Can case cutout sealing keep the original IP rating?

Answer: Not automatically. The port carries its own seal, and a flange plus groove has to hold 0.3 bar without seepage before the case counts as restored.

What flange size suits a 20 mm hole?

Answer: 46 mm outside diameter, the bore plus twice an 8 mm ring, with six M4 bolts at 1.2–1.5 N·m, a 3 mm silicone pad and a 4 mm backing plate.

Can the groove be milled into the case wall?

Answer: No. A 2.2 mm groove in a 3.0 mm wall leaves 0.8 mm and the floor cracks at torque; grooves belong on a flange 5 mm or thicker.

Can a potted port be rerouted later?

Answer: Yes, at a price. The bore grows 0.5–1.0 mm and the original flange will not seat again.

Case Cutout Sealing: Case Cutouts and Sealing

Quick answer: Case cutout sealing rests on how wide a sealing ring the wall can offer, not on the bore: a 20 mm hole in a 3 mm wall leaves 3 mm to clamp. A 46 mm flange, six M4 bolts at 1.2–1.5 N·m and a 3 mm pad move the leak path outside.

What a cutout takes off the wall
Flange clamping spreads load over six bolts
How grooves and rings hold the bore
When potting or rubber pads replace a flange
Placement clearances and holding the rating
FAQ

1. What a cutout takes off the wall

A monitoring project drilled a 20 mm cable port through one side wall, fitted a rubber grommet and ran a 30 minute rain test. The case took in 220 mL, and the water came through the bore, not the rim. The wall there measured 3.0 mm, the grommet covered under 3 mm of flat face, and it went solid after 0.4 mm of compression.

A cutout removes three things at once: wall thickness, sealing face width, and flatness around the bore. Lose one and a retrofit part buys time, not a season.

Flatness is the quiet one. A hole 18 mm from a corner sits in the shrink-stress band, where the face bows 0.6 mm; bolted down it crushes on one side and floats 0.2 mm on the other. So the checks run backwards: 4.5 mm of wall, an 8 mm ring of flat face, 25 mm from the corner.

2. Flange clamping spreads load over six bolts

Size the flange outside diameter at the bore plus twice an 8 mm ring: a 20 mm hole takes a 46 mm flange, six M4 stainless bolts at 1.2–1.5 N·m, and a 3 mm silicone pad at 40 Shore A held at 25 %–30 % compression.

Case cutout sealing shells stacked in a workshop, dark grey cases open in columns, blue racking and metal parts behind, a floor fan at left

Bolts need something to push against. Torque 1.5 N·m into a 3.0 mm wall and the panel sinks 0.3 mm, slackening the gasket the torque was meant to load. A 4 mm nylon backing plate, or a flange clamped from both sides, spreads that load over the whole ring.

Pitch follows the circumference. A 46 mm flange measures 145 mm around, so six bolts sit 24 mm apart; four bolts stretch the pitch to 36 mm and let the pad bulge 0.15 mm between fixings, which is where water enters.

Bore	Flange OD	Bolts	Torque	Backing plate
12 mm	38 mm	4 × M3	0.6–0.8 N·m	3 mm
16 mm	42 mm	4 × M4	1.0–1.2 N·m	3 mm
20 mm	46 mm	6 × M4	1.2–1.5 N·m	4 mm
25 mm	52 mm	6 × M4	1.5–1.8 N·m	4 mm
32 mm	60 mm	8 × M5	2.0–2.5 N·m	5 mm

3. How grooves and rings hold the bore

The flange supplies the face; the groove gives the ring a home. Cut it at 1.25 times the cord width and 0.75 times deep and compression lands near 25 %: a 3.0 mm cord in a 3.8 mm groove, 2.2 mm deep, squashes 0.8 mm.

Hold the groove floor to 0.1 mm, because that is compression budget rather than fussiness. A floor bowing 0.2 mm lets the ring under-compress in one arc, dropping from 25 % to 18 %.

Cord	Groove width	Groove depth	Compression	Bore range
2.0 mm	2.5 mm	1.5 mm	25 %	8–12 mm
2.5 mm	3.1 mm	1.9 mm	24 %	12–18 mm
3.0 mm	3.8 mm	2.2 mm	27 %	16–25 mm
3.5 mm	4.4 mm	2.6 mm	26 %	22–32 mm
4.0 mm	5.0 mm	3.0 mm	25 %	28–40 mm

The bore edge needs work too. A step drill leaving a 0.5 mm × 45° chamfer and a wall finished under Ra 1.6 μm closes the path; 6.3 μm tool marks let water walk the helix.

Never mill the groove into a 3.0 mm wall. A 2.2 mm groove plus 0.9 mm of floor leaves 3.1 mm of panel, and that floor cracks before the bolt reaches torque.

4. When potting or rubber pads replace a flange

Where the cable never moves again, potting beats a flange. Two-part polyurethane at 1:1, poured 8 mm deep, cures 24 hours at room temperature to 60 Shore A with 1.5 N/mm of adhesion.

Case cutout sealing facing rain: black case on a muddy forest track, water beading on the lid, mud splashes, an SUV and wet tyres behind

Back the bore with 10 mm of closed-cell foam before pouring, or resin runs inside. The trade is permanence: peeling 1.5 N/mm of resin takes about 20 minutes a hole, and the bore widens 0.5–1.0 mm.

Method	Reopenable	Cost per hole	Bore range	Best for
Flange clamp	Repeatedly	18–35 CNY	8–60 mm	Cables under service
Groove and ring	Yes, spare ring	12–28 CNY	8–40 mm	Small bores, frequent checks
Potting	No	6–15 CNY	5–30 mm	Sealed once, no service
Butyl pad	About three times	8–20 CNY	10–35 mm	Rare maintenance

A butyl pad sits between the two: 3 mm of butyl under a 2 mm plate survives about three reopenings, and returns 92 % of its thickness after 20 cycles from -30 °C to 90 °C.

5. Placement clearances and holding the rating

Placement decides more than the part does. Keep the bore centre 25 mm from a corner, 20 mm from the rim seal line and 30 mm from a latch seat, because all three guard wall thickness that changes.

Panels run 0.8 mm thinner between ribs than at the root, so a bore in the middle sags 0.4 mm under clamp load and the sealing line opens.

Whatever rating the case carried does not survive the drill. After a cutout the local rating belongs to the new sealing line alone, and one failed port sets the number for the whole case.

Space ports apart. Centres closer than 30 mm overlap the clamp rings, and the 10 mm strip between them lifts first. Pressure needs a way out too: a 40 °C swing can push 8 kPa and pin the ring, so add a 2 mm vent.

Conclusion

Case cutout sealing is settled by four checks in order. Measure the wall first: under 4.5 mm, skip grooves and use a flange with a backing plate. Measure placement second: within 25 mm of a corner, move the bore rather than upgrade the part. Ask third whether the cable will ever be reopened, since a yes means a flange. Choose the part last, sizing the flange at bore plus twice an 8 mm ring. The hole is only an opening; the 8 mm ring of clamp face and the bolts loading it keep water out.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.