Air drilling???

[irving2008]

I did my back in picking some paper of the floor by my desk so no work this weekend on my lathe restore and a couple of days off work at home.

Wandering round CNCZone I got bitten by the bug and a bit carried away on fleabay (you know how it is! ) and now have enough material for a 300mm X axis and a 200mm Y axis (rails, linear bearings, leadscrew) plus 4 steppers, a 500VA transformer and a 22000uF smoothing capacitor. Stepper driver chip samples are on the way as are power transistors and a few other parts...

Haven't quite worked out what I am going to build exactly (esp the Z-axis) but something that will mill PCBs and do some light aluminium work. All the calcs I have done suggest I could take a .15mm cut with a 10mm endmill in 6061-T6 ali with the stuff I have if I come up with a rigid enough frame.

The calcs suggest to do this I will need a 50W spindle motor at 3000rpm. I'd want this to be as lightweight as possible and looking at motors that could do the job I was dismayed by their weight (typically 2 - 3kg). Then I was reading up about coolant and how mist cooling is the 'next big thing' and I was musing on how I could use my air compressor to provide the pressurisation using a modified airbrush head when an idea dawned.... why not use the air pressure to drive the milling spindle?

So, has anyone done this and if not, why not?

[Boots]

Forget about using air to power the Spindle. You will not have enough power to mill anything other than marshmellows. I'm serious.... you need real programmable power that only High Frequency motors can give you. I have run air drills in the past and they never have much power and can only do light drilling. Once they start taking on a load they slow right down to a stall. If you ever invented an air spindle that could do heavy work it would be soooo big it would dwarf your machine. Good luck.....

[irving2008]

Originally Posted by Boots Forget about using air to power the Spindle. You will not have enough power to mill anything other than marshmellows. I'm serious.... you need real programmable power that only High Frequency motors can give you. I have run air drills in the past and they never have much power and can only do light drilling. Once they start taking on a load they slow right down to a stall. If you ever invented an air spindle that could do heavy work it would be soooo big it would dwarf your machine. Good luck.....

I did wonder about the torque curves for an air drill but a quick Google didnt come up with much relevant. I do have an air drill attachment with a 3/8" chuck but its still in its plastic wrapping since I've never had need to use it... maybe I never will!

[Boots]

When I used to work for Walploe Woodworkers they had A Thermwood machine that had Horizontal Drilling up to 3/8 Dia. . We thought that the air spindle and our current air supply were enough for it but later found out we had to purchase a seperate air compressor just for the Machine in case we had to use the drilling attachment. The compressor was around $6,000.00 for the CFM we needed for it. I couldn't feed to fast with it or it would boog right down. I wasn't very impressed.