Diameter tolerance is the field most often copied from the loosest class in the standard, and the field that most often decides whether bar runs cleanly or fights the machine. It is also written two different ways: as an ISO 286 h grade taken from the drawing, or as a plus and minus band taken from the supplier. This selector maps a diameter and an end use onto what Beiyu actually holds on the precision ground bar route, and returns the order line to write.
What to write on the order
This tool reports the Beiyu supply envelope for precision ground titanium bar and what that means for the order line. It does not reproduce ISO 286 tolerance tables: state the grade your drawing calls for and it is confirmed against the current standard at quotation.
What Beiyu holds on precision ground bar
| Parameter | Beiyu supply envelope |
|---|---|
| Diameter range, precision ground | Ø3.175 mm to Ø25.4 mm (0.125 in to 1.000 in) |
| Standard diameter tolerance | ±0.0127 mm (±0.0005 in) |
| Tightened tolerance | ±0.0076 mm (±0.0003 in), by agreement at enquiry |
| Surface | Polished, 32 microinch RMS as specified |
| Condition | Annealed as the normal supply condition |
| Above 25.4 mm | Supplied peeled or turned, tolerance agreed against the drawing |
The tolerance is held at the centerless grinding line. No later operation corrects it, which is why the tightened band has to be agreed at enquiry rather than requested after the order.
Why the two ways of writing tolerance are not interchangeable
| ISO 286 h grade | Plus and minus band | |
|---|---|---|
| Shape of the zone | Unilateral: from nominal downward only | Symmetric around nominal |
| Where it comes from | The drawing, usually from the designer | The supplier, describing what the process holds |
| What it assumes | Nominal is the maximum size | Nominal is the centre of the band |
| Practical consequence | Parts never exceed nominal, which suits a fit | Stock allowance is the same on both sides |
Because the zones are different shapes, a bar can satisfy one and not the other at the same nominal size. State which system the order uses. If the drawing carries an h grade, put the grade on the order and it is confirmed against the current standard at quotation.
The three fields that travel with tolerance
| Field | Why it belongs on the same line | What happens if it is left off |
|---|---|---|
| Straightness | Bow over length decides whether bar feeds through a guide bushing | Diameter is in tolerance and the bar still will not run |
| Surface | Stated as a roughness value, not the word polished | Polished is a workshop word and cannot be accepted against |
| Condition | Annealed is the normal supply condition for ground bar | Mechanical results on the certificate may not match the delivery condition |
Specification detail with sources
The numbers this selector returns come from the Beiyu Titanium precision ground bar programme: diameter tolerance plus or minus 0.0127 mm (0.0005 in), tightened to plus or minus 0.0076 mm (0.0003 in) where the drawing calls for it and it is agreed at enquiry, across a diameter range of 3.175 mm to 25.4 mm (0.125 in to 1.000 in). Those figures describe that one route and are not a general tolerance for every diameter Beiyu supplies.
The h grades this page maps against are ISO 286 limits taken from the drawing rather than Beiyu values, and the two ways of writing tolerance are not interchangeable: an h grade is a one-sided band referenced to the nominal size, while a plus-and-minus value is a two-sided band. ASTM B348 governs the industrial bar route, with ASTM F67 and ASTM F136 among the medical ones; the tolerance that applies to a given order is the one written on that order, so this page returns the line to write, not an approval.