Liberty4Ever's Laser Build Log

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Re: Liberty4Ever's Laser Build Log

Postby Liberty4Ever » Wed Sep 26, 2012 2:10 pm

loopingz wrote:I might hard to explain/justify to madam...

I told her after the fact, last night.

"I just ordered over $1300 worth of laser parts."

I just got the wide eyed stare and the unspoken hope that I had money to pay the bills this month. :) Obsessions aren't much different from addictions. Both are costly and neither is well associated with rational thought processes.

I'm heading out the door now to buy a cheap 19" LCD and maybe a PC to run LinuxCNC as my laser controller. Craig's List FTW!
Apparently, I didn't build that! :-)
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Re: Liberty4Ever's Laser Build Log

Postby bdring » Wed Sep 26, 2012 2:17 pm

As Adam Savage says (paraphrasing) ....It's not like I have a choice in the matter...I have to do it.
Bart
"If you didn't build it, you will never own it."
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Re: Liberty4Ever's Laser Build Log

Postby Liberty4Ever » Wed Sep 26, 2012 9:41 pm

bdring wrote:it's not like I have a choice in the matter...I have to do it.


Apparently I had to buy three 19"-20" LCDs this morning! One went on the big CNC machine across town, one is going on the laser project I just started, and the other will go on the CNC milling machine that I SWEAR I AM NOT GOING TO START UNTIL AT LEAST TWO CURRENT PROJECTS ARE FINISHED! :D

The three LCDs cost a total of $100 from a Craig's List seller. I had to buy them. :)

His PC didn't like LinuxCNC. High latency jitter on the realtime kernel. So I'm still looking for a PC. I think I'll return to Craig's List and try to score an identical pair of small PCs that like LinuxCNC. I'm so project crazed that I'm buying control hardware in bulk!

With a PC and a monitor, I can decide on the stepper drivers and interface electronics. I looked at MESA last night and it looks like they don't have a good solution to fit my needs. The Y axis servo is 4 amps, and most of the stepper drives I'm seeing are 3 or 3.5 amps. They'd work, but I wouldn't get maximum speed. There are plenty of 7 amp stepper drives too, but not cheap and integrated with MESA Electronics hardware. I'll check out the laser section of the LinuxCNC forum and CNC Zone and see what people are using for control electronics and stepper amps. I don't need much I/O for the laser. A minimalist system could probably get by with an optoisolated parallel port breakout board. I'd like analog in to measure coolant temperature, it might be good to measure and display laser output current, etc. I have a lot of research to do on this topic. I want a reasonably full featured solution that is easy to implement in LinuxCNC.

There is plenty of other stuff to buy along the way, like an air pump, coolant pump, exhaust fan, etc.

I got the emails this morning saying that LightObject.com had already shipped my order from late last night. That was fast!
Apparently, I didn't build that! :-)
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Re: Liberty4Ever's Laser Build Log

Postby Liberty4Ever » Fri Sep 28, 2012 6:19 am

I Just Ordered A Lot More Stuff: I just placed my second order with LightObject.com, now that I've had time over the last two days to consider a lot of the laser design and the features I want on my laser.

SKU Description Quantity Price
ECNC-2M542 2 Phase 4.5A 1-axis Stepping Motor Driver. Support to Nema 16~34. Leetro replacement 3 $135.00
ESW-5MLMT-C1 A pack of 5 Micro Limit Sensor Switch C1 1 $5.00
EPM-3D100MAG 3 digit Mini Green LED 100mA Current Meter for CO2 laser machine 1 $11.50
LSR-HVCBL High Voltage HV Cable for CO2 Laser Power Supply 5 $4.25
EWP-SNR104 Water-flow On/Off Sensor (G1/2) 1 $12.50
EW-W01 Water Level Sensor 1 $8.50
LSR-R5MW 5mW 650nm Red Laser with adjustable focus 2 $11.50
EWP-D50C2440T High volume 35L/m (565GPH) DC24V Brushless Water/ Oil/ Gasoline pump 1 $42.50
WC-WAT240 240mm Water Evaporator/ Cooler for spindle or CO2 Laser Cooling 1 $32.50
EFAN-FFB1212EHE Ultra Strong 12cm DC12V Cooling fan. 200CFM 2 $33.00

The second order cost $317.06. This pretty much completes my LightObject.com shopping list.

