Has anyone converted Bridgeport Vari-drive to fixed ratio?

[CRM]

I'm wondering if anyone has removed their Vari-drive in favor of a fixed ratio pulley system when they are using a VFD?
If so, what ratio did you settle on, and what type of belt did you use? (polygroove, vee, timing)
Where did you source the components?

If you used something other than a timing belt and pulleys, and you have a spindle encoder, how did you drive the encoder? (I have a power drawbar)
I assumed if I wanted to run a spindle encoder, I would need to mount it to the motor shaft, which would require a timing belt set up. I took a peek inside the Clausing/Fagor retrofit we have at work, and was surprised to see a polygroove pulley arrangement at what looks to be a 1:1 ratio. However, the machine does NOT have a spindle encoder. It seems the lower half of the spindle sheave is still there also.

[cnckeith]

i've seen several guys do it with custom aluminum pulleys and multi vee belts.
(timing belts are not good spindle belts they make a ton of noise)
most bport vari drive owners just lock the stock vari drive in an approximate 1:1 position and use a VFD in conjunction with the allin1dc for true programmable spindle speed.
the heavy parts of the vari drive acts as a flywheel and helps with torque demands when taking big cuts, so some want to retain that advantage.
and some run it that way until the eventual bearing replacement is necessary and then move forward with the removal of the vari drive and installation of multi vee pulleys and belts since you have to take it all apart anyways.
spindle encoders should be connected to the spindle, not the motor, in a 1:1 ratio. usually a small timing belt and aluminum pulleys are used.

[ghack]

Yes, i have its a milltronics but the same setup. i used 1:1 drive with a 1 inch wide micro v belt my whole head was shot so i used a motor and vfd from automation direct 3hp.
Todd

[CRM]

Well, since I had some delays due to converting from a step down transformer to direct rectification, I decided to forge ahead with the spindle conversion. I had some parameters I wanted to meet: 5,000 max spindle RPM, and no more than 1.5 times base motor speed (90 hz on the VFD). EDIT--My motor has a base speed of 1720 rpm; I had to increase my max motor speed to 2x nameplate (3440 rpm). That meant that I needed to stray from the usual 1:1 drive ratio and go to 1.5:1. After determining shaft center distance and looking up available belt lengths, I came up with 5.250" on the motor pulley, 3.500" for the spindle pulley to land in the proper belt tension adjustment range.
At this time, I opted not to install a spindle encoder due to an empty wallet. Here are some pics:

start of the motor pulley

motor and spindle pulleys before broaching and set screw holes

another view of the pulleys

finished spindle pulley

[CRM]

I had to slot the original motor mounting holes to allow for belt tensioning. Not too bad of a job; 4 recessed holes hold the bolts that keep the end frame on. I pulled the end frame off, took it to work and milled the slots on the Haas VF3 SS. Can't wait until I no longer have to do my "home projects" at work.
Here are a couple pics of the pulleys installed:

slotting the motor mount holes for belt tension adjustment

motor pulley installed

spindle pulley installed

I'm assuming I will need to tweak the PLC program a little to account for the spindle drive ratio.
First things first, I need to figure out why the either the ALLIN1DC or the CNC11 program refuses to invert the spindle direction when the low range switch is active.

[cncsnw]

First things first, I need to figure out why the either the ALLIN1DC or the CNC11 program refuses to invert the spindle direction when the low range switch is active.

If you have a reasonably standard, reasonably recent PLC program:

• Your SpinLowRange input (typically INP12) needs to be closed (green) in low range, open (red) in high range.

• If your range switch is working correctly, then you should see PLC word variable W24 change between 1 (low range) and 4 (high range).

• You should enter the low-range speed, as a fraction of high-range speed, in Machine Parameter 65. For example, if the spindle runs 1/8 as fast in low range, then you would set Parameter 65 = 0.125 (but see next item regarding sign).

• If your spindle runs the opposite direction in low range, and therefore requires that the motor be reversed, then make the value in Parameter 65 negative. E.g., with 8:1 reduction and reversed direction, you would set Parameter 65 = -0.125.

There should be no changes required in PLC logic. Just set the "Maximum spindle speed (high range)" setting on the Control Configuration screen to the spindle RPM at 100% output in high range; and set Parameter 65 as described above.

[CRM]

1) I am using the latest version of the basic mill PLC program (well, whatever was identified as most current in Feb 2017) with NO modifications.

2) Input 13 is what the real time I/O identifies as SpinLowRange (INP 12 is SpinZeroSpeed according to the I/O screen)

3) Input 13 is RED (open) in HIGH RANGE, and toggles to GREEN in LOW RANGE

I did NOT check the PLC word variable W24 to see if it changes; I will do this tomorrow (Tuesday) and report back
HOWEVER, I did monitor OUTPUT #8; and it does NOT change state when INP #13 does. (nor does it when I use the keyboard to toggle INP #12 green)

The spindle DOES reverse when using the spindle direction buttons on the Jog panel. I take this to mean there is nothing wrong electrically and mechanically.

The info on parameter #65 is exactly what I'm looking for in regards to low range spindle speed calculation. Thank you!

[cncsnw]

The info on parameter #65 is exactly what I'm looking for in regards to low range spindle speed calculation.

But note again my fourth point: Parameter 65 determines direction in low range, as well as speed. You need to make the Parameter 65 value negative if you want the motor to run the opposite direction in that gear range.

[CRM]

CNCSNW--I stumbled into that realization before seeing your reply, but thank you for the clarification. The first time I read the post, I didn't understand the significance of the minus sign; I assumed it was simply to DISPLAY rpm on the screen as positive (forward) or negative (reverse) spindle speed--I didn't realize it also affected PLC output logic. I had not entered anything into parameter 65 until heading out to the shop last night. I had to determine exactly what my low range ratio was (I actually came up with 8.64:1) and once I entered -.1157 into parameter 65...low and behold, problem solved. I actually had to tweak the Max and Min spindle speed in high range values also, so I didn't know precisely which parameter/input did the trick until seeing your post. Thanks again.

I have some parameters in my Hitachi SJ200 VFD to sort out yet, I end up tripping the VFD alarm when stopping from relatively high spindle speeds. My work around for the time being is to disable controlled deceleration and just allow Free Run to Stop (coast). I may need to add a braking resistor...a battle for another time.

Is it normal to have a couple of dead steps at the extreme ends of the spindle speed + and - adjustment? In my case, if I repeatedly press the minus key on the jog panel, (to manually ramp the spindle speed up and down thru it's entire range) the spindle stops turning two steps before the spindle speed % on the display reaches zero. In the same manner, the spindle reaches maximum speed 1 step before the last step in the spindle speed % indicator bar. My 0 to 10v output voltmeter checks were right on the money. It is possible I need to tweak the parameters in the VFD to trim frequency output to match the input voltage a little better. I haven't studied the manual close enough to understand if there's a parameter out of adjustment.

[martyscncgarage]

Curiously how did you make out with this and how is your conversion getting along? Did you finish it?
Nice work on the pulleys by the way.
Marty