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How to choose a Rockwell hardness tester: dial, digital, touch screen or fully automatic
Every Rockwell tester applies the same 60, 100 and 150 kgf loads and reads the same 0.002 mm per hardness unit. What separates a dial machine from a fully automatic one is who does the work, how repeatably, and what happens to the result afterwards. Decide from your parts and your shift, not from the brochure.
Definition: Choosing a Rockwell hardness tester means matching four things to the parts you test — the load-application method (dead-weight or closed-loop load cell), the readout (dial gauge or digital depth sensor), the degree of automation (manual, motorised or fully automatic cycle) and the frame size (throat and vertical capacity) — while meeting the verification requirements of IS 1586 (Part 2), ASTM E18 and ISO 6508-2.
1. Start from the parts, not the brochure
Answer five questions before opening a catalogue; each eliminates a class of machine.
- Material and scale. Hardened and tempered steel, tool steel and case-hardened parts are tested on HRC (150 kgf, diamond cone; about 20–70 HRC). Annealed steel, malleable iron, brass, bronze and most aluminium alloys use HRB (100 kgf, 1.588 mm ball; 20–100 HRB). Very soft aluminium moves to HRF or HRE; cemented carbide uses HRA. Order indenters and balls for the scales you will actually use.
- Hardness range. Note the lowest and highest values you expect; you will need certified test blocks near both ends of each scale for daily checks.
- Part size and height. The throat (indenter axis to frame column) fixes how far in from an edge you can test on a plate, ring or housing. The vertical capacity (anvil to indenter with the screw fully lowered) fixes the tallest part. Most bench testers accept parts around 200 mm high; a 400 mm tall frame exists for shafts, dies, long bolts, gear blanks and assemblies that must stand on end.
- Thickness. IS 1586 (Part 1) / ISO 6508-1 require the part to be at least ten times the indentation depth for diamond indenters and fifteen times for ball indenters, with no mark visible on the back face. A 60 HRC part indents about 0.08 mm and needs roughly 0.8 mm of solid metal; 90 HRB with a ball needs about 1.2 mm. Sheet, strip, tube walls, thin case-hardened layers and plated parts fall below this and need the superficial scales (15/30/45 kgf, HR15N to HR45T). See the IS 1586 / ASTM E18 / ISO 6508 guide for the full rules.
- Tests per shift. Under about 30 readings a shift, operator time is irrelevant. Between 30 and 150, repeatability of the load cycle dominates the spread of results. Above 150, or with 100 % inspection, the tester is a production station and throughput plus data capture decide the payback.
Minimum thickness ≈ 10 × h (diamond) or 15 × h (ball), where h = (100 − HRC) × 0.002 mm or (130 − HRB) × 0.002 mm
2. The four tester types compared
All four apply the 10 kgf (98.07 N) preliminary force, then the total force of 60, 100 or 150 kgf (588.4, 980.7 or 1471 N), hold it, remove it and report the permanent depth increase.
| Type | Operator dependence | Resolution | Throughput (indicative) | Data | Typical user |
|---|---|---|---|---|---|
| Dial / analogue hand lever, dead-weight, dial gauge | High: operator controls load rate, dwell and release, zeroes and reads the dial | 1 HR (0.5 with care) | 30–50 tests/hour | None; register entry | Small heat-treaters, machine shops, tool rooms, colleges; sites without reliable power |
| Digital hand or motor-assisted load, electronic depth sensor, LCD | Medium: operator starts the cycle; auto zero, no dial to misread | 0.1 HR | 40–60 tests/hour | Conversions (HRC to HB, HV, MPa), tolerance limits, printer or USB | QC labs that must file results; incoming inspection |
| Motorised / automatic cycle motor applies, dwells and removes load to a timer | Low: operator brings the part to preload; the cycle is identical every time | 0.1 HR | 60–90 tests/hour | As digital, plus batch statistics | Heat-treatment job shops, forging and casting QC, tier-2 automotive |
| Touch screen / fully automatic auto-start on contact, motorised head, screen or camera guidance | Very low: place part, press start or let contact start the cycle | 0.1 HR | 90–150 tests/hour, more with fixtures | Batch reports, Cp/Cpk, CSV/PDF export, PC or network link, operator login | Tier-1 automotive with 100 % inspection, bearing and fastener plants, accredited labs |
Throughput figures are for a trained operator on unfixtured parts and show the ratio between types only. Resolution is display resolution, not accuracy: a 0.1 HR display does not make a machine more accurate than its verification certificate says.