The LinuxCNC Control PC: I picked up two 19" LCD monitors from a guy on Craig's List yesterday for $33 each. Tonight, I bought two Compaq EVO tower PCs from a different Craig's List seller, for $60 each. He let me test them with the LinuxCNC live CD, which verified that the CD works and is bootable, the video hardware autodetects and won't be a problem, and I ran the Latency Test from the CD (Menu-CNC-Latency Test) to make sure the PC can run the realtime Linux kernel fast enough for CNC control. A Max Jitter under 20,000 ns is good. These PCs clocked in at about 11,000, which should be very good. Don't assume that a fast PC will work. LinuxCNC doesn't need a fast PC, but it needs a PC that allows LinuxCNC to be in full control. Many PCs with fast processors have hardware interrupts that put the main processor on hold while something else takes precedence, such as a video card interrupting to access system RAM. You need to do the latency test. Sometimes, various hardware can be disabled to restore realtime control to the processor, but it's usually easier to pick a PC that "just works".

One PC and LCD from the recent Craig's List purchases is going to be used on my CNC laser, and the other is for a future CNC milling machine conversion. I installed Ubuntu and LinuxCNC together from the live CD (easy three click install) and made sure the PCs boot and seem OK. I'm currently running a thorough memory test to make sure there are no mysterious intermittent problems reading and writing all of those bits that could send a CNC machine into lala land. Three hours and five complete passes of the memory test with zero errors. So far, so good. I'll leave the memory test running all night for a pseudo burn-in.

Here's a list of known good PCs if you'd like to take the guesswork out of shopping for a LinuxCNC PC:
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Latency-Test

Cooling System Calculations: I spent a little time today designing the laser cooling system. Real calculations! (iPod Touch calculator app while on the throne) In rough numbers, the waste heat from an 80W CO2 laser tube is about 800 watts, which is about 200 cal/second. You can type "800 watts in cal/s" into Google and it'll do the unit conversions for you. Knowing that a calorie is a degree C increase for a gram of liquid water, I calculated that If I used ten gallons of water, I'd probably get two hours of continuous lasing before it overheated at 75 degrees C. I'm planning on using pet safe water/antifreeze mix, aka RV antifreeze, so I assumed it'd have a specific heat less than the 1 cal/C of water. That two hour number was tempting, but the 2'X2' laser cutting area will allow me to run some continuous 4-5 hour full power laser jobs, and even for jobs that are easier to interrupt, I tend to work for 4-5 hours at a time. I could have used 20-30 gallons of water, but I decided to use less water (2-5 gallons) and add a radiator and fans for active forced convection cooling. I even entertained the idea of plumbing the aluminum extrusion frame and running the coolant through the inner cavity, and using the frame as a big passive radiator, but that seemed "too clever by half" and the $70 for a radiator and a couple of professional grade fans smelled like the right way to do that job. I'm cheap, but I don't want to spend a lot of money and have an extra cheese result because I tried to skimp another 10% on cost. I want a nice laser that's a good value, and not the cheapest thing I can build and still call it a laser.

Next Up: I need to take another look at the control electronics. For this fairly straight forward XYZ stepper configuration with minimal I/O, I can probably get by with having LinuxCNC direct drive the optically isolated stepper drivers directly from the parallel printer port, but if I want the extras like a digital display of coolant temperature on the PC, I'd need some analog inputs, and that will require MESA Electronics (or another manufacturer, but I've pretty much standardized on MESA for these home brew CNC projects). I think I'll just buy a little stand alone digital thermometer for the front panel, next to the stand alone laser current meter, and avoid the cost and implementation time of the MESA Electronics cards. I'll have the controls hardwired to shut off the laser if the door is open, or the coolant isn't flowing, or the coolant level is too low, or the coolant temperature is too high. I'll have laser reverse engraved fault indicators on the front panel so the fault is explained in English.

The bare minimal PC I/O now looks like this:

Outputs:
STEPX
DIRX
STEPY
DIRY
STEPZ
DIRZ
MOTION ENABLE
LASER ENABLE


Inputs:
LASER ENABLE (Sum of coolant flowing, coolant not overheated, etc.)
X+ LIMIT SWITCH
X- LIMIT SWITCH
Y+ LIMIT SWITCH
Y- LIMIT SWITCH
Z+ LIMIT SWITCH
Z- LIMIT SWITCH

I might need to either combine the +/- limit switches on each axis and assume that motion in the positive direction activated the positive limit switch and negative direction activated the negative limit switch, or I may need to get a $79 7i43P interface board from Mesa Electronics.

