Tapping in a CNC question

[Rob Frink]

For the CNC gurus....

My CNC machine is capable of the G84 tapping cycle and I use it often. I've only used it with the spindle set in low gear (60-2150 rpm ..inverter speed control).

The typical tapping speed that I use is 300 rpm. And I use a compression tapping fixture.

On several occasions, I've found that I would like to run the machine in high gear (600-6000 rpm) to take advantage of a specific cutting tool and I would also like to tap in the same program/set-up.... but I've never tried to tap at 600 rpm. Nor do I know if there is enough torgue in high gear.

Buying a self reversing tapping head is currently not an option,

Is 600 rpm an appropriate speed for compression tapping?

Any thoughts or guidance?

Thanks
-Rob

[Thrud]

Rob
Consult the owners manual of your machine or get in contact with the OEM - they can tell you what the machine can withstand without stressing it. You would be amazed at what they know!

Generally you get better results with higher speeds - but this is codependent on the tap and workpiece material.

[L_Miller]

Can you add some lines in the program that down shifts to low before you tap. Then shifts back to high when finished?

N000 M5 Spindle stop
N000 M40 Low range
N000 M3 S300 Spindle start


N000 G84 Tap cycle


N000 M5 Spindle stop
N000 M41 High range
N000 M3 S1000 Spindle start

This might be able to be shortend.
I have seen where the spindle stops could be left out too. It would automaticly slow to a gear change speed, change gears and keep going hardly missing a beat. But I like the stops better myself.

If you are going to be tapping many diferant holes and sizes, do all the tapping at the same time. So it saves on shifting so mutch.

If you are doing high numbers of parts like in the thousands. Then you might want to look for a supper tap of some kind. And try tapping at high speeds. Just to save on the gear box.

I hope this helps.

Larry Miller

[This message has been edited by L_Miller (edited 05-16-2002).]

[Rob Frink]

Hello Larry,
Thank you for the feedback. I found a solution that works for me......I was able to adjust the decel parameters on my inverter to get the spindle to stop quicker for higher speed tapping. The default was a 3 sec decel...ouch...it is now set at 1 sec which is a fast as it will tolerate w/o over current faults. My machine doesn't have a mechanical spindle brake. I found that the spindle stops quicker and with less current in high gear at a spindle speed of 600 rpm than in low gear at 300 rpm. I guess because the motor is spinning slower in high gear. Less inertia...etc.

Over all, the inverter setting change has really increased the speed of tool changes as well since I don't need to wait 3 secs for the spindle to stop.....I think the factory was a little too conservative on this one!

I wish I was running 1000's of pieces....but just 10-20 max .... sometimes only 3-4.

Thanks again Larry.

-Rob