Best way to cut a 3" hole in the airstream skin?

[gomotomoto]

What's the best way to cut a 3" hole in the airstream? I'm installing a heater vent pipe, and I've nave cut the skin before.

[musketeer]

A hole cutter attached to a drill work perfectly for me. I had to replace my furnace and the new holes didn't line up with the old. Good luck!

[rmkrum]

Mark very carefully. Check twice.

Use blue painters tape to cover the edges of the cut area, draw the circle with a compass onto the tape.

Check the measurements at least twice again. Don goggles and heavy gloves for personal protection.

Use a smaller hole saw, say 2" or so. Drill slowly and carefully, stop when you just cut through the outer skin to avoid snagging wires or insulation. The edges will be rough and sharp. Using gloves, clear the insulation and look for wires. Then check hole location again.

Using a nibbler or aviation snips, trim the hole to the final cut line. Use the hole saw pilot hole in the inner skin to line up and complete the other part of the hole.

Be careful and work slow. Edges of the aluminum will be sharp.


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[AWCHIEF]

Just do not use what Airstream uses, a nibbler. Unless you are skilled it it's use. Seems almost every factory cut hole in my trailer has butchered finger cutting edges. Just my opinion.

[Tom Nugler]

I've used 24 tpi blades in a jig saw to cut larger pieces of skin, but for this I agree with rmkrum that the hole saw is a better option.
Hole saws in a hand held drill tend to chatter in aluminum and leave a very rough opening.
For a 3 inch hole I wouldn't go any bigger than a 2 1/2 inch bi-metal saw. Then I'd dress the opening with a Dremel motor tool with a high speed steel cutter to the line on the tape.

Good Luck,
Tom

[J. Morgan]

I guess I am lazy, I always try to use a hole saw that is the right size and makes a hole that needs little if any trimming.

(Try a dry run on a scrap to make sure before cutting on the trailer)


Gradiens super tenui glacie.

[rmkrum]

It's been my experience that hole saws in sheet metal chatter and dig in to ruin the edges. And the pilot bit can be pulled to the side sometimes.

That's why I suggest cutting smaller and trimming. bigger. Aviation tin sips are good for carefully enlarging holes without messing up the edges. A proper power shear in a drill might work, but I'd try it on scrap first. A 3" hole is kinda small radius to turn the tool.

In any case lots of blue tape to protect the shiny parts left behind.

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[HiJoeSilver]

I cut 6 large (2-3/4" to 4")holes in my AS with hole saws. Many more small ones. All came out flawless. Measure many times. Use some tape and cardboard cut to desired size to visualize the hole. Go slow, small pilot hole to center the larger hole saw center drill to keep it from walking at first. Concentrate on keeping the hole saw straight so that it cuts with even force around its edges, prevents walking and uneven cutting. Assuming you have both skins to drill through. Figure out where your center will be on the inside. Then off center drill 3/4" inspection holes between the center and outer diameter in a way that the hole doesn't touch the center point or outer edge, then feel around for wires or condensate drain line. The larger hole saw will cut out around the smaller holes.

[MarkR]

Hole saw w/ hand held drill.
I've cut at least 7 holes in my trade wind.
Keep drill perpendicular to skin, keep drill speed up, push lightly.

[Naper]

Hole saw is the way to go. I would cut the hole size i needed in the first shot. If you cut a smaller hole first you will have trouble with the larger one as the drill bit will no longer centre the saw. Buy a hole saw that is made to cut thin steel or aluminum the more teeth the better. A general purpose or wood saw will be hard to use and leave rough edges. A good quality whole saw will not be cheep. Do not force the saw, light even pressure.

[joel]

All above will work . Other options are get a flexible attachment for a dremel and then get there diamond wheel to make the cuts . The thin flex handle allows you to work close to surface and controll the cut easily. They also make hole saws with a diamond edge a little easier to controll . Due to usually working on someone else's trailer I tend to be a little conservative. Small hole saw first than finish with the dremel and diamond wheel.less chance of disaster.good luck.

[Melody Ranch]

Don't make the hole to large. Most of those vent lines are 2 1/2 in. I'd go with a 2 1/4 inch hole saw and then finish up with a rotary file to make a tight fit so the water sealing will go well.

[craftsman]

Forget all the extra steps, just use a quality hole saw , go slow and drill that three inch hole. Not hard,not rocket science, doesn't take an apprenticeship. Test it ion a scrap piece of metal and you'll convince yourself just how easy it is.

[55AS]

Originally Posted by MarkR

Hole saw w/ hand held drill.
I've cut at least 7 holes in my trade wind.
Keep drill perpendicular to skin, keep drill speed up, push lightly.

I have cut four round holes in my vintage AS skin (shore power, water fill, and two for the furnace). I used hole saws for all four. Once the agonizing measurement process was complete, cutting the holes was relatively easy.

