Hand Tools and Basic Machining

You don't need a CNC machine to build a combat robot. Many insect-class robots are made with a drill press, a saw, a few files and a tap set. This page covers how to make robot parts by hand: marking out, drilling, tapping threads, cutting plate, bending sheet, and working with the plastics and metals builders use most. For the basic tool kit (soldering iron, wire strippers, drivers, drill, rotary tool), see Tools For Beginners first.

Safety first: read Safety below before you start, and see Safety for the wiki's general advice.

Measuring and marking

Good parts start with good layout. A hole that's 0.5 mm off can stop two plates lining up.

Calipers. A cheap digital caliper measures outside size, inside size and depth to about 0.02 mm, which is plenty for robot work. Use it to check screw sizes, bearing bores and plate thickness, not just to measure your own parts.
Steel rule and square. A small engineer's square keeps edges and lines at 90°.
Layout fluid (or a permanent marker) colors the metal so scribed lines show up clearly. Scribe lines with a carbide scriber or the tip of the caliper jaws.
Center punch. Punch every hole location before drilling. A drill bit wanders on a flat surface, but it follows a punch mark. An automatic (spring-loaded) punch is easy to use one-handed.
Print a template. If you've drawn the part in CAD (see CAD for Combat Robots), print it at 100% scale, check the scale with your caliper, and glue it to the plate. Punch through it at each hole center.
Drill matching parts together. Clamp two plates that must line up and drill through both at once. They'll match even if your layout was slightly off.

Drilling

Drill press or hand drill?

A drill press drills straight, repeatable holes and lets you control speed and pressure. Even a small benchtop drill press is one of the most useful tools a builder can own. Many makerspaces have one.
A hand drill is fine for plastic and thin aluminum, and for repairs at events. Holes won't be perfectly square, so start with a small pilot hole and keep the drill upright.
Clamp the work with a drill-press vise or clamps, never by hand. A bit that grabs a small plate can spin it into your hand.

Good habits

Pilot holes: for holes larger than about 6 mm (1/4"), drill a small pilot first, then open it up.
Step bits cut clean round holes in thin sheet (aluminum, polycarbonate, thin steel) where a twist drill would grab and tear.
Back up the exit side with scrap wood or plastic to stop breakout and burrs.[1]
Peck: pull the bit out every few millimeters to clear chips, especially in plastic and deep holes.
Lubricate metal. Use cutting fluid or tapping fluid on steel and titanium, and a little cutting fluid or WD-40 on aluminum to stop chips sticking to the bit. Don't use oils on polycarbonate (see below).

Speeds

The right speed depends on the material and the bit size: larger bits and harder materials need slower speeds. Little Machine Shop's drilling chart lists cutting speeds of 350–400 ft/min for wrought aluminum (such as 6061-T6), 60–100 ft/min for low-carbon steels such as 1018, and 30–90 ft/min for 4140 alloy steel.[2] Plaskolite gives 100–200 ft/min for its Tuffak polycarbonate.[3] To turn a cutting speed into RPM, use RPM ≈ 3.82 × speed (ft/min) ÷ bit diameter (in). As a rough guide for HSS drill bits:

Material	1/8" (3.2 mm) bit	1/4" (6.4 mm) bit	Notes
Aluminum (6061)	As fast as your drill press goes	About 5,000+ RPM (most drill presses top out lower)	Lubricate; clear chips often
Mild steel (1018)	About 1,800–3,000 RPM	About 900–1,500 RPM	Cutting fluid; steady pressure
Alloy steel (4130/4140)	About 900–2,700 RPM	About 450–1,350 RPM	Use the low end, with cutting fluid
Polycarbonate	About 3,000–6,000 RPM	About 1,500–3,000 RPM	No cutting oils; air cooling
UHMW	Moderate	Moderate	Peck often; slow down if it melts or strings
Titanium (thin sheet)	Slow	Slow	Sharp bits, about half your usual speed, firm pressure, cutting fluid

If smoke, squealing, blue chips or melted plastic appear, slow down. If the bit just rubs and makes dust, it's dull or you need more pressure.

Tapping threads

Tapping cuts threads into a hole so a screw can go straight into the part. It works well in aluminum, steel and acetal, but don't tap fine threads into UHMW – it strips. Use self-tapping screws for plastic in a correctly sized pilot hole instead (see Fasteners and Hardware).[4]

Tap drill sizes

These sizes are from Little Machine Shop's tap and clearance drill chart, which gives a slightly smaller drill (about 75% thread) for aluminum, brass and plastics, and a slightly larger one (about 50% thread) for steel and stainless, where a full thread is hard to cut and rarely needed.[5]

