Short answer: before anyone touches the door, measure three things on the new monitor, its active image, its connector depth and its rear bolt pattern, and set them against the flat, the depth and the operator space you have. Give any new opening 0.5 in [13 mm] of door flat on every side, and leave 2 in [50 mm] behind the connectors or one full cable bend radius, whichever is larger. If the old door has that room, enlarge the opening; if it does not, a factory-cut replacement panel or a new custom enclosure, delivered in 10 business days from your approval of the drawing, keeps a seal a field patch will not. A 15.6 to 17.3 in swap, the common "about an inch bigger" upgrade, needs a 15.3 x 8.7 in opening and 6.5 in [165 mm] of clear depth; the arithmetic follows.
What the new monitor actually measures
Start with the active image, the lit rectangle, and treat the rest as trim. For a 16:9 panel the width runs 0.872 times the diagonal and the height 0.490 times it, so a ruler across the glass plus the class size lands within 0.1 in [3 mm] before any datasheet loads. The bezel adds roughly 0.5 to 0.75 in [13 to 19 mm] per side, and the maker's panel-cutout drawing beats every estimate when one exists.
| Panel class | Active image, in | Opening at +0.2 in fit, in | Minimum door flat, in |
|---|---|---|---|
| 15.6 | 13.6 x 7.6 | 13.8 x 7.8 | 14.8 x 8.8 |
| 17.3 | 15.1 x 8.5 | 15.3 x 8.7 | 16.3 x 9.7 |
| 18.5 | 16.1 x 9.1 | 16.3 x 9.3 | 17.3 x 10.3 |
| 21.5 | 18.7 x 10.5 | 18.9 x 10.7 | 19.9 x 11.7 |
| 24 | 20.9 x 11.8 | 21.1 x 12.0 | 22.1 x 13.0 |
Behind the glass, the VESA mount standard puts the four holes on a 100 mm [3.9 in] grid, 100 x 100 mm on panels this size, and holds each hole within ±0.5 mm of nominal. That tolerance leaves a drilled door no slack, so mark from the drawing rather than from the old panel's holes.
One thing the bigger glass will not buy you is workspace. At 1920 x 1080 a 17.3 in panel shows exactly the pixels a 15.6 in one does, so the CNC software gains nothing until the resolution itself rises. Set 1920 x 1080 in the operating system after the swap and confirm the screen reports it.
The three clearances that decide the fit
Flat around the opening. Keep 0.5 in [13 mm] of door flat between the opening and any bend, weld seam or neighbouring hole, so the gasket bears on undisturbed metal. On factory Type 4X panel doors, openings wider than about 24 in [610 mm] are built into a flanged frame rather than a plain cutout, because a gasket line that long needs a frame to hold even compression.
Depth behind the door. Leave 2 in [50 mm] behind any door-mounted connector as the floor, and more for video. Most HDMI and DisplayPort cables specify a minimum bend radius near 10 x the jacket OD, so a 0.3 in [8 mm] cable turns in about 3 in [80 mm]. Add the plug body, about 1.5 in [38 mm] with its boot, and the panel itself. If depth is the thing that fails, how shallow an HMI enclosure can be walks the same arithmetic from the other end.
Operator space. Buy screen without selling the controls. Keep the E-stop clear, keep the door swinging its full travel, and remember NEC 110.26(A) wants clear working space with doors opening at least 90 degrees where the panel is serviced energized. A compact keyboard with a trackball wants about 12 x 6 in [305 x 152 mm] of flat, and it is usually the first thing a bigger screen eats.
The swap in numbers
Run the common upgrade, one class up from 15.6 in to 17.3 in, through the three checks:
- Active image: 0.872 x 17.3 = 15.1 in wide and 0.490 x 17.3 = 8.5 in high, against 13.6 x 7.6 for the old panel. You are asking the door for 1.5 in more width and 0.9 in more height.
- Opening: active image plus 0.2 in [5 mm] of fit margin = 15.3 x 8.7 in [389 x 221 mm].
- Door flat minimum: opening plus 0.5 in [13 mm] per side = 16.3 x 9.7 in. That pair is your go or no-go number: at or above it, re-cut the door; below it, replace the door or the whole box.
- Depth: 2.0 in panel body + 1.5 in HDMI plug and boot + 3.0 in bend radius (10 x a 0.3 in jacket) = 6.5 in [165 mm]. An 8 in [203 mm] deep body leaves 1.5 in of wiring room to the backplate.
- Keyboard: an 18 x 12 in flat minus a 15.3 x 8.7 in opening leaves about 1.3 in on each side and 1.6 in below. Plan a drawer or an arm for the keyboard from the start.