[us3rnam3]

Originally Posted by gomotomoto

What's the best way to cut a 3" hole in the airstream? I'm installing a heater vent pipe, and I've nave cut the skin before.

There are 2 tools that can be used, A 3" circular saw tool chucked in your drill motor. With this tool you drill a 1/4" hole first. Then the arbor of the tool fits through the hole and the hole is used to center the 3" circular tool as you cut it with the drill motor. Yes cut slowly and cut that 1/4 inch guide hole with a Unibit to get an nice round 1/4" pilot hole. The 3" tool and unibit are available at Lowes or Home Depot.
Another tool is a Flycutter. You will also need to cut a 1/4" gyide hole. This tool is designed to work in your drill also, but you can cut the hole by simply turning the tool by hand. It takes some patience but it works. Since your not using the drill motor it's a very safe but slow method. I use a Harbor Freight tool it can be adjusted to the exact diameter you need. Use one hand to hold the Flycutter in the 1/4" hole and turn the cutting in with your other hand as you press the cutter into the aluminum. Make several rotations and you will see the metal peel away as it cuts into the aluminum.I've built two aluminum airplanes and used both methods.

[AlaskArt]

To get a perfectly round, burr-free hole, use a Greenlee punch. They are available at electrical supply houses and I think at auto parts outlets as well. They are a little pricey, so if you have an electrician friend, perhaps you could borrow one (or get him to help you with it.)

[Melissa Lee]

Use a 1/4 drill to locate hole on each side of wall, drill all the way through. Then on the inside use your jug saw with fine teeth to open up the cut that you need. For the outside hole, use a Electrical knockout punch of the the size that you need, the outside hole will be clean with out any narrely edges. The knockout punch is a two part tool that comes in sizes from 1/2'' EMT to 6" EMT, it is used in the electrical trade to knockout holes in meter boxes, ect......

[rvb]

Originally Posted by us3rnam3

There are 2 tools that can be used, A 3" circular saw tool chucked in your drill motor. With this tool you drill a 1/4" hole first. Then the arbor of the tool fits through the hole and the hole is used to center the 3" circular tool as you cut it with the drill motor. Yes cut slowly and cut that 1/4 inch guide hole with a Unibit to get an nice round 1/4" pilot hole. The 3" tool and unibit are available at Lowes or Home Depot.
Another tool is a Flycutter. You will also need to cut a 1/4" gyide hole. This tool is designed to work in your drill also, but you can cut the hole by simply turning the tool by hand. It takes some patience but it works. Since your not using the drill motor it's a very safe but slow method. I use a Harbor Freight tool it can be adjusted to the exact diameter you need. Use one hand to hold the Flycutter in the 1/4" hole and turn the cutting in with your other hand as you press the cutter into the aluminum. Make several rotations and you will see the metal peel away as it cuts into the aluminum.I've built two aluminum airplanes and used both methods.

I have used a flycutter (adjustable beam hole saw) with good effect on thicker aluminum. You can also use the fly cutter to scribe a perfect circle then cut it out with aviation tin snips.

[ijustlee]

I would use a hole saw bit of the size you want the hole and turn it with a 1/2 inch variable speed drill motor. A 3" cutter should be turned about maybe 200 RPM or so not 1500 RPM and this would be punishing your 3/8 drill unless it's the kind with a low/high speed gearbox. Feed lightly through the first skin and remove the first plug then push the insulation aside and check for wires or pipes. The pilot bit should have made a hole through the second skin but if not hopefully the cutter body will be tall enough to center the bit in the second skin. If you have a choice buy a long pilot bit or a deep cutter body, most home centers and large hardware stores sell these hole saws but they are not cheap. Expect to pay $50 to $100 for one if you can't borrow one from a tradesman friend. Be careful not to cut into a rib or anything else!

[GeeSag]

Here is just a suggestion:
Try getting a Greenlee hole punch in a much smaller diameter and a hole saw of the same diameter and try both on a scrap piece of aluminum.
Consider picking up a small diameter punch at a local Lowes / Home Depot such as something around the 1 inch diameter. Big enough to start to get into the wander/tilt/bite/grab/bend problems of hole saws. 3 inches is a lot of torque when the hole saw wants to bite through the far side of the hole.
Experiment with an affordable punch.
Try both.
See how much cleaner and perfect the cut is with the punch.
Then consider how much you have invested in the new heater project to see if the purchase of roughly a $250 punch would then be worth it compared to the total price of your project.
It is amazing how clean a hole the the punches produce.

"Do you Fell Lucky"

Please, let us know how it turns out and which method you chose.

If nothing else, we all like reading about what others have done to their Precious!
Maybe it makes all of us feel better.