Plasma CNC Table

Any chance we would ever get a plasma CNC table? :crossed_fingers:

I believe the plan is to have a fiber laser.

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It’s certainly possible. The fiber laser project has dibs on floor space right now, but I believe dual-cutter (plasma + laser) CNC tables are a thing.

I’d wait and see what can’t be done with the laser before adding a plasma cutter to the machine. We have a big laser waiting for a CNC table right now. …alternately we could buy a plasma CNC and mount the laser on it.

@EricP and @JoeN are looking into how we get that running this summer.

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SICK!!! That is super exciting.

I’m talking with a friend to trade for some al extrusion to build a cnc table for a fiber laser or plasma combo. Once another fiber laser is setup at another shop. It will be used as a road map to build ours.

The project will probably not get off the ground until the fall. We will need machining help. There is a nucleus of people qualified on the lathe, mill, and Tormach. I will enlist students to also make parts. It is a big project. Eric and I have done some talking. That is the extent of our planning.

I did a quick search and found a fiber/plasma combo. Here
Let’s get one thing going before adding variables.

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Just curious, what is the benefit of a plasma/ laser combo? I’ll admit, I haven’t researched fiber lasers much, always thought that was an expense I’d never have access to. Just always assumed the fiber laser would be more desirable than the plasma. And don;t get me wring, a plasma cnc is still a dream come true.

Having both might be a pipe dream. Plasma is cool because of the cost effectiveness of the machine. It 's wider kerf and dross leave something to be desired. You can tune the feeds and speeds to reduce or eliminate dross. You can also run fine cut consumables to get a smaller kerf. I miss my plasma because you can blast out brackets very quickly. You can also cut much thicker metals for for a lower cost. The main running cost if the electricity, dry compressed air, and consumables. Retail on plasma tables is $7000 to $40,000.

Fiber lasers cost more, and are more expensive to run. The kerf is considerably smaller and there is basibally no dross. You have to have different gas setups such as an oxygen, nitrogen, and dry compressed air. Fiber lasers also need consumable tips. Fiber Lasers tables start $30,000 to $250k

Yes the fiber laser costs more, but once it is working. Asmbly and it members will spend less on post processing with abrasives removing dross. Less dust in the air from grinding. Also the electro magnetic frequencies (emfs) from plasma can cause havoc on electronics. The grounding on a plasma table has to be done to exist in the space. There are pros and cons to both machines. I think we only need one or the other.

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Thanks Joe. I had guessed cost would be an important part of the decision, but was unfamiliar with the consumables. I do know the kerf is quite different and so is post processing. I always just chalked the plasma post processing time up to the benefit of being able to CNC metal.

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I found this video for comparison. Here

I found out a tidbit while doing more research about fiber lasers. The models coming from China require 480v with a step down to 380v. This voltage provides stability for the whole system. I don’t know the requirements of a Coherent fiber laser and the whole system.

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Fiber lasers seem to outperform plasma on every front that I can think of. As per Joe’s comparison, the fiber laser’s cuts are much cleaner and accurately render much smaller features. With the fiber laser, a plasma cutter would seem redundant.

Fiber laser is not very expensive to run per hour. The source should have a very long life. On the other hand, the water table often (but not always) used under a plasma bed seems like a mess to maintain on an ongoing basis. It collects fine particles of metal (maybe rust by that point) that I guess mucks up regularly- Joe would be the one to know about that more than I.

Cutting with nitrogen or oxygen gas is basically the same sort of option on plasma as it is on fiber- there are scenarios where it desirable to use one or the other, but either is logistically problematic as this is a consumable that would be delivered and stored in large pressurized or cryo tanks. Oxygen drastically accelerates the cutting speed and cuts deeper (especially on carbon steel) because it burns the vaporized metal for additional heat, but leaves an oxide edge. Nitrogen is the opposite, it shields the cut zone from oxidation and cools the cut zone, so it will be cutting slower. Air it’s far simpler, cheaper and a middle ground between these two. And most fiber laser cutting will do just fine on air too, and it seems shops commonly do that even for production as it’s cost-effective and the results are fine for most applications.

Correct me if I’m wrong, but I think we don’t often see plasma cutters set up with nitrogen or oxygen assist gases is because if the task has cut qualities requiring it, most often you’d probably upgrade to a quality fiber laser first to get better performance and cut quality and the assist gas options would be a possible upgrade after that.

As far as “consumables” go, the fiber laser does not expose its lens to the environment like a CO2 laser cutter. There is a nozzle cone like a CO2 laser (like Red), but in the case of the fiber laser there is an additional fused quartz window between the lens and nozzle. The window and nozzle require replacement periodically, but I believe it’s infrequent and cheap. But unlike a CO2 laser, which projects the beam through the air and bounces off mirrors to reach the head, the fiber laser routes its beam through a fiber cable that must flex as the head moves around. These cables do have a finite bending life, which depends strongly on how tight of a radius it flexes in normal use. They’re not super cheap to replace but usually last such a long time that the per-cut amortized cost is still quite low.

Either fiber or plasma will slowly erode the bed of sawtooth material supports. They are replaceable. I believe a fiber laser would erode it considerably slower than plasma.

The 1KW Coherent HighLight and cooling system we have will run off 208v single phase. With compressed air, that will cut 1/8" carbon steel easily, it would cut twice as thick on oxygen but that’s not likely going to be practical. People have definitely tweeked the air pressure This, or any fiber laser, will require clean dry air (CDA) that the Atlas Copco compressor will produce.

The two “??” concerns are laser safety and ventilation. They don’t seem to create all that much for fumes, but we do keep the whole shop air conditioned so whatever gets in the air is going to be recycled for some time. All fiber lasers have a wavelength of ~1,060nm. As far as I know, this wavelength will not be stopped by ordinary glass or acrylic barrier. Although both are infrared (invisible), a CO2 laser operates on a wavelength of 10,600nm (10x longer) and that wavelength is completely stopped by any glass, polycarbonate, or acrylic barrier. Transparent shielding against fiber is a different material, but I don’t think it’s prohibitive, just another consideration on the list.

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I think the shielding should be a somewhat tractable issue. This calculator suggests that we’d need ~5.7 OD, so hypothetically I think that this sheet would even work (although it’s probably too small). I can call Allied Plastics to see if they have the right kind of material in stock.