45 degree firestop fabrication?
pgproject
| Posted in Energy, Heating & Insulation on
I need to pass the 8 5/8″ dia. vent pipe for a gas fireplace through a wall at a 45 degree angle. A firestop (sheet metal w/ a hole in it) is required. Any of you have a suggestion as to how to get the right shaped ellipse for this hole? My sheet metal guy says to make a template in cardboard, starting w/ a round hole. This seems a little crude. I tried to figure out how to do it in Sketchup, but no joy. Help!!
Replies
Simplest is to take your duct and measure it across a 45-degree line. You can then guestimate the profile of the oval close enough.
An easy non-mathmatical way to do it would be to make a template from a piece of cardboard formed in a circle and cut at 45 degrees. Run a string around it to make a mark it at the right place.
If you use the string method, I believe the foci would be as far apart as the diameter of the pipe.
If the foic on the pipe are as far apart as the dia of the pipe, how much would you add if you laid it out on a flat plane? Would you draw a circle and then add half the dia to each side? A quarter on each side seems closer just visualizing here.
Here's one way. Draw an 8-5/8" circle on your workbench. Temporarily attach a piece of thin plywood to the ceiling above the bench at a 45* angle--tack one edge to the ceiling and let the opposite edge hang down, supporting it at the correct angle. Using a laser level with a vertical beam, move around the circle in small increments, marking the dot on the piece of plywood. That will get you a very accurate ellipse.
I just had a firestop made by a sheetmetal shop for a gas flue that goes thru a 10:12 roof. The shop that did it has a CNC machine that cut the ellipse. That's cheating, eh?
Get a big piece of paper and roll it into a 8 5/8" cylinder. Then cut where your firestop would intersect. You got's your template.
Here's a template I made in autocad. Just print 2 copies to make 1 pattern.
This is for a 8-5/8" hole, so if you need any clearance you'll have to add that to the pattern.
The axes should be 8-5/8" x 12-3/16". You'll have to make sure adobe (if that's what you're using to print) doesn't scale it down, so be sure to measure the axes.
Model it in Sketchup
Do the math.
16.97 / 12 X 8.625 = 12.19" Thats the long axis. The short axis is 8.25".
Do the string trick.
Bob's next test date: 12/10/07
Thanks to all of you for your help. I'll use the PDF template sent by MiCrazy. I also need the same thing for a 6 5/8" pipe, so I can just scale it.I didn't want to screw around with cutting a cardboard template and getting it 'close enough' when there's a hi-tech way to do it. I tried in Sketchup for an hour or so without success- I need some practice and/or training, clearly.Thanks again.
My high tech method is simply cutting a dowel at 45 degrees, scanning the cut end and adjust picture size to match your duct.
Beer was created so carpenters wouldn't rule the world.
Brilliant!
Cool!
Forrest