Dial to digital removes reading error and gives you a record. Manual to motorised removes the operator from the load cycle: IS 1586 (Part 1) / ISO 6508-1 specify a total-force dwell of 2–6 s, and two operators on one dial machine can differ by a full HRC unit through dwell alone. Fully automatic buys throughput and traceability, not accuracy.
3. Dead-weight or load cell?
Independently of the readout, a tester applies force in one of two ways.
| Aspect | Dead-weight | Closed-loop load cell |
|---|---|---|
| Principle | Calibrated masses on a lever; force = mass × g | Motor pushes the indenter; a load cell measures force and the controller corrects it in real time |
| Accuracy and drift | No drift with age or temperature; errors come from lever friction and worn knife-edges | Meets the same ±1 % force tolerance of ISO 6508-2 when calibrated; cell and amplifier can drift and need re-verification |
| Installation | Must be level and vibration-free so the weights hang freely; a dashpot controls load rate | Largely insensitive to level and floor vibration |
| Load cycle | Fixed loads; scale change by weight selector | Any force in range by software; faster cycle |
| Verification | Direct force verification is simple; few parts to fail | Same, plus the electronics; a failed cell stops the machine |
| Relative price | Lowest, especially in dial form | Higher; the premium narrows at the automatic end |
Under about 100 tests a day, a well-made dead-weight machine on a solid bench is hard to beat for the money and the easiest to keep in verification. A load-cell machine earns its premium on a production floor, for many scales on one head, or for the cycle time of a fully automatic station.
4. Combination machines: Rockwell-cum-Brinell and Rockwell-cum-Superficial
Because the frame, elevating screw and loading system are already there, two extensions cost far less than a second machine.
- Rockwell-cum-Brinell adds 187.5 kgf (1839 N, HBW 2.5/187.5) and 250 kgf (2452 N, HBW 5/250), sometimes 62.5 kgf, with the matching balls. It is the standard answer for foundries and forge shops, where castings, forged blanks and normalised bars are specified in HB and the larger ball averages the microstructure. Brinell indents must be measured optically, so the quotation must include a measuring microscope or camera; a depth reading alone is not a Brinell result under IS 1500 (Part 1) / ASTM E10. See the Brinell testing guide.
- Rockwell-cum-Superficial ("twin") adds the 3 kgf preliminary and 15, 30 and 45 kgf total forces for the N (diamond) and T (ball) scales. It pays off the day you test carburised or nitrided parts with a case under about 0.5 mm, spring strip, tube, sheet or plated parts. If more than one job in five is thin or case-hardened, buy the twin.
A combination machine needs test blocks and verification for every scale you claim. A Rockwell-cum-Brinell with only HRC blocks is, for audit purposes, a Rockwell tester.
5. What to insist on in a quotation
Anything missing from this list is a cost you bear later.
- Standards compliance stated explicitly: verified to IS 1586 (Part 2), ASTM E18 and ISO 6508-2, with the scales covered listed.
- Calibration certificate for force (preliminary and each total force) and for the depth-measuring system, traceable to national standards, plus indirect verification on reference blocks in each scale supplied.
- Certified test blocks: at least one high and one low HRC block (around 60 and 25–30 HRC) and one HRB block, each with a certificate; more for every scale on a combination machine. See hardness test blocks: verification, calibration and certificates.
- Indenters: certified diamond cone and 1.588 mm (1/16 in) ball as standard, plus a spare diamond. A chipped diamond is the commonest reason a tester fails verification.
- Tables and anvils: flat, V and spot anvils as a minimum; a large flat table for plates, a V-anvil sized to your shafts.
- Warranty that names the load cell, depth sensor and motor drive, not just "the machine".
- Software and data: export formats (CSV, PDF, Excel); whether each result carries date, time, operator, scale and part ID; and whether data can be read without proprietary software.
- Installation and training on site, including verification with your blocks in front of your operators.
- Retrofit and service path: can the machine later take a digital controller or camera, and what is the turnaround on indenter, load cell and controller replacement.
6. Total cost of ownership
The purchase price is the smaller part of ten years of ownership. Budget, relative to machine class, for:
- Annual verification. IS 1586 (Part 2) / ISO 6508-2 expect indirect verification at least every twelve months and after any move or repair, with direct force verification at longer intervals. Dial and digital cost about the same; a load-cell machine adds the electronics to the check.
- Test blocks. A block is used on one face only; a busy shop replaces daily-check blocks every one to three years per scale.
- Indenter replacement. Diamonds chip on hard or oblique surfaces and balls flatten; a spare on the shelf avoids a week of downtime.
- Downtime. A dial machine can be repaired by a fitter; a digital or automatic machine needs the maker's controller and spares. Prefer a supplier whose electronics are designed in-house and can still be supported in ten years.