The I/O count is minimal because many of the fault signals are combined into one LASER ENABLE input and the laser is disabled in hardware without LinuxCNC being in the decision loop. Philosophically, I hate hardwired control logic for anything but an E-Stop circuit, but I'm having trouble justifying the cost and time to configure the MESA Electronics board. Besides, the various fault interlocks are sort of like an E-Stop circuit. It's nice to have the fault directly disable the laser to avoid a situation that could be hazardous to people or property, without relying on the PC to be running properly to halt the motion and laser.

If I wanted to get fancy, I could run the various fault signals into LinuxCNC as separate signals and I could make a custom Axis (my preferred LinuxCNC GUI front end interface) control screen that displayed the faults on the monitor, but I think I'll just go old school and have red LEDs light up fault status indicators on the reverse laser engraved front panel, and leave the PC for designing parts in CAD or a graphics program, and monitoring & controlling the job progress in LinuxCNC... and watching YouTube videos while keeping an eye on otherwise unattended laser operation for those long and boring jobs.

Here's a list of supported hardware for LinuxCNC that can be a big help in deciding what interface hardware to buy:
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?LinuxCNC_Supported_Hardware

The above I/O list is subject to change as I still need to research how LinuxCNC should modulate the laser power for cutting and engraving. I think it can use PWM, but I'm not sure if the LASER ENABLE signal is modulated, or a separate LASER PWM POWER signal. I have read enough to know that it's a bit of a trick to fool LinuxCNC into being a vector laser cutter, and it's a much bigger trick to fool LinuxCNC into being a raster laser engraver. Relatively few people have used LinuxCNC to control a desktop laser. If I have a simple and useful implementation, I'll see if it can be documented and added to the growing list of LinuxCNC canned configurations available at startup so it'll be much easier to use LinuxCNC for a stepper motor driven laser engraver. I'll make YouTube videos and a webpage, as well as this build log.

Here's Everything You Always Wanted To Know About LinuxCNC But Were Afraid To Ask:
http://wiki.linuxcnc.org/cgi-bin/wiki.pl

My Clever But Not Original Targeting/Focus Laser Idea: The two 5mW red lasers that I just bought will be mounted on opposite sides of the laser head and aimed at the focal point of the 80W IR laser, so I can see where the cutting and engraving will occur when the lid is raised for a practice alignment, and it'll also serve as a quick focusing tool for the IR laser. The two red lasers converge on the IR laser focal point from 45 degree angles. When the material to be cut is at the IR laser focal point, the two red lasers will form a single dot. Above or below the IR laser focal point, the two red lasers diverge into two red dots. I thought that was clever, but saw where someone else on BuildLog.net was already doing this. Oh well, it's still clever, even if someone else thought of it before me.

To Do List, For Tomorrow and Beyond: More research about LinuxCNC control of lasers. Research DraftSight 2D CAD software for Linux. There is supposedly a one click install for Ubuntu, so I'll install it on the laser control PC along with GIMP for creating and manipulating images. Decide on how LinuxCNC will control the laser cutter (motors and I/O), draw some preliminary schematics of the various accessories (pumps, etc.) and interlocks (E-stop, door closed, low coolant level, etc.) Specify and purchase the air assist pump and the exhaust fan. Create a bill of materials, including vendor, part number, and purchase date, and post it online, and place a link to it in this thread. Start doodling on the frame ideas that are bouncing around in my brain pan.

After the order I just placed, I'll have another big order for the laser tube and power supply, and another big order for the as-yet-undesigned Misumi aluminum extrusion frame and lid, an order for the skin panels for the frame, orders for the laser bed, the air assist pump and the exhaust blower, an order or two for whatever I decide to use for the Z axis height adjustment, and several small McMaster-Carr orders for miscellaneous plumbing and wiring and hardware as those issues arise. But so far, the design and the parts ordering is progressing well, although this obsession is starting to cut into my other projects and I'm currently very sleep deprived. I'm also a bit concerned that, based on other projects, there will be weeks of finalizing the design, with daily $50 McMaster-Carr orders. Those add up, and will probably endanger my $3,500 target cost.

