Shoptask VFD upgrade

[bprager]

I've decided to try and upgrade the shoptask with a VFD. Question to those who have done it, what did you do with the current innards?

Did you just match the pulley diameters between the new motor and the spindle and run direct, did you keep the exisiting setup so the clutch is still useful and you have a basic low/high speed at whereever you left the belts?

I do a lot of threading, so the gears have to stay, and originally I was going to remove all the pulleys etc, but wasn't sure that was the best way to go.

Also, when you wired it up, how did you do it? Metal conduit to the VFD and then flexible BX to the motor? I'm going to want to run both the mill and lather from the VFD, of course, One at a time. How have people done that?

The VFD I'm using is a TECO N3 with 1750 single phase 230V motor.



Advice, opinions and experiences are all very welcome!

[fastlanecafe]

Here is a link to a guy who did the conversion

http://forums.delphiforums.com/Shopt...ges/?msg=613.1

[bprager]

Thanks, but he did the mill, and I'm trying to figure out how to do both the lathe and the Mill. In particular, what do I do with the Clutch/belt mechanism (keep, throw out) and how do I have the VFD control 2 drives (one at a time!) safely.

Bruce

[digitalmdj]

If you use one VFD drive you will have to add two relays to switch between motors. I have two VFD drives so I can still use my power feed on my X and Y axis. I also have a brake for the VFD drive and added a jog switch. I no longer need a clutch or any of the excess pulleys. If I want to thread I just add a smaller pulley to the motor for more torque and pull a few segments out of the Vbelt.

[smallblock]

That is the big issue I see with the VFD conversion is that you really need 2 drives in order to utilize the power feed when milling. I am not an electronic type, so I don't know if the drives could be split internally to drive 2 motors, but with seperate controls for the speed and direction. Even if you could, you would need a larger drive rated at 7-8HP. As far as threading goes, I calculated that a 2HP 3phase 3600 rpm motor could run from the original lathe pulley directly to the smallest of the spindle pulleys and give you a usable range of 25- 2000 rpm which would cover threading and most all turning.

[digitalmdj]

Before I set up my VFD drives I talked to several electricians at work and found out that if I used a 3600 rpm motor I would lose to much Torque at low rpms so the 1750 rpm motor is a better choice. Changing pulleys is a better way to go when you do threading to get the extra torque at low rpms. There is always a sacrifice when it comes to these kind of things.

[fastlanecafe]

That's probably correct, since the formula is torque X rpm = HP. If you have a 2hp motor rated at 1750 rpm, it's inherent torque must be about twice that of a 2 hp 3600 rpm motor. Some other 3 in1 machines use a DC drive motor which is rated at 1.5 hp, but runs in the 5000 rpm range, so they are lacking in drive power at the low end. Shoptask suggested that you could get the best of both worlds by using one of the old style motor pulleys with 4 sheaves driving direct to the spindle. Because the sheaves were the same ratios, you could just roll the belts from one to the other when you want to get down to the low rpm range.

[digitalmdj]

A 1750 rpm motor has 4 poles and a 3600 rpm motor has 2 poles. That where your torque is lost with the fewer poles. Also you have less problems with a motor at lower rpms. Gearing is everthing and thats where pulleys come in.

[dahui]

That reminds me, I need to post my x axis power feed mod. Pretty basic, just plugged in a DC gear motor in the hole where the CNC motor would go. Hooked it up with a timing belt, little DC controller from ebay, some buttons, voila, power feed.

As for threading. I'm not sure what size threads you are cutting but I personally wouldn't worry a lick about enough torque at low RPM. Just hook your motor up to the VFD, run it real slow and grab onto the shaft. G'head, I dare ya. (Disclaimer: actually, don't try that).