Harold Lanfear
Well Known Member
An easy, fast way to cut panel cutouts is with a router and pattern bit (having a bearing on top of the cutter which is the exact diameter of the cutter).
After measuring a marking the size of the panel directly on the panel; I constructed a simple frame of scrap plywood to the exact size of my EFIS opening. The frame has alignment blocks on the top and bottom (more scrap), also glued in place. Make the pattern large enough to allow for clamps that won't interfer with the router as it passes by.
Clamp the frame to the panel (don't use spring clamps, they may shift), drill a starting hole and cut out the center. Wear gloves, these chips will be hot - ask me how I know that?
This method gives a tight fit and only needs a quick touch with a file to clean up the corners and burrs.
You can also use the same method to cut VSI, Altimeter cutouts with the extra knob cutout. If you have one, use another panel as a pattern to make your plywood pattern. You will need spacers to allow for the gap between the bearing and the cutter.
For simple round holes, I still prefer a fly-cutter. Make cuts on scrap until you have a hole the exact size you want. Adjustments can be made accurately using a digital dial calipers referencing the drill bit edge to the outside cutter edge. It doesn't give an accurate hole size since your are using the whole diameter of the center drill bit, but you can make very accurate changes. Just remember that whatever change in the radius you make is doubled in the hole diameter.
After measuring a marking the size of the panel directly on the panel; I constructed a simple frame of scrap plywood to the exact size of my EFIS opening. The frame has alignment blocks on the top and bottom (more scrap), also glued in place. Make the pattern large enough to allow for clamps that won't interfer with the router as it passes by.
Clamp the frame to the panel (don't use spring clamps, they may shift), drill a starting hole and cut out the center. Wear gloves, these chips will be hot - ask me how I know that?
This method gives a tight fit and only needs a quick touch with a file to clean up the corners and burrs.You can also use the same method to cut VSI, Altimeter cutouts with the extra knob cutout. If you have one, use another panel as a pattern to make your plywood pattern. You will need spacers to allow for the gap between the bearing and the cutter.
For simple round holes, I still prefer a fly-cutter. Make cuts on scrap until you have a hole the exact size you want. Adjustments can be made accurately using a digital dial calipers referencing the drill bit edge to the outside cutter edge. It doesn't give an accurate hole size since your are using the whole diameter of the center drill bit, but you can make very accurate changes. Just remember that whatever change in the radius you make is doubled in the hole diameter.
