Spindle speed control for tapping.

[greeder88]

Unclear what is required for rigid tapping.
Do I need a Sensorless Vector or a Flux Vector? What are my options?

Does the encoder signal go to my CNC2PC C6 "Variable speed control" or the inverter? Does the inverter need a special card?

I mainly need the spindle to index for a tool changer. Rigid tapping accuracy is not so critical since I can use a spring loaded tap holder.

It is easy to waste a ton of money here.

[SORCHEROR]

two questions,what machine are you using,and what are you doing?
you ask about tapping,than state you need tool changes,are you planning to put a tool changer on your machine?need to know before can answer
steve

[greeder88]

I'm making a tool changer for a Bridgeport with a three phase 2hp ac motor. I need to get my spindle in line for a tool change when it stops. I also want to eliminate the noisy variable belt system and control the speed with "speed override" and program control. I might as well add rigid tapping since I will need an encoder to align the spindle. However if there is a less expensive way to go with a less precision spindle control system (cheaper inverter) I would do that to save money but I must have the spindle indexing for tool changes.

My thinking is that rigid tapping needs a lot of precision to keep from stripping the threads but I can use a spring loaded tap holder if that will lower the inverter requirements. My knowledge of inverters is too sketchy to be ordering one just yet and they get very pricey.

[samco]

You cannot just use the index pulse for rigid tapping (it needs the quadrature signal for knowing the direction the spindle is going). You could just time it out using normal feeds and speeds with floating holders. You need a quadrature encoder + index for real rigid tapping. I have seen as low as 360 line (I would not go any less than that - but too much will limit your spindle tapping speed as the computer needs to be able to read each transition).

Some good info here. (rigid tapping is sexy)

http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Pjm

sam

[samco]

YouTube - Rigid Tapping M3X 5 750rpm

YouTube - Rigid Tapping M3X 5 750rpm

YouTube - emc2 first rigid tapping

YouTube - emc2 first rigid tapping

[dpuch]

Drill chuck... *shudder* Avoid holding a tap in a drill chuck is not a good idea as it can come lose on you.

[jmelson]

Originally Posted by greeder88 Unclear what is required for rigid tapping. Do I need a Sensorless Vector or a Flux Vector? What are my options? Does the encoder signal go to my CNC2PC C6 "Variable speed control" or the inverter? Does the inverter need a special card? I mainly need the spindle to index for a tool changer. Rigid tapping accuracy is not so critical since I can use a spring loaded tap holder. It is easy to waste a ton of money here.

You need a spindle encoder with index pulse. Forget the fancy spindle motor drives, they are not accurate enough. Any method that allows you to reverse the spindle, including contactors and a 3-phase motor, will actually do. In other words, you don't need precise control of the spindle, you want the REST of the machine to follow what the spindle does, precisely.

I demo'ed rigid tapping at the recent NAMES show (and at the CNC Workshop in 2008) with a sloppy servo drive running the spindle open loop. Due to motor resistance, the spindle slowed down significantly as the tap cut into the work. But, EMC followed the spindle speed, and the threads were perfect.

As for spindle indexing, any VFD should be able to do it, although somewhat slowly. How precisely does the spindle need to position for the tool changer to work? A couple degrees?
Does it need to hold the spindle rigid while the tools swap, and does that impart any torques to the spindle? If so, you may need a flux-vector drive to hold the spindle precisely locked during that operation. If the tool change doesn't torque the spindle, and the positioning requirements are not all that tight, you should be able to do it with an ordinary VFD.

Jon

[greeder88]

Flux vector if the spindle needs to be locked...easy enough.
Can you explain how the encoder ties in to a regular VFD? Do I need any special options on the VFD or does the encoder only connect to EMC2?