CNC enclosures

[owhite]

Hey people,

This is kind of by way of introducing myself, I'm making a relatively large cnc table which will be used in conjunction with a 100 watt CO2 laser for cutting sheet metal.

Okay, this will be the fourth cnc table I've built, but I've never gone to something this size. It has to be around 8 x 6 feet.

The laser will release undesireable fumes when its cutting acrylic and galvanized metal so it needs to be relatively airtight. There'll be ventilation to be certain.

sooOoooo, I'm looking for suggestions on different enclosures. Right now its looking in my mind like a room within a room, probably 6 feet high 10 feet wide, 6 feet deep, made mostly from 2x4 and plywood, with a pizza oven-like door with plexglas windows. Sounds clumsy and inelegant to me.

what thoughts people? feel free to be creative.

Owen

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[ToyMaker]

You might not need to completely enclose your machine. The chemical and electronics industries use exhaust hoods in their "nasty fumes" departments. They partition 3 sides of the work station and the hood sits on top. The air flow captures 100% of the noxious stuff.
Then there is the question of how to filter the captured air. You probably can't just vent to the outside (osha, epa, other regs?).
I don't have a link handy but Altavista or google will no doubt turn up hours of reading material.

robotic regards,

Tom

[owhite]

point taken. I guess I was thinking of enclosing it because I've seen a number of pictures on sites where they completely enclose the lasers. maybe to reduce problems with sparks. when you cut metals it basically produces a flame that looks like a mini-cutting torch.

o

[bcromwell]

There is more to CO2 Lasing than just fumes to worry about, Don't forget about reflection, you don't want to take someones eye out... Even though Co2 lasers can't pass through the corina to get to the retina they can (will) do serious burns on the outside of the corina which is almost as bad...

[owhite]

Yes.

My optics chain is completely enclosed until the beam leaves the cutting head and hits the part. That leaves an open gap of less than 0.06 inch. Reflection off the part is still a possibilty at that point if it were to hit something other than a flat surface.

Because of a their long wavelengths CO2 beams reflect off of anything. I was running some tests with a 25 watt and used a traditional beam stop which was a brick. The beam reflected off and scorched my chest. My first attempt at home tattoo removal.

But your point is a good one and probably accounts for why many (certainly not all) CO2 cnc systems are enclosed. Curiously, I've seen some in the 1-2kW range that are simply big flat open beds.

My enclosure will use either glass or plexi both of which do a good job of blocking the beam.

Just to keep the thread on topic -- still looking for suggestions on various enclosures -- verbal and pictorial suggestions welcome.

Owen

[ToyMaker]

Good point about eye protection. I saw (with both eyes, thank you) a sign in an optics lab that read:
CAUTION
Do not observe operating laser with remaining eye!

Grim humor, but I still chuckle

robotic regards,

Tom

[Hobbiest]

A full plexi enclosure that someone could walk inside of would be really expensive! Somethign that they would do on Monster House would be a pexi enclosure that drops down from the cieling and that would be so cool! Bit impractical though! I'd build it like a small workshop, with an industrial sized exhaust fan at the top to vent to gasses to the outside. That way you could just put an inspection window in it...better yet, one small one on each side...and you don't pay through the nose for plexi.

[owhite]

I agree, there's no chance I'd make the whole enclosure out of plexi. I'm thinking of mostly 2x4s and plywood box with a front cabinet door with horizontal hinging a lot like a pizza oven -- the plexi would simply be a window on that door.

If I was operating on a bigger budget using plexi I'd go with the aluminum extruded framework with internal plexi panels.

This gives an idea.... of what I dont want to do, that is.

Owen

[balsaman]

I would make a room with a man door and the pizza door. Interlock the man door with the laser shutter so you can walk in safely to do adjustments etc.

E-man

[pack rat]

I kinda have a problem with 2x4,plywood in presence of a cutting torch. What about metal studs and metal siding?

[Hobbiest]

Thats a great choice...cheap, easy to install, light too. But this is a CO2 laser right? No flame right?

