Short answer: punch a shallow divot, drill a 1/8 in [3.2 mm] pilot hole, then open the hole with the step bit — on a drill press, with the box clamped to a backing board. The pilot, not the divot, holds the position. A step bit starts cutting at the edge of its first step, with no point to seat in a punch mark, so it walks until a tooth bites off center. A twist bit has a point that stays put. With a press, a pilot and a clamp, centers land within about 0.02 in [0.5 mm] of the mark. A hand drill alone wanders 0.06 in [1.5 mm], which is why a row of buttons comes out looking crooked. The whole sequence takes about ten minutes for a three-hole lid.
Why the divot alone lets a step bit wander
A punch mark is about 0.02 in [0.5 mm] across, and the first step of a step bit is several times wider. The bit touches down on the corner of a step, feels nothing pulling it back toward the mark, and cuts wherever it first grabs. A twist bit behaves differently: its point sits inside the divot and self-centers as it starts to cut.
Match the pilot to the bit's web, the solid center at the tip, measured with calipers. Most mid-size step bits have a web near 1/8 in [3.2 mm]; small ones run closer to 1/16 in [1.6 mm]. Walls on hobby boxes run 0.06-0.12 in [1.5-3 mm] thick; they flex under hand pressure and add wander of their own. Press each divot in with a spring punch on its light setting, because a hammer blow on ABS or acrylic can crack the face.
What you need
- An automatic center punch on its light setting
- A 1/8 in [3.2 mm] twist bit for pilots, or whatever size matches your step bit's web
- A step bit whose steps cover the final sizes; common ranges run 1/8-1/2 in [3.2-12.7 mm]
- A drill press or bench drill; a hand drill serves for one or two holes
- A sacrificial backing board, such as scrap plywood or MDF
- A clamp, masking tape, and calipers or a rule
- A deburring tool or a countersink turned by hand for the exit ring
Lay out the centers on paper first
Draw the lid in any drawing program with a center mark on every hole, print the sheet at 1:1, and tape it to the panel. Punch each center through the paper. Put a 100 mm [4 in] scale bar on the drawing and measure it after printing. Home printers scale by 1-3 percent; at 3 percent, the last hole on a 6 in [152 mm] lid lands 0.18 in [4.6 mm] off its mark.
Hold each center at least one finished diameter from an edge or bend; that is 0.886 in for the 22.5 mm pushbutton. Make it two diameters on brittle sheet such as acrylic. Keep adjacent centers at least half the sum of the two finished diameters apart, which is (22.5 + 16) / 2 = 19.25 mm [0.76 in] for a button beside an indicator. For rows of indicators, the pilot light spacing article covers pitch and alignment in detail.
Worked example: three devices on a 6 in lid
A 6 in [152 mm] lid carries a 22.5 mm pushbutton, a 16 mm indicator and an M20 gland in a row. Centers sit 1.0 in [25 mm] down from the top edge and 1.5 in [38 mm] apart. The row then spans 3.0 in [76 mm] and leaves 1.5 in [38 mm] to each side. The side margin clears the 0.886 in edge rule. Both center gaps clear the half-sum rule as well: (22.5 + 16) / 2 = 19.25 mm [0.76 in], and (16 + 20) / 2 = 18 mm [0.71 in]. All three holes start from the same pilot bit and finish at 0.886 in, 0.63 in and 0.79 in.
Punch, pilot, then step
- Tape the printed layout to the panel and punch a divot at every center, spring punch on light, so each mark is about 0.02 in [0.5 mm] across.
- Clamp the box flat to the backing board, with the first divot over open board so the bit breaks through into scrap rather than into the far wall.
- Chuck the pilot bit and, with the spindle off, lower it by hand until the tip sits in the divot. Clamp the box down. The lower-and-clamp trick scales to production work; a long-run drill press setup walkthrough covers the fixture side in depth.
- Drill the pilot through at 1,000-1,500 rpm with a light feed, lifting the bit once mid-hole to clear the chips.
- Swap in the step bit and seat its smallest step in the pilot. Run 500-1,000 rpm in ABS or polycarbonate, half that in acrylic, with a steady light feed; back out at each step to clear chips.
- Stop once the step for your size passes through flush, then hand-run the countersink over the exit ring. Wear eye protection; the exit ring leaves as a sharp chip.
- Test-fit the device before moving on: a 22.5 mm pushbutton should pass through its 0.886 in step with light thumb pressure.
No press on the bench yet? The article on drilling plastic without a drill covers hand-tool holes for a one-off panel, and the drilling jig article shows repeatable batch work.