Preliminary Z Axis Musings: For the Z axis, I'm actually considering four inexpensive NEMA 17 stepper motors wired together, driving four acme screws in the four corners of the bed, with four zero height adjustment screws in the centers of the table edges at the absolute Z bottom position, just after the Z- limit switch is reached (disable the Z- limit switch to level the bed by bottoming out on the hard stops). I wouldn't design it that way for a commercial product, but the conceptual simplicity of four motors and four acme screws greatly reduces the design time and the fabrication needed to implement the powered Z stage. It'd be about as easy as any manual Z stage adjustment I could design for a one-off prototype, and the Z axis is only adjusted before the job starts so the Z axis motion hardware should last forever. Basically, I'm trading the cost of four stepper motors (about $60) against more clever and complicated Z axis parts that take longer to design and install.

The bed will probably consist of an outer framework of 40mm X 40mm Misumi aluminum extrusion, with a narrow inner shelf secured with T nuts in the frame slots. The shelf will support the table bed laser cutting grid (http://www.cuttinggrid.com/lazergrids.shtml). The top of the grid will be a couple of mm below the outer frame, so it'll serve as an alignment edge. I'll almost certainly need the frame to have some 20mm X 20mm supports underneath to keep the grid from sagging. The grid will be a fairly tight fit in the outer frame, but will lift out for replacement. I need to devise some sort of crumb tray underneath that can be cleaned easily, although most of my jobs don't generate little pieces dropping through the grid. Occasionally, I cut small holes in acrylic, and those do fall through the laser bed. I probably wont make a pull out crumb drawer. If the grid is stiff enough, I'll probably just pull it up and out of the frame so I can vacuum out the debris.

A lot of the design will happen as I order the critical path parts, get them in hand, and see how they feel. That will determine how they'll be used and how the design should accommodate them.
Apparently, I didn't build that! :-)
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Re: Liberty4Ever's Laser Build Log

Postby jv4779 » Fri Sep 28, 2012 9:15 pm

Just a caution that if you want to use Ben's or my raster engraving in LinuxCNC solution, you can't use a Mesa card. Both methods require software step generation so the engrave pulses can be correctly timed.

Jeremy
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Re: Liberty4Ever's Laser Build Log

Postby Liberty4Ever » Fri Sep 28, 2012 11:32 pm

jv4779 wrote:Just a caution that if you want to use Ben's or my raster engraving in LinuxCNC solution, you can't use a Mesa card. Both methods require software step generation so the engrave pulses can be correctly timed.

Ooh! That's a good warning. It's an example of one of the many little details that probably wouldn't occur to me until after I bought something and it didn't work. Hopefully, the stuff I've already bought, with the possible exception of the three stepper drives, are fairly generic and unlikely to be mistaken purchases, but I'm running out of the simple components like water pumps. Before buying the motion and control hardware, I really should spend a lot more time reading and designing until I have a much firmer grasp on the entire project.

I've been thinking about the LinuxCNC engraving a lot today. I'm not getting very far by thinking about it. Unfortunately, there isn't an obviously correct path to raster nirvana in LinuxCNC. A lot of the jobs that I do on the laser require an outline to be vector cut and some text or graphics to be centered within the cut area. The alignment precision can be fairly demanding. Given two different tool chains to produce vector and raster output on the laser will probably require some tricks and attention to detail to ensure the precise alignment.

I often cut and engrave in two separate operations. Lately, when making reverse engraved labels, I'll engrave the mirror image on the back of a plastic sheet. I remove the plastic from the laser and spray paint the engraved back with the color I want for the text or graphic, rather than the old school method of coloring the text or graphics with a paint pen. After the paint dries, if I want peel and stick adhesive, I'll attach that to the back. Then, I return the plastic to the laser, and carefully recreate the original alignment. I then use the laser to cut the outline. It's a great way to make device labels for machines, operator panels, warning labels, etc.

As long as I can precisely align the raster and vector operations, the two software paths won't bother me. For my production jobs with raster engraving and vector cutting, I think I can cut and paste the raster and vector G codes together to make Frankencode, and use G92 to generate offsets to align the various elements within the G code program.

Thanks for the "been there, done that" warning. It's always better to have a map to the minefield. Thanks also to you and Ben for blazing the trail through that minefield. I'll be looking carefully to see where you guys stepped, and perhaps more importantly, where you didn't step. Maybe I'll even help to make a better worn path that's a little easier for others to follow.
Apparently, I didn't build that! :-)
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Air Assist Pump

Postby Liberty4Ever » Sat Sep 29, 2012 4:51 am

Air Assist Pump
I read the various posts about air assist pumps on this forum. It seems that the consensus is that 35-70 liters per minute (LPM) is a good air flow rate. As a good engineering guess, 1/2 to 1 liter a second out a small nozzle should prevent any smoke from getting to the optics. A good exhaust system should have that smoke moving sideways, away from the nozzle, and the air assist should help to move the smoke in the right direction.

