Tapping Threads -- Question re 115 VAC VFD

[carbuthn]

My VFD has an acceleration and deceleration time set at 3 seconds. I it appears to stay in those times. The parameter P1.00 is to ramp to stop (not coast to stop). I always drill/bore as deep as I can, all the way trough if I can. The Z axis should remain lock to the spindle and make a good thread (if it doesn't bottom out), you may be able to shorten the thread depth a little to allow for the extra turns.

Depending on the thread size you maybe able to cut threads internally.
Chuck

[cnc_smith]

Please send a current report. Needs to see what your current setting are for the tapping/threading. The over shot can be controlled by the threading parameters.

[Dave_C]

My VFD has an acceleration and deceleration time set at 3 seconds. I it appears to stay in those times. The parameter P1.00 is to ramp to stop (not coast to stop). I always drill/bore as deep as I can, all the way trough if I can. The Z axis should remain lock to the spindle and make a good thread (if it doesn't bottom out), you may be able to shorten the thread depth a little to allow for the extra turns.

Depending on the thread size you maybe able to cut threads internally.
Chuck

I've been able to successfully do multiple threaded holes using the ridged taping function but I had to shorten my accel/decell times to .5 sec!

The drive can't slow down any faster than what your decal time is set at so in order to do instant reversing to come out of the hole and not overshoot your depth by 3 seconds, you need a shorter deceleration time. This is also why you need a braking resistor!

Dave C.

[tblough]

If you are always tapping the same size hole in the same material, you can tune the rigid tapping parameters to pretty much eliminate the overshoot without a braking resistor on the VFD. In this case, you are letting the inertia of the system determine how long it takes the spindle to stop and therefore, the cutting forces from the tap/material have a huge effect on the deceleration rate.

With a braking resistor, the motor becomes the largest deceleration force in the system and then the tap/material torque has a much smaller effect on the system. Now when you tune the rigid tap settings to the system overshoot, this tuning will apply to a much larger range of tap sizes.

[Dave_C]

If you are always tapping the same size hole in the same material, you can tune the rigid tapping parameters to pretty much eliminate the overshoot without a braking resistor on the VFD. In this case, you are letting the inertia of the system determine how long it takes the spindle to stop and therefore, the cutting forces from the tap/material have a huge effect on the deceleration rate.

With a braking resistor, the motor becomes the largest deceleration force in the system and then the tap/material torque has a much smaller effect on the system. Now when you tune the rigid tap settings to the system overshoot, this tuning will apply to a much larger range of tap sizes.

All true "IF" all you want to do is tap the same size hole, the same depth and in the same material. Otherwise getting a machine to tap a blind hole takes a little more tuning of the tapping parameters and the drive parameters.

So it does depend on what you want for an outcome.

Here is a short video of my machine taping five holes in 1/4-20 thread.



Dave C.

[briuz]

The new VFD will be in tomorrow. Hopefully I'll have this machine tapping this week!

[briuz]

VFD Installed, tuned, and works great! Next step is to connect the braking resistor then start tapping.

[briuz]

First tapping test finished using some Teflon stock I had around. It works! I'll try brass next.

[tblough]

Best material for testing is machinable wax. If you can peck tap (i.e. re-enter the same thread multiple times) a fine thread in wax without destroying the top thread, you've got everything set correctly. Plastics deflect where was is brittle.

[briuz]

I need to get some machinable wax. How do you setup a peck tap? I didn't see it as an option.

Best material for testing is machinable wax. If you can peck tap (i.e. re-enter the same thread multiple times) a fine thread in wax without destroying the top thread, you've got everything set correctly. Plastics deflect where was is brittle.