Power Tools and Shop Machines
Cordless battery energy, the drill press, bandsaw, grinder and sander: speeds, torque, what to buy first and how the machines compare.
Cordless tools and batteries
Cordless tools are convenient and a battery platform is the biggest decision: stay with one brand so that batteries are shared. A battery stores energy E = V × Ah (watt-hours); how long it runs depends on how hard the tool works it.
Worked example: an 18 V 5 Ah battery
- Stored energy: 18 V × 5 Ah = 90 Wh; 80 % usable gives 72 Wh.
- Drilling at 400 W average: 72 ÷ 400 = 0.18 h = 11 minutes of continuous drilling; at a light 100 W, 43 minutes.
- Driving screws (150 W for 3 s each): about 576 screws per charge.
- The current from the battery for 400 W is 22.2 A; a high-drain tool (saw, grinder) at 1 200 W pulls 67 A and needs a high-discharge pack.
- Energy density: 90 Wh in a 0.65 kg pack is 138 Wh/kg; at $80 that is $0.89 per Wh. A lead-acid battery gives about a quarter of that.
- Motor torque is power over speed: T = P ÷ ω = 500 ÷ 157.1 = 3.2 N·m at 1 500 rpm. Gearing trades speed for torque (a two-speed gearbox), and a hammer-drill clutch limits it.
- Brushless motors are more efficient, run cooler and last longer than brushed ones.
- Do not leave batteries hot or in a hot car; charge at room temperature and store at about half charge for long periods.
- Set the clutch so a screw stops at the right torque; start low.
- Corded tools give constant power for long jobs (saws, sanders, grinders), where a battery runs out quickly.
The drill press
A drill press holds the drill square to the table, gives an exact depth and a steady feed, and lets you clamp the work. It is usually the first machine to buy. The speed is set by changing the belt on a stepped pulley (or by an electronic speed control): small drills need high speeds, large drills low ones.
n = 1 000 v ÷ (π d)
Worked example: speed and power for a 12 mm hole in steel
- At 25 m/min (typical for HSS in mild steel): n = 1 000 × 25 ÷ (π × 12) = 663 rpm. For a 6 mm hole in aluminum at 60 m/min the speed is 3 183 rpm, and for a 20 mm wood bit at 80 m/min about 1 273 rpm.
- Feed 0.15 mm per revolution gives a feed rate of 99 mm/min. The material removal rate is π ÷ 4 × 12² × 99 ÷ 60 = 188 mm³/s.
- With a specific cutting energy of 3 J/mm³ for mild steel (typical) the cutting power is 563 W; at 60 % efficiency the motor draws 938 W. The torque on the drill is 563 ÷ 69.4 = 8.1 N·m: use a vise or clamp, never hold the work by hand (see Workholding, Clamping and Fixtures).
- See Speeds and Feeds for more materials and for the milling and turning equivalents.
| Pulley (motor / spindle) | Spindle speed | Surface speed |
|---|---|---|
| 50 / 150 mm | 575 rpm | 0.0 m/min on a 12 mm drill |
| 75 / 125 mm | 1 035 rpm | 0.0 m/min on a 12 mm drill |
| 100 / 100 mm | 1 725 rpm | 0.1 m/min on a 12 mm drill |
| 125 / 75 mm | 2 875 rpm | 0.1 m/min on a 12 mm drill |
| 150 / 50 mm | 5 175 rpm | 0.2 m/min on a 12 mm drill |
- Clamp the work to the table; the drill can catch and spin it.
- Center punch, then pilot drill for large holes; back the work with scrap to stop breakout.
- Peck to clear chips and use cutting fluid on steel.
- Set the depth stop for blind holes and tapped holes (see Drilling, Tapping and Fasteners).
The bandsaw
A bandsaw cuts a curve or a straight line with a thin continuous blade. The blade length is set by the wheel spacing and diameter, the speed by the wheel speed, and the tooth pitch by the thickness of the work (at least three teeth in the cut).
Worked example: blade length and speed
- Two equal wheels of 300 mm diameter at a center distance of 400 mm need a blade of L = 2C + πD = 2 × 400 + π × 300 = 1 742 mm.
- For a blade speed of 45 m/min (mild steel; wood runs at hundreds) the wheel turns at 45 000 ÷ (π × 300) = 48 rpm.
- A 10 TPI blade has a pitch of 2.54 mm: it cuts material of 7.6 mm and thicker with three teeth in the cut; thinner stock needs a finer blade.
- Curves: the minimum radius depends on the blade width: narrow blades cut tight curves, wide blades cut straight.
Grinders and sanders
A grinding wheel is a tool that can burst. Every wheel has a maximum safe surface speed printed on it (about 35 m/s for a common vitrified wheel); the speed of the grinder must not exceed it.
Worked example: wheel speed
- A 200 mm wheel on a 3 000 rpm grinder has a rim speed of π × 0.20 × 3 000 ÷ 60 = 31.4 m/s, under the 35 m/s limit.