I'm currently cutting some Santoprene (rubbery plastic) and some resilient polyurethane foam, and both generate a lot of nasty smoke. The exhaust system is anemic on the laser I'm borrowing, and it has open optics with an air assist that's nothing more than a small tube that blows down at a 45 degree angle at the focal point. By selectively taping over the exhaust to concentrate it where I need it, I can cut for an eight hour shift before there is even a little bit of contamination on the focusing lens. The fully enclosed final lens with the downdraft air assist nozzle that we're all using now is a MUCH better design.

Aquarium and pond pumps are often rated in GPH, or gallons per hour. The 500 to 1000 GPH pumps would probably be appropriate. Some aquarium pumps are rated in gallons, and that's the volume of the aquarium they'd aerate. Most pumps rated this way are too small for use as air assist pumps.

The big issue is noise. These are reciprocating pumps. The smaller ones have a diaphragm, but the larger pumps compress air directly with a reciprocating piston. Probably the best strategies for attenuating the noise is going to include burying the air assist pump in the bowels of your laser where the sound will be muffled, mechanically decouple the frame of the pump from the frame of your laser, and possibly add some extra noise absorbing material around the pump. The mechanical decoupling can be as simple as rubber vibration dampening feet, or as complex as suspending the pump between elastic cords to the frame of your laser. If adding sound proofing foam, the egg crate surface is a bit more effective than flat foam, and open cell foam on the inside and denser closed cell foam on the outside does a better job of blocking a wider range of frequencies. Be careful that the foam doesn't block the airflow and overheat the pump, as most of these inexpensive pumps are already operating on the edge of overheating.

I checked eBay first, but it seemed that the same pumps on Amazon were consistently a few dollars less.

Here's the air pump that I just bought. Being a guy, I usually think "ridiculous" is a good range for any power setting, but I deliberately went on the low end of the air flow rating to reduce the noise. I think this is a 38 LPM air pump for $38.52, delivered. I'll take appropriate noise abatement measures later, as needed.
http://www.amazon.com/EcoPlus-Commercial-Air-Single-Outlet/dp/B002JLJC0W/ref=sr_1_11?ie=UTF8&qid=1348890897&sr=8-11&keywords=pond+air+pump

If I decide it's still too noisy, maybe I'll get this $174 Hakko air pump. :D Hakko makes excellent soldering equipment, so I assume this pump is a winner in every category but price.
http://www.amazon.com/Hakko-Aeration-Ponds-Water-Gardens/dp/B004MU7ZOI/ref=sr_1_20?ie=UTF8&qid=1348889878&sr=8-20&keywords=pond+air+pump

Maybe I'll buy the exhaust fan next. Harbor Fright, here I come!
Apparently, I didn't build that! :-)
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Laser Exhaust & Venting

Postby Liberty4Ever » Sun Sep 30, 2012 11:07 am

Once again, I've researched a laser build topic and hope to provide a (mostly) concise summary of the concepts that resulted in my design and purchasing decision. I researched laser exhaust and venting on this forum and others, and here's what I've determined.

Selecting A Blower:

Many people seem to think that any 600 cubic feet per minute (CFM) blower will suffice. If that were only so! I could have bought the 2,200 CFM box fan (aka "window fan") that was on sale for $9 at the end of the summer blowout sale at Walmart last week.

We need to consider two numbers when specifying an exhaust blower for a laser. We need to move a large volume of air, so the CFM rating is important, but we also need to consider the static pressure. Fans have blades that are designed to move a lot of air at essentially no pressure. The laser and the pipe or hose used for the exhaust creates a back pressure that the blower must overcome. If I bought a cheap box fan and built a plenum for it and tried to use it to pull or push air through the laser, the fan blades would stall and very little air would flow. In the laser application, we need a blower, and not a fan. We need an air mover that can operate effectively against some back pressure.

TANSTAAFL - There ain't no such thing as a free lunch. If we want to move a lot of air, and do so against a resistance to air flow, we must pay the piper. In this case, we generally pay twice. Blowers use more power than fans, which makes sense as they're doing more work overcoming the resistance to air flow, and blowers are usually much noisier than fans.

A good laser exhaust blower might move 600+ CFM of air with a static pressure rating of 4 to 6 inches of water. Inches of water is an old measurement system that's still in use today. It's simply a method of measuring differential pressure, or in this case, as in most cases, it measures gauge pressure, which is the pressure relative to atmospheric pressure.

