Short answer: order a 24 x 20 x 8 in (610 x 508 x 203 mm) sealed steel enclosure with a subpanel and 30-40% spare backplate space. It houses a typical four-axis stepper setup for less than the cost of buying the wrong box twice. The PC tower you were going to convert is the problem: drive bays, expansion slots and a power-supply cutout fight you, and no gasket seats anywhere on that folded sheet metal. Size the box from your DIN rail count and your watts, pick the cheapest rating the room needs, and seal it shut. The worked numbers below: 18 module slots filled of 28 mounted, a 60 W heat load, a 10 °C rise over shop temperature.
Why the PC tower and the wooden cabinet fail
A tower case gives you a sheet-metal maze. Drive bays, expansion slots, an IEC inlet and a power-supply cutout each leak air. The folds leave no flat plane for a gasket. You plug holes for a weekend and the box still breathes dust for years. A wooden cabinet is worse at the seams. Dust packs into the corners, and the timber holds moisture against your boards. It also brings the safety questions set out in the wooden electronics enclosure safety article. A steel box with a gasketed door and a removable subpanel hands you one sealed plane and a free hand at layout: mount rail where the wiring wants it, and move it when the build grows.
The cheapest rating that fits the shop
NEMA Type 12 is built for indoor use against falling dirt and drips of non-corrosive liquids. These boxes come without knockouts, so every entry you drill gets sealed on purpose. That covers a garage or basement shop where dust falls and nobody sprays the panel. Type 1 is cheaper and guards against touch, but it does nothing about dust, so skip it for any shop that makes chips or sawdust. Type 13 adds oil and coolant spray for a machining cell that mists. Type 4 takes hose-directed water; Type 4X adds corrosion resistance in 304 or 316L stainless. Type 3R keeps rain, sleet and snow off an outdoor wall, and an unheated shed wants the anti-condensation heater math on top.
Ratings are manufacturer ratings for the specified design, not UL listed; NEMA itself tests and certifies nothing. If your drawing set arrives in IP terms, IEC 60529's first digit 6 means dust-tight and 5 means dust-protected. In a US shop, NEC 110.28 makes the enclosure Type number the rating that counts.
| The shop | Order this rating | What it buys |
|---|---|---|
| Dry basement or garage, sawdust now and then | Type 12, painted steel | falling dirt and drips sealed out, lowest cost |
| Wood or plasma dust all day | Type 12, painted steel, sealed | fine dust stays off the boards |
| Coolant mist or oil spray | Type 13, painted steel | protection against oil and coolant spray |
| Hose-down or washdown nearby | Type 4 / 4X, 304 stainless | hose-directed water; 4X for the chemicals |
| Outdoor wall, rain, unheated shed | Type 3R or 4X plus anti-condensation heater | rain and sleet; the heater kills night-time condensation |
For a panel living beside a wet or dusty machine, the control cabinet inside a dusty machining cell article sets the sealing order of battle.
Size the box from the backplate
Count modules before you shop. The example four-axis build stacks up on the rail like this:
| Part | Width on rail |
|---|---|
| Switching supply, 48 V DC | 180 mm |
| Four stepper drives | 4 × 90 mm = 360 mm |
| Breakout board | 45 mm |
| Two relays | 2 × 45 mm = 90 mm |
| Terminal blocks, 22 at 6 mm | 132 mm |
| Total | 807 mm = 18 module widths of 45 mm |
The widths are example values; take yours off the datasheets and redo the sum. In this box the subpanel runs about 18 in wide by 22 in high. Two inches of wiring duct at each end leaves 14 in (356 mm) per row, which is 7 module slots once you leave margin at the rail ends. Four rows on a 3 in pitch take 12 in of height and mount 28 slots. That gives 18 filled, 10 free, 36% spare — inside the 30-40% band that absorbs the second supply and the terminals every build grows into.
Depth passes too: the 8 in depth minus 0.25 in panel standoff, 3 in supply depth (read yours), 2 in of duct and wire front, and 0.75 in of door and gasket leaves about 2 in of air. The electrical enclosure sizing guide carries the full method, the minimum depth for DIN rail devices article works this sum for shallower boxes, and the CNC control enclosure size article applies it to a mill retrofit.
The heat check against the walls
Add losses, never nameplate watts. The example supply delivers 300 W at an assumed 88% efficiency, so it wastes 300 × 0.12 ÷ 0.88 = 41 W. Four drives at an assumed 3 W each add 12 W, and boards, relays and coils add about 5 W. Design the box around the resulting 60 W.
Walls at natural convection then set the temperature. Painted steel transfers k = 5.5 W/m²K (the site's reference value for painted steel), and this box presents 2 × (0.610 × 0.508) + 2 × (0.610 × 0.203) + 2 × (0.508 × 0.203) = 1.07 m² of wall. Rise over ambient: 60 ÷ (5.5 × 1.07) = 10 °C. At a 25 °C shop the interior sits near 35 °C, under the 40 °C ambient that drives and most electronics take unless a named datasheet allows more. At a 30 °C shop you touch the 40 °C line, so upsize or move air.
