What happens when Acorn doesn't have an encoder reading spindle rpm when the CAM program calls out a spindle speed?

A place to discuss and ask questions about all things Machining for Mills, Lathes, Laser, and Routers

Moderator: cnckeith

Post Reply
Setlab
Posts: 51
Joined: Tue Sep 29, 2020 10:00 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

What happens when Acorn doesn't have an encoder reading spindle rpm when the CAM program calls out a spindle speed?

Post by Setlab »

I've ran into probobly a dumb question while just beginning to learn how to use my Acorn retrofitted mill. I bought an encoder for my spindle but I need to machine the brackets to actually mount it. If I send a CAM file to my mill to make these parts what will happen when say the tool being used requires 6000rpm but there is no encoder feedback to verify that speed. Does Acorn send an error code or does it just make the spindle turn at 100% when a spindle speed is called out?
tblough
Posts: 3022
Joined: Tue Mar 22, 2016 10:03 am
Acorn CNC Controller: Yes
Allin1DC CNC Controller: Yes
Oak CNC controller: Yes
CNC Control System Serial Number: 100505
100327
102696
103432
7804732B977B-0624192192
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Boston, MA
Contact:

Re: What happens when Acorn doesn't have an encoder reading spindle rpm when the CAM program calls out a spindle speed?

Post by tblough »

If the commanded rpm is greater than the maximum rpm of your machine, CNC12 will run the spindle at max rpm. It does not prevent the program from running. This nehavior is the same with or without an encoder.

You need to set the maximum rpm of your machine in your CAM program so that it can adjust the feedrates correctly.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
Setlab
Posts: 51
Joined: Tue Sep 29, 2020 10:00 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

Re: What happens when Acorn doesn't have an encoder reading spindle rpm when the CAM program calls out a spindle speed?

Post by Setlab »

Ok so the CAM program will try to do its best to guess spindle rpm based on how I define my machine max rpm. If max is 6000rpm and I tell it the tool needs 3000rpm it will essentially adjust spindle rpm to be 50% right?
tblough
Posts: 3022
Joined: Tue Mar 22, 2016 10:03 am
Acorn CNC Controller: Yes
Allin1DC CNC Controller: Yes
Oak CNC controller: Yes
CNC Control System Serial Number: 100505
100327
102696
103432
7804732B977B-0624192192
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Boston, MA
Contact:

Re: What happens when Acorn doesn't have an encoder reading spindle rpm when the CAM program calls out a spindle speed?

Post by tblough »

Some CAM systems have adaptive toolpaths where you tell them what material you are machining and the program selects depth of cut, step-over, spindle speed, and feed rate. In these cases, it's important to tell the software your spindle Hp and max speed.

Normally, you select the milling parameters including the spindle speed. In those cases, you need to be aware of your spindle limitations, and select machining parameters accordingly.

Normally, it is not critical that the spindle speed is exactly what is programmed. That is why most machine tools have open-loop speed control. Accurate spindle speeds become more important when you are programming feedrates in feed per tooth and when using smaller end mills.

Normally when you calibrate your VFDs 0-10V input to Centroid, if you are within 5%, you are good. CNC12 will display your programmed feedrate since it doesn't really know the actual speed. When you add a spindle encoder, CNC12 will display the actual spindle rpm, but it does not "close the loop" and adjust the actual rpm to match the commanded rpm.

When tapping with an encoder, CNC12 still does not adjust the spindle speed. What it does do, is adjust the Z feedrate to synchronize it with the measured spindle speed.

Finally, there is how the G-code intreperter deals with the "S" command word. If the commanded spindle speed is less than the minimum spindle speed, then CNC12 sets the spindle output to the minimum spindle speed configured in Setup. CNC12 will issue a warning that this is happening, but does not halt operation. Comparable behavior occurs when the programmed spindle speed is greater than the machines maximum speed.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
Post Reply