[CNC] Self-reversing Tapping Head On Cnc, Experience?

[Jamespvill]

There is some allowance between jamming the tap at the top and before the clutch will disengage on mine. I believe there is .150 " of travel. My cam then recommends underfeeding the rpm of the spindle feed slightly to compensate for feed rate (in/rev) possibly not being correct. If the tap outruns the feed, it simply stops. If the feed were to outrun the tap, it would jam at the top of the travel and bad things surely would happen. As I stated earlier, once I got my parameters properly set with a 3mm tap, did about 47 holes full depth in 1/2" 6061 with no problems.

It has been my hope that the extra travel built into the unit itself would give me a bit of a fighting chance in terms of getting speeds and feeds dialed in. That's nice to hear that I can only screw up badly in one direction! Thank you for the extra info!

 

[Jamespvill]

The tapping heads I use rely on down pressure to keep the clutch engaged and are self feeding via hand pressure and feel, which would mean that using one on a cnc mill, one would have to have the feed rate almost spot on.

Feed rate shouldn't be an issue with the CNC, in fact, in a perfect world my machine would be servo based and I could just rigid tap the whole thing without the use of an additional head. For me, it's an issue of the spindle staying in tune with the Z axis. Perhaps with the minimal load that a 0-80 thread puts on the spindle motor, it may actually stay in tune... Might have to sacrifice a tap to the cause to investigate that one!

 

[Country_Bubba]

For rigid tapping, you also need an encoder on the spindle so your controller has the necessary feedback. This is why the machines that I am aware of that can rigid tap actually use a servo motor for the spindle drive. My converted mill/drill uses a standard 3 phase motor with an inverter, and I know for a fact (cause I have checked it) that if I set X amount of rpm that it will NOT be exactly that when I measure it with a digital tach. Also I use a rather lengthy acceleration and deceleration time on the motor so that means it will continue to run even when I turn it off and of course this means it cannot immediately reverse. Therefore the reason I use the tapping head on my machine.