Why Do Gas Spring Cylinders Need Inner Grooves? Oil Groove Function, Patterns and Grooving Machines
Open up a tailgate strut or an office chair gas lift and you will find a few thin longitudinal grooves on the inside wall of the cylinder. These are oil grooves (also called damping or bypass grooves). Machining them is called inner grooving, and the machine that does it is an inner grooving machine.
What the grooves do
Where the piston passes a grooved section, oil or gas flows around the piston through the groove and the movement is fast. Where there is no groove, the fluid can only pass through the small orifice in the piston, so the movement is damped and slows down. The length, depth, number and start/end position of the grooves therefore set:
- the opening speed curve of a tailgate and its end-of-stroke cushioning
- the feel of an office chair or furniture gas lift
- the damping characteristic of a shock absorber or damper
Common groove patterns
| Pattern | Description |
|---|---|
| Single groove | One longitudinal groove, the simplest design |
| Two grooves at 180° | Symmetrical, more even loading |
| Three grooves at 120° | Evenly spaced around the bore |
| Segmented grooves | Several segments on one line for different speed zones |
| Different depths | Different groove depths in one cylinder for progressive damping |
What matters for quality
- Consistent groove length and depth from cylinder to cylinder, for a consistent product feel.
- Accurate start and end positions, so the cushioning zone is where it should be.
- A smooth bore after grooving, with no burrs to damage the seal.
Close first or groove first?
Both sequences are used, depending on the cylinder design. End closing and inner grooving are the two core cylinder operations, so clamping and locating are best planned together.
Servo or hydraulic inner grooving?
| Model | Drive | Best for |
|---|---|---|
| TD-627 servo inner grooving machine | Servo slide; groove length and depth set by program, recipes stored and recalled | Many sizes, frequent changeovers, tight depth consistency |
| TD-61530 hydraulic inner grooving machine | Hydraulic; groove length set on screen, width and depth adjustable | Fixed specifications, high-volume tailgate strut / gas lift lines |
Why TONG DA
- TONG DA builds both inner grooving and tube end closing machines, and runs gas spring cylinder contract production on its own machines.
- Grooving tools are made to the cylinder bore and groove width, with long-term supply.
- CE certified; machines sold to the USA, Germany, Turkey, the UK, India, China and more.
FAQ
How many cylinder sizes can one machine handle?
Change the tool and fixture to switch bore sizes – one tool set per bore.
Can I send samples for a trial?
Yes. Send the cylinder OD, wall, material, length and the groove drawing (length, depth, number, position); TONG DA runs a trial and returns samples.
How do I ask for a quotation?
Send your cylinder specification, groove drawing and requirements to sales@tdco.com.tw and we will reply promptly.