Air Grinder and a small form factor compressor

[Daniel "yOPERO" Garrido]

Hi all

Recently someone in my HackerSpace showed me  very nice air grinder http://www.ebay.co.uk/itm/AIR-MICRO-GRINDER-Pencil-Type-Micro-Grinder-56-000-RPM-1-8-Die-Grinder-60-Hose-/261584614862?pt=LH_DefaultDomain_0&hash=item3ce7a875ce

​The air micro grinder its a cool idea a small factor tool that can be attached properly and reduce the stress on the XZ carriage and z axis, in addition it can get up to 56000rpm if you can provide 2 CFM of flow.

I have been doing some research on a small factor compressor as our Cyclones are desktops machines and I found out that the air brush compressors.. yeahh the ones used to do arty paintings and body painting (Dimension: 310x130x310mm)(link below) can provide 23 litres/min of flow.

http://www.ebay.co.uk/itm/Mini-Airbrush-Compressor-With-Tank-AS186-Kit-1-/351236983649?pt=UK_Crafts_DrawingSupplies_EH&hash=item51c75b0b61

​

As said above the air micro grinder(56000 rpm) consumption is 2 CFM (56.6 litres/min) average.

If we can join them that can give us around 22000 rpm which in the case of milling PCBs is awesome. 

I have not got experience with compressors whatsoever so please comment if you have experience and if it is doable.

Regards, 

yOPERO

[Iceflow]

A cheaper one:

http://www.ebay.es/itm/1-8-3mm-Air-Micro-Grinder-Air-Micro-Pencil-56000-RPM-90PSIWithout-Box-x-1-/251315540712?pt=LH_DefaultDomain_0&hash=item3a8392d2e8

For the air compressor, you can do it with a fridge compressor and a empty fire extinguisher, im tracking the fridge compressor now hehehehe already have the extinguisher :P

I think that this can be a good system, but apart from the RMPs i dont know if the torque would be good or it will stall easy... :S

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[Joco]

I think the answer is in the RPMs.  That is how a Dremel works.  Relatively low torque motor but able to spin really fast.   So long as you don't over do the feed rate and have a high RPM then it will probably do the job.

In my case I have a full size compressor within easy reach.   I will have to dial back the air pressure on it to run one of these.   Fortunately it has adjustable pressure.  :-)

[Joco]

I managed to get one of these cheap on NZs local version of eBay. I'll report on how it goes in a few weeks once it turns up and I get clamps designed for it.

[Joco]

Air tool arrived today.  Initial inspection looks promising.

[1] the collet looks a little fiddly to tighten up but i think with a bit of practice it should be fine.

[2] I tried a tool in the collet and after tightening the tool feels solid. No obvious play in the spindle of the tool.

[3] We will need to come up with a revised clamping/mounting system as the tool handle which can be clamped is quite short.  Unless you are using quite long bits they won't reach the work surface. This is where the revised Z mount under discussion at Issue #32 could be the right solution.

Anyway this weekend will see how to looks with some hand held tests.

[Daniel "yOPERO" Garrido]

That was fast!

Please let us know how it goes and if possible share some pictures and links of the compressor and air pen that you have gotten.

I was only theorizing and  you just bought it and went practical instead. Good on you!!.

[Joco]

Will do.

Initial tests will be using a full sized compressor (since that is what I have already).  One able to deliver in excess of 140PSI and has a ~5 litre air tank.

Looking at the tool and doing some more reading I suspect it will do PCB's quite happily but I suspect it won't have enough base torque to deal with soft metals. HOWEVER I do have some 3mm aluminium bar stock that I plan to do some milling tests on using the Cyclone/Dremel setup.  I will use some of that to do some hand tests with the air tool using one of the dremel high speed cutter bits.  It should give an indication of how the air tool handles something with more resistance than a PCB.  I'll report back tomorrow against the above.

Still waiting on the PCB blanks and end-mill bits from eBay to turn up.  The PCB V-bits have arrived.  :-)

[Carlos García]

Neat idea as always yOPERO!!

Those high RPMs are definitely a good thing.

Will the air grinder have enough strenght to cut PCBs? Can't wait to hear from Joco's tests!! :-P

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[Joco]

As they say "Houston we have a problem".

The documentation stays "3mm or 1/8 inch".  BUT when you measure the shafts of the heads that come with the grinder they are 2.91mm. However the shaft of a true 1/8inch tool is more like 3.1mm.

Bottom line I can't get the normal 1/8inch engraving bit and end mills into the collet as.

There is no easy/obvious way to swap collets so I'm going to have a think about if I can pass a 1/8inch drill through the collet to open things up a bit. And how I can secure the collet and stop it from turning while in the drill press vice.

[Joco]

FIXED! The collet had become "squished" after the initial mounting of one of the supplied grinding stones that had a 2.9mm shaft. I found a needle point probe I had and pushed that into the hole which re spread open the collet. Now I can mount my standard 3.1mm shaft engraving bits.

[Joco]

Okay I have some results.

Preamble

The grinder comes with a 13mm hose nipple.  My setup uses the 8mm standard.  Fortunately I had a spare fitting.

I have an existing air compressor which can deliver up to ~150PSI at a reasonable flow rate.

There is a micro oiling in the kit which I used a light grade sowing machine oil in.  I "hope" its working.  There isn't an easy way to tell.  These micro oilers are supposed to be able to last ~4 days of use before needing to be topped up again.

I made sure I used some safety gear (for a change), especially before making dust with the PCB since its FR4.

The Test

I used a 30 degree V engraving bit.

Set the compressor at 90 PSI and let it build up pressure.

[1] For the first test I used a bit of MDF I had about.  Turning the air flow up to max on the grinder and it was spinning live a dervish.

Observations:

- its turning FAST

- handle is cool, not feeling any heat

- very small vibration feeling through the handle but nothing that would be an issue once clamped in a mount

- psi on the compressor gauge drops to ~70 psi under full load.   This reflects the level of air being let through.  It also might be an indicator that my DIY grade compressor isn't enough to supply the full 90psi continuously?

- started hand cut on the mdf.  "Hot knife through butter" would be a very good description.

[2] For the PCB test I secured the board, sprayed a little water on it (just to reduce dust since I didn't have a handy vacuum) and started engraving.

Observations:

- same as for MDF test.  "Hot knife through butter".   No issue at all in cutting into the pcb blank.  I could have very easily used the grinder and V bit to completely cut through the entire PCB board.

- no detectable load on the tool while etching out my initials

All in all I think pretty successful.   The next challenge will be on the air source front.   I have a reasonable sized compressor, hobby grade, but definitely a class above the 12v tire pumping ones that are available.   I think the next test needs to be using one of those style air supplies.   Many of them are rates to 150ps but no idea if they can be limited to a lower value. The other angle will be the consistency of the air supply.   My compressor is designed to give a constant flow without pulses.   These tyre style ones might be inclined to pulse the air flow which might not be good for the grinder? Or for the usage we are looking to put it to?

Anyway, hope the data points supplied are of assistance.  Happy to answer any questions if I can.

[Daniel "yOPERO" Garrido]

Joco

Great job indeed! let us know when you plug the small air compressor, I know by experience that the air grinder works like a treat with standard size compressors.

The air grinder not only give us more revs, reduce noise but also frees some weight from the xz carriage having an air grinder is going to have the same effects as having a bowden in a 3d printer(++precision ++speed)