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Messages - RogerJames

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Sorry Matd,

I just reread your post and see that you were already asking how to make the pwm signal. As I said in my earlier post, no hardware other than my bob is required (in my case anyway).

To make the pwm signal, in mach, setup the spindle to make the pwm and the z axis to turn it on and off (since I assume your laser machine doesn't have an actual spindle or z-axis). To do this, go to "ports and pins" on the "Spindle Setup" tab set the following in the Motor Control section: "Use spindle motor output" to on, "PWM Control" to on. "PWMBASE Freq to 4166 (I could use some help understanding this. I do know a lower freq seems to cause the power to be lower (I think)) "Minimum PWM" set to 0. In the "General Parameters" section set all delays to 0. In "Special Options" everything is off.

In the "Motor Outputs" tab, The spindle is set up as follows: Enalbed checked, step pin set to 16, the dir pin is 0 (we are not changing the direction of the spindle signal. remember we are using the Z-axis to do that.) Dir LowActive and Setp Low Active both unchecked. Step and dir ports both set to 1.

Also in the "Motor outputs" tab, set the Z-Axis as follows (all we are using is the direction signal). Enabled checked, step pin is 0, dir pin 1, dir lowactive checked, step lowactive unchecked, step and dir ports set to 1. ) I have to use pin 1 which is hardwired in my bob to control the relay on my bob.

Under Config>Spindle Pulleys, set the current pulley to number 1, min speed = 0, max speed 100, ratio 1, reversed off.

Of course, you can change the pins per your setup. In this case though, I have two wires going to the control terminals on my laser.... one from the common on my BOB, the other is hooked to the normally open side of the relay on my bob. The common side of the relay is hooked to pin 16 (the pwm signal). This way the relay can open and close the circuit which is sending the pwm to the laser.

Hope this helps,


On my machine, I am using the pwm signal from my PMDX-122 BOB directly as the 0-5V control voltage. No hardware other than my bob is required. If you put an analog volt meter on the "spindle" signal wire you will see the voltage appear to vary from 0 - 5V as the spindle speed is changed in mach 3.

In my case, the laser tube came out of a working unit (the table was just too small). Before dissassemblinig the unit, I put a scope on it. The control signal turned out to be a 5V PWM signal (The tube is a Synrad RF excited Co2 25Watt)

Let me know if you need to know how to the get pwm signal.



General Mach Discussion / Re: machine pauses after spindle/laser is triggerd
« on: September 16, 2009, 09:42:00 PM »

The gcode is pretty easy. If the shape you want to cut out is in dxf or can be translated to it, you can open it in lazycam and post it out to G-Code. You will probably have to edit it to make it work for your laser. This can be done with 3 or 4 find and replace operations in a text editor.

Lazycam, as you may already know, comes with Mach3.

Good luck,


General Mach Discussion / Re: machine pauses after spindle/laser is triggerd
« on: September 16, 2009, 12:48:02 PM »
Hi guys,

It's been a while but...

I have tried the technique described above by Chip with very good success. What I did was to to generate a pwm signal from the spindle output and use the relay on my BOB (PMDX 122) to open and close the circuit between pin 16 (the pin outputting my pwm) and the laser. The relay is opened and closed with the direction signal from my Z-Axis (Since my machine has none). There is little or no delay like there was with the M3 / M5 commands.

In my gcode, the power level of the laser is changed with an S command from S 0 to S 100  for 0-100% power. So at the start of my program I toggle the direction to down to make sure the relay is open (G0 Z-.001), set the power with S command then turn on the spindle with M3 and leave the spindle on thru out the program. To toggle the laser on and off, I issue G0 Z0.001 for laser on and G0 Z-0.001 for laser off.  At the end  of my program, I issue M5 to turn off pulse generation.

I can post more info about my setup when I get home (I'm on lunch at work now) if anyone is interested. Just let me know.

The next step is to figure out how to vary the power as a function of the speed of the x and y axis while using the relay to open close the signal to the laser unit. I would like to use one of the rotary axis to generate the pulses instead of the spindle but haven't yet figured out the setup to do this. Any suggestions are welcome.

Thanks for all the help guys.


If this relay switching the pwm signal turns out to work, I wonder if we could use one of the rotary axis to generate the pwm and inturn get the benifit of CV to vary the laser power?

Any thoughts?



This goes along with what Sid was thinking (turning the laser on and off). The problem is, the laser is not a simple on off device. I also need a way of controlling the power (just like you would do to control the spindle speed with normal milling).

I suppose I could create an external circuit with a rheostat to manually control the power but this really seems like a hack. Besides I then loose all hope of doing some sort of CV type power modulation.

What type of laser are you running? How do you control the power level of your laser?

I’m wondering if I could use the onboard relay on my PMDX122 BOB to open and close the PWM circuit. This way I could use the spindle output to generate the PWM Signal. I would leave the spindle on all the time and just send a signal to the relay to allow the pwm to get thru to the laser or not. This should fix the delay (unless the control signal to the relay has the same delay problem.)

I wonder if there will be a switch bounce type problem induced?




It sounds like you have experience with the M3 delay. Is this something that is well known? If the M3 delay can't be fixed, I'm going to abandon this method of control and look for another method of control. Do you know if this is part of Mach3 or some broader issue?

As for CV mode, how would the CV mode be used to produce a relationship between spindle speed (laser power) and feed rate?




I'm having the same problem with a pause after M3 to turn laser on. I'm using the spindle output in PWM mode to control laser power.  

I need to cut intricate shapes in paper and fabric. And then make slits around the perimeter of each shape.

The first problem is the pause as discussed in this post which is burning up a lot of time (pardon the expression).
This has a secondary effect of creating a round burn spot much larger than the normal curf at the start of each slit and anywhere else a cut starts.

It would be helpful if the solution to this also included the ability to vary the power based on xy feed rate since my corners are also getting burnt round.

I have also tried to use the z axis to control the laser power but when I start moving the Z axis, the voltage jumps to 5V and dosen't drop back to 0V even after the Z-Axis has reached it's destination.
Other issues I can't get my head around if this turn out to be the answer:
1. how to cause the Z-Axis to turn on and stay turned on (would I tell it to go to 7million?)
2. how to setup the motor tuning for the Z to vary the PWM from 0 to 5V
3. how dro scaling would fit into the picture (As i've read in some other older posts)

So far I love Mach 3 but this is really throwing cold water on the project.

Please help... I'm getting desperate!

Thanks in advance.


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