- Retrofit path. A sound dead-weight frame outlives its electronics. A frame that can later take a digital depth sensor, motorised cycle or camera lets you buy dial now and upgrade when volumes grow; see upgrading an old hardness tester.
7. Recommendation by use-case
| Use-case | Recommended type | Why |
|---|---|---|
| Heat-treatment job shop, mixed batches | Motorised digital Rockwell; add superficial if case-hardened work is frequent | Repeatable dwell across operators and shifts; printed results for each batch card |
| Forging or casting foundry | Rockwell-cum-Brinell, digital or touch screen, with microscope or camera | Castings and forgings are specified in HB; the same machine covers HRC on heat-treated parts |
| Machine shop QC, low volume | Dial Rockwell with HRC/HRB blocks | Lowest cost, no power needed, easy to keep in verification; upgrade later |
| Automotive tier-1, 100 % inspection | Fully automatic touch-screen Rockwell, load-cell preferred, with fixtures and data export | Auto-start and batch reports remove operator effect and feed the customer's traceability system |
| Engineering college laboratory | Dial or entry digital, preferably Rockwell-cum-Brinell | Students see the load cycle and dial; Brinell adds a second method for the same budget |
| Incoming inspection of thin sheet or strip | Rockwell-cum-Superficial (twin) digital tester | Regular scales mark through thin material; 15T/30T and 15N/30N are the correct scales |
Frequently asked questions
Is a digital tester more accurate than a dial one?
Not by itself. Both must meet the same force and depth tolerances of IS 1586 (Part 2) / ISO 6508-2, and a well-kept dial machine passes verification as readily as a digital one. The digital machine removes reading error and parallax and resolves 0.1 HR instead of 1 HR; its real gains are repeatability between operators and a printed, time-stamped record.
What is the advantage of a motorised load cycle?
The load is applied at a controlled rate, held for the set dwell within the 2–6 s the standards allow, and removed identically every time, whichever operator is on shift. Hand-lever machines vary in approach speed and dwell, which alone can spread results by around one Rockwell unit on the same block. Motorised cycles also reduce fatigue over hundreds of parts.
Do I need a load-cell machine?
Only if the machine will stand on a vibrating shop floor, if you want many scales including Brinell and superficial selected by software on one head, or if you are buying a fully automatic station where cycle time matters. For a laboratory or a shop doing up to about a hundred tests a day, a dead-weight tester is accurate, stable and cheaper to keep in verification.
Which scale for hardened steel and which for aluminium?
Hardened and tempered steel is tested on HRC (150 kgf, diamond cone), valid roughly from 20 to 70 HRC. Most aluminium alloys, brass and soft steel use HRB (100 kgf, 1.588 mm ball, 20–100 HRB); very soft aluminium goes to HRF or HRE. Cast iron and forgings are normally specified in Brinell. See our Rockwell vs Brinell vs Vickers guide.
How high a part can a standard tester take?
Most bench Rockwell testers accept parts up to about 200 mm between anvil and indenter, and the throat limits how far in from an edge you can test. Long shafts, dies, tall bolts and assemblies that must stand upright need a tall-frame tester with around 400 mm vertical capacity. Measure your tallest part on its test face before ordering and allow for the anvil height.
Can old dial testers be upgraded?
Usually, yes. A mechanically sound dead-weight frame can be fitted with a digital depth sensor and controller, a motorised load cycle or a camera system for Brinell measurement, then re-verified to IS 1586 (Part 2). It is often the most economical route to digital records. Our guide on upgrading an old hardness tester explains what can and cannot be retrofitted.
Which ETS machine
- RASN dial Rockwell and RASN-SPL tall frame (400 mm)Dead-weight dial testers for machine shops and colleges; the SPL takes shafts, dies and assemblies up to 400 mm high.
- RASN-D digital RockwellDead-weight frame with 0.1 HR readout, conversions and printout for QC labs that must file results.
- RSNE automatic digital and RSNE-T touch screenMotorised load cycle for repeatable dwell across shifts; the T adds batch statistics and data export.
- RASN-TSFA fully automatic and RASNB-TSFA Rockwell cum BrinellAuto-start touch-screen stations for 100 % inspection; the RASNB adds 187.5 and 250 kgf Brinell for foundries.
- RASN-Twin-D Rockwell cum Superficial and all Rockwell testersRegular plus 15/30/45 kgf superficial scales for thin and case-hardened parts; full range from dial to fully automatic.
Need help choosing? Tell our engineers what you test — material, size, standard and volume — and we will recommend a machine, scales and test blocks from our range.
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