Questions about building own laser cutter

[GlacialWanderer]

I've built a CNC machine and it works wonderfully, but I use it mostly for cutting shapes out of 1/4 inch plywood. I also want to cut 1/4 inch and thinner plexiglass. I'm wondering what watt laser I would need to cut these materials at a reasonable speed (doesn't need to be super fast).

I also have read the cheap Chinese CO2 laser tubes have a shelf life. For instance people say if they let them sit unused they don't work after about 1-2 years. Presumably higher quality US lasers like the ones made by Universal don't have this problem, right? Does anyone know why Chinese lasers do this?

If anyone has suggestions about a laser I could use and the approximate cost that would be great. Also if you have resources handed about buying mirrors, laser power supplies, and focusing units I would appreciate that too.

Thanks guys!

[bushmac]

Hi, sorry to see you have not had a reply. I am looking for similar information and will let you know if I get lucky...following with interest

[zax15uk]

I would recommend a 50W CO2 laser for 1/4 inch Acrylic, you could certainly cut it with less but at a slower speed and possibly requiring a 2nd pass.

Some Chinese tubes CAN suffer from a shelf life due to minor gas leakage (permeation) but others do not. The US made ones are typically RF excited and not only cost more but have better shelf life and also higher output.

You can buy a suitable laser, PSU, mirrors and focus lens on ebay. Yes they will likely be Chinese tubes, but these offer the best 'bang for the buck' if it's just for hobby use. It may also be cheaper to buy a complete system, and them part out anything you don't need - the driver board, etc.

Zax.

Originally Posted by GlacialWanderer I've built a CNC machine and it works wonderfully, but I use it mostly for cutting shapes out of 1/4 inch plywood. I also want to cut 1/4 inch and thinner plexiglass. I'm wondering what watt laser I would need to cut these materials at a reasonable speed (doesn't need to be super fast). I also have read the cheap Chinese CO2 laser tubes have a shelf life. For instance people say if they let them sit unused they don't work after about 1-2 years. Presumably higher quality US lasers like the ones made by Universal don't have this problem, right? Does anyone know why Chinese lasers do this? If anyone has suggestions about a laser I could use and the approximate cost that would be great. Also if you have resources handed about buying mirrors, laser power supplies, and focusing units I would appreciate that too. Thanks guys!

[MonoNeuron]

I think Zax is on the money.
50-60 watt would be my minimum wattage if I had to build a laser again. 30 watts is really just too limiting due to time constraints. Whether you are a hobbyist or a production worker you will get sick of waiting for the cut to finish if you go too small on the wattage. The speed will be sickeningly slow.
If you are setting yourself up to do work for the general public then I would save up and buy an RF laser tube even if it took me 2 years to do so. If you are only a hobbyist then go for the glass ones as the cost is 1/10 of the RF sealed tubes.
If it's your first build then a cheap glass one might be right up your alley.
eBay for just about everything and its mostly cheap.
Don't forget to serialize the build.
Rich.

[oneeye]

Hello, I started my adventure with lasers buying a 18w tube and installing directly on the Z axis of my router and making the laser fire through a mechanical switch stuck to Z. well ...... I learned a lot with that ... then after i bought a cheap chinese desktop machine with 35W , it came with old software and drivers (it could not cut vector and was slow as a slug ..) I swapped the drives (I put two cnc router drivers ) and made the laser fire using the signal to down the Z using the parallel port pin signal and using Mach2. (I did Mach2 "think" that was controlling a 3-axis router, where the Z down the laser fire), This works perfectly for both cutting and for engraving.
Now I want to buy a machine a little bigger and want the software controlling the laser power in real time.
The control of the laser power supply is made with 0-5v, I thought to use a 3-axis driver and use the driver of the Z axis for this. The mach2 will keep think that are controlling a 3-axis router, but ll have no step motor in Z axis, . but the driver send pulses to the motor and I do not know how these pulses could control a current of 0 to 5v.
Someone have some idea how can I do that? maybe i dont need the Z axis driver to do it , maybe anothe simple circuit?
Excuse my poor English.
Thanks

[MonoNeuron]

Interesting idea.
have you though about controlling the laser through the spindle output in Mach3 as I think that goes from 0 - 5 volts which would be good for the control of the laser power output (I think)
I'm not really sure but it would be worth trying before you shelled out for some very expensive software.

