Spindle speed display slowly increasing- Resolved with new VFD

[kevincnc]

Hi all,

I am just getting my lathe running, using an Acorn for the first time. The spindle has a 1024 line encoder coupled 1:1, and the I have successfully cut a pawn, but spindle speed isn't quite right. If I enter S1000, and M3 in MDI, the speed display slowly increases as it runs. It started out at 1000 and now after several minutes of running it's at 1075. Actual speed and VFD frequency display is staying steady. Shutting all the way down doesn't reset it to 1000 either, it picks up where it left off.

Spindle speed running the PAWN-enc varies with radius, but doesn't reach full speed for some reason either. which may or may not be related.

Any ideas? Let me know if I didn't provide enough info.

Kevin

[cnckeith]

viewtopic.php?f=60&t=1043

[kevincnc]

Sorry here's more info, I was in a hurry.

The machine is built using the headstock from a Grizzly 12X37 belt drive lathe, and the rest custom. I'm a little embarassed to show the whole machine while it's still naked. It will get an enclosure and flood coolant. It has Machdrives BRB servo drives running DC Servo motors for X and Z. Wiring is as per the Acorn schematics, nothing special except that it's all crammed into an unreasonably small enclosure. Home switches are mechanical. Here is the Drive manual -> https://machdrives.com/pdf/BRB%20BRC%20 ... Manual.pdf

The VFD is a TECO MA 7200 running a 3HP spindle motor. The manual is here-> https://www.tecowestinghouse.ca/wp-cont ... _11_10.pdf

The spindle encoder is an Omron E6B2-CWZ1X, 1024 P/R, timing belt driven 1:1

The computer is a Dell Optiplex 7010 with a Planar Helium PCT2235 Touch Screen.

Let me know if I missed anything that's needed please.
Thanks,
Kevin

[cnckeith]

nothing to be embarrassed about.. ....that looks like a nice install..good work..

and thanks for the good into.. i see you are on 4.12.

Please update to v4.18 so you are on the latest.. and we will go from there..

https://www.centroidcnc.com/centroid_di ... loads.html

[martyscncgarage]

Hi all,

I am just getting my lathe running, using an Acorn for the first time. The spindle has a 1024 line encoder coupled 1:1, and the I have successfully cut a pawn, but spindle speed isn't quite right. If I enter S1000, and M3 in MDI, the speed display slowly increases as it runs. It started out at 1000 and now after several minutes of running it's at 1075. Actual speed and VFD frequency display is staying steady. Shutting all the way down doesn't reset it to 1000 either, it picks up where it left off.

Spindle speed running the PAWN-enc varies with radius, but doesn't reach full speed for some reason either. which may or may not be related.

Any ideas? Let me know if I didn't provide enough info.

Kevin

Tell me how you wired the analog signal to the VFD. What cable/wire method did you use?
As a temporary experiment, take a pair of 18 gauge wires, twist them with a drill, connect them from Acorn analog output directly to the VFD analog input, no shield, keep the pair short and away from noise. By passing your existing wiring...

Use the MDI to call speeds and see if the spindle speed is stable and hits the target speed by the accelleration time set in the VFD.
Report back.

Marty

[kevincnc]

Thanks guys. Marty, The analog signal uses a 2-wire shielded twisted pair 18 or 20ga cable with the shield attached to the proper terminal at the VFD only as per the manual. I don't think that's it but will try what you suggested if you still think that could be it after reading below.

I updated to v4.18 and the speed display is steady now but something is still not right. I followed the procedure here viewtopic.php?f=63&t=1650 and confirmed that the max frequency of 69.7Hz produced the desired 2200 RPM which is the max set in the wizzard.

At that point I got the following when running from MDI:
S2000=2065 Actual RPM
S1000=1073
S640= 715

After reducing max frequecy to get 640 RPM accurate, I got:
S640=639
S1000=962
S2000=1850

I did confirm that the RPM displayed on the screen is accurate with two different handheld tachometers. This is my first attempt at a lathe, but starting this thing up has been so easy with the Acorn (which I absolutely love,) I must just be missing something simple.

Everyone likes pictures, so here is the machine in it's current state-

This is what I will look like when finished-

Here is a new report file-

report_780473842B28-0131191600_2019-05-23_19-31-45.zip

(259.02 KiB) Downloaded 154 times

Thanks for the help-
Kevin

[martyscncgarage]

Machine looks pretty cool. I've never seen aluminum extrusion bent like that.
If your spindle speed is steady and where you want it, that's what matters
Marty

[kevincnc]

Thanks Marty, Misumi makes the bends. Wouldn't you say there is still a problem though with only reaching 1850 RPM when it's programmed for 2000? Also my max speed is only 1975 RPM now, and I want it to go 2200, and possibly 2500 later on.
Kevin

[martyscncgarage]

Thanks Marty, Misumi makes the bends. Wouldn't you say there is still a problem though with only reaching 1850 RPM when it's programmed for 2000? Also my max speed is only 1975 RPM now, and I want it to go 2200, and possibly 2500 later on.
Kevin

First, make sure your motor can take the RPM and insulation rated for a VFD.
You want a top speed of 3500rpm, program that in the Wizard for high and 0 for low.
Then adjust the Max frequency in the VFD accordingly, following the guide Keith made to hit the high end. If you are going to do rigid tapping, your low end accuracy is a bit more important.

I would do a test by disconnecting the drain wire to see what effect that has for you

[kevincnc]

Thanks Marty, Misumi makes the bends. Wouldn't you say there is still a problem though with only reaching 1850 RPM when it's programmed for 2000? Also my max speed is only 1975 RPM now, and I want it to go 2200, and possibly 2500 later on.
Kevin

First, make sure your motor can take the RPM and insulation rated for a VFD.
You want a top speed of 3500rpm, program that in the Wizard for high and 0 for low.
Then adjust the Max frequency in the VFD accordingly, following the guide Keith made to hit the high end. If you are going to do rigid tapping, your low end accuracy is a bit more important.

I would do a test by disconnecting the drain wire to see what effect that has for you

Okay the motor is VFD rated, good for 120Hz. The Wizzard is set for 2200 max, 0 min. My post above shows the numbers I got when following the guide, and I do want to do rigid tapping. Disconnecting the drain wire had no effect. I get the full RPM range with the manual Spindle Control on the VCP, I think the Acorn is not sending the correct analog voltage when it's commanded through MDI or a program.