The next size up, 24 x 24 in on the wall, carries 1.24 m² of wall and cuts the rise to about 9 °C. Stainless sheds less than painted steel: at 3.7 W/m²K the same load gives about a 15 °C rise, worth knowing before you choose 4X. The control enclosure heat load article walks the loss count for bigger panels.
Cooling without feeding it dust
When the numbers above leave margin, seal the box and let the walls work; an internal fan only stirs heat toward the walls, and the walls still carry it out. When a hot shop leaves no margin, a filter fan trades the wall for an air exchanger. At 100 cfm (170 m³/h) the through-flow carries about 57 W per °C (0.047 m³/s of air at 1.2 kg/m³ and 1,000 J/kg·K ≈ 57 W/K), so the full heat load lifts the through-air roughly 1 °C.
The bill arrives in sealing and in dust: the filter, not the box, sets what the assembly keeps out, and in a wood shop the pads load within weeks. So decide by dust before heat. A dusty shop upsizes the box (the 9 °C wall above); a clean shop that runs hot all day fits the filter fan on the intake and services it on a schedule. The seal-or-filter article for a dusty shop floor settles that choice, and the cabinet fan intake filter article keeps the fan from choking on its own filter.
Entries, duct and sealing
Bring every cable in through the bottom wall. A Type 12 box arrives without knockouts, so drill each hole to the gland size, deburr it, and fit a gland matched to that cable's outside diameter. A matched gland seals the entry, and an oversized or taped one unseals the box. Group mains, motor and sensor entries in their own zones so the ducts stay apart. Fill wiring duct to half its interior cross-section — NFPA 79 section 13.5.2 is the citation behind the 50% fill figure, and the air gaps between round cables eat most of the rest anyway. Inside, the DIN rail and backplate layout guide sets the duct-and-rail geometry, and the CNC control box layout article sorts supply heat, e-stop placement and routing.
What to put on the order
| Line | Order | Why |
|---|---|---|
| Enclosure | 24 x 20 x 8 in (H x W x D) sealed steel box, powder-coated carbon steel (RAL 7035), Type 12, hinged gasketed door | indoor dust, 10 °C rise at 60 W |
| Subpanel | plate sized to the box, removable | four rail rows, 36% spare |
| Cutouts | bottom-wall pattern, one gland cutout per cable, mains on its own | every entry sealed to the rating |
| Cooling | none at this heat load; a filter fan only if the shop tops 30 °C | the heat check above |
| Delivery | delivered in 10 business days from drawing approval | built from one piece, minimum quantity one |
The decision, shop by shop: a dry garage or basement takes the sealed Type 12 painted-steel box at 24 x 20 in on the wall and nothing more. A coolant-mist cell steps to Type 13. Washdown and outdoor walls step to Type 4X stainless, and you either accept its 15 °C rise at 60 W or add through-flow with a filter fan. For a freestanding retrofit cabinet, the CNC retrofit cabinet checklist covers the rest. Compare sizes and grades in the enclosure selector, spec the box line by line in the custom enclosure builder, and filter every grade by outside size in the stainless size finder.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 30 × 24 × 10 in | 304 stainless | 30 x 24 x 10 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
How big should a budget CNC electronics enclosure be?
Work from the backplate, not the outer size. A 24 x 20 x 8 in box takes a subpanel about 18 x 22 in, four DIN rail rows of roughly 7 modules each, and a four-axis build fills about 18 of those 28 slots. That leaves 36% spare, inside the 30-40% band that absorbs the second supply and the terminals you add later.
Is a NEMA 12 enclosure enough for a garage CNC?
Yes, when the machine lives indoors and the water threat is drips rather than a hose. Type 12 is built for falling dirt and dripping non-corrosive liquids, and a sealed painted-steel box shedding 60 W sits about 10 °C over shop temperature: near 35 °C at a 25 °C shop, under the 40 °C ambient most drives take.
Can I add a fan and still keep the dust out?
Only with a filter fan, and then the filter sets the sealing, not the box. At 100 cfm a filter fan cuts a 60 W load from a 10 °C wall rise to about 1 °C, but in a wood shop the pads load within weeks. The cheaper answer in a dusty shop is the next size up: a 24 x 24 in wall drops the rise to about 9 °C with nothing to service.
How much heat does a four-axis stepper setup really add?
Count losses, not ratings: a supply delivering 300 W at an assumed 88% efficiency wastes 41 W, four drives at an assumed 3 W each add 12 W, and boards and relays about 5 W, so you design around 60 W. Drive dissipation is the figure to read from its datasheet; it moves with current and holding torque more than with supply size.
