The standard diameter range for chrome-plated and ground bar is Ø4 mm to Ø140 mm, with larger sizes made to order up to Ø200 mm for the soft shaft and the 45 Steel Ground Round Bar. The usable window depends on grade and heat treatment: quenched and tempered bars generally start at Ø8 mm, while the induction-hardened chrome shaft and the linear shaft stop at Ø130 mm. The 40Cr and 42CrMo Q&T chrome-plated bars have no standard range and are made to order only.
What is the standard diameter range?
The standard range runs from Ø4 mm to Ø140 mm across the chrome-plated and ground products, but the limits are set per product, not per supplier. Soft shaft and ground bar start at Ø4 mm; quenched and tempered products start higher, and two of the three chrome-plated quenched and tempered products (40Cr and 42CrMo) are made to order only, while the 45 Steel Q&T Chrome-Plated Bar has a standard range of Ø8–140 mm.
A standard range is the band in which a product is normally quoted. It does not mean that every diameter in the band is ready to ship; the lead time for each size is confirmed in the quotation.
| Product | Grade and condition | Standard range | Made to order |
|---|---|---|---|
| 45 Steel Chrome-Plated Soft Shaft | 45 steel, not induction hardened, hard chrome | Ø4–140 mm | up to Ø200 mm |
| 45 Steel Induction-Hardened Chrome Shaft | 45 steel, induction hardened, then hard chrome | Ø4–130 mm | — |
| 45 Steel Chrome-Plated Linear Shaft | Same route as the induction-hardened chrome shaft | Ø4–130 mm | — |
| 45 Steel Ground Round Bar | 45 steel, not Q&T, ground | Ø4–140 mm | up to Ø200 mm |
| 45 Steel Q&T Ground Round Bar | 45 steel, induction Q&T, ground | Ø8–140 mm | — |
| 45 Steel Q&T Chrome-Plated Bar | Q&T base, then hard chrome | Ø8–140 mm | — |
| 40Cr Q&T Ground Round Bar | 40Cr, induction Q&T, ground | Ø5–140 mm | — |
| 40Cr Q&T Chrome-Plated Bar | 40Cr, induction Q&T, then hard chrome | — | Ø8–140 mm |
| 42CrMo Q&T Chrome-Plated Bar | 42CrMo, Q&T base, hard chrome | — | Ø8–100 mm |
For the induction-hardened chrome shaft and the linear shaft, the published range is Ø4–130 mm, cold drawn to Ø28 mm and peeled from Ø30 mm. If your design sits near that transition, state the diameter on the inquiry so the bar is quoted on the correct basis.
Which diameters are made to order?
Made-to-order sizes fall into two groups: diameters above the standard range for two products, and two chrome-plated products that are made to order across their whole range. For the 45 Steel Chrome-Plated Soft Shaft and the 45 Steel Ground Round Bar, diameters above Ø140 mm are made to order up to Ø200 mm; the other standard-range products are quoted on their published range. At Yixin Precision Machinery (Changzhou), the 40Cr Q&T Chrome-Plated Bar is made to order in Ø8–140 mm, with a custom heat treatment lead time of 10–20 days, and the 42CrMo Q&T Chrome-Plated Bar is made to order in Ø8–100 mm with a minimum order of 1 t and a lead time of 7–10 days.
The reason a large or made-to-order diameter is not quoted like a standard-range size is that the finished tolerance, straightness and surface condition have to survive heat treatment and grinding. Yixin publishes 7–10 days for a non-standard diameter and 10–20 days where custom heat treatment is involved; cut-to-length from stock is quoted at 3–5 days, plus sea-freight booking. Confirm the grade, the heat treatment and the finished tolerance together, because all three decide whether a given diameter can be produced economically and whether it is quoted within the standard range or made to order on a drawing.
How should the diameter tolerance be specified?
