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View Full Version : Converting to a VFD - several questions



turbostang
06-27-2007, 11:01 AM
Please forgive me, I'm still noobish to the DIY CNC routine. I've searched and didn't find what I was looking for, but perhaps, I am looking for the wrong thing.

I have a grizzly G3617 that I have started purchasing the parts to convert it to CNC. I have the servos already, some of the necessary tooling etc...but I had questions in regards to the VFD conversion process.

The pulley/belt arrangement on this thing is a major PITA to change. I want to change to a variable frequency drive - but I have very little idea of what needs to be done.

At the very least I'd like to maintain the speed the machine was able to do from the factory 3600 RPM, more would be very nice though...all without changing belts anymore :)

Can tapping be done once changed to a VFD? I'm assuming the motor would need some sort of encoder system on it, correct?

What other things need to be considered? Can MACH3 control the VFD?

Sorry if there are any terribly obvious questions...

Al_The_Man
06-27-2007, 11:10 AM
You will need a 3 phase motor as well as the VFD.
To do synchronous tapping, you will need a system that syncronizes the Z axis to the spindle encoder.
You may get away with floating tapping, depending how well the control of your spindle is, usually requiring fast accel/decel of the spindle.
Depending again on the VFD, you may require to retain one reduction to go down to low speeds.
If you get a 4 pole motor, you can generally run at 2x base frequency ( 120hz instead of 60hz).
Al.

turbostang
06-27-2007, 11:23 AM
Ah.. I see.. Well, if it requires a 3 phase setup, I won't be able to do that without some sort of phase converter. No 3 phase avaialble in the neighborhood here. Are there other alternatives?

I thought about the 1 reduction already, I figured it would be needed to run the bigger stuff slower and still have some usable torque.

Al_The_Man
06-27-2007, 11:41 AM
I should have explained, you do not need 3 phase as the VFD will accept 1 phase in and output three phase, it produces 3ph electronically.
Most 3ph motors go down to 220v so it is normal to input 240 1ph which you should have in your panel.
Al.

turbostang
06-27-2007, 11:49 AM
Ohh.. Now it all makes sense. I didn't think all of these DIY'ers had 3 phase! :)

What things should I pay particular attention to when I look for a VFD and motor?

Do you happen to know if MACH3 can control the VFD?

Thanks Al!

Al_The_Man
06-27-2007, 01:51 PM
Look for a good quality if used such as Baldor etc, if buying new, check if the motor is invertor or vector rated.
If you get a 4 pole 1725rpm, you should be able to run at 120hz which will give you close to 3400 rpm.
Most VFD's have a ±10vdc control, so you will need a pwm to analogue convertor, If you search here there should be a link, unless someone can point to a link.
Al.

mxtras
06-27-2007, 01:59 PM
Here is a link to the speed board I am using:

http://www.cnc4pc.com/Store/osc/index.php?cPath=25

If you have yet to purchase your BOB, I would suggest getting this board from cnc4pc:

http://www.cnc4pc.com/Store/osc/product_info.php?cPath=33&products_id=48


Also, see the following thread for more info:

http://www.cnczone.com/forums/showthread.php?t=15600

Scott

Ron111
06-27-2007, 07:35 PM
Turbostang,
Just download a manual from driveswarehouse and read through it and it will begin to make sense.

As far as tapping, I use a tapping head. You still need to pay attention to the RPM as you go down with the tap (-Zfeed rate) and with my tapping head it automatically reverses at 1.6 times the speed when you back out(+ Z feed)

So, if you mount a spindle speed monitoring circuit (I did this on a couple of lathe conversion in the mini lathe forum in order to do automated thread cutting) I would think you can specify the feed per rpm in mach 3 for your tapping head for both forward (going into the hole) and reverse (coming out of the hole).

Ron

DIY-Guy
04-02-2008, 03:26 PM
Hi, just jumping into the thread here-

Regarding http://www.cnc4pc.com/Store/osc/prod...products_id=48

Thanks for the URL, except... they changed their site and that URL does not go to a product anymore. So I called the number on the website before 4 pm their local time, and the phone rang and rang without any answering machine.

What specific product are you using from cnc4pc? (I'd like to find it if it's better/cheaper than BOB.)

Thanks! Diy-Guy "Becoming a little more than a newbie."


Here is a link to the speed board I am using:

http://www.cnc4pc.com/Store/osc/index.php?cPath=25

If you have yet to purchase your BOB, I would suggest getting this board from cnc4pc:

http://www.cnc4pc.com/Store/osc/product_info.php?cPath=33&products_id=48


Also, see the following thread for more info:

http://www.cnczone.com/forums/showthread.php?t=15600

Scott

mxtras
04-17-2008, 08:58 AM
Thanks for the URL, except... they changed their site.

They have changed the board a bit also, but this is the board:

http://www.cnc4pc.com/Store/osc/product_info.php?cPath=25&products_id=58&osCsid=8a6448f307902aa6848926cd6e3b90c0

Scott