Step by step
- Write the monitor's numbers down: active image, bezel, panel-cutout drawing if one exists, connector positions and depths, VESA pattern. A ruler on the glass beats a size class.
- Compute the opening and the minimum flat with the two rules above, +0.2 in [5 mm] of fit margin and +0.5 in [13 mm] per side.
- Compute the depth budget: panel body + plug + one bend radius, set against the clear door-to-backplate distance.
- Mock up the operator side full size. Tape a paper template of the screen rectangle, keyboard, E-stop and latch to the door, then open and shut the door with it in place.
- Choose the path. Enlarge in place when the new opening fully contains the old one, and cutting a hole in a stainless enclosure covers the field method. Order custom stainless replacement panels when the door flat runs out, and a new enclosure when depth or operator space fails too; the guide to cutouts, glands and HMI windows holds the window and gasket fundamentals.
- Order the cutting with the metal. The cutout designer lays the display opening and gland holes on any face and exports the layout; the enclosure builder sizes a new body in 3D with the opening already in the door. Custom work is delivered in 10 business days, counted from your approval of the drawing.
- Swap the wiring dead. Lock out the machine supply and verify absence of voltage before opening the old monitor's connectors, and label each cable as it comes off.
- Mount and route. Seat the panel on its gasket, tighten the fasteners in a cross pattern, and clamp the video cable about one bend radius behind the plug so the connector carries no load.
- Power up and confirm 1920 x 1080. Check the screen reports the resolution, run the CNC screens, jog display, program graphics and soft keys, then close the door on the result.
Checks once the new monitor is in
- The door closes without force and the gasket shows an even compression line all round, with no gap at the corners of the new opening.
- Swing the door through its full travel, at least the 90 degrees of the working-space rule, and watch the video cable for pinch or tension at both ends of the swing.
- Every opening you are not using carries a rated blank, because one open hole sets the whole assembly to that part's rating. For the small leftovers, old pilot devices and retired connectors, rated blank covers for unused panel cutouts list the sealing sizes.
- After the first washdown, open the door and look for water tracks at the edge of the new gasket before you call it done.
Mistakes that cost the rating
Cutting to the bezel instead of the panel-cutout drawing is the classic one: the opening ends up proud of the screen and the gasket has nothing left to bear on. The second is the "cooling" hole, a vent or drain added to a sealed door drops the assembly to that part's rating, so if heat drove you there, a bigger box or a heat exchanger is the honest fix. Leaving the old opening unblanked when the display moves to an arm costs the same way. And a keyboard screwed over the stop controls trades a convenience for an injury path. What rating a panel keeps after you cut it and mount devices traces each of these to the part that fails. Our enclosures are rated NEMA 4X / IP66 by the manufacturer and are not UL listed, and they hold that rating exactly as long as every part on them carries an equal one.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 17.3" HMI enclosure | 304 stainless | 12.56 x 19.13 x 4.02 in | IP65-type front seal with the display installed, manufacturer rated; not UL listed |
| 15.6" HMI enclosure | 304 stainless | 11.69 x 17.64 x 4.13 in | IP65-type front seal with the display installed, manufacturer rated; not UL listed |
| 8" HMI enclosure | 304 stainless | 8.39 x 9.98 x 3.92 in | IP65-type front seal with the display installed, manufacturer rated; 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
Can I enlarge the old cutout instead of replacing the door?
Yes, when the new opening fully contains the old one and the door still has 0.5 in [13 mm] of flat beyond it on all sides. Cut with a hole saw and file, deburr, refinish, and seat a fresh gasket. When the old opening crosses the edge of the new one, order a replacement panel instead: a patched stainless face rarely seals as evenly as a clean one.
How much depth does the larger monitor add behind the door?
Budget the panel body plus one plug plus one bend radius. In the 15.6 to 17.3 in example that is 2.0 + 1.5 + 3.0 = 6.5 in [165 mm], so an 8 in [203 mm] deep body leaves 1.5 in of wiring room to the backplate. A video cable bent tighter than about 10 x its jacket OD will fail at the connector first.
Does a bigger 1920 x 1080 screen show more of the CNC software?
No. The workspace follows the pixel count, not the diagonal, so a 17.3 in panel at 1920 x 1080 shows exactly what a 15.6 in one does, with pixels about 0.20 mm across instead of 0.18 mm. After the swap, set 1920 x 1080 in the operating system and confirm the screen reports it before you trust the layout.
Will the keyboard still fit on the door?
Count the flat left over. A compact industrial keyboard with a trackball needs about 12 x 6 in [305 x 152 mm], and a 15.3 x 8.7 in opening in an 18 x 12 in flat leaves strips of about 1.3 in on the sides and 1.6 in below, which is no room at all. Move that keyboard to a slide-out drawer or a swing arm.
