Part 2 — Mechanical

What makes a module fit a row and a row fit a rack: the HP and the rack unit (5.1), the front panel and the boards behind it (5.2), the rails, inserts, and mounting screws (5.3), and the enclosure (5.4). The requirements here are the Doepfer A-100 conventions restated with the few figures they left open, and the Intellijel 1U format for 1U rows. Part 2 is EIS Core: every module and every enclosure meets it.

Contents

• 5.1 Rack dimensions: The 19-inch frame a row sits in
• 5.2 Modules: A module, its panel, or its boards
• 5.3 Rails, inserts, and mounting screws: What makes a panel fit a row
• 5.4 Enclosures: The case a module mounts in

5.1 Rack dimensions

The HP and the rack unit bind modules and enclosures: one HP shall be 5.08 mm (RACK-001) and one rack unit shall be 44.45 mm (RACK-002), quoted from IEC 60297-3-101:2004. A rack-mount frame, one that fastens into a 19-inch rack, shall meet IEC 60297-3-101:2004 and IEC 60297-3-100:2008 for the flange width, the flange mounting-hole positions and tab, the 3U subrack aperture height, and the 84 HP row width (RACK-003). A desktop or portable case needs no flanges; its rows keep the same HP, rack unit, and mounting-hole span (PANEL-009).

The figures RACK-003 applies:

IEC 60297-3-100 applies H1, H2 and H3 to front panels, chassis and subracks alike (its clause 5.1). Detail A draws the tab as an oval open at the outer edge, 6.8 mm high (+0.5 / 0) and 14.7 mm deep (±1.2), and also permits a second hole type; the card draws the open oval. The 12.7 mm and 31.75 mm steps are the rack grid.

A front panel sits in the 3U aperture, between the rails. The IEC publications do not set rail depth; Annex A gives the recommended section.

The figures are in data/standards.json. The panel and flange figures (482.6 mm, H1, H2, H3, detail A, 1U, 84 × 5.08 mm) were read from the publications' own pages, IEC 60297-3-100:2008 clause 5 with Figure 2 and Table 1 and IEC 60297-3-101:2004 Figures 3 and 5, which the IEC's public preview reaches (bibliography). The rack mounting grid (465.1 mm centers, 12.7 mm and 31.75 mm steps) is in IEC 60297-3-100:2008 clause 6, beyond the preview, and was transcribed from the Schroff standards summary; where that summary and the publication differ, the publication governs. The IEC publications themselves are not stored in this repository.

5.2 Modules

A module fills HP in a row: a front panel, the boards behind it, and the parts on them. It takes power from the row's bus board through its power entry and screws to the rails of an enclosure.

A module shall be 1U or 3U high (PANEL-001); the panel height, the mounting holes, and the board clearance follow that choice. Its width is any positive whole number of HP (PANEL-002). A module shall publish its width in HP and how far it extends behind the panel's back face (PANEL-003), so that a buyer can check it against a row's published width and depth.

Fitting a module into a row, with the current check that comes first, is in Assembling a system.

Tolerances

A dimension of clauses 5.2 and 5.3 shall hold within the tolerance the register states for its requirement, and a dimension with no tolerance stated is a limit (PANEL-013). The tolerances are in data/requirements.json and tabulated here:

5.2.1 Front panels

The plate on the front of a module, or a blank 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, from 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 (Annex J). The screw length window in 5.3 assumes a panel no thinner than 1.6 mm and keeps room for one up to 2.0 mm; a front panel thinner than 1.6 mm shall ship with mounting screws whose length fits that window for its own thickness (PANEL-014), since the enclosure's screws can bottom out through it.

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

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.

Height

A 3U front panel shall be 128.5 mm high (PANEL-006). Three rack units are 133.35 mm, so a 3U panel is 4.85 mm shorter and sits in the 132.55 ± 0.4 mm aperture of 5.1. The 4.85 mm is clearance, not a rail lip; the lip EIS recommends, where a rail has one, is at most 1.5 mm (Annex A).

A 1U front panel shall be 39.65 mm high (PANEL-007), the Intellijel 1U format. That is 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). The hole span is the panel height less 6.0 mm, 122.5 mm at 3U and 33.65 mm at 1U, and it shall be the same on the panel and between the inserts of a row's two rails (PANEL-009).

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 is at least the nominal width of its row, so a row of panels at either width fits it.

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, and a short slot takes up the position error of a rail 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. Measured from the panel center, the holes of an odd-HP panel are a whole number of HP out, and those of an even-HP panel a whole number of HP plus 2.54 mm. The outer hole is 7.62 mm in from each nominal edge, except that a 1 HP panel has one hole on its center and a 2 HP panel has its holes at ±2.54 mm. Each rail gets the same row of holes.

The cards show an 8 HP panel. Each dimension runs from the panel center to one hole; the other three holes mirror it.

Four holes are the usual pattern. How wide a panel can be on four screws before it flexes under a plug, and where to add holes on a wider one, is in Annex J.

The numbers are in data/module.json. tools/module.py derives the hole spans and widths, computes the hole patterns of Annex J, and draws these cards.

5.2.2 Boards

The circuit boards behind a front panel. A module has a parallel board, a right-angle board, or both.

Edge clearance

The one board requirement that affects fit is edge clearance. A board shall stay at least 9.25 mm clear of the top and bottom panel edges, and a rail shall cover no more than 9.25 mm of the panel face at each edge (PANEL-012). The opening between the rails' inner faces is then at least 110 mm at 3U, and a 110 mm board is the tallest that fits; at 1U the opening is at least 21.15 mm, and the usual board, two rack units shorter than the 3U board, is 21.10 mm.

