A guide pillar shaft usually carries three separate requirements that are often compressed into one line on a drawing: substrate hardness, the hard-chrome layer, and the fit. Hardness comes from the steel and its heat treatment, chrome hardness and case depth are independent characteristics, and fit follows from the tolerance zone together with the conditions under which the part is measured. Each one has to be specified and accepted on its own terms.
Which hardness do you actually need on a guide pillar shaft?
The hardness you need depends on how the pillar is guided and loaded, and it should be ordered as a treatment route rather than as a single HRC number. A number on its own says nothing about where in the section it applies or how deep it goes, so the route and the depth matter as much as the value.
Three routes are common. A shaft that is not hardened and is then hard chrome plated keeps its base hardness — for example, the 45 Steel Chrome-Plated Soft Shaft has a base of approximately HRC17. A shaft that is induction hardened before chrome carries an induction-hardened case of at least HRC55 in the steel at approximately 2 mm deep, as with the 45 Steel Induction-Hardened Chrome Shaft. Quenched and tempered (Q&T) bars sit between the two: they are quenched and tempered rather than surface hardened, and have no induction-hardened case.
| Route | Yixin product example | Hardness stated on the order | What the number describes |
|---|---|---|---|
| Not hardened, hard chrome | 45 Steel Chrome-Plated Soft Shaft | base approximately HRC17 | Base material only; no case |
| Induction hardened, hard chrome | 45 Steel Induction-Hardened Chrome Shaft | case at least HRC55, approximately 2 mm deep | Case hardness and case depth |
| Q&T, hard chrome | 45 Steel Q&T Chrome-Plated Bar | surface hardness HRC25–28 or HRC28–32, chosen per order | Surface hardness only; not core or through hardness |
| Q&T, hard chrome | 40Cr Q&T Chrome-Plated Bar | Q&T hardness HRC28–35 | Q&T hardness |
| Q&T, hard chrome | 42CrMo Q&T Chrome-Plated Bar | Q&T hardness HRC30–38 | Q&T hardness; intended for heavy or shock loads |
Grade 45 is specified to GB/T 699-2015; 40Cr and 42CrMo are specified to GB/T 3077-2015. Comparable grades in other systems — C45, S45C and SAE 1045 for 45; 41Cr4 and SCr440 for 40Cr; 42CrMo4 and SCM440 for 42CrMo — are for reference only, because the chemistry limits differ between standards.
Does hard chrome make the shaft harder?
Chrome hardness can reach HV800+, but that value describes the plated layer, not the shaft. Chrome hardness and case depth are separate characteristics, and one cannot be substituted for the other. The layer is measured in tens of micrometers, so the substrate still carries the load and still determines how the pillar behaves against its bushing.
Where a case is required, the substrate is induction hardened before hard chrome. That order matters: the case is created in the steel, and the chrome is applied afterward as a surface finish. If a drawing asks for a high hardness without saying which characteristic it means, the supplier has to guess whether the requirement applies to the chrome layer or to the steel underneath, and the two are accepted by different measurements — HV on the layer, HRC on the steel.
Adhesion is a separate question again. The appearance of a chrome layer cannot prove adhesion; adhesion requires an agreed test or inspection method. If adhesion is a mandatory acceptance item for your application, name the method in the inquiry rather than leaving it to visual inspection at goods-in.
How thick should the chrome be?
Hard chrome on Yixin shafts is 10–50 μm per side, chosen per order. The right value inside that band depends on what the layer has to do: a modest layer for wear resistance and a smooth running surface, a thicker layer where the surface will see more abrasion or where a corrosion rating has been requested.
Thickness is never a free choice, because plating adds material to the diameter. The chrome layer, the grinding allowance and the final tolerance have to be agreed together, and the finished size is what gets inspected. If a drawing gives a final diameter and a chrome thickness but no indication of how they interact, confirm which dimension is measured before plating and which after.
Thicker chrome layers are quoted with a lead time set per order. 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 tolerance and fit should I specify?
