ISO 3245 — Drawn cup boundary dimensions

ISO 3245 does for a drawn cup what ISO 1206 does for a needle roller bearing with machined rings: it fixes the mounting envelope, so that a cup pressed into a housing from one maker fits the shaft and the bore prepared for another. A drawn cup is made from sheet steel by deep drawing, not turned from bar, and the standard's own section on dimensions heads both of its tables with "with open ends or one closed end" — one table serves the open-ended cup and the single-closed-end one alike, because the two are one envelope and differ only in which end of the cup is formed into a base. What the standard tabulates is those two tables, the tolerance values that go with them and the GPS specifications; this library tabulates 100 designations from the first and none of the second.

Fw

Nominal bore diameter of the needle roller complement. It is the same symbol and the same idea as the Fw of a machined-ring bearing, and on a drawn cup it is the diameter the shaft has to be ground to, because the cup has no inner ring for the needles to run on. This is also the first of the two numbers in a designation: the 12 of HK1210 is Fw 12 mm.

D

Nominal outside diameter of the drawn cup — the dimension the housing bore is prepared for, since the cup is pressed in rather than clamped. It is the one boundary dimension a drawn cup designation does not carry.

C

Nominal width of the drawn cup, and the second of the two numbers in a designation: the 10 of HK1210 is C 10 mm. A drawn cup has a single width, so there is no B beside it as there is on a machined-ring bearing.

C1 and C2

Nominal bottom thickness of the formed base and of the flat base, in the closed-end cup. The standard's table carries both because the base can be drawn or pressed flat; this library publishes neither, so neither is claimed anywhere on the designation pages.

r

Nominal chamfer dimension. ISO 3245 does tabulate it, row by row, in the same table as Fw, D and C — but no page in this library prints a chamfer for a drawn cup. The reason is stated in full in the section below on what is not taken.

The last column is the whole point of this standard, and it comes from this library's own data rather than from the table: the two rows describe the same Fw and give different outside diameters, and the designation for each has the same four digits. A reader who takes HK1210 for a 12 mm bore and reads the outside diameter off the designation will be wrong twice — once about which dimension is 12 mm, and again about how far across the cup is.

The two numbers in a drawn cup designation are Fw and C, and nothing else: HK1210 is 12 mm across the needle complement and 10 mm wide, and HK1212 is the same 12 mm across the needle complement in a 12 mm width — yet they are 16 mm and 18 mm outside respectively. Nothing in either string says so. The outside diameter comes from the standard's table for the diameter series the size belongs to, which is why this library prints each row's outside diameter beside its designation and never derives one from the other.

Drawn cups are catalogued as two products — HK, with both ends open, and BK, with one end formed into a closed base — and ISO 3245 heads one table with both. The data bears that out: 37 of the sizes here are made in both forms, 25 only as HK and 1 only as BK, and wherever both exist the boundary dimensions agree cell for cell, because they are one row read twice. That is not a coincidence to be expected of any two series in this library; it is the standard saying so. Where they differ is not in size but in what the bearing does: an open cup is retained by its housing bore alone, a closed one also takes the axial location of whatever runs against it.

Two things are deliberately left out. The first is the chamfer: ISO 3245 tabulates an r for every row, but a cell enters this library only when two independent sources agree on it, and the catalogue tables consulted for this type — NTN's and Schaeffler's, both checked row by row — print Fw, D and C and stop. One source is not enough, so no page here claims a chamfer for a drawn cup. The second is that not every row in this library is a size the standard tabulates: 4 designations sit at an Fw its two tables do not reach, and 15 more have an outside diameter the standard gives but a width it does not list for that Fw. Those are real sizes — every cell still has two independent sources — but they are catalogue sizes, and the designation pages mark them as such rather than letting a reader assume the standard fixes every number on them.

Radial internal clearance belongs to ISO 5753-1, not here, and that standard's tables are drawn up for bearings with rings. A drawn cup is a single stamped outer ring and a needle complement, so there is no table for it to take a row from — and this library does not substitute the row for a machined-ring needle bearing, which is a different assembly with a different ring stiffness. The ISO 5753-1 page states which tables do have a page here.