Just a thought.
Rich.

[oneeye]

Originally Posted by MonoNeuron Interesting idea. have you though about controlling the laser through the spindle output in Mach3 as I think that goes from 0 - 5 volts which would be good for the control Just a thought. Rich.

Hey Rich
not bad idea to try! but maybe this way i ll have to edit all gcode to make spindlle signal do it...... imagine engraving a picture in 3D (2.5D). if i use the Z signal when the Z " go down" to engrave more deep the laser encrease power, no edition needed. ... hmmmmm. i just had a idea, nothing technical but......... , i use the Z axis driver with i small step motor and put a Potenciometer directly in motor axi , this Pot is wired in laser power supply , huh?
the lifespan of Pot ll not be longer but is cheap.

[GlacialWanderer]

Other projects keep popping up, but you guys convinced me that this should be doable. I would build the table and motor drivers first so if the laser is a leaker then at least I'd get some use out of it.

My plan is to use a current mach3 license I have. My current thinking is that I'd use a 4th axis in Mach3 to control the laser power. I'd hook up the parallel port pin for that 4th axis to a microcontroller like arduino. Then I'd write a simple driver to count steps and use that to control and analog output module to control the laser. I'm sure this would work, but I'd want to put more thought into it in case there is some easier or more reliable way. The problems I see with this are:

1) You'd need to add in the laser power controls into your gcode yourself.
2) You'd need to reset that axis depth and your microcontroller during start up to insure both pieces were in sync due to the nature of stepper motor drivers.

Edit:
Arg, for some reason the previous two posts didn't show up in my browser. This spindle speed control idea seems interesting. Another bonus is that I have my current Cut2D software set this. This fixes both of the problems I mentioned. Brilliant!

[MonoNeuron]

Quote
"i use the Z axis driver with i small step motor and put a Potentiometer directly in motor axi , this Pot is wired in laser power supply"

That sounds like a good idea and you could gear it down to get a better resolution if you wanted or just use a 5 phase stepper set at 1/2 steps that would give you 1000 steps per rev. Pretty good resolution and you would only need a size 17 stepper and not even have it mounted on the gantry anywhere near the Z axis.
Worth a try.
You're right about the spindle setup. Not easy to change the code on hundreds of lines of code. Scrap that. :-)
Rich.

[oneeye]

Originally Posted by MonoNeuron Quote that sounds like a good idea and you could gear it down to get a better resolution if you wanted or just use a 5 phase stepper set at 1/2 steps that Rich.

yes Rich,
get resolution ll b better, i have a microstep card 1 to 1/16 , ll try all speeds.
engraving need hight speed so i cant slow dows it too much...
thank you , nice hint

Rick

[oneeye]

Originally Posted by GlacialWanderer Other projects keep popping up, 1) You'd need to add in the laser power controls into your gcode yourself. 2) You'd need to reset that axis depth and your microcontroller during start up to insure both pieces were in sync due to the nature of stepper motor drivers. Edit: Arg, for some reason the previous two posts didn't show up in my browser. This spindle speed control idea seems interesting. Another bonus is that I have my current Cut2D software set this. This fixes both of the problems I mentioned. Brilliant!

Gkacial, me and Rich was just talking about that, u ll get the power controls into your gcode yourself, if u use the Z axis signal to do it. u just need make the Mash3 " think" that is controling a 3 axis router.

[DaveDoesIT]

Mach3 has a very low frequency PWM output for spindle control. Check this site for DigiSpeed boards.

www.homanndesigns.com

Dave