Two tolerance families are standard, and the one you need follows from the diameter band. For Ø4–11 mm the published band is −0.02/−0.05 mm. From Ø12 mm you may specify 0/−0.02 mm, −0.01/−0.03 mm or −0.02/−0.05 mm.
| Diameter band | Published tolerance options |
|---|---|
| Ø4–11 mm | −0.02/−0.05 mm |
| From Ø12 mm | 0/−0.02 mm, −0.01/−0.03 mm or −0.02/−0.05 mm |
Quenched and tempered bars start at Ø8 mm, so for those products the small-diameter band applies from Ø8 mm to Ø11 mm; the 40Cr Q&T Ground Round Bar is the exception and starts at Ø5 mm. From Ø12 mm the 45 Steel Chrome-Plated Linear Shaft is normally supplied at 0/−0.02 mm, which is the figure linear-bearing users work to. Write the nominal diameter and the tolerance band as a pair on the drawing, and put the same pair on the purchase order, because a tolerance band quoted without a diameter cannot be checked against the mill and plating records.
Does diameter affect straightness, surface finish and chrome thickness?
Chrome thickness, finish and straightness are specified separately from diameter, but they are all read together on the same drawing. Hard chrome is applied at 10–50 μm per side, chosen per order, and chrome hardness can reach HV800+. Surface finish is Ra ≤ 0.4 μm on chrome-plated bar and Ra ≤ 0.8 μm on ground bar. Straightness is approximately 0.1 mm/m from Ø25 mm and approximately 0.2 mm/m below Ø25 mm, so a small-diameter bar carries the looser per-meter figure.
For Yixin bars, hard chrome plating and machining are carried out by long-term partner plants to Yixin's specification, and Yixin checks chrome thickness, diameter and surface before packing; this is why the layer thickness is agreed as an order item rather than assumed. Where corrosion performance has to be stated, salt-spray performance is not part of the standard specification. Where a rating is required, we specify a thicker chrome layer and can have the order tested by a third-party laboratory.
What bar lengths and cut lengths can I order?
Full bars are supplied in 4 m, 6 m, 7.5 m or 8.1 m. Bars can be CNC cut to length from 200 mm, and cut ends are left as sawn.
Length is normally decided after diameter, because the cut length and the per-meter straightness figure together determine whether the bar will run true in the application. If the bar is going into a machining line, saw-cut ends are usually sufficient; if it is going straight into a cylinder or a linear assembly, say so at inquiry stage so that the cut length, the end condition and the diameter tolerance are quoted as one package. Bars are supplied in metric diameters, and full-bar lengths are quoted in meters, so keep the drawing and the inquiry in the same units to avoid a conversion error on the order.
What to put in your RFQ
- The exact product name and condition, for example 45 Steel Chrome-Plated Soft Shaft or 42CrMo Q&T Chrome-Plated Bar.
- Nominal diameter in millimeters and the tolerance band: −0.02/−0.05 mm for Ø4–11 mm, or 0/−0.02 mm, −0.01/−0.03 mm or −0.02/−0.05 mm from Ø12 mm.
- Surface requirement: hard chrome or ground only, with the chrome layer in μm per side if a figure is needed.
- Total length and cut length, plus whether sawn ends are acceptable.
- Quantity, allowing for the 1 t minimum order and 20–50 kg samples.
- Any third-party inspection or test requirement, which is arranged per order on request.
- Packing and marking instructions, including whether your brand is to be printed on the packing.
- Destination and preferred loading port, FOB Shanghai or Ningbo.
Summary
The standard range for chrome bar and ground bar is Ø4–140 mm, and the practical starting point is Ø8 mm for quenched and tempered products and Ø5 mm for the 40Cr Q&T Ground Round Bar. The induction-hardened chrome shaft and the linear shaft top out at Ø130 mm; the soft shaft and the 45 Steel Ground Round Bar can be made to order up to Ø200 mm. The 40Cr Q&T Chrome-Plated Bar and the 42CrMo Q&T Chrome-Plated Bar are made to order only, at Ø8–140 mm and Ø8–100 mm respectively.
Specify the diameter with its tolerance band, the surface condition, the chrome layer if a figure is required, and the cut length. For the 45 Steel Chrome-Plated Soft Shaft and the 45 Steel Ground Round Bar, sizes above the standard range are made to order up to Ø200 mm; other products are quoted on their published range. On the made-to-order path, the grade, the heat treatment and the finished tolerance are confirmed on the drawing and order.