Key takeaways
- The post gauge follows rail screw pull-out, not compression: an M6 screw holds about 2.5 kN in 2.0 mm CRCA and about 1.0 kN in 1.2 mm, and a 500 kg slide-out server puts 1.2 kN on each front screw.
- Dropping the frame from 2.0 mm to 1.5 mm saves about 15 kg on a 42U 600 × 1,000 frame, which matters when the rack is moved up a ramp, not when it stands still.
- Specify CRCA for a conditioned hall, pre-galvanised for a humid room, 304 for wash-down and aluminium only where weight is worth the earthing problem.
- Mask the earth stud, the rail contact faces and the door hinge points: 80 µm of powder on a bonding face is 80 µm of insulation, and the rack bonds through its frame.
- A 42U frame needs 1,867 mm of panel space at 44.45 mm per unit, so the overall height lands near 2,000 mm and the 4,450 mm brake forms a full post in one handling.
A data centre 19-inch rack frame is a dimensional instrument that happens to be made of steel. The 482.6 mm width and the 465.1 mm mounting centres are fixed by IEC 60297-3-100, and no material choice changes them. What material choice does change is whether the frame survives being loaded, moved, bonded and cleaned for ten years without the rails pulling out or the paint blistering.
The dimensional rules and the weld sequence are covered in the rack frame design guide and the frame manufacturing route. This page is about the material and gauge decision: what the frame is made from, what each gauge buys, and where the cost sits.
The worked example is a 42U frame, 600 mm wide × 1,000 mm deep, rated for 1,000 kg static. Its panel space is 42 × 44.45 mm, or 1,867 mm, and the complete frame lands near 2,000 mm tall.
What jobs does the frame do?
Three. It holds the 482.6 mm interface in the right place, so a rail kit, a server and a blanking panel all line up. It carries the load from the rails and the plinth to the floor. And it provides the earth path and the thermal boundary that the rest of the hall depends on.
Only the first job is fixed by the standard. The second is a structural question that the gauge and the bracing answer. The third is a finish question, and it is the one most often lost between the drawing and the powder booth.
A rack frame is not a sealed enclosure and is not designed as one. It is a frame with removable panels, and the panels contribute stiffness only when they are fitted. Design the bare frame to stand square on its own, then treat the panels as a bonus.
Data centre 19-inch rack frame material and gauge decision
| Material and gauge | Frame weight, 42U × 600 × 1,000 | Rail screw pull-out, M6 | Where it fits | Ganesh limit or note |
|---|---|---|---|---|
| CRCA 2.0 mm posts, 1.5 mm rails | 55–65 kg | about 2.5 kN | 800–1,200 kg halls, default choice | laser cut, formed on the 200 T brake, welded in fixtures |
| CRCA 1.5 mm posts, 1.5 mm rails | 45–50 kg | about 1.7 kN | network racks to about 300 kg | same route, 25% less steel |
| CRCA 1.2 mm posts, 1.2 mm rails | 36–42 kg | about 1.0 kN | light patch racks, wall-mount frames | local denting under a lever; not for slide-out servers |
| Pre-galvanised 2.0 mm | 55–65 kg | about 2.5 kN | humid or unconditioned rooms | cut edges need zinc-rich touch-up, oxide removed before coating |
| Stainless 304, 1.5 mm | 42–48 kg | about 2.0 kN | wash-down, food, coastal C5 | no powder; brushed or passivated finish |
| Aluminium 5052, 2.5 mm | 20–24 kg | about 1.3 kN | mobile or weight-critical frames | isolate from steel rails; design the earth path |
| Powder film, all steel | 60–80 µm | — | CRCA and galvanised | seven-tank pretreatment, 18 ft × 14 ft booth |
| Earth continuity | 0.1 Ω or less | — | every frame | masked stud and rail contact faces |
Why the rail fixing decides the gauge
Compression is never the problem
Load a 42U frame to 1,000 kg and each of the four posts carries 2.45 kN. On a 2.0 mm post with a developed area near 280 mm², that is 8.8 MPa against a yield of 250 MPa. Even at 1.2 mm the stress is 15 MPa. A rack frame does not fail by crushing its posts.
The load that decides the gauge arrives through a screw. A rail is fixed to the post with M6 cage nuts or thread-forming screws, and a slide-out server on rails puts roughly twice its weight on the front pair of fixings as the mass leaves the frame. A 500 kg server on a pair of rails is 4.9 kN, shared over four front screws, or 1.2 kN each. A thread-forming screw pulls out of 2.0 mm CRCA at about 2.5 kN and out of 1.2 mm at about 1.0 kN. At 1.2 mm the fixing is at its limit before the server is fully extended, and the first hard stop strips the thread.