Specify the basic size, the tolerance zone and the measurement conditions together; a fit designation on its own is not enough. For the 45 Steel Chrome-Plated Linear Shaft, the zones typical for linear bearings are −0.02/−0.05 mm for Ø4–11 mm and 0/−0.02 mm from Ø12 mm. Across the chrome-plated and Q&T ranges, from Ø12 mm the zones 0/−0.02 mm, −0.01/−0.03 mm or −0.02/−0.05 mm are available. Note that Q&T bars generally start at Ø8 mm (the 40Cr Q&T ground bar starts at Ø5 mm), so a −0.02/−0.05 mm zone on a Q&T bar applies from Ø8–11 mm, or Ø5–11 mm for the 40Cr Q&T ground bar.
Fit is decided by the zone plus the geometry around it. Surface roughness, straightness and cylindricity are separate requirements and should be listed separately. Chrome-plated bar is supplied at Ra ≤ 0.4 μm and ground bar at Ra ≤ 0.8 μm; straightness is approximately 0.1 mm/m from Ø25 mm and approximately 0.2 mm/m below that. A long pillar measured at one temperature and accepted at another can pass on the drawing and still fail in assembly, so state the measurement conditions for long or precision shafts, including where along the bar the diameter is checked.
How do I inspect guide pillar shafts on receipt?
Inspect against the items written on the drawing and order, using one agreed method per characteristic. Appearance alone confirms very little: diameter, hardness, chrome thickness, straightness and roughness each need their own check, and adhesion needs an agreed test if it is a mandatory acceptance item.
| Characteristic | What to check | Record |
|---|---|---|
| Diameter and tolerance zone | Measured at agreed positions along the bar, at an agreed temperature | Measured value against the zone on the drawing |
| Substrate hardness | HRC on the steel, at an agreed location and depth for a case-hardened route | Route, value and, where relevant, case depth |
| Chrome hardness | HV on the plated layer, kept separate from substrate hardness | Layer value, not substituted for case hardness |
| Chrome thickness | Per side, by the agreed method | Value in μm, with the final diameter it produces |
| Straightness and cylindricity | Per the agreed method, over the agreed length | Value in mm/m and the length basis |
| Surface roughness | Ra on the finished surface | Chrome-plated or ground value |
| Adhesion, where mandatory | The agreed test or inspection method | Result against the agreed acceptance item |
What to put in your RFQ
- The treatment route: not hardened, induction hardened with case depth, or Q&T — plus the hardness value and whether it applies to the surface, the case or the Q&T condition.
- The chrome requirement: thickness per side in μm, and whether the stated diameter is measured before or after plating.
- The basic size, the tolerance zone and the diameters over which it applies, written as a range rather than a single size where the pillar is stepped.
- Straightness, cylindricity and Ra as separate line items, each with its measurement basis.
- The measurement conditions for long or precision shafts: temperature, support points and the positions where diameter is checked.
- Adhesion as a mandatory acceptance item, with the test or inspection method named, if the application requires it.
- The material grade with its standard, and any comparable grade noted as reference only.
- Packing and delivery scope, including cut length, end condition and how the bars will be handled on arrival.
Summary
Hardness, chrome and fit are three specifications, not one. Hardness is set by the treatment route — not hardened, induction hardened with a case of at least HRC55 at approximately 2 mm deep, or Q&T — and the value must say which characteristic it describes. Chrome is a layer of 10–50 μm per side whose hardness can reach HV800+, but it neither replaces a case nor proves its own adhesion. Fit comes from the basic size, the tolerance zone and the measurement conditions, with straightness, cylindricity and roughness listed separately. Writing all three on the drawing, with the acceptance method for each, is what makes a guide pillar shaft order inspectable.
References
- GB/T 699-2015 — the standard to which Yixin's Grade 45 is specified.
- GB/T 3077-2015 — the standard to which Yixin's 40Cr and 42CrMo are specified.