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Laser Cutter
04-19-2015, 02:59 PM, (This post was last modified: 04-19-2015, 03:00 PM by ABearden.)
Laser Cutter
I've got a few things I want to cut out and prototypes to try, but waiting for the router when it's a 2D cutout or drawing is getting really old. Even worse when I need fine detail (cutting with a 1/32" bit? painfully slow). Solution? Laser time. I thought about throwing in and helping with Dan's, but I've got a lot to cut out so I need one at home. Plus spending Spokane Create time on the laser would take away from the delta; then I fall back into the habit I've been trying to break: too many projects and none of them get finished. Hopefully, the laser helps me finish the resin printer by allowing rapid prototyping for the frame.

Hit eBay, found lots of laser tubes, drivers, and mirrors, but at $200, $250, and $100 average each for the Chinese parts it was looking expensive. Thankfully, a factory in China makes an 8" x 12" laser cutter/engraver (DC-K40III) which gets imported and sold cheap. The whole machine is cheaper than the three components above! My savings account did a little happy dance.

Today I finally had a chance to get it setup and tested. Poured a gallon of distilled water into a pot so I could submerge the aquarium pump that came with the machine, and vented the smoke fan out onto the balcony. Seemed to run fine, but it would only engrave wood. Turned out the laser path was barely on the mirror, defracting off the side and severely reducing the amount of laser actually making it to the focusing optics. A quick bit of calibration and I was back in business. Well, once I remembered to turn the power back up. Heads up for anyone looking to duplicate this, the software is woefully underdocumented unless you can read Chinese and it's interesting to get working. It's a knock-off version of Corel that's been modified with support modules for the laser and requires a USB key much like MasterCAM does.

The tiny 8" x 12" area isn't quite enough for my needs, so the plan is to mount the laser and optics to my ShapeOko and use GRBL to run the laser with the spindle enable and spindle speed outputs (PWM signal to replace the Chinese controller). Once that's in place and operational, I can add 3D printed forced air and vacuum vents to keep the smoke under control and help reduce any flame ups that mar the work surface. Also need to print some covers to put over the optics so I can still use the ShapeOko as a router when I need 2.5D cutting (like the frame plates for the delta) but keep the material chips out.

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04-21-2015, 08:08 PM,
RE: Laser Cutter
Got things torn down tonight. Probably need to make an enclosure for the power supply and control board. Maybe the first laser project?

Looks like the control input is literally just 0 to 5V, which means it's a direct plugin on an Arduino controller. Might need a firmware change as I think GRBL uses PWM, but changing PWM output to analog output is pretty easy. Two wires to add a laser to my CNC table. Doesn't get much better than that.

Also now have a spare 8" x 12" 2D movement frame I need to find a use for. Big Grin

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04-27-2015, 07:14 PM,
RE: Laser Cutter
Spent the weekend getting sick and prototyping brackets. Got a chance to install them this afternoon. Need some work, but they'll do for now!

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04-28-2015, 06:30 AM,
RE: Laser Cutter
Me likey. Nice job.
05-03-2015, 10:00 PM,
RE: Laser Cutter
Felt weird going to a pet store and buying aquarium bits when I don't have any pets, but Lauren didn't seem to mind the time to pet everything. Picked up an aquarium aerator for my forced air setup (and a small tank heater for the resin printer). Just need to model and print the combined vacuum and forced air nozzle; positive pressure in the cone to keep the lens clean and negative pressure in the cylinder to keep my lungs clean.

Spent the rest of the day making an adjustable mount for the laser, then getting some of the mirrors calibrated. Didn't have any T-nuts handy for mounting to the extrusion, and I don't know of anywhere local that stocks them, so I improvised by grinding the heads of a few 1/4" caphead bolts to fit the extrusion slot. Worked great, but getting the mirrors right on a 1m x 1m table is a pain and I don't have an enclosure yet so there's lots of stacking of 2x4s until I'm certain where the mirror is initially pointed at each point. I'll have to finish that step up later.

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05-13-2015, 03:06 PM,
RE: Laser Cutter
Another few hours of messing with the laser cutter now that my schedule is open. Might as well be productive, right?

Got the first CNC-driven cuts done. With some experimentation, I figured out the focal point of the laser is about 1/2" off the work surface. That's great because aluminum expandable hex sheets come in 1/2", so it'll put the workpiece right where it needs to be.

Also figured out that while an aquarium pump does great at maintaining positive pressure near the lens thus keeping the smoke off of it, it's crap at producing enough flow/pressure to blow the smoke out of the cut. Was a hell of a head scratcher when I could barely cut through 1/20" of wood and the edges of the cut were charred where the flame followed the smoke. Fired up the air compressor and cranked it to 20psi then manually followed the beam with a nozzle; perfect. Now to figure out how to make it work automatically.