Screw	Tap drill: aluminum/plastic	Tap drill: steel	Clearance drill (close / free fit)
M2 × 0.4	1.6 mm	1.75 mm	2.1 / 2.2 mm
M2.5 × 0.45	2.05 mm	2.2 mm	2.65 / 2.75 mm
M3 × 0.5	2.5 mm	2.7 mm	3.15 / 3.3 mm
M4 × 0.7	3.3 mm	3.5 mm	4.2 / 4.4 mm
M5 × 0.8	4.2 mm	4.5 mm	5.25 / 5.5 mm
#2-56	#50 (0.070")	#49 (0.073")	#43 / #41
#4-40	#43 (0.089")	#41 (0.096")	#32 / #30
#6-32	#36 (0.1065")	#32 (0.116")	#27 / #25
#8-32	#29 (0.136")	#27 (0.144")	#18 / #16
#10-32	#21 (0.159")	#18 (0.1695")	#9 / #7

Check the chart for other sizes; the Little Machine Shop tap drill page also lists them.

How to tap

Drill the tap hole square to the surface; a drill press helps. Chamfer the top of the hole slightly so the tap starts cleanly.
Use a tap wrench (a T-handle wrench is easiest for small taps), and start the tap straight. Check it with a square after the first couple of turns.
Use tapping fluid in metal.
Turn forward about half a turn, then back a quarter turn to break the chip, and repeat. If it gets tight, back out and clear the chips. Small taps (M2, #2-56) snap easily; never force them.
In blind holes, drill deeper than the thread you need, and finish with a bottoming tap if you need threads close to the bottom.
Threads in aluminum need more length than in steel. A rule of thumb is engagement of about 2× the screw diameter in aluminum and 1× in steel (see Fasteners and Hardware).
A broken tap is very hard to remove. Prevention is much easier than the cure.

Cutting plate and bar

Tool	Good for	Notes
Hacksaw	Aluminum bar and plate, thin steel, plastics, cutting off screws and shafts	Fine teeth (24–32 TPI) for thin material, so at least three teeth are always in the cut. Cheap, slow and accurate.
Jigsaw	Curves in UHMW, HDPE, polycarbonate and thin aluminum	Use a new blade kept only for plastic, about 10 TPI for HDPE, lower blade speed and a little wax on the blade. For tight curves, rough-cut about 1 cm outside the line, then trim.[6]
Bandsaw	Straight and curved cuts in plastic and aluminum; a metal-cutting bandsaw handles steel bar	Much faster and squarer than a jigsaw. Plaskolite suggests 8–12 TPI blades for its thicker polycarbonate grades.[7]
Oscillating multi-tool	Plunge cuts, trimming parts already mounted	Slow in metal; useful for repairs.
Rotary tool with cut-off wheel	Thin steel, titanium, screws, slots	See below.
Aviation snips / metal shears	Thin aluminum and steel sheet	Leave a bent, sharp edge that needs filing. Not for titanium or hardened steel.

What's realistic by hand

UHMW and HDPE: easy with any saw. Keep the blade cool, or it melts and gums up.
Polycarbonate: a normal sharp drill, a fine-toothed hacksaw and sandpaper are all you need.[8] Leave the protective film on while you work.[9]
Aluminum (up to about 6 mm / 1/4"): quite doable with a hacksaw, jigsaw or bandsaw, plus files.
Thin titanium sheet (around 1 mm): Team Run Amok says no special tools are needed for thin titanium sheet: use very sharp bits and blades, about half the usual speed, firm pressure and a cutting fluid.[10] Expect it to be slow and to wear blades.
AR400/AR500 and other hardened steels: very hard to cut, drill or machine at home, so they're usually laser, plasma or waterjet cut by a service.[11] Order these parts with the holes already in them.
Carbon fiber and G10/Garolite: cut with an abrasive disc or fine hacksaw, with a dust mask and eye protection.[12] See Armor and Materials.

Filing and deburring

Every cut and hole leaves burrs that cut fingers and wires and stop parts sitting flat.
A deburring tool (a swivel blade on a handle) cleans hole edges and plate edges quickly. A countersink bit turned by hand also works for holes.
Files: a medium flat file and a small half-round file cover most jobs. Files cut on the push stroke; lift on the return. Rub chalk into the teeth when filing aluminum to stop clogging, and clean them with a file card.
Sanding: for plastics, finish edges with sandpaper on a flat block. Smooth edges on polycarbonate also help stop cracks starting there.

Bending sheet

Aluminum: 5052 bends well; 6061-T6 and 7075-T6 tend to crack if bent tightly. SendCutSend, for example, offers bending in 5052-H32 but not in 6061 or 7075.[13] Bend along a straight edge clamped in a vise, with a generous inside radius.
Titanium: Grade 2 titanium bends; Grade 5 (6Al-4V) has heavy springback and thicker pieces need heat to form, so SendCutSend doesn't bend it.[14] Plan Grade 5 parts as flat plates.
Polycarbonate up to 4.5 mm thick can be bent cold on a brake to 90°; thicker sheet should be heated along the bend line. It can also be curved cold into place to a radius of at least about 100 times its thickness.[15]
Hardened steel and carbon fiber should not be bent; they crack.
A cheap bench vise brake or two pieces of angle iron clamped in a vise gives clean bends in thin sheet. Hammer with a soft mallet or a wood block, not directly on the part.

