600mm pipe, and the major axis will be determined by the angle, If you want the ash to slid off and into the tray you want it fairly steep.

Once you have the ellipse traced out on your sheet, then mark out across the center for the width of the slot that the ash will fall through, and cut out the two halves.


Regards
Ray

PS Here's a Youtube video, which shows how to get the size right.
How to Draw a Perfect Oval Any Size - YouTube

[jack620]

Kraits,
If Ray's technique doesn't work for you, you should be able to do it using Google Sketchup (free download). I imagine it would be as simple as drawing a tube of the appropriate diameter then intersecting it with a square at the correct angle. By deleting all the unwanted bits you would be left with an ellipse of the correct shape and size. If you print it at 1:1 scale and tape the bits together you will have a template. Haven't tried it myself, but should work.
Cheers,
Chris

[kraits]

thanks fellas, i was looking at sketch up earlier , i think it might be the way to go, either that or i will end up making a template of card board.

[mic-d]

Kraits,
If Ray's technique doesn't work for you, you should be able to do it using Google Sketchup (free download). I imagine it would be as simple as drawing a tube of the appropriate diameter then intersecting it with a square at the correct angle. By deleting all the unwanted bits you would be left with an ellipse of the correct shape and size. If you print it at 1:1 scale and tape the bits together you will have a template. Haven't tried it myself, but should work.
Cheers,
Chris

Chris is right about Sketchup, you can do it pretty easily like he says. I did a fairly complicated intersection between a duct and a shroud in Sketchup, and made up a paper pattern from it. THe hardest part was printing out the pattern, there seems to be a bug in the Mac version. Here's a link to the post (http://www.woodworkforums.com/f200/building-better-dust-extraction-133133/index3.html#post1309998).