Air Drill issues

[Gary Campbell]

Vassil...
In general, what Nat says is correct, I will add to it. I bought my first PRS before ShopBot produced a drill for it, and I did a great amount of experimenting in this area. I have used many different options for both plunging and switching, wont say I'm an expert, but have drilled tens of thousands of holes testing electric, hand held inline (like the SB) and the ARO industrial programmable drills. I have recorded video of most different actions. Here is one of the ARO drills working as you desribe: http://www.youtube.com/user/Islaww1#p/u/5/Tr5TvVV5YNE

Although this worked, it requires the drill to traverse its entire stroke for each hole. This is usually 3-4 inches. The plunge speed can be adjusted somewhat with flow controls, but it usually takes a good number of tests to get good results. In order to insure that the machine "stays" in position till the hole is completely drilled, I added prox switches to the bottom of the stroke. When slow plunge speeds are required, it is not efficient to plunge 3-4" to drill 1/4" deep holes. This is the only option for drill control that I am aware of that will work with Gcode. Other than those drills that run continuously during a drill cycle, this configuration uses the most air. Air is used to plunge, retract and drill for each hole.


In 2009 ShopBot software developers added some "trickery" to the code that triggers an output during a plunge only move. This allowed users of the SB drill to add the dual control as Nat refers to above and cut air consumtion considerably. It also decreased cycle times. Here is a video that was taken just after this new code was implemented. It shows the drill plunged for the complete drilling file, and the enhanced code turning on the drill, only during the down drill move. http://www.youtube.com/user/Islaww1#p/u/7/QmYlwc4Cmlw


This advancement has shown to use the least air, and allow full software control of the plunge speed. This may be the best feature of the PRS style drill over the PRT. I have used plunge speeds ranging from .125 to over 4 inches per second. This range of adjustment is not avalable using flow controls on plunge cylinders. This is one of those areas where we SB users have an advantage over Gcode machines.

Hope this clarifies those drill actions.

[Gary Campbell]

Vassil...
You and I were posting at the same time. I can give some info for your questions to Nat.

Most sheetgoods I have tested use plunge speeds from 1 to 2.5 ips or 60 to 150 ipm. I dont have good numbers for Melamine. Often as slow as .125 ips for aluminum.

If you use a single solenoid, 5 port valve for your plunge control and a dual rather than single action cylinder, the retract will have the same power as the stroke. This gives that additional advantage that retract speed can be controlled by flow control valves also.

[vassilm]

Gary,
As always, your answers are very thorough. Thank you very much. It is now much clearer.
As right now I do not have a second solenoid installed and I cannot control plunge and spinning separately, what air consumption am I to expect if I use the method where the drill is on all the time and it moves along Z with the stepper motor? And is it a viable way of using the drill on a continuous basis if I don't have this second solenoid?
Vassil

[Gary Campbell]

Vassil...
I do not know what your drill consumes, so I cannot even venture a guess. I can say, based on the experience of owners of the SB PRS drill, that the cfm seemed to be more then 25cfm when used continuous. Intermitent use enabled by addition of the 2nd solenoid and the new control options lowered this to under 10 cfm.

For example, my IR SSE-5 5hp 60 gal compressor puts out around 15cfm @ 90 psi. You can see that those of us with similar sized compressors went from a non working to a working situation.

All of the different setups are viable, just different. And each has a different air cfm requirement.

[vassilm]

I was wondering, do you think I can put a regular drill bit in the spindle (I mean one that would normally be used in the Air Drill)? And if yes, at what rpm speeds should I spin it for drilling?
I am trying to have 2 different drilling diameters.
Vassil

[bleeth]

There is not a problem putting a drill bit in your spindle. I just did that recently for a load of holes in aluminum. I spun the spindle at around 1750 similar to the speed I would have from my Milwaukee hand drill but faster than a drill press. Feed was pretty slow since it was aluminum and I used peck drilling to keep the flutes clear. An air drill usually spins quite a bit faster than a Milwaukee, in fact many other drill motors do. I would start there, but if it were wood use a more normal plunge rate. .5ips-1.5ips

[Gary Campbell]

Vassil...
Now that I have an ATC all bits are placed in the spindle. For my cabinet related boring I use Carbide tipped Boring Machine bits. Sizes 3mm to 20mm. RPM from 2500 to 6000. Feeds from .5 ips to 4ips. All use a 10mm collet.

I have tried both regular and brad point bits and wasnt as happy with the results.

[vassilm]

Again. Thanks a lot. This discussion was very helpful.
Vassil.