5.2.1 Front panels

A front panel is the plate on the front of a module, or a blank panel that fills unused width in a row. It screws to the rails through a rail insert.

A front panel shall be no more than 2.0 mm thick (PANEL-004). EIS recommends 5052 aluminum or FR-4 circuit board, 1.6 mm to 2.0 mm thick. FR-4 is less stiff, so an FR-4 panel needs extra mounting holes at a narrower width than aluminum (Extra mounting holes).

A front panel thinner than 1.6 mm shall ship with M3 mounting screws with a head at most 7.0 mm across, whose length fits the window of 5.3 for its own thickness on a rail of the section 5.3 recommends (PANEL-014). The enclosure's screws are sized for panels of 1.6 mm to 2.0 mm and can bottom out through a thinner one.

A patch jack shall be a 3.5 mm mono (TS) socket (PANEL-005). 7.1 recommends insulating jacks from the panel; the panel and 0 V says how.

A blank panel plays the panel role of 4.1 and meets the same height, width, thickness, and hole requirements as a module's panel.

The panel and 0 V

A panel makes two choices, and they are independent. A module shall publish both: whether its front panel is connected to its 0 V, and whether the panel is bonded to the rails (PANEL-015).

Bonded to the rails (bare metal under the screw heads, 6.3) Floating from the rails (coated or masked up to the holes)
Insulated from 0 V (no jack sleeve, pot body, or switch frame reaches the panel) The panel is chassis: it shields and drains static, and carries no signal. What EIS recommends for a metal panel. The panel is inert. Fine; the usual result of an anodized panel or an FR4 panel masked everywhere.
Connected to 0 V (the panel bonded to the module's 0 V at a jack bushing or a screw, through bare metal, GND-004) A 0 V to chassis tie at this module. With the system's tie at its power entry this is a second tie, and EIS recommends against it; only the product at the tie does this. The Eurorack convention. The panel sits at the module's 0 V, and two panels butted edge to edge join two modules' 0 V through their bare cut edges; one butted against a chassis panel is a second chassis tie. Tolerable; the loops it makes are why EIS recommends insulating.

EIS recommends the first row: a panel insulated from 0 V, bonded to the rails if it is metal and the maker wants a shield, floating otherwise. Insulated means that nothing at 0 V touches the panel: not a jack's sleeve, a pot's bushing, a switch's frame, or an encoder's body.

Insulated jacks on an FR4 panel

The usual 3.5 mm jack has a metal threaded bushing, about 6 mm across, a hex nut of 8 mm across the flats (9.2 mm across the corners) and a washer of about 9.5 mm. On an FR4 panel the board itself is the insulator, and the jack is insulated by keeping the panel's copper away from everything the jack touches:

The jack's sleeve is then at the module's 0 V on the board behind the panel and nowhere else, and the panel's copper is free to be bonded to the rails through finished lands at the mounting holes, or left floating.

EIS · An insulated jack on an FR4 panel: the copper keeps away from everything the jack touches hole Ø6.2, unplated copper keep-out Ø12, every layer nut 8 across flats, 9.2 across corners 1.6 solder mask: cosmetic only copper plane, both faces jack body behind the panel: plastic on the usual jacks bushing, washer, and nut at 0 V: they meet no copper The board is the insulator. Nothing the jack touches, the hole's bore, the washer, the nut, the body, meets copper, so the sleeve stays at the module's 0 V on the board behind and the panel's copper is free to be chassis or to float (PANEL-015, 6.3). Mask is allowed over the copper; a nut turned to torque cuts through it, so it is not the insulation. The same keep-out serves a pot or switch with a metal bushing.

Insulated jacks on a metal panel

A metal bushing through a bare metal panel is a connection, and through an anodized one it may or may not be: anodize in a hole's bore is thin, and a bushing turned into it cuts through or does not. To insulate a jack on a metal panel, use a jack whose bushing is plastic, or an insulating shoulder washer in an oversized hole with a flat insulating washer under the nut. Pots, switches, and encoders with metal bushings take the same treatment. Otherwise the panel is published as connected to 0 V, and EIS recommends that the connection be made a bond, bare metal under at least one bushing's nut or washer, rather than whatever a bushing scratches through anodize.

Height

Format Panel height Hole span Holes from panel center Provenance
1U 39.65 mm 33.65 mm ±16.825 mm inherited: Intellijel 1U
3U 128.5 mm 122.5 mm ±61.25 mm inherited: Doepfer A-100

A 3U front panel shall be 128.5 mm high (PANEL-006): 4.85 mm under three rack units (133.35 mm), so it fits within the 132.55 ± 0.4 mm 3U height H1 of 5.1. The 4.85 mm is clearance, not a rail lip; where a rail has a lip, EIS recommends at most 1.5 mm (5.3).

A 1U front panel shall be 39.65 mm high (PANEL-007), the Intellijel 1U format, 4.80 mm under one rack unit. EIS defines no other panel height.

Mounting holes shall be 3.0 mm in from the top and bottom panel edges (PANEL-008). A panel that is to be chassis is bonded to the rails only by what is under its screw heads (6.3): EIS recommends a bare 7 mm disc at each hole on a coated panel, or a finished copper land on an FR4 one. The hole span is then the panel height less 6.0 mm, and it shall be 122.5 mm at 3U and 33.65 mm at 1U, the same on the panel and between the inserts of a row's two rails (PANEL-009).

