Air Sealing; another alien topic for a woodworker new to CNC!

Background: New to Onefinity, wanted a little work with brass clock dials, but mostly the all-wood opportunities of CNC. After 2 months of very fine brass work, spindle bearings failed. Despite 3HP cyclone dust control, brass got into the device. Maker recommended an air seal. Now it’s arrived and I’m stumped. I speak rudimentary German, but pre-school electronics. So if you also are interested or experienced in using air seals to keep damaging dust out of your spindle, please read on!

Please see the image. I used letter labels because I don’t know the correct terms.

  1. I’m not sure whether the parts are displayed in the proper order. Plastic tubing (not shown) connects (perhaps?) from (A2) to (B1) and from (B2) to (C1). Is that correct?
  2. (A1) connects to an air compressor, but a German one. Is there a term I use, when contacting a vendor for a coupling between the German fitting and my American compressor? If I should use an American replacement for A1 (instead of the German one) I’ll need to know the proper size for the threaded end.
  3. (C2) is the same size as the hole at (D), but that’s my guess on where C2 attaches. The metal hexagon doesn’t spin, and the “L” shape prevents (C) from rotating into the hole more than 180 degrees. (All components shown bought from the same manufacturer, Mechatron. No reply yet from them).
  4. What do the three wires at (F) attach to? Its label identifies it as Festo company, MHJ10-S-0. The solenoid diagram seems to show that when activated it permits air to pass but is normally closed. There are labels saying BU: Gnd BN: 24V and BK: Trigger 3-30V. But the colors in German would be blau (blue), brunn (brown) and schwarz (black). Is BU “blau” and BN “brunn”?
  5. What happens at (E)? Is it a waste port (e.g. oil)?

Hey David,

welcome to the world of pneumatics! You will now have to get into this new matter a bit in order to know how to attach this and make it run.

A spindle that supports sealing air will live much longer, since it is impossible that dust comes into the spindle. Tom @TMToronto connected one more recently than I :slight_smile:

The connector on the right is for a one-hand quick-release ISO 4414 connector that you find on air compressor hoses. See this article in Fluid Power Journal.

The maintenance unit is explained here: Festo MS4-LFR. What you can let out is condensed water at (E).

The air solenoid valve Festo MHJ10-S-0,35-QS-4-MF switches the sealing air on and off by a relay which you can be controlled by your VFD just like it controls water coolant pump. Yes black is BK, blue is BU and BN is brown.

All hose connectors are tool-less Festo QS system.

Yes, the piece end (C2) goes to spindle openening (D). This is the input for the sealing air. You should be able to spin the hexagonal nut on the L piece, is this not the case? It should look like on this spindle when mounted.

Please don’t buy one of these oilless compressors or you will service it once a year.

Recently there was a good article in german Make Magazine about Pneumatics for CNC users. Not only you can have spinde sealing air and automatic tool change control with it but you also control pneumatic actuators with it e.g. to clamp your workpieces. In the article, they suggested the encapsulated oil bath compressors from Jun-Air (formerly Blue-Air) (EU, US). They are quite expensive but extremely silent and service-free. They look and work like the encapsulated oil bath compressors that everyone knows from refrigerators, which are also very silent and service-free.

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Thank you!

The air filter/controller describes the pressure desired on input (6-10 bar, or 70-90 PSI) but the compressor selections are described in the volume per unit time (CFU / min). I assume the volume of air in this application is so small that all of the models offered will suffice in that regard?

Hey David,

you remember, Mechatron said, for the sealing air 1 – 1.5 bar pressure is enough. I don’t know how much air flow rate the spindle will let through, but usually pneumatics need very small flow rates as you don’t really consume the air. That would be rather the case if you used the air to blow chips away. The Jun-Air compressors provide 8 bar max.

The pressure is measured in Pascal (Pa), here mostly still in SI-derived bar (US/imperial: psi) and the volumetric flow is measured in cubic meter per second (m³/s) (US/imperial: cubic feet per minute (cfm))

1 m³/s = 60 m³/min = 3600 m³/h
1 m³ = 1000 dm³ = 1000 l
1 l/s = 60 l/min = 3600 l/h

1 bar = 100,000 Pa (= 100 kPa)

SI to Imperial and U.S. Customary Conversion:

1 l/min = 0.0353146667 cfm
1 cfm = 28.316846592 l/min

1 bar = 14.50377 psi
1 psi = 6.894757 kPa = 689.4757 mbar

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@Arzt, was your spindle that failed air or water cooled? Thanks!

Water-cooled. As I mentioned, my first guess was wrong. I thought it overheated because I put the cooling unit too close to a cabinet side. Finding brass dust inside changed everything. I understand your question: did air as a coolant cause this? Nope. But I imagine it could be worse with air cooling.

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It’s like you read my mind!