[jbailey19]

I am close enough that I need to quit lurking and get this thing done hopefully with your guys help.

I decided that I needed to build a laser cutter for my hobby business (www.midwestfoamplanes.com) so that I can better control quality and add flexibility to my business. I will mainly be cutting 9mm thick EPP foam in sheets that are 3'x4' but would also like to cut up to 1/4" plywood but not very often.
I have already built my base and rails. The base is 2 layers of 3/4" MDF laminated and skrewed together and to the table below. I sourced the aluminum from a local surplus yard. The blocks are built up from aluminum 1" square tubing and 1"x2" angle. I used quality skate bearings and it turned out better than I thought it would. Both axis move very free with little friction.

Help #1
I have a friend who is getting me a free 40+ watt medical laser with low time on it. This is my first unknown. I have yet to see it. All I know is that it requires a CO2 bottle and 220v and has a wand that extends about 3' which I assume is using fiber optic. I am hoping to take a look at it soon so I can make a decision if I want to use it. I will take it no matter what as I can always sell it. I have looked at the lasers at www.lightobject.com and wonder if I would be better off with a sealed CO2 laser for simplicity. Looks like $500 for a 40 watt or $800 for a 60 watt both with a power supply.

Help #2
Controller board. I built a 4-axis hotwire several years ago from a hobbycnc kit and was happy with it. I am leaning towards getting a prebuilt unit from www.mikebeck.org but it does not have PWM or other laser control and I am not sure if the 300oz.in stepper would be over kill and add excess weight to the gantry. My gantry right now weighs 8.5 lb. I do have some 4 and 6 wire steppers that I can use (3.9v, 1.35A, 1.8 deg/step). I saw that lightobject has a TB6560 3 axis contoller board but there is little info on the site. Does it have PWM laser control? Will it work with my steppers?

Help #3
If I do use the medical laser I am thinking about using the wand and just attach it to the y-block on the gantry for simplicity but I will have to see the cut quality from the end of the wand. If I do not use the wand then I will need some recomendations for mirrors, a final focus lense and mounts.

Help #4
Cutting surface/support. I was thinkin about using an aluminum sheet over the MDF. On top of this would be 1" angles placed like ^ running the length of the table. On top of the angles would be 1/2" aluminum honeycomb. What about the laser reflecting off of the aluminum? Can I paint it with a hi heat paint? Rustoleum hi temp can handle 1200 deg F. Is this enough? Will skuffing the aluminum spread the light enough or is the dull surface enough?

I am sure that I will have more questions and I will thank you in advance for any help. I hope to have this thing cutting in the next several weeks.
Mike

[austin.mn]

I just ordered one of the lightobject driver boards the other day, so I should be able to chime in with a bit of info for you once it arrives.

[zax15uk]

Mike,

Nice job so far. I would suggest keeping the mass and inertia down with smaller steppers, especially for your application (EPP).

#1... A CO2 medical laser does not use fiber optics for the delivery system, it will have mirrors inside the arm (at each section joint). It most likely has a very small depth of field (working distance) so you will need to replace the lens. Depending on your gas cost, it may work out cheaper to get a Chinese sealed gas tube and PSU, but the 'free' laser would be a good start.

#2... There are plenty of options for the driver if you are going the step/direction route. I am guessing you intend to use Mach3 for the software, in which case you could use a DigiSpeed or equivalent to drive the laser power (0-5v signal). There are other options too, but watch out as most of the PWM boards are for spindle controllers and not fast enough for a laser PSU input. An alternative is a custom driver designed for a laser, check out Full Spectrum Eng. or head over to http://www.buildlog.net/forum/index.php and see the other options.

#3... The wand would be ok once you replace the final lens, or you could salvage the mirrors from the arm and use them in a more traditional arrangement.

#4... Just the honeycomb will be fine, there shouldn't be any need to paint it.

Have you laser cut the EPP before? I am surprised you find it better than hot wire, except the obvious internal cuts. In my experience you'll need a long FL lens to get an acceptable straight cut, the standard 50-75mm produce too much beam convergence/divergence )(.