[pack rat]

it is the word association thing. "yea I use state of the art laser to cut metal panels with 6000F temperature inside the large wooden crate". I think that is the reason why he brought the question up in the first place. Another tought. There are panels use in porch covering made out of fiberglass and also of metal, with sealant foam for edges. Maybe make rooftop that you can remove easily to gain acess from the top.

[TopSpin80]

I didn't read all the replies. but you might want to look at the fan systems for paint booths. My dad has built one to put fire trucks in and it is huge and moves a lot of air. another thought is to use a walk in refrigerator as the case around the machine... you can find used ones and they are built to be air tight with decent sized access doors.

ernie

[BIG AL]

The great thing about what you build is that you can control the air movment and vent along with all of that, you can get by with PVC pipe frame or I think I might prefer EMT and visqueen walls, a stand to set my air blower on and flex duc for my vent, oh yeah don't forget the Red Green favoret " DUC TAPE", yes cheap is my middle name but controlling air movement is what I done for a living for 25 years now. I can tell you for sure their is no better clean room inviroment than this and being how the fumes you will produce are a real haz-mat issue I would not do it anyother way. The things you can do with this type of a setup are mumerious and yes cheap, remember that all haz-mat removal is done this way.

[owhite]

regarding the amount of flame "is this a cutting torch in a box?" issue -- I havent gotten the laser on line yet to test the actual amount of flame produced. however, I've seen videos of higher power lasers and there's only a moderate amount of flame. Much less than a flame from a butane mini-torch or sparks from a plasma torch, for example.

Oxygen is blown through the cutting head to help consume the steel. I have been concerned about sparks being thrown away from the point of contact of the beam and sheet metal.

There will be a adonized aluminum table underneath the cutting head where the beam will meet the part. I was also planning on lining the bottom of the cabinet (which so far I imagine would be composed of mdf) with a layer of sheet metal. 4x8 sheets are around $40 which seems relatively cost effective.

Two walls around the area I'm working in are cinder block. If I make an enclosure (might not, see below) I was planning on making use of those to simplify construction. Basically the plywood would come in for the two remaining sides and top.

One point I got from this thread is that an airtight enclosure may not be in order anyway. Rather, an exhaust hood around the cutting area might suffice. A second post pointed out that a full enclosure would reduce risk of exposure to beam scatter.

Perhaps a combination of exhaust hood, protected fully from the front by a plexi sheet to completely block beam scatter. I'm picturing metal stand for the table, an exhaust hood, plexiglas protection in front. That way if there are any sparks they'd simply fall on the concrete floor or metal table. I like 1) not dealing with reaching in or walking in to a pizza oven arrangement. I'll be lifting 4x4 sheets of metal into the cutting area -- heavy and awkward 2) less lumber as fire risk, 3) better access for plumbing/wiring 4) simpler construction.

still not entirely sure, I might go over the alternatives with the guy I got the laser from who has a lot of industrial experience.

owen

[buscht]

owhite,
I would not recommend a solid table under the material to be cut. You need a honeycomb type structure.

The laser is melting the metal of the cut part and the assist gas is blowing the molten metal out the bottom of the kerf. If you have a solid plate under the part, there is nowhere for this slag to go, but back up the kerf, causing all kinds of problems.

The designs that I have seen and used have an eggcrate type honeycomb table made out of sheet metal to support your material. Underneath is a fan to suck up the fumes.

The honeycomb top is considered disposable and after awhile gets cut up by the laser and must be replaced.

Sparking of the laser is caused by pecking through the metal when starting a cut. When cutting normally, you won't see sparks or even the bright weld torch light mentioned above, because the laser nozzle and Z axis follower covers up the cutting area. Safety glasses are a must to block sparks and reflected light.

Another point, is that the laser beam must be properly focused to cut correctly. It's just like using a magnifying glass to start a paper fire by focusing sunlight to a pin point. Moving the glass up and down until you get the proper focus.

Commerical laser cutters have a floating Z axis that follows your part. As steel is heated and cut, it sometimes warps and the laser must maintain a constant dimension above the surface.