- On a 3 450 rpm grinder the same wheel runs at 36.1 m/s: above the limit. The centrifugal stress goes as speed squared: 10 % over speed is 1.21 times the stress.
- The highest safe speed for a 200 mm wheel at 35 m/s is 3 342 rpm; the same wheel worn down to 150 mm has a rim speed of only 23.6 m/s at 3 000 rpm, so grinding gets slower as it wears (move to a new wheel).
- Ring test: tap a wheel with a wooden spoon: it should ring. A dull thud means a crack. Never use a cracked wheel.
- Wear a face shield, stand to the side when starting, set the tool rest within 2 mm of the wheel, and never grind on the side of a straight wheel.
| Sandpaper grit | Use |
|---|---|
| P60 | removing stock, paint |
| P120 | general smoothing |
| P220 | before finishing |
| P400 | between coats |
- Belt, disc and orbital sanders: let the abrasive do the work; clear the dust; step through the grits without skipping more than one.
- Dust: sanding makes the finest dust; use a collector and a mask (see Power, Lighting and Compressed Air).
Other saws: mitre, table, jigsaw
| Saw | Best at | Notes |
|---|---|---|
| Mitre saw | Cross-cutting and angles in boards and trim | Needs outfeed support; keep hands out of the blade path |
| Table saw | Ripping and sheet goods | The most dangerous common machine: use a riving knife, a push stick and a guard; never rip freehand |
| Circular saw | Cutting sheet and long boards on site | Clamp a guide; support the offcut; set the depth about 5 mm beyond the work |
| Jigsaw | Curves and cut-outs | Rough edges; use the right blade for the material |
| Bandsaw | Curves, resawing and metal | Versatile and safer than a table saw |
| Reciprocating saw | Demolition | Rough; not for fine work |
Which machine first?
Worked example: cost per hour of a machine
A bench drill press at $250 used for 100 hours a year over 5 years costs $250 ÷ (100 × 5) = $0.50 per hour of use. A machine that you use ten hours a year costs ten times that per hour: buy the machine when the job demands it, and use a makerspace for the rare ones.
| Priority | Machine | Why |
|---|---|---|
| 1 | Cordless drill and driver | Holes and screws; the most-used tool |
| 2 | Drill press | Square, accurate, safe holes |
| 3 | Bandsaw or mitre saw | Straight and curved cuts without effort |
| 4 | Bench grinder and sander | Sharpening and shaping |
| 5 | Table saw, router, lathe, mill | Add when jobs demand; consider the space and the dust |
Running machines well
- Read the manual and learn each machine’s stop before you start.
- Use the guard and the right blade, and keep it sharp; a dull blade needs more force and burns.
- No gloves, loose sleeves, jewelry or long hair near rotating tools.
- Let the machine reach full speed before cutting and let it stop before you clear the table.
- Unplug before changing blades, bits or wheels.
- Eye, ear and dust protection, every time (see Workshop Safety).
Troubleshooting
| Problem | Likely cause | Try |
|---|---|---|
| Drill bit smokes or turns blue | Speed too high, no fluid, blunt | Lower the speed (see the chart); cutting fluid; sharpen or replace |
| Hole is oversize or rough | Bad point grind, bent bit, work moving | Sharpen; check runout; clamp the work |
| Bandsaw blade wanders | Dull, too much feed, guides out of adjustment | New blade; lighter feed; set the guides |
| Machine trips the breaker | Start-up surge or overload | See Power, Lighting and Compressed Air |
| Burn marks on wood | Dull blade, slow feed | Sharpen; feed faster; clean resin from the blade |
| Grinder vibrates | Out-of-balance wheel, worn bearings | Dress the wheel; replace it; check the bearings |
Related
- Shop Tools: the overview of this guide.
- Workholding, Clamping and Fixtures: clamping the work for the machine.
- Organizing, Buying and Budgeting: what to buy and in what order.
- Speeds and Feeds, CNC Machining and Workshop Safety.
FAQ
What speed should I run my drill press at?
Divide 1 000 times the cutting speed (25 m/min for steel, 60 for aluminum, 80 for wood) by π times the drill diameter in mm; big drills turn slowly.
Cordless or corded?
Cordless for convenience and light jobs, corded for long, heavy jobs. Keep to one battery platform.
Which machine should I buy first?
A cordless drill and driver, then a drill press, then a bandsaw or mitre saw.
Is a bench grinder dangerous?
It can be: use the correct wheel for its speed, check it for cracks, keep the tool rest close and wear a face shield.
References
- Oberg et al., Machinery’s Handbook (cutting speeds, drill speeds, grinding wheel safety).
- ANSI B7.1 and EN 12413 (safety requirements for grinding wheels).
- Battery University, Lithium-ion battery pages (energy and discharge).
- Tool makers’ manuals for each machine.
Last reviewed: October 2026. Speeds, powers and prices are typical: follow your machine’s manual.