Zax.

[jbailey19]

Mike,

Nice job so far. I would suggest keeping the mass and inertia down with smaller steppers, especially for your application (EPP).

#1... A CO2 medical laser does not use fiber optics for the delivery system, it will have mirrors inside the arm (at each section joint). It most likely has a very small depth of field (working distance) so you will need to replace the lens. Depending on your gas cost, it may work out cheaper to get a Chinese sealed gas tube and PSU, but the 'free' laser would be a good start.

This particular laser is for busting up stones and uses a cath. to get the laser inside the patient.

#2... There are plenty of options for the driver if you are going the step/direction route. I am guessing you intend to use Mach3 for the software, in which case you could use a DigiSpeed or equivalent to drive the laser power (0-5v signal). There are other options too, but watch out as most of the PWM boards are for spindle controllers and not fast enough for a laser PSU input. An alternative is a custom driver designed for a laser, check out Full Spectrum Eng. or head over to http://www.buildlog.net/forum/index.php and see the other options.

Thanks for the link. I do plan on running Mach3 initially. I have a back ground with g-code so I think I will be ok. I would like to find a board that can control the steppers and the laser.

#3... The wand would be ok once you replace the final lens, or you could salvage the mirrors from the arm and use them in a more traditional arrangement.

#4... Just the honeycomb will be fine, there shouldn't be any need to paint it.

I will still need the aluminum sheet on top of the MDF right?

Have you laser cut the EPP before? I am surprised you find it better than hot wire, except the obvious internal cuts. In my experience you'll need a long FL lens to get an acceptable straight cut, the standard 50-75mm produce too much beam convergence/divergence )(.

My sheets are .375" x 36" x 48". I do not have a good way to hot wire them. I do have some internal cuts. Right now I am farming out some of my kits to have them water jet cut.

Zax.

Mike

[jbailey19]

I just ordered one of the lightobject driver boards the other day, so I should be able to chime in with a bit of info for you once it arrives.

I called them today and their standard boards only do on/off for a laser. It would be nice to have PPM control so I can set up values in mach3 for different materials. It looks like the fullspectrumengineering 4 axis board is supposed to have ppm control. I emailed them for price and availability.
Mike

[bgirit]

I've struggled with the honeycomb table problem and I 'd like to know if you've figured out a solution. First of all, I havent been able to find the kind of thicker walled honeycomb that they use on the Universal/Epilog lasers. I've seen very thin honeycomb which is far too flexible and not appropriate for a rigid flat table. I ended up using a rectangular aluminum grid that was sold as a light reflector, but it was sufficiently rigid to work. However, the problem I'm having with that is that the thin aluminum heats up enough to leave tiny burn marks on the bottom of the material that I'm cutting right at the cut edge. I was thinking that perhaps a high-heat paint might prevent this. However, I can imagine that burning paint might be far more troublesome than the current problem.

I'd like to hear other peoples solution for this.

[jbailey19]

I had planned on ordering 1/2" or 3/4" honeycomb depending on the cost and then support it with several angles spaced close enough to keep it from sagging.

I do have a question about guide tracks. I saw a nice design using 90 deg v-groove rollers that run on a rail with a 90 deg v-edge. Mcmastercarr has them but the bearings are $25 a piece so $75 for the 3 that I need.
http://www.mcmaster.com/#v-groove-rollers/=5ypx0p
Anyone seen these cheaper?
Mike

[jbailey19]

I had planned on ordering 1/2" or 3/4" honeycomb depending on the cost and then support it with several angles spaced close enough to keep it from sagging.

