This tutorial covers how to cut into a dash or other area of the boat when installing a chartplotter, flush mount a VHF radio, switches, or anything similar. Quite often, dash material consists of an aluminum panel over a fiberglass deck. I have tried many different approaches with varying degrees of success. To complicate things, it is often not practical to remove the dash for cutting, and the cutting must be done on the boat, with a minimum of available resources. This is a summary of what I have found to work well.
Available methods. There are three basic methods available for cutting into a dash:
Jig saw. There are several basic types of jigsaws available. The traditional jigsaw will cut into most materials, however it suffers from being rather bulky, and is generally hard to fit into tight spots. Also, the saw's base can scratch the material you are cutting into.
The XPR attachment fits onto the end of a Dremel tool, and is lightweight, and is easy to manouver in and around tight spots. However, this saw is not built very well, and you might even destroy the saw in the process of cutting the helm (I did exactly that).
The third type is a pneumatic saw, and you can buy one at Harbor Freight for under $30. Sure, its Made in China quality, but it us usually sufficient. This is the best of the three saws, having the power of the traditional jig saw, as well as the ability to get into tight spots. The only down side is the investment of a small air compressor, and having to lug all that stuff to the boat.
Dremel tool. With the proper bit, a Dremel tool can cut into metal and fiberglass. However, a Dremel tool doesn't have the duty cycle to cut out large panels, as its more suited as a cut-off tool. I have burned these tools up making panel cuts. Also Dermel tools are fairly hard to control, and you'll likely run the tool across the helm or fiberglass area as you are trying to make the cut.
Nibbling Tool. Either pneumatic or hand tool, is effective for light gauge aluminum; less than 0.062 (1/16" thick). Thicker aluminum will damage the tool, ripple the aluminum, or both. You generally cannot use a nibbling tool on fiberglass as its usually too thick.
When I cut out the helm for my multi-function display, I used the Dremel XPR system. It certainly was not up to the task, and I had to stop about every foot or so and let the tool cool down. The tool literally became too hot to handle.
That is how this pneumatic saw worked. I use it with my modest Porter Cable pancake portable air compressor. The compressor and saw combined is under $200, which is not that far from the cost of the other solutions.
My recommendation is to invest in a portable "pancake" air compressor, such as a Porter Cable C2002. You can usually find one for under $150. Then a few pneumatic tools, such as the pneumatic saw shown in this tutorial can be found at Harbor Freight and other outlets for $20~$30, as well as a pneumatic file, 3/8" drill, and other accessories, all in the similar price range. You can even get a 1/8" collet tool that will take Dremel tool bits, and you won't suffer from overheating issues.
Each of these tools is under $30, and all can be easily powered with the Porter Cable air compressor. And I am sure you can think of dozens of other uses for an air compressor.
Here is a scenario; how do you enlarge a hole in the helm. Say you have a 2" gauge that you want to replace with a 3 1/2" gauge. How do you enlarge the hole with a hole saw? Simply attach a "cover" to the 2" hole, which provides a stable hole center for the hole saw, then redrill the hole out for the desired size.