The assist gas (Oxygen is used in steel to help heat up the metal) is blown thru a nozzle around the laser beam. It is important that the nozzle tip be a certain size and exactly concentric around the beam. Otherwise the slag doesn't get blown out of the kerf properly and you get dross hanging up on one side of the part or the other.

[owhite]

buscht,

thanks very much for your comments.

>I would not recommend a solid table under the material to be cut. You
>need a honeycomb type structure.
>
>The laser is melting the metal of the cut part and the assist gas is
>blowing the molten metal out the bottom of the kerf. If you have a
>solid plate under the part, there is nowhere for this slag to go, but
>back up the kerf, causing all kinds of problems.

point taken. I can see I'm getting myself into to trouble by not giving enough information. For example, I should have pointed readers to my blog which has more information:

http://nilno.com/laser_dir/blogger.html

(I also figured that since its got a lot of correspondance so most people wouldnt bother to go through it). I have been planning on a honeycomb between the part and the table. I hadnt looked into the best spec, was preliminarily planning on using this:

http://www.mcmaster.com/param/asp/ps...629;1090=43216

which is .5 inch aluminum and I like the price. Other honeycombs I've seen are really expensive. I'm hoping that once I have something that cuts sheet metal, I can cut my own honeycombs.

>The designs that I have seen and used have an eggcrate type honeycomb
>table made out of sheet metal to support your material. Underneath is
>a fan to suck up the fumes.

Message recieved. I'll look into fume evacuation from below the table.

>The honeycomb top is considered disposable and after awhile gets cut
>up by the laser and must be replaced.

check.

>Sparking of the laser is caused by pecking through the metal when
>starting a cut. When cutting normally, you won't see sparks or even
>the bright weld torch light mentioned above, because the laser nozzle
>and Z axis follower covers up the cutting area. Safety glasses are a
>must to block sparks and reflected light.

check.

>Another point, is that the laser beam must be properly focused to cut
>correctly. It's just like using a magnifying glass to start a paper
>fire by focusing sunlight to a pin point. Moving the glass up and down
>until you get the proper focus.

check. A sketch of the optics chain is here:

http://nilno.com/laser_dir/optics_flat2-Model.jpg

the set of optics here:

http://nilno.com/laser_dir/pics/completeset.jpg

an incomplete sketch of the configuration here:

http://nilno.com/laser_dir/optics-Model.png

The optics are currently off at a optics machine shop who is making some adaptors to fit the components together and adding gas ports.

>Commerical laser cutters have a floating Z axis that follows your
>part. As steel is heated and cut, it sometimes warps and the laser
>must maintain a constant dimension above the surface.

I'll have a cnc controlled z-axis, not floating, and I've been quite concerned about the warping while cutting. Even in cases where I cut sheet metal with traditional tools its not uncommon for it to start to curl. I thinks its some "shape-memory" because 4x8 foot sheets originally still come from a roll that is sent to the steel yard and then cut. When they get cut they go boing even without heat. I'm pretty sure I'll be okay if I have to put some float into the z-axis, was just waiting to do some cutting to see what happens. A lot of my applications will not require large (or thick) sheets to be cut and I was wondering if it would work just to pin the sheet down with strategically placed holds.

>The assist gas (Oxygen is used in steel to help heat up the metal) is
>blown thru a nozzle around the laser beam. It is important that the
>nozzle tip be a certain size and exactly concentric around the
>beam. Otherwise the slag doesn't get blown out of the kerf properly
>and you get dross hanging up on one side of the part or the other.

understood. I've been working with the laser head manufacturer, see:

http://haaslti.com/

the president is a nice guy and he's assured me the head is set up well for my application.

I appreciate your comments though, and I'd be interested to know if the honeycomb material I'm planning on using will do the job. Some of your post is raising points that I've postponed making final decisions until I can gather a bit more run-time experience. this is a home project and I only have so much time -- I estimate it'll be about a year before the entire system is completely on-line.

owen