Making the Cut - TM Technologies

Making the Cut

Home > Education > Articles > Making the Cut - TM Technologies

Making the Cut

Aluminum sheet meets its match

from Sport Aviation, June 2003
by Kent White

I used to think that cutting out sheet metal parts was a hassle, because I never had enough resources (tools) to adequately resolve the task, or enough bandages to stop the leaks in my sweaty shaking hands when finished. This is still true for me when cutting stainless, and maybe copper or brass, and, well, even mild steel still gives me problems on occasion. But aluminum? No problem. Hearty anticipation is all I feel now when going after a fresh panel or skin of T3, or half hard, or even S-0. This doesn’t mean I won the lotto and bankrolled the shop into a digital laser cutting station. What I have is a compilation of a few years’ experience and a selection of neat hand tools, some of which are fairly capable of doing additional duty on wood. Yep, even “carpenter metal” can be cut with some of the tools I’ll show you. But, and I do mean but, do not think for one moment that you can always improvise on other metals with these tools, because aluminum is special when it comes to cutting.

The electric router with attached guide will make long, straight cuts. The electric router with attached guide will make long, straight cuts.

When cutting out large skins that need straight edges, what tool comes to mind? A 12-foot shear? That’s what I used to visualize, but not anymore. How about a router? With a guide mounted on it, a router is great for cutting aluminum if you use the right bits, and carbide is not what I mean. High-speed steel will do just fine. Laminate bits can be used for straight cuts as well as for curves. For freehand cutting I like the single-edge spiral bits, as most router speeds are high enough (12,000 to 30,000 rpm) so that one edge is all you need. If you’re doing a stack of Bearhawk ribs, then make a cutting guide out of hardwood, MDF, or particleboard and then use a laminate bit with the guide bearing on the end of it so the wood pattern will guide your cutter to blank out a set of perfect ribs.

For freehand work, I use the Roto Zip with the spiral bit. To cut lightening holes, for instance, I mark out the hole, either spray the cutting area with some kind of oil or wipe the path with beeswax, put on the safety gear, and plunge in with the router. No de-burring needed (well, hardly any). And on thick sections, say for form blocks, the router makes beautiful radiused edges. One drawback: A snowstorm of aluminum flakes will scatter everywhere.

The saber saw can make rapid, accurate cuts that do not distort the surface. Best for curves and openings.The saber saw can make rapid, accurate cuts that do not distort the surface. Best for curves and openings.

The jigsaw, or saber saw, is a fine tool. The best ones are loaded with speed adjustments, chip blowers, and blade rake adjustments and have good balance and weight. Some hollow-ground, extra sharp blades designed for wood will do a great job on aluminum if the speed is set correctly. Use a lube to free the chips, and tape two pathways along the cut line for the saw to ride on or else the chips will scar the finish of your new skin!

Nibbler. Cheap and available tools for clean curved cuts.Nibbler. Cheap and available tools for clean curved cuts.
For fast, straight cuts, and the cordless circular saw does wood, too! For fast, straight cuts, and the cordless circular saw does wood, too!

Nibblers are powered by either electricity or air, but the air models are cheap and available. You must keep the punch and die lubricated with light machine oil or else aluminum will build up in the clearance, and then you could have bits of shattered tooling lying around. Controllability can be an issue with the light air models, so I generally relegate them to freehand work— cutting curves, circles, or rough cuts on blanks. The large electric models are expensive but make smooth cuts that will very nearly follow a fine line. Drawback: The chips will fill your shoes with very sharp little bits.

Cordless or battery-powered circular saws are ideal for light cutting tasks. Available in 12v, 14v, 18v, and 24v, some have a fine balance of weight and power in 14.4v, such as the DeWalt model, whereas the larger voltages lose a bit of the feel in favor of having more power. Blades can be bought specifically for aluminum, or just use a fine panel blade. Some will cut 1/4-inch plate reliably enough for mobile fabricators. Again, tape down a glide path and think about using lube to free the chips from the blade. Drawback: straight cuts only.

The electric shear is a standard tool of the aviation shop, and it will cut and trim large curved panels rapidly. Good for fairly straight cuts. The electric shear is a standard tool of the aviation shop, and it will cut and trim large curved panels rapidly. Good for fairly straight cuts.
Curling shear. It is medium-priced, and is very effective for curved and reasonably straight cuts. It will burr and mark the edge of the sheet. Curling shear. It is medium-priced, and is very effective for curved and reasonably straight cuts. It will burr and mark the edge of the sheet.
A mini air saw cuts slowly and straight, and leaves a thin kerf with no distortion. A mini air saw cuts slowly and straight, and leaves a thin kerf with no distortion.

Electric and pneumatic shears, also known somewhat erroneously as “nibblers,” are common in many shops, but do tend to distort or mark the edges of the sheet. Two styles exist; “bypass” shears work like scissors, and “curling shears” lift a 5/32-inch wide curl ahead of the shear. The bypass shears are usually expensive, and are made by Black & Decker, Bosch, and Metabo, to name a few. Kett, Milwaukee, Fein, and Makita manufacture the electric curling shears, and a variety of manufacturers make pneumatic models. Because of the gradual startup and slowdown of a VSR electric shear, I tend to prefer them to the pneumatic ones, but this is just a personal preference. Drawback: good for curves, but not for straight edges. They do not like stainless at all.

Mini air saws make a lot of dust, but they can make openings for louvers and ducts and will do minor cutting operations that other tools cannot. They will cut large curves but are better for straight cuts, and they can use thin abrasive blades that make 3/32-inch kerfs. Excellent for cutting welds, removing old damage, or making openings, the air saw will follow a fine line and does not distort the work. Drawbacks: slow and dirty.

Please exercise your best safety practices when cutting aluminum. Protect eyes, ears, and your lungs. Wear cotton or Kevlar knit gloves to protect your hands, and aim any spray of chips in a safe direction. Enjoy using these tools; now go make some parts!

EAA Technical Counselor Kent White achieved master technician’s status in 1976 at Harrah’s Auto Collection, where he restored metal components for aircraft and autos. He started his own metal restoration company in 1977 and now teaches, writes, and develops tools for metalworking while he still pounds out parts. He encourages any welder or metalworker to contact him in regard to preserving the traditions of aircraft metalworking.
Contact him.