This video documents the complete custom fabrication process of two replacement end caps for a hydraulic accumulator, for which original equipment manufacturer (OEM) parts and drawings are unavailable. Starting with an offcut of 115mm induction-hardened chrome bar, the process begins on a lathe to machine off the hardened outer layer and turn the main body, including the external thread and grooves for seals. The video then transitions to a milling machine where critical features are added. This includes drilling and tapping a central port for nitrogen gas charging, creating precisely located holes on a pitch circle diameter (PCD) for a spanner wrench, and adding threaded holes for a protective cover plate. A key point discussed is a design flaw in the original part that allows moisture ingress; the customer opted for a practical workaround using a silicone sealant during reassembly rather than a full redesign. The video concludes with the successful completion and test-fitting of the two custom-made parts.
Fabricating Custom Hydraulic Accumulator End Caps
0:00:20Material Selection: The end caps are fabricated from an offcut piece of 115mm induction-hardened chrome bar, chosen because it was available in the workshop.
0:00:44Reverse Engineering from Scratch: With no OEM specifications or drawings available, the new parts are designed and dimensioned by referencing the opposite end of the accumulator.
0:01:10Lathe Machining: The initial major machining is done on a lathe. This includes turning off the hard chrome layer, facing the part, and machining the outer diameter down to the final size for the main thread (106.2mm).
0:06:40Addressing a Design Flaw: The original design lacks a proper seal against the environment, allowing moisture and dirt to enter. Instead of a costly redesign, the customer opted for a simple workaround: applying a bead of silicone during final assembly to create a seal.
0:07:47Machining Sealing Details: The end cap is machined with grooves to house the necessary seals and a shoulder that acts as a positive stop, preventing it from being screwed too far into the accumulator barrel.
14:52Creating the Gas Port: A central hole is drilled and tapped to accommodate the fitting used for charging the accumulator with nitrogen gas.
25:25Milling Spanner Wrench Holes: Using the mill's digital readout (DRO) with a Pitch Circle Diameter (PCD) function, three holes are precisely drilled to allow a spanner wrench to tighten or loosen the end cap.
29:49Adding Cover Plate Mounts: The final machining step involves drilling and tapping three holes for 3/8" bolts, which will be used to secure a cover over the central nitrogen fitting.
37:08Project Success: The video successfully demonstrates the creation of two complex, custom-fit components from raw, salvaged material, providing a solution where OEM parts are no longer available.
37:25Final Test Fit: Before finishing, the newly machined end caps are threaded into the salvaged accumulator barrels to confirm a perfect fit.