At HL Hydraulics’ cylinder facility, new rods are machined daily to replace those that are scratched, dented, or bent. In this blog post, we’ll walk through the key stages of rod machining, what to consider—especially from an assembly perspective—and how most machining errors can be avoided with proper planning.
We’ll use a simple example to break down the process: a forestry machine extension cylinder, where a chain had left the rod covered in fine scratches and the damper pin was heavily damaged. As a result, a new rod needed to be manufactured based on the original model.
Measuring the blank and creating a machining plan
First, the dimensions of the old shaft are measured—specifically the piston rod length and the length needed for the new blank. When ordering the blank, it’s important to allow for machining margins and to make sure the blank matches the original. In this case, we ordered a shaft blank with a 5 mm allowance.
A machining plan is also created based on the old shaft. All key measurements are taken using a calibrated micrometer and recorded in the plan.
Dimensions are taken from the flat surfaces, seal grooves, and the damper cone. When checking thread pitch, it’s worth using a thread gauge to confirm the correct pitch. (Tip: keep the matching part close to the lathe to use as a reference when turning the thread.) Having a clear plan saves time, as the machinist doesn’t need to remeasure everything during the process.
Handling considerations
When machining cylinder rods, it’s best to use a crane for moving heavier blanks—even if they seem manageable. Many of the worst dents and dings happen when someone tries to lift a rod by hand and it ends up hitting a sharp edge. Chrome-plated rods are more delicate than they look. Steel can be replaced, but a crushed finger is another matter—so careful handling is also about personal safety.
Soft jaws are used when turning cylinder rods. If you clamp the rod tightly with hard jaws, you’ll likely leave marks on the blank before machining even begins.
Removing the old rod eye
The eye attached to the cylinder rod is still in good condition, so we aim to reuse it. To do this, the old rod is mounted in the lathe, and the eye is removed using a parting tool. The old eye provides valuable information for the welding process, such as the thickness of the hub and the width of the weld bevel. Before reusing it, the old rod eye can be cleaned up for welding by securing it in the lathe and cleaning the bevel area with a blade.
Machining the new rod
Extra care should be taken when handling the new rod—more so than with the old one. For example, when removing the protective plastic, avoid sliding a blade along the rod surface, as a knife or any sharp object can easily leave scratches. It’s also essential to use a support sleeve made of technical plastic in the spindle to prevent the full weight of the rod from resting on the chuck jaws alone.
The rod is lifted into the lathe using a crane and then dialed in. Dialing ensures concentric alignment between the rod and the piston. In this case, a center hole is drilled with a center drill to seat the live center. If the area to be turned is even slightly long, using the live center helps prevent vibration and tapering of the machined surface. After the live center is in place, the rod should be re-dialed to ensure proper alignment.
Select a suitable tool, rotation speed, and feed rate. Material removal is started step-by-step, from a larger diameter to a smaller one, according to the previously drawn plan. It’s important to ensure that the chamfer rounding is done with great care. Seals will be placed over the chamfers during assembly, so if sharp burrs are left during machining, they may damage the seal. Final finishing can be done using a file or sandpaper.
Thread Maching
The thread is turned using the piston as a reference gauge. When machining threads, it’s important to ensure the thread isn’t too tight—there should be a proper clearance so the piston can be screwed into place by hand. This helps prevent damage to the O-ring between the piston and the rod, which could otherwise lead to internal leaks.
Bevel Machining for Welding
Once all necessary edge cleanups are done, the rod is turned around using the crane and a weld bevel is machined at the opposite end using a ball-end tool. The new rod is now ready to move on to the welding phase.
Hopefully you found these tips helpful for machining a rod! If you have any questions or would like an assessment for your rod machining needs, feel free to get in touch!
