Creating a hydraulic cylinder involves several steps, and it requires some engineering and machining skills. Here is a basic overview of the process. Keep in mind that safety precautions should be followed, and the design should adhere to engineering standards.

Materials and Tools:
Materials:

Cylinder tube (typically made of steel)
Piston rod (also usually made of steel)
Seals (O-rings and other sealing elements)
End caps
Hydraulic fluid
Various fasteners and fittings
Tools:

Lathe (for machining the cylinder tube and piston rod)
Milling machine (for machining end caps and other components)
Welding equipment (if welding is necessary)
Hydraulic press (for assembling the cylinder)
Thread taps and dies
Calipers and measuring tools
Hydraulic fluid reservoir and pump
Steps:
Design:

Define the specifications of your hydraulic cylinder, including bore diameter, stroke length, and operating pressure.
Determine the materials and dimensions for the cylinder tube, piston rod, and end caps.
Design the seals and ensure they can handle the hydraulic fluid and pressure.
Machining:

Use a lathe to machine the cylinder tube to the required dimensions, ensuring a smooth interior surface.
Machine the piston rod to the desired length and diameter.
Use a milling machine to create the end caps. The end caps should have ports for hydraulic fluid and fittings for connecting hoses.
Seals and O-Rings:

Install seals and O-rings on the piston rod to prevent hydraulic fluid leakage.
Ensure proper alignment and lubrication of the seals.
Assembly:

Insert the piston rod into the cylinder tube.
Attach the end caps to the cylinder tube using fasteners or welding, ensuring a secure and leak-proof connection.
Install fittings for hydraulic hoses on the end caps.
Testing:

Check for any leaks by pressurizing the cylinder with hydraulic fluid.
Test the cylinder’s functionality by extending and retracting the piston rod.
Ensure that the cylinder operates within the specified pressure and load limits.
Finishing:

Paint or coat the hydraulic cylinder to protect it from corrosion.
Installation:

Install the hydraulic cylinder in the intended application, connecting hoses to the hydraulic system.
It’s important to note that designing and building hydraulic components should be done by individuals with knowledge of fluid power systems and engineering principles. Additionally, compliance with safety standards and regulations is crucial to ensure the reliability and safety of the hydraulic cylinder. If you are not experienced in hydraulic system design and fabrication, it’s recommended to consult with professionals or engineers in this field.