What's the best tool for making this cut?

[doodah man]

I'm installing air conditioning in my 72 Chevy truck and need to cut holes for the factory side vents. The vent tube that goes through the hole is round but the dash has a curve on it near the glove box. I'm thinking I might get into trouble with a hole saw not going in at exactly the right angle, so I'm looking for an alternative. The edge of the cut will be covered so it doesn't have to be perfect. I've got a dremel so could I use one of the cutting bits they sell? Maybe drill a bunch of pilot holes? Pics of the dash and template for the cut:

 

[doodah man]

Here, the arrow shows where the hole needs to be cut. The same thing goes on the other side.

 

[woody 73]

My memory is sometimes not the greatest but I do remember this: Milwaukee made a special bit set that could overcome corners darn that small set was very expensive but I don't remember any of the #'s. I seem to think it came in a set of 5 self-feeding type bits for around $75.00 dollars that was in 1990 prices; not even sure if they are still made.

 

[jjjrmx5]

If me, I'd cut a template in cardboard off the paper pattern adn then position it where you want it and trace around teh cardboard with a grease pencil.

Since it;s not a round hole, I;d use a hole saw as large as the largest round part of the patten that will allow it thus speeding up mat'l removal.(Looks like you may need a right angle drill if that door will not open enough for access ).

Then I'd take an air saw or air die grinder with a carbide burr to cut out the rest of the hole that is remaining based upon the grease pencil line. Then i'd takle the dremmel with sandpaper drum bit and knock down any burrs or sharp edges just to be safe.

The big challenge is what is on the other side of that metal dash as you do not want to cut , pierce or dril thru anything of importance that you cannot see or you need to dig up under there an move it out of the way.

Not a hard job to do clean and mean tho.

Good luck.

 

[woody 73]

My mistake I found on the web something like what I was talking about: It is called a MULTI ANGLE DRILL BIT that will go around corners but for wood only. I am sure it could go into the plastic ok but I am not sure about sheet metal.

 

[OceanSpray]

Nice looking truck. I thought about getting an older truck for the ease of maintenance. Figured it would eat me alive in gas though. Want kind of mileage does that thing get?

 

[Zeke]

You can cut a hole that appears to be round from your vantage point on any shape surface and at any tangent. Project the shape you want to cut on the surface from the angle you want it to enter. Get a single filament light source and shine it through a tube the size of the hole you want. Hold your light set up on a fixture such as a tripod and then trace out the "circle" on the object to be cut.

Use whatever cutting tool that will follow that line.

 

[Brad54]

Nice looking truck. I thought about getting an older truck for the ease of maintenance. Figured it would eat me alive in gas though. Want kind of mileage does that thing get?

My '61 Suburban gets 16-17mpg on the highway, with a later 350ci engine.
The carb needs to be tuned, the distributor needs to be replaced, the Edelbrock intake is 1960s technology, the exhaust manifolds are very small diameter (restrictive), and the front end alignment is HORRIBLE and needs to be rebuilt... I'm sure that alone is scrubbing off 2mpg!

With a smart build, and smart gearing, you can get decent MPG with a vintage truck.

-Brad

 

[bad_idea]

Very clever Zeke. I would think the dremel may be your best choice.

I realize it is apples to oranges, BUT, my 02 Z28 gets 18 city/ 29 highway. I think the biggest helper in the mileage is the 6 speed manual. I think a classic truck like that with a LS1 backed by a 6 speed would get good mileage.

 

[Brad54]

To the OP, there are a couple of options, I think.
You could use a long pilot bit on the hole saw.
Depending on how handy you are, you could make your own pilot/guide.
Does the hole go in squarely to any surface?
If it does, you could drill a simple hole, and use a piece of tubing for the guide... just thread the OD of the tubing, slip it through the hole you drilled in the dash, and put a nut on both sides of the panel to hold it in place. Then drill with the hole saw.

The other thing that might make your job easier, is to remove the door.
I've found that we frequently make jobs a LOT harder because we try to save time or effort.
For instance, every time I work under a dash, I spend 10 minutes removing the seat, so I'm laying on the floor comfortably.

-Brad

 

[JASTECH]

What about a nibbler?

 

[vintagefan]

What about a nibbler?

Yeah, this is really a job suited for a right angle air nibbler. You can get a decent(ish) one at HF for pretty cheap.