However, as a testament to the joys of prototyping, I figured out my first prototype of the vacuum shroud didn't work in a spectacular fashion. Always have a fire extinguisher nearby just in case. Didn't need it, just cut the laser power, but it could've been worse.

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05-14-2015, 09:54 AM, (This post was last modified: 05-14-2015, 09:55 AM by TroyCoon.)
RE: Laser Cutter
You could build an enclosure and make a negative air flow. That is pretty much how most work. You need to be venting gasses anyway, after you have done some cutting you will definitely know why. The gases from laser cutting can be caustic and an irritant. They also, even with a vented machine can stink up a space and make people Angry

Troy Coon
Lead Geek
05-14-2015, 01:25 PM,
RE: Laser Cutter
(05-14-2015, 09:54 AM)TroyCoon Wrote: You could build an enclosure and make a negative air flow. That is pretty much how most work. You need to be venting gasses anyway, after you have done some cutting you will definitely know why. The gases from laser cutting can be caustic and an irritant. They also, even with a vented machine can stink up a space and make people Angry


Working on that part, though with the shroud and my shopvac vented outside my garage fumes weren't a problem at all. It is readily apparent when the system isn't on though! I'm more worried about incidental laser reflection during a mirror failure.

The failure of the shroud was not enough airflow into the kerf to blow the smoke out of the way, and the weight of the shopvac hose caused it to torque into the laser path which caused fire.

The plan at the moment is to redesign the lens enclosure to strictly protect the lens with positive pressure (might cast it in aluminum), then make a second piece (to avoid torque issues) to house a compressed air hose blowing toward the pickup for the shopvac. When the pickup is so close to the focal point of the laser, it moves more than enough air to keep fumes at bay.
05-17-2015, 09:52 PM, (This post was last modified: 05-17-2015, 09:55 PM by ABearden.)
RE: Laser Cutter
Another few hours of testing in. Cut up the old shroud to experiment a little bit. Trimmed it down to just the lens enclosure and tapped a hole for a 1/4" NPT quick-connect fitting. Unfortunately my 1.5 gallon air compressor doesn't do very well keeping up so I re-piped a few things to piggyback a reservoir. It helps buffer the demand a little bit, but long term I'm going to need more reservoir.

Once I finished with the air testing, I started on the last bit I needed: the trigger. First thing required was an update from GRBL 0.8 to 0.9. They swapped some pins around so the spindle enable pin could be utilized as a spindle speed control. I loaded the sketch, edited a few settings, then uploaded it. And nothing. Nothing at all. No response to commands, no stepper pulses for movement, nada. Did a lot of searching and eventually found a forum reply with info not mentioned in the GRBL documentation: the default baud rate changed from 9600 to 115k with version 0.9. Hmm, might be important to know. Unfortunately that takes my favorite software out of the mix for now (it's written specifically for GRBL 0.8, thus 9600 baud only).

With that situated, I moved to the hardware. I read somewhere it's bad to turn the tube on and off quickly with PWM, but I can't find that source now and everything else I read says that PWM is just fine. But because I don't trust the Chinese power supply and the stock setup runs analog, I popped a simple RC circuit made of a 510 ohm resistor and 4.7 uF capacitor onto the pin output to change the signal from a square wave to DC with a little ripple just to be safe. Verified with an oscilloscope (man, haven't used one of those in a while).

Hopefully, I'll get a chance in the next day or two to hook it all together into a seamless system.
05-29-2015, 12:17 AM,
RE: Laser Cutter
Got everything hooked up, but apparently the power supply on this thing is active low. Instead of trying to reverse all of the M3, M5, and S my first thought was to add a hardware inverter. I rigged up a 741 OpAmp and what do you know they really don't like operating as an inverter on 4 (despite minimum power being 3V). Then I tried to remember my EE classes from college and rig up a single-transistor as an analog inverter. Given the random collection of unmarked transistors I had laying around, that didn't go well either. See what 10 years of mostly forgetting EE math gets you?

When hardware fails you, implement in software! Took about an hour to trace the GRBL code down to the specific portions controlling the spindle. Added a macro to enable a secondary code path that inverts all of the PWM output logic when defined. Poof, laser works as intended with M3, M5, and S codes all working normally. Once I'm allowed to make noise (shop vacs at 1am make for very angry neighbors), I'll fit the Arduino back into the CNC table and fire it up!

Going with a heavy wood cut surface for now due to cost and availability, but at some point I need to switch over to expanded aluminum. So much nicer.

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