The hole sizes that cover most front panels
| Device | Final hole | Pilot | Note |
|---|---|---|---|
| 22.5 mm pushbutton or selector | 22.5 mm [0.886 in] | 1/8 in [3.2 mm] | The ~30 mm [1.18 in] flange hides a slightly oversize step |
| 16 mm indicator or small switch | 16 mm [0.63 in] | same pilot | Keyed faces need the anti-rotation cut too |
| M20 cable gland | 20.0-20.3 mm [0.79-0.80 in] | same pilot | Exact size follows the gland, not the drill chart |
| M16 cable gland | 16 mm [0.63 in] | same pilot | Same rule as M20, one step smaller |
Three different finals from one pilot size is the point of the method. A keyed indicator also needs the flat in the right position, and the 16 mm switch hole article shows the keyed-punch, washer and ring options. For glands, the M20 gland hole size guide gives the tolerance in plastic versus aluminum; the gland seals on the panel face, so an over-tight hole is as much a fault as a loose one. Displays, connectors and D-sub shells take rectangles rather than rounds: a hand nibbler makes small ones, and the rectangular cutout article walks the layout for bigger openings.
Checks when done
- Measure each center against its mark with calipers. Within 0.02 in [0.5 mm] is press-and-pilot work; a 0.06 in [1.5 mm] miss means the clamp or the tape slipped.
- Push each device home. The 22.5 mm button seats with thumb pressure, and its 30 mm [1.18 in] flange covers the hole edge all the way round.
- Tilt the panel under a light and look for hairline cracks radiating from the hole. A crack grows with vibration, so move the device or scrap the panel.
- Run a finger over the exit ring. It should feel flat, with no raised lip to keep a washer or flange from seating.
- Sight along a row of buttons. Centers within 0.02 in [0.5 mm] of each other read straight at arm's length.
Mistakes that cost the rating
A finished box is only as tight as its weakest opening, so treat every hole as a seal question. An open pilot hole passes a water jet, and IP65 is a jet rating, so the box fails the very test its mark promises. Seal every opening with its device, a gland or a blanking plug. An IP65 mark is the manufacturer's rating; like our boxes, rated NEMA 4X / IP66 by the manufacturer, it is not UL listed.
Keep every hole at least 1/4 in [6 mm] inside the lid's gasket line, because a hole that clips the gasket bead leaks however good the gasket is. If a hole came out in the wrong place, plug it and re-drill beside it; the wrongly drilled hole article covers plugs and plates that hold the seal. The fundamentals of openings, glands and windows are in the site's cutouts and glands guide.
Order the holes cut instead
When the panel is production work, or the enclosure is one of our stainless boxes, order the openings cut at the factory. The cutout designer lays out holes, glands and display openings on any face and checks the spacing. The layout goes with the quote, so the box arrives with every opening already in place, and custom work is delivered in 10 business days from your approval of the drawing. Stainless changes the tooling: speeds, feeds and bit choice all differ from plastic, and the stainless drill-bit speeds and feeds article has those numbers. For bodies that need openings beyond a standard size, the custom stainless cutouts page compares factory openings in a standard body against a new custom body.
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 |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 14 × 8 in | 304 stainless | 16 x 14 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Why does my step bit wander off the punch mark?
A divot is only about 0.02 in [0.5 mm] across, and a step bit starts cutting at the rim of its first step, so it slides until a tooth grabs somewhere it shouldn't. A pilot hole matched to the web, typically 1/8 in [3.2 mm], gives the finishing bit a real seat. The same holds for a hole saw: its center drill is the only thing keeping position, so drill that pilot square and clamped.
Can I hold 0.02 in accuracy with a hand drill?
Usually not. A hand drill lands 0.03-0.06 in [0.8-1.5 mm] off even with a pilot, because the bit tilts with your wrist and thin walls flex under the push. Clamp the box to a backing board and keep the drill square to the face, and treat rows of buttons and display openings as drill press work, where the 0.02 in [0.5 mm] figure holds.
What size pilot hole goes before a step drill bit?
Match the pilot to the web, the solid center at the bit's tip, measured across with calipers. Most mid-size step bits run near 1/8 in [3.2 mm]; small bits closer to 1/16 in [1.6 mm]. A pilot smaller than the web flexes and can snap; one larger than the web leaves the finishing step with nothing to center on.
A hole came out off center — can it be saved?
Often, yes. A standard 22.5 mm pushbutton wears a flange about 30 mm [1.18 in] across, so it hides a hole opened up to 1.0 in [25 mm]; step the hole up one size until the flange covers the rim. For holes further off than that, plug and re-drill beside the original, and keep the plug sealed so the box keeps its rating.