Countersinking

Countersunk (flat-head) screws sit flush, so spinners have nothing to catch.[16]
Match the angle. Metric flat-head screws are 90°. Imperial flat-head screws are usually 82°, though 90° and 100° exist.[17] Check what you bought.
Use a countersink bit at slow speed in a drill press, with a depth stop if you have one. Test on scrap until the screw head sits just flush.
Leave enough material under the countersink: in thin plate, the countersink can go right through and leave no grip. As a rough guide, the plate should be at least as thick as the screw head is tall.
Don't countersink polycarbonate (a counterbore is fine) or carbon fiber.[18][19]

Working with UHMW and polycarbonate

UHMW and HDPE

Soft and slippery, with very poor heat conduction, so heat builds up and melts the cut. Use sharp tools, keep the feed moving, and cool with compressed air.[20]
Chips come off as long strings that wrap around bits. Peck often and clear them.
It springs back, so drilled holes end up slightly smaller than the bit.
Fasten with self-tapping screws for plastics, not tapped threads.[21]

Polycarbonate

Plaskolite's guide for its Tuffak sheet says to drill holes slightly oversize, keep holes at least two hole diameters from the edge, and use air or a clean water mist for cooling instead of cutting fluids, because many fluids attack polycarbonate.[22]
Bits made for plastic work best, but a sharp ordinary bit works fine.[23]
Avoid threadlockers on polycarbonate, since many crack it (see Fasteners and Hardware).

Rotary tools

A rotary tool (such as a Dremel) is the most versatile small tool in a robot shop:

Cut-off wheels cut thin steel, titanium, screws and shafts. Fiber-reinforced wheels are tougher than the thin unreinforced ones.
Carbide burrs shape aluminum and clean up pockets; sanding drums smooth plastic edges.
Hold the work in a vise, wear eye protection, and stand out of line with the wheel. Cut-off wheels can shatter.
Run slower on plastic so it doesn't melt.
Titanium makes bright sparks and fine dust: see Safety.

Lathes and mills

If you can use a lathe or mill, for example at a makerspace or school shop, many parts get much easier: weapon hubs and shafts, wheel hubs, spacers, motor mounts, and pockets to save weight (see Weight Management).

Get trained. Most makerspaces require a sign-off before you use a lathe or mill, and for good reason.
A small benchtop mini lathe handles aluminum, acetal and mild steel well, and is very useful for shafts, spacers and hubs.
A small mill (or a drill press with an X-Y table, for light work only) can cut slots and pockets in aluminum and plastic.
Hardened steels like AR500 are too much for hobby machines. For a machined steel part such as a drum, Team Run Amok suggests 4130 chromoly, which is cheap and machines well, or an aluminum drum with waterjet-cut AR500 impactors fitted to it.[24] See Armor and Materials.
For shafts and bearing fits, see Weapon Shafts, Bearings and Mounting.

When to outsource

Hand tools are great for prototypes, simple frames and repairs. Send the job out when:

The part is hardened steel, thick titanium or a complex weapon shape.
You need several identical parts, or a weapon that must be balanced.
The holes need to be accurately placed, for example a bearing pattern.

Online laser, waterjet and CNC services are now affordable even for small insect-class parts. See Fabrication Services for services and tips on ordering, and 3D Printing for printed parts.

Safety

Eye protection every time, for everyone in the room. Drills, saws and rotary tools all throw chips. Use hearing protection for loud cutting and grinding.
Clamp the work. Use a vise or clamps, not your hand, especially on the drill press.
No gloves, loose sleeves, jewelry or loose hair near rotating tools (drill press, lathe, mill). They can catch and pull your hand in. Gloves are fine for handling sharp sheet, but take them off before using rotating tools.[25]
Never clear chips by hand while a tool is running. Stop it and use a brush. Metal chips, especially from steel and titanium, are razor-sharp.
Titanium dust and sparks: solid titanium is not flammable, but very fine dust from grinding, sanding or polishing can ignite on its own, and can form explosive dust clouds. Don't let dust build up, keep it away from sparks and flame, and never put water on burning titanium: smother it with dry salt or a Class D extinguisher.[26]
Ventilation and dust: cutting carbon fiber, G10 and some plastics makes harmful dust or fumes. Work in a well-ventilated area, wear a dust mask, and clean up with a vacuum rather than compressed air.
Keep your workspace tidy, and keep batteries and LiPos well away from sparks and hot chips (see LiPo Battery Safety).
Follow the posted rules and training requirements at your makerspace or school shop.