Positive air connection (how?)

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I’m preparing to supply air pressure to the spindle. The purpose is not to cool it, but to prevent dust from fouling the bearings (brass dust caused an expensive repair).

The air system parts are straightforward from compressor (and its required specs) to the in-line filter. I’m struggling with two further steps.

  1. A solenoid allows air to flow, but I’m not clear on its purpose nor its position. Perhaps it’s a bad thing to have the compressor sending air into a spindle that’s not in use, but why? Is it simply wasteful to a filter that has a finite lifespan or are there additional reasons? The solenoid has 4 mm push-connectors on the input and output sides, so it surely goes between the filter and the spindle (not between compressor and filter). If so, then it’s protecting the spindle but not the filter, so (again) why is it needed?.
  2. The solenoid has to be wired to turn on (open) when the VFD tells the spindle to operate. I haven’t figured out how that’s done. The docs tell me it needs a 24v source, but there must also be some instructions to code into the VFD.

CNC dust boot
CNC dust boot1267×950 172 KB

  1. What’s the best way to run the 4 mm tubing through the dust boot? The spindle’s air port sits just above the collet. My boot has 3 parts: “Roof” (with a finger nut clamp) which remains in place, “Body” which uses magnets to connect to the “roof” and encloses the lower 25% of the spindle/ collet nut and “Brush” that extends suction power to the workplace surface without banging into the hold-downs. I usually remove the boot’s body and brush when changing bits, but disconnecting the tubing at that frequency will cause harm to the tubing, if not the connector itself.
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Some details would be helpful…
Please provide a reference to the make and model of your VFD.
What controller are you using?

Using air for this purpose uses a great deal, so the solenoid provides both a method of control and a way to limit wasteful use of the compressor air/electricity. It typically is the last in the chain before the spindle, and is not meant to ‘protect’ anything. Having it after your 2 or 3 stage filter system will also protect its seals from debris.

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VFD: Hitachi S1-00130SFE.
Spindle: Mechatron HFS 8022 (2.2 kW)

Here’s a photo of the manual page that (I suspect) has the answer to where connections go. But honestly, this is a foreign language to me, and I’ve learned that some things that seem straightforward are anything but.

Control circuits
Control circuits1288×966 202 KB

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I have a different model of Hitachi VFD, but the functionality and connections may be similar.
I set up my purge air in a similar manner as described in the below linked video - see 10:30 mark if you want to skip ahead (Clough42 is a great channel BTW and I recommend looking at some of his other YT video content).

NOTE: keep in mind it is a different VFD model, and that he is creating a more complicated/functional overall circuit, but the steps and parameter settings may prove helpful.

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