On a rail whose inner face is 5.075 mm from the hole center, such as Schroff 34560-184, the 3U opening is 112.35 mm and a 110 mm board has 1.175 mm to spare on each side. Annex A gives inner-face measurements of catalog rails.

The rest of this clause describes common construction and places no requirement. The numbers are in data/module.json.

Parallel boards

A parallel board faces the panel. Its front face is usually 10 mm behind the panel's back face, the height of a jack body. Its width is 0.6 mm under the nominal width of the panel, twice the panel clearance:

board width = N × 5.08 − 0.6 mm

An 8 HP parallel board is 40.04 mm wide and 110 mm tall at 3U, or 21.10 mm tall at 1U. 1.6 mm FR-4 is the usual material.

Right-angle boards

A right-angle board stands square to the back of the panel, with no gap. Its edge toward the panel is the left edge of the board, and the board faces right. Its height is the board height above; its depth back from the panel is a design choice, commonly 30, 35, 40, 45, or 50 mm. A 30 mm right-angle board already extends past a rail of the recommended section (5.4).

Module depth

EIS recommends that a module extend no more than 50 mm behind the panel's back face, measured to its deepest point. A deeper module still conforms; its published depth (PANEL-003) is checked against the row's (ENC-001). In the survey of Annex F, 94.8 % of 287 modules are within 50 mm and the median is 35 mm.

5.3 Rails, inserts, and mounting screws

A front panel screws to a pair of rails through a threaded rail insert in each. Five things make a module fit any conforming row:

Rails and inserts

The holes in a rail insert shall be 5.08 mm apart (RAIL-001), so that every panel hole meets one. A rail for an N HP row shall give at least N × 5.08 mm of mounting length (RAIL-002).

An insert shall be threaded M3 (RAIL-003) and shall be at least 1.5 mm thick, three thread pitches (RAIL-004).

Mounting screws

A mounting screw shall be M3 (RAIL-005): its thread pitch shall be 0.5 mm (RAIL-006) and its major diameter 3.0 mm (RAIL-007), as ISO 261:1998 gives them. M3 is the thread of the Doepfer A-100 frame, of nearly every Eurorack case on sale, and of the screws modules ship with. IEC subrack hardware is often M2.5, and the Vector T-strut takes #4-40 groove nuts; a case built on such rails is not an EIS row, though a module's Ø3.2 mm hole (PANEL-010) still clears those screws.

The screw shall engage at least three full threads through a 2.0 mm panel (RAIL-008). Its length L shall fall inside this window, which keeps the tip off the cavity floor through a 1.6 mm panel, the thinnest EIS recommends, and the throat in front of the insert shall clear the 3.0 mm major diameter (RAIL-009):

2.0 mm + seat + 1.5 mm  ≤  L  ≤  1.6 mm + D

Seat is the depth of the insert's front face behind the rail's mounting face, and D is the depth of the screw cavity behind it (Terms). The screw head shall be at most 7.0 mm across (RAIL-010): the narrowest catalog rail face reaches 3.7 mm past the hole center (Annex A), so a head of that size bears on the panel and on the rail face of every catalog rail, and an ISO 7045 pan head or a 7 mm washer fits.

The enclosure shall state the mounting-screw length, and shall supply those screws or name them (RAIL-011). A module need not ship with screws.

Recommended practice

Everything else about a rail, an insert, and a screw is construction: the extrusion section and its lip, the groove, the insert width and ends, the screw lengths, the tap drill, the head form, and the finish. Annex A gives the section EIS recommends for a new rail, the 5.0 mm × 2.0 mm insert, the 6, 8, and 10 mm screw lengths, and the screw that fits each catalog rail. The numbers are in data/rail.json, data/insert.json, and data/screw.json; tools/rail.py, tools/insert.py, tools/insert_card.py, and tools/screw.py check them and draw the cards.

5.4 Enclosures

The case a module screws into. An enclosure is made of rows; each row has a pair of rails with an insert in each, and a bus board behind the panels.

Rows

A row is 1U or 3U, matching the front panels it holds; a 6U case is two 3U rows. A row's usable width is a whole number of HP. 84 HP fits a 19-inch rack; wider rows, such as 104 HP, are a case choice.

An enclosure shall publish, for each row, its width in HP and the depth it keeps clear behind the panel's back face (ENC-001).

Frame

The frame is a 19-inch rack frame, which meets RACK-003 (5.1), or a desktop or portable frame with the same rows and hole span (5.3).

The front rails take the mounting screws of 5.3. Other rails carry the bus board or stiffen the frame. Side plates, top, bottom, and rear covers, and on a rack frame the mounting flanges, close the box. Mains inlet, fusing, and the construction of a supply are outside EIS.

Depth

A rail of the recommended section (Annex A) is 25 mm to 28.5 mm deep, front face to back face. EIS recommends that a row keep at least 50 mm clear behind the panel's back face, the module depth 5.2.2 recommends. In the case catalog behind Annex F, 20 of 25 current cases give 50 mm somewhere in the row and 17 give it over the whole row; the shallow part is usually over the supply or the bus board.

Built-in supply

An enclosure with a built-in supply is also a power supply, and one with a built-in bus board is also a bus board: what is built in claims its own role (4.1), and the enclosure's documentation carries what each publishes. The built-in supply publishes its rail ratings and its ripple and noise (PWR-002, SUP-001), meets SUP-002 to SUP-007 (6.2), and publishes how its 0 V meets protective earth (GND-003, 6.3). The built-in bus board publishes its totals and its per-header limit (PWR-002, BUS-012).

EIS recommends that an enclosure publish, for each row, the dissipation it carries for a 10 °C rise above room temperature; Annex O gives the method.

The informative row budget is a planning table for one row: header count, bus and supply currents, and video reference distribution.