The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

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  • Laser Cutter: Assist Air Flow vs. Pressure

    A question on the LightBurn forum prompted a quick-n-dirty measurement of the assist flow rate vs. inlet air pressure, which required a bit more oomph than the laser’s air pump can provide.

    So a small air compressor with a buffer tank on a T fitting in the Basement Shop provides the air:

    Laser assist air flow test - compressor
    Laser assist air flow test – compressor

    The far end of the green 50 ft hose has a horrific quick-disconnect 1/4 inch NPT to 6 mm tube adapter replacing the laser cutter’s air pump:

    Laser assist air flow test - inlet adapter
    Laser assist air flow test – inlet adapter

    Protip: If you’re trying to run an actual air tool at the end of fifty feet of 1/4 inch ID hose, you’re doing it wrong.

    Flow measurements come from the flowmeter inside the cabinet:

    OMTech Laser - air flowmeter installed
    OMTech Laser – air flowmeter installed

    The normal dual-flow assist air setup has a flow control valve (the knob sticking up on the right) normally set for 2 l/min from the air pump:

    OMTech Laser - air assist - plumbing
    OMTech Laser – air assist – plumbing

    I cranked that valve completely open to allow unrestricted flow with the solenoid (block in the middle) closed and varied the compressor’s output pressure while measuring the air flow.

    Without further ado, the assist air flow rate as a function of the inlet air pressure just upstream of the Y fitting on the left:

    Assist Air flow vs inlet pressure
    Assist Air flow vs inlet pressure

    Fairly obviously, the flow is not 5.5 l/min at 0 psi inlet pressure and the long & skinny air hose limits the flow above 15 l/min. The eyeballometric line looks pretty good in the middle, though.

    Other measurements not shown here suggested the outlet pressure, as measured just downstream of all the plumbing / upstream of the flowmeter & hose to the laser head, is about 1 psi at 10 to 12 l/min flow, with 0.2 psi at 8 l/min. My pressure gauges have terrible accuracy at such low pressures, so I don’t trust those numbers, but the plumbing definitely accounts for most of the inlet-to-outlet pressure drop.

    The nozzle on the laser head is 4.1 mm ID → 13.2 mm²:

    Magnetic Honeycomb Spikes - MDF
    Magnetic Honeycomb Spikes – MDF

    A flow of 10 l/min produces a 13 m/s = 28 mile/hr wind through the nozzle, which seems adequate to blow the fumes out of the kerf, and the low-flow default of 2 l/min might be a 5 mph breeze.

    More air pressure would produce more wind, but it’s not clear how much better the resulting cuts would be.