EIS · The 3U and 1U vertical budget, at one scale 3U = 133.35 panel 128.5 holes 122.5 board ≤ 110 3U 1U = 44.45 panel 39.65 holes 33.65 board ≤ 21.15 1U Millimeters, on 8 HP panels. Panel heights PANEL-006 (3U) and PANEL-007 (1U); holes 3.0 mm in from each edge (PANEL-008), span PANEL-009. Grey: the most a rail may cover, 9.25 mm at each edge; blue: the board, at least 9.25 mm clear of each edge (PANEL-012).

Width

The nominal width of an N HP panel is N × 5.08 mm, where N is any positive whole number. An N HP panel shall be no wider than its nominal width (PANEL-002). EIS recommends making it 0.3 mm narrower, so that neighboring panels do not bind:

panel width = N × 5.08 − 0.3 mm

The board behind the panel is 0.6 mm under the nominal width (5.2.2). A rail gives at least the nominal width of its row (RAIL-002), so a row of panels at either width fits it.

EIS · Panel and board widths on the HP grid HP grid, 5.08 mm 4 HP 20.02 mm 20.32 nominal 8 HP 40.34 mm 40.64 nominal 3 HP 14.94 mm 15.24 nominal the joint, enlarged nominal edge panel board 0.3 mm 0.6 mm An N HP panel is no wider than N × 5.08 mm (PANEL-002). EIS recommends a panel N × 5.08 − 0.3 mm wide, so that neighbors do not bind, and a board N × 5.08 − 0.6 mm wide. Each panel is centered between its nominal edges, so the clearance splits evenly between neighbors. The joint is drawn about 27 times larger than the row.

HP Nominal (mm) Panel (mm) Board (mm)
1 5.08 4.78 4.48
2 10.16 9.86 9.56
3 15.24 14.94 14.64
4 20.32 20.02 19.72
6 30.48 30.18 29.88
8 40.64 40.34 40.04
10 50.80 50.50 50.20
12 60.96 60.66 60.36
14 71.12 70.82 70.52
16 81.28 80.98 80.68
18 91.44 91.14 90.84
20 101.60 101.30 101.00
24 121.92 121.62 121.32
28 142.24 141.94 141.64
32 162.56 162.26 161.96
36 182.88 182.58 182.28
42 213.36 213.06 212.76
84 426.72 426.42 426.12
104 528.32 528.02 527.72

Mounting holes

Mounting holes shall be drilled Ø3.2 mm, or slotted 3.2 mm wide and no longer than 5.5 mm along the rail, centered on the hole position (PANEL-010). Either clears the M3 mounting screw; a short slot takes up a rail's position error without letting the panel drop.

Along the rail, each mounting hole shall be a whole number of HP plus 2.54 mm from the panel's nominal left edge (PANEL-011). The nominal edges are N × 5.08 mm apart and centered on the panel, so every hole meets a hole in the rail insert, whatever the panel's width and wherever it sits in the row. The top and bottom rows of holes are the same.

Measured from the panel center:

EIS · Mounting holes from 1 to 8 HP, over one rail insert 1 HP 0 2 HP ±2.54 3 HP 0 4 HP ±2.54 6 HP ±7.62 8 HP ±12.7 rail insert: a hole every 5.08 mm, 2.54 mm in from each HP boundary Each hole is a whole number of HP plus 2.54 mm from the panel's nominal left edge (PANEL-011), so it meets an insert hole wherever the panel sits in the row. Holes are Ø3.2 mm or slotted (PANEL-010), 3.0 mm in from the top and bottom edges (PANEL-008). Under each width: the hole positions from the panel's center, in millimeters. From 3 HP up, the outer holes are 7.62 mm in from the nominal edges.

The two cards below show an 8 HP panel.

EIS · 3U front panel, 8 HP ±12.70 mm ±61.25 mm 0 40.34 × 128.50 mm (PANEL-006). Holes Ø3.20 mm (PANEL-010), dimensioned from the panel center; the other three mirror the one dimensioned.

EIS · 1U front panel, 8 HP ±12.70 mm ±16.825 mm 0 40.34 × 39.65 mm (PANEL-007). Holes Ø3.20 mm (PANEL-010), dimensioned from the panel center; the other three mirror the one dimensioned.

Extra mounting holes

EIS sets no hole count; four holes are the usual pattern. A wide panel needs more so that a 10 N push at midspan, about the force of seating a plug, bows it no more than 0.5 mm between screws. On four screws a 3U panel reaches 41 HP in 1.6 mm 5052 and 26 HP in 1.6 mm FR-4, the most flexible recommended sheet; past that, a hole is added on each rail, a middle hole first, until every gap is inside the span. On an even-HP panel the middle hole sits 2.54 mm to one side of the center, on the hole grid.

EIS · Screws a 3U panel needs as it gets wider, per sheet 0 20 40 60 80 100 4 6 8 10 12 14 panel width, HP screws 5052, 2.0 mm 5052, 1.6 mm FR-4, 2.0 mm FR-4, 1.6 mm Extra mounting holes (5.2.1): each gap short enough that a 10 N push at midspan bows the panel no more than 0.5 mm; each step is the first whole HP that needs more screws.

The numbers are in data/module.json. tools/module.py derives the hole spans and widths and computes the extra-hole patterns; tools/cards_system.py draws the span card.