Image

The problem is, many blowers, particularly low cost blowers, don't specify a static pressure rating. Cheap blowers are more like fans. They can move a lot of air, but their ability to move air decreases quickly if there's any resistance to the free flow of air. The manufacturers would prefer not to specify static pressure. This makes it difficult to compare blowers and make an informed engineering decision.

Fortunately, we can often use TANSTAAFL to our slight advantage. While there are differences in blower efficiency that could make one blower better than another for a particular application, there is a minimum power needed to move the amount of air we need across the resistance of a laser exhaust system. In general, we'll probably want something close to a 1 HP blower, or a blower with an electrical power consumption of around 750 watts. You may be able to get by with a 1/2 HP blower, although the exhaust may be a bit on the weak side. If you see an air mover that consumes 1/4 HP or 1/8 HP, or a current draw of around 1 or 2 amps at 120 VAC or a 125W or 250W power rating, that device will almost certainly not be suitable for a laser exhaust system.

I searched eBay, Amazon.com, and even searched Craig's List hoping to find a suitable industrial blower or cheap used dust collection system, but I ultimately decided on the solution that many others have chosen. The 1 HP dust collector from Harbor Freight.

http://www.harborfreight.com/13-gallon-industrial-portable-dust-collector-31810.html

I haven't actually made this purchase yet. I may find a better sale at Harbor Freight, and I'd like to drop by my local Harbor Freight store this week and see what they have in stock. I might get lucky.


Exhaust Design Options - Vent Outside Or Filter And Vent Inside?

Ignoring complex designs such as air-to-air heat exchangers, there are basically three laser exhaust design options, and as always, they each have pros and cons:

1) Vent Outside
This seems to be the most common option. An exhaust blower is used to suck air through the laser, pull out the smoke and noxious fumes, and vent them outside. It's a simple system that's easy to implement, and with the bare minimum of impediments to air flow, it'll achieve the most ventilation for the smallest blower (less power consumed, and less noise produced). The problem occurs when the inside air is much hotter or cooler than the outside air. For ever cubic foot of air that's vented outside, there will be a cubic foot of air from outside that enters the workspace. The need to heat or air condition that much air will tax your HVAC system, and you may be shocked by your next gas or electric bill. It might seem that it would be better to use the blower to push clean air into the laser rather than having the exhaust blower in the path of the exiting smoke and flaming bits of plastic. I think the reason the exhaust blower is on the back side is to pull a negative pressure in the laser. Pressurizing the laser would push noxious fumes out every crack or hole, but possibly even more importantly, it'd blow the lid off the popper (a lame reference to an old Orville Redenbacher commercial). The large lid usually rests on top of the laser by the force of gravity alone. Even a slight pressure over that large area would lift the lid and shut off the laser. Negative pressure can be designed to pull the smoke down and away from the optics directly above where the laser cutting is occurring, and the negative pressure can also act as a weak vacuum fixture to pull the sheet stock flat against the laser bed.

2) Vent Outside, With Outside Return Air Supplied To The Laser
This is the obvious solution to the problem of option #1, high heating or cooling costs. Of course, TANSTAAFL always applies. In this case, the outside air used to feed the laser may not be appropriate. If warm moist air from outside is drawn inside where the laser is in an air conditioned room, condensation could form inside the laser. A condensing atmosphere is bad. I've chosen option #2, because I need to use the laser approximately 20 hours per month, and I can choose when I use it. I can wait for favorable weather. I plan on having the exhaust exit low, maybe a foot or so above ground level. I'll vent it though a dryer vent with louvered shutters that automatically close to keep out bugs when the air isn't flowing. I plan on sucking in clean outside air from much higher. I'll probably run class B vent pipe up the side of the building, with a finely screened cap on top to keep out the rain, the birds and the bugs. I hope I don't have a nosy building inspector tell me that my dryer or water heater vent pipe isn't installed per code, because those sorts of people have been known to blow a head gasket if they hear, "That's not my gas water heater. It's the vent for my laser." :shock:

3) Filter The Exhaust And Vent Inside
This is another solution to the high heating and air conditioning costs associated with venting your laser outside. I found a good website where people were building activated charcoal filters for their lasers and were having good success. Basically, 2" to 4" of 2mm to 4mm activated charcoal filter media is used to extract all of the nasties from the exhaust before the cleaned air is returned to the ambient room air. I liked several aspects of this option. I'd have a completely contained system that's very neat and compact without external pipes or hoses. Running vent pipe and cutting holes in walls is a major PIA and it prevents the laser from being readily moved. And nobody outside would have any idea I was operating a laser. But I was put off by the cons. I wasn't bothered too much by building the filter, but I didn't like the idea of the ongoing cost and hassle of changing the filter media, even though the cost was maybe $50 a year, and it'd only require ten minutes a couple of times per year. Most people using this method were making a big assumption. "That which can't be smelled can't hurt you." I think that's not always a valid assumption. I engage in a lot of behavior that's risky to my health. I no longer fly experimental aircraft, and I may have done my last white water kayaking, but I eat too much greasy takeout Chinese food, I don't get enough sleep, and I drink too much Mt Dew. I don't want to add possible inhaled carcinogens to the list. When running the same air through the laser over and over, and anything that gets through the filter is ultimately going into my lungs, I'd prefer to err on the safe side. YMMV. People laser engraving wood are probably OK. People cutting acrylic might be OK. I cut weird foam and rubbery plastic, and they might generate odorless but toxic fumes. I'd rather not do that experiment on myself. If you'd like to look into filtering options, here are a couple of useful links.

Low cost homemade laser exhaust filter design:
http://www.sawmillcreek.org/showthread.php?143725-DIY-air-filtration-unit-for-lt-200

Good source for activated charcoal filter media (or search Amazon for 'carbon bulk':
http://www.amazon.com/LV-CARBON-BAG-52LB-BULK/dp/B000YJ4BNO

There are also hybrid exhaust venting possibilities that can trade off the various pros and cons, usually with new cons created in the bargain. :) For example, you might decide to vent outside with the supply air to the laser from outside, unless it's raining, and then you will switch over to a system that pulls room air into the laser and filters the exhaust air before returning it to the room. You'll have low energy bills in either case, and you won't deplete the filter media very quickly if it's only used on rainy days. On the down side, you laser exhaust system will have more cost and complexity, and you'll spend a few minutes swapping it between the two operating modes.

A fairly popular hybrid system is filtering the exhaust before venting it outside. That probably sounds crazy, but many people have neighbors nearby. Maybe you have a business with a laser in a strip mall, and the adjacent business is a bakery, with a patio. The bakery customers probably won't enjoy their muffins if they taste like burned acrylic. When venting outside, you can probably get by with less filter media, or with changing it less often. Filtering isn't as critical as it is for inside operations, where you're cooped up with the laser.

I gave some thought to designing my laser so a portion of the clean air side of the exhaust system was pulled through the radiator that cools the water for the laser tube. The concept is valid, and if I was designing a commercial laser, I'd explore that option and probably go in that direction. I'm only building one laser (I hope!) and any money I saved on fans for the laser coolant radiator would be more than spent trying to design a plenum system that cools the laser tube while not adversely impacting the exhaust efficiency. If I was designing a commercial laser product, I'd probably run the coolant water through a piece of aluminum tubing on the frame, with some snap on cooling fins, and save most of the cost of a radiator and cooling fans, but for a one-off machine, making the machine less clever and more of a sum of its component costs has a different form of elegant simplicity. The design becomes compartmentalized. If something breaks, a substitute part can be used without wondering how it'll impact the other related systems. There's something to be said for KISS. Besides, I had already ordered those two awesome cooling fans for the radiator. :oops:

Hopefully soon, I'll stop blogging about building my laser, and actually start BUILDING my laser. I should have some parts here soon. My initial order with the XY table and all of the optics and optics mounts is heading east, somewhere between San Pablo California and Lexington Kentucky. It should be here Wednesday. Then, the laser build begins in earnest. It's good to do most of the up-front research, decide on the components and various other aspects of the design, and purchase most of the parts in advance. When the parts arrive, I can jump into assembly mode without stopping to figure out some pesky detail, order the parts, and put the project on hold as I wait for the new parts to arrive.

I'll try to spend some time tomorrow, nailing down the lingering and nagging issue of how LinuxCNC will control the laser. What electronic interface hardware do I need to operate the stepper motors and the laser? Can I use simple optical isolation connected directly to the parallel printer port? That'd be cheap and easy, and would give LinuxCNC direct control of the motors and lasers. Direct control would be good because the relative timing of the laser to the motion is critically important when engraving. A parallel port doesn't allow many I/O signals, but the laser isn't all that complex, so it doesn't need many signals to and from the PC.