That is the argument for 2.0 mm posts on a dense compute rack, and it is why the rail itself should be 1.5–2.0 mm even when the post is thicker. The screw needs material to thread into, not just material to sit against.
What a load rating should actually state
"1,000 kg" on its own is not a specification. A rack frame rating should say which load it refers to: a uniformly distributed static load on the rails, a point load on a single rack unit, or a slide-out load on a pair of telescopic rails. They produce very different stresses at the same nominal figure.
A 1,000 kg distributed load puts 2.45 kN on each post, which any of the gauges above carries. The same 1,000 kg concentrated as 250 kg on a single 1U shelf puts 2.45 kN on four screws and bends the rail between its supports. A slide-out load of 500 kg doubles the front fixing load and adds a moment at the plinth, which is the case that cracks coatings and loosens anchors in a hall.
State all three on the drawing, and state whether castors or levelling feet are in scope. A 65 kg frame on four castors is rated by the castor and the floor, not by the posts.
What the gauge costs in weight and handling
A 42U frame in 2.0 mm CRCA weighs 55–65 kg. At 1.5 mm it is 45–50 kg, and at 1.2 mm 36–42 kg. In a hall, that weight does not matter. During installation it does: two technicians can lift 45 kg up a step, and 65 kg on a ramp or a stair is a handling risk that shows up as a bent frame and a damaged powder coat.
The gauge also changes how the frame behaves when it is moved while loaded. A populated rack pushed across a floor joint flexes at the plinth, and the joint between the post and the base is where the coating cracks. A 2.0 mm post with a gusseted base takes that; a 1.2 mm post with a folded foot does not.
Sheet grade, not just thickness
CRCA to IS 513 drawing quality is the default because it forms cleanly and takes powder well. The grade matters at the bend: a D-grade sheet at 2.0 mm bends to a 2.0 mm inside radius without cracking, while a commercial-quality sheet of the same thickness may need 3 mm and still show orange peel on the outside of the radius.
Thickness tolerance matters as much as the nominal figure. Sheet is supplied to a tolerance band, and a 2.0 mm nominal coil can arrive at 1.9 mm. On a rail screw that is 5% less material to thread into; on a 42U frame it is 3 kg less steel than the quotation assumed. Check the incoming coil with a micrometer at three points across the width, and quote from the measured thickness rather than the nominal.
Pre-galvanised sheet to IS 277 is a zinc-coated substrate. Laser cutting burns the coating back from the edge, leaving a zone that will rust first unless it is touched up with a zinc-rich primer. That is fine in a dry room and not fine in a humid one.
Finish and earthing: the material decision continues
The finish is part of the material system, not a coat of paint applied afterwards. A rack in a conditioned hall sees C3 to ISO 12944-2 at worst, and 60–80 µm of polyester powder over seven-tank pretreatment meets it. A rack in a coastal or unconditioned room is C4, and the film goes to 120–160 µm, usually as a primer and a topcoat.
Earthing is where the finish and the frame meet. Powder is an insulator, and a rack bonds through its frame, its doors and its rails. Mask the earth stud and a 20 mm ring around it, mask the rail contact faces, and mask the hinge points. Then check continuity from the farthest door to the earth bar at 0.1 Ω or less.
Panels and doors are not just cladding
A 1.0–1.2 mm side panel weighs 15–20 kg on a 42U frame and contributes stiffness the moment it is fitted. Design the frame to stand without it, then use the panel: a rack with both sides and a perforated front door is considerably stiffer than the bare frame, which is why a frame that feels flexible in the weld shop can feel solid in the hall.
The door is a different load case. A 20 kg perforated door hanging on two hinges puts 98 N at 400 mm from the hinge line, or 39 N·m, into the post. A 2.0 mm post with a welded hinge plate takes that without visible deflection. A 1.5 mm post with a folded hinge tab lets the door sag 1–2 mm over a few hundred cycles, until the bottom corner catches on the frame.
Perforation is the other material decision. At 78% open area only about a fifth of the door section is steel, so the door behaves as a frame with a screen in it. Stiffness has to come from the return flange or a welded stiffener, not from a heavier gauge. A flat perforated door 2,000 mm tall will oil-can the first time it is opened with one hand.
The route from coil to coated frame
Cutting a rack frame is a nesting exercise. A 42U side panel is about 2,000 × 1,000 mm, and the 12 kW fibre laser with the 40 ft × 16 ft bed takes it and its rail blanks in one nest, which keeps the grain direction and the bend lines consistent across the batch.
