My spindle was damaged by brass dust after I tried engraving. The maker rebuilt the spindle and returned it with two devices I’d never used (filter/pressure control and a solenoid). This post is for people who go through what I did: want to protect the bearings, but have a poor understanding of both air delivery and electronic control. I hope people with the experience I lack will improve this post with corrections and advice.
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Who cares?
For me, it was brass dust, but the fine dust from cutting MDF also coated the air holes next to the collet. How much of that gets in? -
What pieces go into the set-up?
A. Air compressor (I chose DeWalt DXCM603)
B. Power to the compressor
C. Air line from the compressor to the CNC control box (or its vicinity)
D. Filter (remove water, oil and debris; one example is Festo MS4-LFR-1/8-D5-C-R-M-WR-Z)
E. Pressure regulator (get consistent pressures, much lower than your compressor can dial in…0.5 to 4 bar. (4 bar = 60 psi). D and E are often one unit.
F. Solenoid valve to allow air through to your spindle. Electronic signals open it…it’s closed when receiving no power). Mine is wired to open when the spindle turns, not when the VFD is on. So it’s inside my control box). Mine is Festo MHJ-10-S-0.35-QS-4-MF)
G. Tubing from the solenoid valve to the spindle.
H. Port on the spindle to let air in. The spindle maker added this to mine when they repaired it.
- What are the requirements for those devices?
If you’re going to run long carves (several hours) the compressor has to rest 2/3rds of the time it’s in use. So you have to know how much air (liters per minute or cubic feet per minute: cfm) will flow through your set-up. Then, your compressor has to be able to deliver 3 times that volume at a realistic pressure. So, for example, if your compressor delivers large volumes but only at trivially low pressures, it does you no good.
The maker of my pressure valve (Festo) writes that it will ask for 100 liters per minute. That’s 3.5 cfm. So I needed a compressor that delivers 10.5 cfm at 90 psi. That spec is offered on the compressor documents that buyers review. I chose a DeWalt 60 gallon unit, that delivers 14.1 cfm at 90 psi. ($1000 at Tractor Supply). The closest competitors were Ingersoll-Rand machines.
The compressors that can do this job use 240V. The DeWalt needed a 30A breaker, which I had in my panel (serving a planer). Because the two devices will never be in simultaneous use, I added a 240 V outlet to my existing line. The Ingersoll Rand machine needs 40A, which would have required a new panel, in my case.
My CNC is not adjacent to my electrical service panel. So a choice was required: either a long air hose and short wiring, or long wiring and short air hose. You will want the short wiring option, even at the price of a long air hose. I strung that in the joists over my basement shop.
The air tubing size from filter to solenoid valve and from valve to spindle is dictated by the device maker. For me, that was 4mm, which fit into my (almost full) drag chains. I puzzled over how to get the tubing to the port next to the collet without interfering with the bits or the projects. The simple solution was a hole drilled in the roof of the dust boot (which stays in place when the boot is removed for bit changes).
Lastly, the solenoid valve needs power. Mine has 3 wires: blue, brown and black. Blue connects to the 0 VDC terminal in my panel. Brown connects to the 24 VDC terminal. If you want it to open when your power comes on, the Black also goes to the 24 VDC terminal. In my case, the VFD uses a 24 VDC signal to the contactor that powers my water (cooling) pump. So with Black connected there, the solenoid valve opens when the VFD starts turning the spindle, (as does the water pump)