DIN 3962 class 5, 0.7~0.9 mm carburizing, 4000 pcs/year: Grinding process for upgrading medium-module gears from class 7 to class 5

In September 2026, a complete-machine manufacturer in Poland that builds screw hoists (LTT260 series) sent 7 drawings to Geyon Transmission. Four of them were m3.5 spur gears (z31, z45), material 16MnCr5, carburized 0.7~0.9 mm, hardened 58~62 HRC; the drawings specified DIN 3962 class 7, and the customer added a line in the email subject: “update class 5” — meaning the accuracy had to be raised by two grades, with quantities quoted in three tiers: 2000 / 3000 / 4000 pieces. Geyon Transmission completed an item-by-item analysis of all 7 drawings, confirmed that class 5 requires grinding after carburizing, factored the carburized layer that grinding would remove into the process allowance, and provided the three-tier quotation basis and inspection item list. This review covers exactly which points of the process and inspection have to change when accuracy is upgraded.

Background#

The customer is in the Silesian Voivodeship, Poland, building LTT260 series hoisting equipment, buying gears externally and issuing their own drawings. The four gears in this inquiry are all drive components in the equipment: small intermediate gear z31, large intermediate gear z45, and a gear disc-shaft (gear ring z31, with a z16 spline on the shaft). The original drawings specify accuracy as DIN 3962 class 7.

The customer’s requirements are stated plainly. Accuracy must be raised from class 7 to class 5; delivery documents must be complete — material certificates, inspection reports, finished-product photos and videos, shipped with the goods after order placement; on method, samples first, with both gears and hubs running at 14 pieces.

The callouts on the drawings are also detailed: pressure angle 20°, spur teeth, profile shift coefficient x=0, general tolerances ISO 2768-1 class f (precision class), and the gear disc-shaft part has a center bore with M24×1.5 thread and two A2.5 center holes per DIN 332. Clearly this is a customer who has been designing drawings long-term and selecting suppliers from drawings.

Where the difficulty lies#

1. A two-grade jump changes the process sequence. Class 7 can be reached with finish hobbing or gear shaving; class 5 cannot — it requires grinding after carburizing and hardening. Heat treatment first, grinding after, and the grinding allowance, locating datum, and inspection items all have to be rearranged accordingly.

2. Grinding allowance must be left inside the carburized case. The customer requires carburizing 0.7~0.9 mm, with 0.5~0.7 mm remaining after tooth profile finishing. The roughly 0.2 mm in between is what grinding removes. When hobbing the gear blank, tooth thickness must be left oversized per the grinding allowance; during carburizing, case depth must be controlled to the pre-allowance dimensions; after grinding it still has to land within the 0.5~0.7 mm window — both the upper and lower limits are constrained.

3. The base tangent length band is very narrow. For z31, W=37.9698, upper deviation +0.120, lower deviation +0.070, measured over 4 teeth, giving an actual band width of 0.05 mm; z45 is W=38.2497, 0/-0.050. Grinding infeed compensation, heat-treatment distortion, and gear blank allowance must all be calculated against this 0.05 mm band.

4. The gear disc-shaft must be precise at both ends. Beyond the gear ring there is a Ø30 k6 bearing seat and a z16 spline (ISO 4156, roughly equivalent to DIN 5480). The spline groove center has an alignment requirement relative to the tooth tip center; after scanning the original drawing, the callout reads “u0,35v”, which per the drawing should be ±0.35′ (arc minutes), and a dot mark is required — this item must wait for confirmation from the customer’s official drawing version, and the alignment fixture must be arranged separately.

5. The bore tolerances are equally tight. The bores of z31 and z45 are both Ø80 K6, upper deviation +0.004, lower deviation -0.015, mating surface Ra1.6. Grinding the bore within this band requires stable clamping and measurement.

6. One process for three quantity tiers. The 2000-piece and 4000-piece runs cannot be two different methods; what the customer wants to see is whether the same process flow holds accuracy in volume production.

How the plan was set#

Step one, drawing analysis. All 7 drawings were checked item by item: module, number of teeth, pitch diameter, pressure angle, profile shift coefficient, base tangent length, bore tolerance, and spline standard were all tabulated. Three gear drawings had vector text layers, so values were extracted directly; the rest were scans, and a few callouts (spline alignment angle, the missing PDF for item 4) lacked sufficient resolution and were uniformly flagged as “pending confirmation from customer’s official drawing version” — no work started on assumptions. This kind of upfront verification is the same task as the engineering review for custom gears , and doing it before quoting saves more trouble than doing it after machining.

Step two, process route. Gear blank turning to maintain datum (gear disc-shaft made with center holes and thread per DIN 332) → hobbing with grinding allowance → normalizing → carburizing and hardening (0.7~0.9 mm, 58~62 HRC) → gear grinding. External teeth use form grinding; the spline on the gear disc-shaft is scheduled for gear shaping or spline grinding; the alignment mark is struck after the tooth tip is ground. Heat-treatment distortion is measured on trial pieces from the same batch, and the tooth thickness grinding allowance is back-calculated from that; after grinding, the carburized case depth is verified piece by piece. For the equipment and process arrangements in the grinding stage, see gear grinding and machining capabilities .

Step three, inspection. Pitch, profile, and helix are run on a gear measuring center; base tangent length W and span-over-balls are measured piece by piece, together with hardness (HRC), carburized case depth (metallography), and mating surface roughness (Ø80 K6 surface Ra1.6). General tolerances are inspected per ISO 2768-1 class f. Material certificates are issued per EN 10204 3.1, and inspection reports, finished-product photos and videos are shipped with the goods as the customer requires. The full setup is described in gear inspection system .

Step four, quotation basis. The 4 gear items are quoted in three tiers: 2000 / 3000 / 4000, with tooling and cutters listed separately as one-time items, so the customer can see for themselves which tier the volume break-even point falls in. The other 3 hub drawings (S355J2 and forged steel parts) are analyzed in parallel, evaluated at 14 sample pieces and an annual volume of 4000 pieces each, and submitted together with the technical agreement.

Results data (as of the review stage)#

This order is currently at the drawing review and quotation stage; volume delivery data has not yet been generated. The table below shows the parameters and engineering outputs already confirmed.

Data comes from the customer’s September 2026 inquiry drawings and engineering review records; final parameters are subject to confirmation by the official drawings and order.

What was done right on this order#

First, the cost of the upgrade was calculated clearly upfront. Going from class 7 to class 5 adds a gear grinding operation; the extra tooling, labor hours, and inspection items were made known to the customer at the quotation stage, so they know which stage the money goes into.

Second, the carburized case and grinding allowance were controlled together. 0.7~0.9 mm in, 0.5~0.7 mm out, leaving a window of only 0.2 mm; how much allowance to leave and how much to grind off is written into the process, not patched into a report after the fact.

Third, uncertain items were laid out openly. The spline alignment angle and the drawing number missing an official version were flagged at the review stage for customer confirmation, not left to guesswork.

Contact Geyon Transmission#

Do you also have gears on hand that need an accuracy upgrade, have tightly constrained tooth profile parameters, and come in several volume tiers to be evaluated? Send over the drawings and inspection requirements, and the Geyon Transmission engineering team will first perform a drawing review, then reply with the process route, inspection items, and quotation. Gear grinding accuracy can reach DIN 3, and reports on pitch, profile, helix, hardness, and carburized case depth can be issued per DIN/ISO/AGMA standards.

More information: Drawing review and quotation ｜ Contact Geyon Transmission