Forming is where the 4,450 mm bed earns its place: a 2,000 mm post is formed in one handling, so the two bends at each end stay parallel and the post does not acquire a twist from being repositioned. The 200 T brake with Delem control holds the bend sequence in a program, so a repeat order starts from the approved setup.
Welding runs on three CLOOS robotic MIG cells or at the manual stations, in fixtures that locate on the mounting faces rather than on the outside of the frame. That is the difference between a frame that measures square and a frame that looks square. After welding, the frame goes through seven-tank pretreatment, then the 18 ft × 14 ft powder booth and the oven.
Ganesh has built this route since 1992, with five units in Mumbai (Vasai) and Nagpur and ISO 9001:2015 and ISO 14001:2015 across the plants. Rack and enclosure work runs alongside lift and genset programmes for customers including TKE, Eros Elevators, Godrej & Boyce and Mahindra, so the coating line is set up for mixed batches rather than one product family.
The data centre rack range covers frames, rails, doors, blanking panels and PDU brackets, and the racks and enclosures hub collects the rest of the guides. Before specifying a load, the rack load calculator will tell you what the floor and the frame are being asked to carry.
What the drawing should say about material
- Sheet grade and standard: "2.0 mm CRCA to IS 513, D quality" rather than "2.0 MS".
- Gauge by member: posts, rails, plinth and panels, because they are not the same duty.
- Load rating and the test that proves it: static, distributed, and whether a slide-out load is included.
- Finish system, colour and film range, with the environment category it is meant to meet.
- Masking zones: earth stud, rail contact faces, hinge points and any conductive contact.
- Earth continuity limit and the points it is measured between.
- Panel and door material, including whether they are load-bearing or decorative.
- Marking and traceability: frame serial, batch and coating batch.
Where the material choice goes wrong
Four cases. An aluminium frame bonded through steel rails will corrode at the joint unless the fasteners are isolated, and the earth path has to be a deliberate conductor rather than the frame itself. A pre-galvanised frame that is powder coated without removing the zinc oxide at the cut edge will lose the coating at the edge within a season. A 1.5 mm frame specified for a 1,000 kg hall will hold the static load and fail at the rail fixings under a slide-out server. And a stainless frame that is powder coated to match the hall gives up the corrosion resistance it was bought for and hides the crevices where chlorides collect.
Ganesh cuts CRCA, stainless and aluminium on the same laser and coats steel on the same line, so the material choice is a real choice rather than a capability limit. Send the load rating, the room environment and the panel schedule with the drawing, and the quotation will state the gauge and finish it assumes.
Related reading: 19-inch rack frame design tolerances, rack frame manufacturing and mounting rail design. The blanking panel guide covers the airflow side of the same frame.
Frequently asked questions
What is a 19-inch rack frame made of?
Most are 1.5–2.0 mm CRCA to IS 513, with 1.5 mm mounting rails and 1.0–1.2 mm side panels and doors. Pre-galvanised sheet is used for humid rooms and 304 stainless for wash-down, at 1.5 mm because the higher yield allows a thinner section.
What gauge should a 19-inch rack frame be?
2.0 mm posts for a rack that will carry 800 kg or more, and 1.5 mm for a network rack up to about 300 kg. The deciding load is the rail fixing: an M6 screw pulls out at about 2.5 kN in 2.0 mm and about 1.0 kN in 1.2 mm, and a slide-out server doubles the load on the front screws.
Does powder coating affect rack earthing?
Yes. A 70 µm film on a bonding face is an insulator, so the stud, the rail contact area and the hinge points have to be masked before coating. Check continuity from the door and the rail to the earth bar at 0.1 Ω or less after assembly.
CRCA or galvanised for a data centre rack?
CRCA with powder coat for a conditioned hall at C3 or better, pre-galvanised for an unconditioned or humid room where the cut edges can be touched up. Galvanised sheet needs the zinc oxide removed at the cut edge before any coating, or the powder keys to oxide rather than steel.
Can a rack frame be aluminium?
Yes, in 2.5 mm 5052 or 6061, and it saves roughly two-thirds of the frame weight. It costs more per kilogram, it needs isolated fasteners against steel rails, and the earth path has to be designed rather than assumed. For most halls the steel frame is the better trade.
Sources and further reading
- IEC 60297-3-100:2008 — Mechanical structures for electronic equipment, basic dimensions of the 482.6 mm (19 in) series · reviewed 3 Nov 2026
- ISO 2768-1:1989 — General tolerances, linear and angular dimensions without individual tolerance indications · reviewed 3 Nov 2026
- ISO 9227:2022 — Corrosion tests in artificial atmospheres, salt spray tests · reviewed 3 Nov 2026
Have a rack frame drawing to cost?
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