I'm fighting the urge to buy the laser tube and power supply sooner rather than later. I'll use a little red solid state laser in a cobbled together fixture to initially align the optics and test everything, and then I should only have minor adjustments when the big laser is mounted. I don't want that big fragile laser tube anywhere near my messy shop until it's ready to be unpacked and immediately mounted and plumbed in place. Logic dictates that the laser tube and power supply should be among the last of the components to acquire, but like all mental illness, Geeky Project Obsessive Disorder is not logical or rational. I'm itching to get an 80W laser so I can start messin' around with it. It's all good fun, until someone loses an eye. 8-) (in this context, that's the blind smilie, not the cool smilie)
Apparently, I didn't build that! :-)
Liberty4Ever
 
Posts: 274
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Location: Lexington KY

Re: Liberty4Ever's Laser Build Log

Postby jv4779 » Mon Oct 01, 2012 3:39 pm

Liberty4Ever wrote:I've been thinking about the LinuxCNC engraving a lot today. I'm not getting very far by thinking about it. Unfortunately, there isn't an obviously correct path to raster nirvana in LinuxCNC. A lot of the jobs that I do on the laser require an outline to be vector cut and some text or graphics to be centered within the cut area. The alignment precision can be fairly demanding. Given two different tool chains to produce vector and raster output on the laser will probably require some tricks and attention to detail to ensure the precise alignment.


There are two distinct styles of rastering when using g-code. First is true raster with variable dot patterns to make a grey scale picture, then there is just running the laser back and forth to frost an area. I mostly use the second flavor with is just a raster filled pocket operation with a beam width stepover and less laser power. When doing it as a raster pocket operation in your CAM program along side the normal vectors there isn't anything to line up externally. I have separate "tools" in VCarve Pro that can specify the feed rate, laser power (as plunge rate), and ppi/duty cycle (as spindle speed). This allows vector cut/engrave and raster fill in the same file.

To do the type of lettering you describe I have had the best results doing very light vector cut that is just enough to cut the acrylic protective cover, peel off only the inside of the lettering, paint with airbrush, peel off the rest and then you can leave it clear or paint again for a background contrast. I was doing a raster fill inside the lettering than then painting that engraved indentation, but it took longer and didn't really look any different.
jv4779
 
Posts: 40
Joined: Fri Dec 09, 2011 10:54 pm

Re: Liberty4Ever's Laser Build Log

Postby Liberty4Ever » Mon Oct 01, 2012 8:02 pm

I have a couple of types of jobs where I use raster engraving. On one, I emboss a logo into Santoprene, a rubbery black plastic. There's a noticeable 3D effect, with the engraved area lower than the surrounding surface. The graphic is a subtle black-on-black. I also make reverse engraved labels. I've used Gravoply, the commercial laser engraved label product, when doing a friend's labels for him on his laser. I haven't been able to locate the commercial material at a reasonable (IMO) price, so I buy acrylic or polycarbonate sheet, peel off the protective film on one side, spray it white, laser engrave the mirrored image of the graphic to remove the white paint and a little of the acrylic, then I spray black paint over the entire back surface to fill in all of the graphics at one time. It's very fast and easy, and the black paint fills the finest detail. For an entire sheet of labels, it would be very tedious to use an X-acto knife under a lighted magnifier to remove the vector cut bits of protective sheet from the insides of the enclosed letters (top of an A, two little pieces inside a B, etc.).

I've also laser engraved black anodized aluminum, which turns a very light gray that is almost white. It looks very good. I've laser engraved black oxide steel, and it looks good but was a lower contrast gray on black. I anticipate a lot of this type of work when I finally finish building CNC tools and get back to product development. My small business is primarily limited by my time.

I've done some messing around with laser engraving gray scale images on clear acrylic and similar arty things, which require different laser power to create the finer gray scale images. At least I think the laser was modulating the power very quickly, as that was hidden from me by the magic of the software and laser driver. For my business, I don't need grayscale art with fine detail images. I could easily get by with raster engraving where the image is monochrome (the laser is on full power or off for every pixel) and the print speed effectively controls the laser power (how much energy is imparted to the surface). It still sounds like it's not going to be easy in LinuxCNC. But hey, it's better than Windows! :D
Apparently, I didn't build that! :-)
Liberty4Ever
 
Posts: 274
Joined: Wed May 30, 2012 1:49 am
Location: Lexington KY

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