Here is an excerpt from a dust collection article I wrote a few years back:
Static Reduction in CNC Dust Collection Systems
Dust collection systems are one of the primary generators of static in woodshops. This static becomes very problematic when the dust collection system is connected to a CNC cutting tool. For those CAMaster owners that have experienced issues caused by static discharge, getting a reasonably priced solution is often difficult to come by. The following should give those users a viable option.
Static is generated by air and dust movement in a non conductive hose. I have used metal ducting to solve a number of static related CNC control issues. The following instructions explain the use of light gauge home improvement store type galvanized 4" ducting in place of the often used flexible plastic dust hose. The advantages of metal ducting are as follows:
• Metal ducting is installed grounded and "drains" any static charge carried inside by the particles
• Increases flow due to less restriction than flexible hoses
• Gives a reliable ground path out to the flex hose at the machine and allows it to be grounded well
• Properly installed, forms an anchor point for the flex hose to attach to
When you install a metal duct system to a CNC machine you should:
• Use as large diameter pipe as can be connected to the dust collector housing, reducing diameter as distance increases.
• Run the metal duct as far as possible, i.e., run it out to over the CNC table in the center 8 to 10' high
• Screw the fittings to the collector housing and to each other
• Tape the joints to reduce leakage
• Verify that the dust collector itself is actually grounded to the electrical system ground
• Make sure that the metal duct is grounded by adding a ground wire to the electrical system or collector housing (if needed)
• Use a 4" flexible dust hose with an embedded wire. DO NOT USE AN ALL PLASTIC HOSE
• Use the shortest length of flexible hose that allows full movement to table extremities
• Make sure that the embedded wire from the flex hose is attached to the metal duct with a screw and crimp connector.
• In high altitude, low humidity, or problematic locations an additional stranded wire run thru the hose may be required. This must also be connected to the ground screw along with the embedded wire from the flex hose
• Do not allow the dust foot end of this wire to come in contact with the metal parts of the CNC machine
Note: Along with the dust hose drain wires, it may also be beneficial to make sure that the dust hose itself has been insulated from any of the CNC components by at least 1/2". This can be done by providing a support near the top of the X or Z plates that work both as a strain relief AND an insulator. When cutting high static producing materials the charge inside the hose can build high enough to discharge thru the hose onto the frame. This problem most often comes to light when surfacing and an errant (charged) hose comes in contact with the machine.
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