A linear shaft specification for linear bearings should state the bearing type and shaft tolerance band, the straightness limit, the surface hardness and case depth, the chrome layer and finish, and the end geometry. Diameter alone does not define a usable shaft: fit, straightness, hardness and working-surface requirements must be agreed together on the drawing and order.
What tolerance should a linear shaft have for a linear bearing?
For the 45 Steel Chrome-Plated Linear Shaft (Grade 45 to GB/T 699-2015), the typical band is −0.02/−0.05 mm for Ø4–11 mm and 0/−0.02 mm from Ø12 mm. That band is a starting point for linear bearings, not a universal answer: the bearing type must be confirmed so the fit can be checked against the drawing.
Tolerance is only one part of bearing fit. A shaft can be inside a nominal diameter band and still be unsuitable if straightness, surface finish or end geometry is wrong. The rule is simple: do not select by diameter alone when bearing fit, straightness, end geometry or working-surface requirements are not yet defined.
Yixin Precision Machinery (Changzhou) supplies this product over a standard range of Ø4–130 mm. Other tolerance bands are reviewed against the customer drawing. When you send an enquiry, give the bearing series, the bore tolerance if you have it, and the nominal diameter. That lets the supplier confirm whether the standard band applies or whether a different band should be quoted. If the bearing is not yet chosen, say so; the shaft tolerance can then be agreed after the bearing is selected, rather than guessed from diameter.
How straight should a linear shaft be?
Straightness for the 45 Steel Chrome-Plated Linear Shaft is about 0.1 mm/m from Ø25 mm and about 0.2 mm/m below Ø25 mm. State the limit on the drawing, and say whether it applies per meter or over the full length.
Straightness is a separate requirement from diameter, surface roughness and cylindricity. A bar can meet the diameter band and still fail a guidance application if it is bowed over the supported length. That is why straightness is grouped with bearing fit, end geometry and working-surface requirements rather than with diameter alone.
The values above are standard capabilities for this product. Any other limit should be agreed before quotation. Define whether straightness is measured on the full bar or on the cut piece, so the inspection plan matches the requirement. Full bars are supplied in 4 m, 6 m, 7.5 m or 8.1 m lengths, and CNC cutting starts from 200 mm. If the shaft is cut to length, put the straightness reference and the cut length on the same drawing.
How hard is the working surface?
The 45 Steel Chrome-Plated Linear Shaft is induction hardened to a case of at least HRC55, about 2 mm deep, then polished, hard chrome plated by a partner plant and final polished. The hardness requirement is a case requirement, not a through-hardness value.
This matters when a buyer writes hardened without saying where or how deep. A surface that is hard only at the chrome layer is not the same as an induction-hardened steel case. For this product, the sequence is induction hardening of the 45 steel, polishing, hard chrome plating by the partner plant, then final polishing. The chrome layer can reach HV800+, but the specified case is the hardened steel beneath it.
Do not apply the same hardness statement to every chrome-plated bar. The 45 Steel Chrome-Plated Soft Shaft is not induction hardened. Quenched and tempered products are not surface hardened and do not have an induction-hardened case; their hardness is stated as Q&T hardness, not case hardness. If the application depends on case hardness or case depth, name the product and put the requirement on the drawing. Case hardness and case depth are standard capabilities for this product.
What chrome thickness and surface finish should I specify?
Hard chrome on the 45 Steel Chrome-Plated Linear Shaft is 10–50 μm per side, chosen per order, with a chrome surface roughness of Ra ≤ 0.4 μm. Specify the chrome thickness and the tolerance band together, because the layer is part of the finished size.
The chrome layer is specified per side, and the shaft is final polished after plating. A drawing that gives only a diameter and tolerance can leave the coating and finishing steps working to different assumptions. State the nominal diameter, the tolerance band, the chrome thickness per side, and the surface finish. If the bearing fit is close, say which feature controls the finished size.
Surface roughness should be called out separately from straightness and diameter. The product data gives Ra ≤ 0.4 μm for the chrome surface and Ra ≤ 0.8 μm for ground surfaces. A general note of smooth surface is not a substitute for a numerical Ra limit. If the application needs a different finish, put the value and the measuring direction on the drawing and have it reviewed. Chrome hardness can reach HV800+, but hardness and finish are separate acceptance points.
How should length and end geometry be specified?
Full bars of the 45 Steel Chrome-Plated Linear Shaft are supplied in 4 m, 6 m, 7.5 m or 8.1 m; CNC cutting starts from 200 mm and ends are left as sawn. End machining such as holes, threads or steps is done by long-term partner plants to Yixin's specification and assessed from the drawing.
Give the finished length, the cut tolerance if you need one, and a dimensioned end drawing. A general note of machined ends is not enough: the supplier needs the thread size, step diameter, hole position and any undercut or chamfer that matters to assembly. If the ends remain sawn, say so; that avoids unnecessary machining.
Bars come in 4 m, 6 m, 7.5 m or 8.1 m lengths, and CNC cutting starts from 200 mm. For long shafts, state how the length is measured and whether the straightness requirement applies to the cut piece. If the shaft is part of a guided assembly, the end geometry and the bearing fit should be shown on the same drawing so that the supplier can check them together.
The table below collects the points that turn a diameter into a linear shaft specification for this product.
| Requirement | What to put on the drawing | Standard capability for the 45 Steel Chrome-Plated Linear Shaft |
|---|---|---|
| Diameter range | nominal diameter and bearing type | Ø4–130 mm |
| Tolerance band | fit class or numeric band | Ø4–11 mm: −0.02/−0.05 mm; from Ø12 mm: 0/−0.02 mm typical for linear bearings |
| Case hardness | required hardness at the working surface | at least HRC55 |
| Case depth | required depth | about 2 mm |
| Chrome layer | thickness per side | 10–50 μm, chosen per order |
| Chrome finish | Ra limit | Ra ≤ 0.4 μm |
| Straightness | limit and reference length | about 0.1 mm/m from Ø25 mm; about 0.2 mm/m below Ø25 mm |
| Length and ends | cut length; sawn or machined end drawing | full bars 4, 6, 7.5 or 8.1 m; cut from 200 mm; ends left as sawn unless machining is specified |
What to put in your RFQ
- Bearing type or series, and the bore tolerance if it is known.
- Nominal diameter and required tolerance band.
- Straightness limit, and whether it applies per meter or over the full length.
- Case hardness and case depth, if the standard values are not sufficient.
- Chrome thickness per side and the required surface roughness Ra.
- Cut length, quantity, and a dimensioned end drawing for threads, steps or holes.
- Inspection documents required; the steel mill certificate for each heat is supplied, and third-party inspection is arranged on request.
- Packing requirements and destination, so that export packing and shipping can be confirmed.
Summary
A linear shaft specification is a set of linked requirements, not a single diameter. For linear bearings, agree the tolerance band with the bearing type, set straightness and surface finish on the drawing, specify the induction-hardened case and chrome layer, and define the cut length and end geometry. The 45 Steel Chrome-Plated Linear Shaft covers Ø4–130 mm with a typical 0/−0.02 mm band from Ø12 mm, a case of at least HRC55 at about 2 mm depth, chrome of 10–50 μm per side, and straightness of about 0.1 mm/m from Ø25 mm. Confirm the final values on the drawing and order.