I do have a question about guide tracks. I saw a nice design using 90 deg v-groove rollers that run on a rail with a 90 deg v-edge. Mcmastercarr has them but the bearings are $25 a piece so $75 for the 3 that I need.
http://www.mcmaster.com/#v-groove-rollers/=5ypx0p
Anyone seen these cheaper?
Mike

Just found some for $10 ea. here.
http://www.vxb.com/page/bearings/CTGY/V-Groove-Bearings
Mike

[Lasershop]

You will scrap the wand. 40 watts is probably minimal to do what you need. Best to use mirrors as flying optics and use the beam right out of the laser. Cutting wood at even 1/4" requires a lot of air pressure out of the laser nozzle. The carbon is your enemy and you need to basically blow it out of the way. Going to take a little practice on the foam also. Its harder to cut than you might think. You will definetly need a way like Mach3 to control the power and feed. Hardley no two materials cut the same. Foam will hourglass the edge if there is too much heat. Not enough power will also build up heat in the cut. I have seen and done it all in laser cutting, nearly 20 years. Ill try to keep an eye on your progress if maybe I can help.

[CNCdn]

Hi Mike.
Just came across your thread and wanted to say that I have some ideas that may interest you.
I had similar goals in mind when I built my first CNC machine. That machine is a very small milling center and completely unsuitable for this project but was built to teach me about CNC and machine building and, for that, was completely successful.
Anyway, my thoughts for cutting foam profile planes (yes, I am a R/C enthusiast).
I had intended to build a hot-wire cutter (vertical wire) but, of course, couldn't deal well with the internal cuts and had some difficulties with holding the sheet as things were cut out.
So, I looked at lasers and decided that they were too complex and costly.
I have tried rotary cutting using a dental bur of only 0.040 diameter and that works quite well. It does create some 'dust', of course but not too much.
I have considered using an ultrasonic knife, which I believe would work very well also but commercial units (so far) are too expensive. I'm still looking to see if I could build a transducer and driver board for this.
One other thought I had was a hot knife. Mach 3 could turn such a knife as it tracks around the shape of the cut (a stepper drives the spindle instead of a high speed motor).
Along the same lines is a completely round hot knife but I haven't experimented with that yet. Don't know how fast you can get the heat down to the tip. I also thought of building 'stiff' hot wire. In this case, I would thread a teflon insulated wire trough a stainless steel hypodermic needle and silver brazing the wire to the lower end. The SS would then heat up through the application of high amp, low voltage.
Of course, the rotary set up and probably the conventional hot knife and possibly the ultrasonic knife would be capable of slotting for carbon fiber etc.
I'd be happy to help you further this project in just about any capacity you'd like (might cost you a kit someday).
Alex

[jbailey19]

Thank you for your comments. I have the machine cutting now but have found that for the EPP foam that I am cutting the 40 watt laser I have is too powerful. The best cuts that I get are with the laser at minimum power and two cuts running high speed, 80 in/min. I need to go faster but I just got my cable carrier tracks installed last night, also I am getting hesitation between arcs that I need to smooth out.
I have a friend at a hospital that was working on getting me a laser but I might have to see about a ultrasonic cutter as we had talked about them some.
The laser is working good but I am having trouble keeping the mirrors aligned.
Mike

[CNCdn]

You're welcome, Mike.
Hope you can get it all 'ironed out'.
I may just pursue some of these ideas myself. It was, in fact, the reason I got into the whole CNC thing in the first place. I simply didn't want to start hand cutting this foam and I's really like to try 3-D flying (not interested in competing with you business, BTW).
I also wanted a machine large enough to be able to cut 'jigsaw puzzle' like cuts in the ends of thin (marine) plywood in order to splice lengths together. I have built some looong kayaks and the splice is one of the most troublesome tasks.
Anyway, please keep posting. I'm really interested in your progress and don't hesitate to contact me if I can help.
Alex

[CNCdn]

Mike.
Just tried the round hot knife concept and in a 30 watt soldering iron, it cuts like crazy.
Since the iron took a 0.150 diameter tip, I put together a number of brass tubes to end up with a 0.062 diameter copper "knife".
Works really well though the melted edges are a bit hard. Suppose that any heat related cut would do the same.
I still my go with the rotary cutter perhaps surrounded buy a vacuum ring to take care of the dust issue.
Alex