CDS Hydraulic Cylinder Tubes: How Much Honing Allowance Is Enough?

A hydraulic cylinder tube may meet the specified steel grade and dimensional requirements, yet still require unexpected machining time before the bore reaches its final size. Some tubes achieve the required finish after relatively little honing, while others need additional material removal to correct bore irregularities or surface defects.

The key issue is often the relationship between the starting tube dimensions and the required finished bore.

For CDS Hydraulic Cylinder Tubes, the right honing allowance should provide enough material to achieve the required bore geometry and surface finish without increasing machining costs unnecessarily or reducing the wall thickness below its design limit.

So, how can the correct allowance be determined before production begins?

1. How Much Honing Allowance Should CDS Hydraulic Cylinder Tubes Have?

CDS stands for Cold Drawn Seamless. Cold drawing improves dimensional control and provides a relatively uniform wall thickness, making CDS tubing a suitable starting material for many hydraulic cylinder barrels.

However, cold-drawn tubing does not automatically meet the final bore requirements for hydraulic seals. Honing is often necessary to achieve the specified internal diameter, roundness, cylindricity and surface texture.

Honing allowance refers to the material available for removal between the original inside diameter and the finished bore.

It can be expressed in two ways:

• Diametral Allowance: Finished ID − Initial ID.

• Radial Allowance: Half the diametral allowance, assuming uniform, concentric material removal.

For example, consider a CDS tube with an initial ID of 79.60 mm and a required finished ID of 80.00 mm.

The nominal diametral allowance is 0.40 mm, equivalent to approximately 0.20 mm of radial material removal per side.

This is an illustrative calculation, not a universal recommended allowance.

Actual tube dimensions must also be considered. If the initial ID ranges from 79.50 to 79.70 mm and the finished bore is specified between 80.00 and 80.05 mm, the required diametral removal could range from 0.30 to 0.55 mm.

More importantly, dimensional allowance alone cannot guarantee complete surface cleanup. Deep scratches, ovality, taper or bore misalignment may require additional correction.

The correct allowance must therefore account for the actual starting bore condition, the finishing process and the minimum permissible finished wall thickness.

2. What Happens When Honing Allowance Is Too Small or Too Large?

Both insufficient and excessive honing allowance can create manufacturing problems, although the consequences are different.

Insufficient Honing Allowance

When too little material is available for removal, the honing operation may reach the specified bore diameter without completely eliminating existing surface defects.

Drawing marks, localized scratches or low spots may remain. Significant roundness or taper errors can also prevent the entire bore from achieving consistent geometry.

These conditions matter because the cylinder bore provides the working surface for the piston sealing system. Poor bore geometry or unsuitable surface texture can affect seal contact, friction, leakage and long-term operating reliability.

Simply meeting the nominal finished diameter is not sufficient if the required surface and geometric conditions are not achieved.

Excessive Honing Allowance

Excessive allowance introduces a different problem: unnecessary processing.

Removing more material than required can increase honing time, abrasive consumption and equipment occupancy. For larger removal volumes, a preliminary boring operation may be more economical than relying on honing alone.

Excessive removal also reduces the remaining cylinder wall thickness.

This becomes particularly important when the original tube has wall eccentricity. The thinnest section after machining depends on the original wall distribution and machining alignment, not simply the nominal wall thickness.

Therefore, ordering a heavier tube does not automatically provide the most economical solution.

The objective is to achieve complete bore cleanup while minimizing unnecessary material removal and preserving the required finished wall thickness.

This is also why properly specified suitable-to-hone tubing can improve production predictability.

3. How Should CDS Hydraulic Cylinder Tubes Be Specified Before Ordering?

The most reliable approach is to start with the finished cylinder requirements and work backward to determine the appropriate raw tube dimensions.

Step 1: Define the Finished Bore Requirements

Before selecting a CDS tube, confirm the required finished inside diameter, dimensional tolerance, bore length and surface finish.

The specified surface texture should match the intended sealing arrangement and manufacturing process.

The minimum acceptable finished wall thickness must also be established.

These parameters define the actual machining target.

Step 2: Evaluate the Starting Tube Geometry

The initial ID and wall thickness tolerances directly affect the available honing allowance.

However, other geometric characteristics also influence machining performance:

• Straightness: Affects alignment and processing over the full cylinder length.

• Roundness and Taper: Determine the material removal required to correct bore geometry.

• Wall Eccentricity: Influences the remaining wall thickness after machining.

• Internal Surface Condition: Determines whether existing marks or defects can be removed within the available allowance.

Dimensional checks should cover representative positions along the tube rather than relying only on measurements taken at one end.

Step 3: Confirm Material, Standard and Processing Route

Common materials for hydraulic cylinder tubing include E355 and SAE 1020/1026, depending on the project requirements.

EN 10305-1 covers seamless cold-drawn precision steel tubes, while ASTM A519 covers seamless carbon and alloy steel mechanical tubing. The applicable grade, delivery condition and inspection requirements should be confirmed for each order.

These standards provide a technical basis for the supplied tube, but compliance alone does not guarantee that an unfinished bore will meet the final honed dimensions or surface requirements.

The intended finishing method must also be considered.

Direct honing, preliminary boring followed by honing, and skiving and roller burnishing have different requirements for starting dimensions and stock removal.

Before full-scale production, representative tubes should be evaluated using the intended processing route. The finished bore dimensions, surface condition and remaining wall thickness can then be checked against the drawing.

A complete specification should connect three elements: the finished bore requirements, the incoming tube tolerances and the planned machining process.

Conclusion: The Right Honing Allowance Starts with the Finished Bore

There is no single honing allowance suitable for every CDS hydraulic cylinder tube.

Too little allowance may prevent complete bore correction, while excessive allowance increases machining time and material removal.

The most effective approach is to define the final bore requirements first, evaluate the raw tube's dimensional variation and select an allowance compatible with the manufacturing process.

TORICH Group

TORICH Group provides precision steel tube solutions for hydraulic cylinder manufacturing, including cold-drawn seamless tubing and customized dimensional requirements.

Planning your next hydraulic cylinder project?

Share your technical drawing, material grade, finished bore dimensions and machining requirements with TORICH Group. Our team can help evaluate suitable starting tube dimensions, tolerances and inspection requirements for reliable downstream processing.

Contact TORICH Group to discuss your CDS Hydraulic Cylinder Tubes requirements.