Cutting a hole for DC exhaust in metal pole barn. How?

[William C Rogers]

I am finally getting my DC set up with my eBay cyclone. It's tough when having to do things mostly by yourself. I am getting to where I need to put a hole in the side of my building for the exhaust. It is a standard ribbed metal building. I have OSB for the walls inside. My thoughts I'd to drill a small hole through both walls to establish a center point. Then use a jig saw to make the holes. Are there metal bits for a Roto Zip? What is the best way to seal the outside where the pipe exits? Just caulk? I intend to make the exhaust 7". The DC mains are 6", any reason not to use 7"? Right now I am thinking making the 90 bend (using 3-4 30 degree elbows) exiting just below the window near the cyclone. Above the window would be shorter, but I need to put a blast gate to open and close in the winter, so within easy reach?
I am using 30 ga for the main, hence the plywood rings. I had initially thought of running the pipe above the ceiling, but that would have been a pain. The plywood ring helps me keep things somewhat level.
I live in a rural area, so getting help is sporadic. I tried several methods to stand the cyclone up without success. So I temporally moved my HF hoist and got it right up. I put 1 1/2" of foam rubber between the wall and the cyclone studs to reduce any vibration effect. The other HF item I bought was the drywall hoist. I initially bought this to put up the OSB, but since I have 12' ceiling it has become invaluable for putting things on high shelves. Note: miscalculated and had to put a small offset to clear a light.

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[James Gunning]

William,

A quick Google showed metal cutting bits available for a RotoZip. That's how I would cut the hole. Jigsaw would work also. Lots of options for caulking. It would depend on how circular the hole was and how tightly it fitted the pipe. I would probably try low expansion spray foam. Cut a plywood doughnut to fit over the pipe on the outside. Use a router or similar to cut a very round hole so it tightly fits the pipe. You could screw through the wall into the OSB and then fill the spaces behind the doughnut with the foam. A 7" pipe for your exhaust would work fine, but I would match the pipe size exiting the blower. 6" should be large enough. I would put two 45's with a short straight between them. The blast gate could go in the short straight. You could put it above the window, just put a long enough handle on the blast gate to reach it from the floor. When you are running your dust collector, you might want to keep that window closed. Otherwise you may have some of the fine stuff wafting back into your shop. Let us know how the eBay cyclone works with your blower.

[Lon Crosby]

I would install a thimble (oversized by 2 inches or so) used for furnace/fireplace flue runs. That gives you a finished outside edge and a semi-finished inside edge. Then run your dust exhaust pipe through and insulate the space between the two. If you steel is ribbed, you'll need to figure out where you want the hole from the outside or cut a 3/4" spacer to fill the gap if you land on a rib.