The importance of air assist

projectinspo

#1

Having just delivered four lasers to customers here in December - it seems that people do not understand the importance of having air assist in their cutting.

Yes, you can cut fine without. Once or twice. But…

Air assist is having a stream of air blowing out from under the lens towards the material - the air is blowing out of the same nozzle as the laser beam.

The air assist aids by:

  1. Removing smoke from the cut - making more energy hit the target area and less dissipate in the smoke
  2. Drastically reduce the build up of gunk and smoke on the focus lens.

It is 2) that is the most important one. Cutting regular plywood with a 40w laser - I observed about 4% diminished power per 10 minutes of cutting without air assist. Eventually, the lens will begin to heat up from the amount of energy dispersed on its surface. If not cleaned in time, the lens might shatter (had this happen once).
Air assist completely removes this build up of smoke and ash.

So what do You need off an air assist system?
I have worked with compressed air, which is great - but requires some type of compressor or pump. This is noisy and adds another item that needs to be turned on and maintained.

Recently I have started to add a simple 80mm computer fan, attached to a fan-shroud (3D printed) that funnels the air to a slender hose, that attaches to the lens nozzle. While this does not generate a huge amount of “blow” - lessening the effect of 1) above - it is easily adequate in keeping the lens free of build up.

While mocking around with the best way to implement this, I added a small divider, sending about 1/3 of the air out ABOVE the lens. This prevents dust from settling on top of the lens in through the laser reflector/ mirror opening - and keeps the top mirror from getting too dusted as well.

The 80mm fan is running off spare power from the PSU in the laser, so it turns on with the system. It is fairly silent.

There is still room for a lot of inventiveness in the laser designs, even tho’ the technology is fairly old. :wink:

Peter.


What to do when a low-power engrave comes out inconsistent?
#2

I believe that Glowforge has already taken this into consideration per the comment from @dan below.


#3

And the lens on the GF are behind glass and not exposed to the “smoke” as it were. So not to worry.

I do however agree that keeping a clean/clear path is always a good idea.


#4

Thanks for sharing your hands-on experience - very few experienced laser users here (yet), good to have some real experience in the mix (vs speculation)!


#5

Will the glass be coated with soot and debris?


#6

@MikeH Yes, the glass might get dirty over time, Thus the second half of my statement “I do however agree that keeping a clean/clear path is always a good idea.” but it will not cause the lens to overheat as they are not connected. It could however cause a performance decrease.

@dan did say someplace on this forum that he so far never cleaned the glass (if I remember correctly).


#7

No experience with lasers here, but plenty with 3D printers. I think you will find a radial blower will be far more effective than an axial fan with a funnel. They produce air flow with a higher pressure. A bit more noisy though.


#8

@spike - OK, I’m having a hard time seeing how the glass won’t need frequent cleaning but experience trumps guesses and sooner or later I’ll be able to see for myself.


#9

Yes. That’s one of the more confusing design decisions. You will just be cleaning the glass windows instead of the optics. Which, from a new user perspective might be better because those mirrors are very easy to damage while cleaning. So same amount of work but potentially lower the cost of replacing mirrors. It’s possible to fully enclose the optical path various ways…more difficult on a flying optics configuration like the GF…but possible.


#10

Well, ultimately there has to be some sort of barrier between the last mirror and the object being cut or engraved and that surface must be subject to fouling by smoke, soot, or debris, I would think. If it’s just a disk of standard glass, that should be pretty easy and inexpensive for the user to replace. I thought there was a recent discussion on specialty glasses that are needed for this purpose so as to avoid attenuation or dispersion of the beam.


#11

Air assist/purge, so it helps keep the smoke from coming in contact with the glass. Thus the lower cleaning maintenance of the glass.


#12

Cleaning intervals will depend on a lot of factors. We cut lots of different materials and the laser is in heavy daily use. Our 45W machine needed cleaning weekly (optics, rails) and frequent tuning of belt and wheel tension. The newer 80W machine needs cleaning more often, optics about every other day and rails much less frequently, but the linear motion mechanics are rock solid so no more adjusting belts and wheels. If they really haven’t cleaned the windows at all then that’s pretty amazing. Maybe it really doesn’t need cleaning or the resulting power drop doesn’t matter for their testing purposes. I would imagine the GF will need more cleaning than most other cutters because the positioning of the exhaust port pulls smoke and soot toward the #2 mirror on the y-axis gantry. Another puzzling design choice.


#13

Be careful with your air source. If using compressed air make sure you filter out any moisture and oils before sending air towards the bottom of your lens.


#14

Ya don’t need to worry about this on the GF. But on a different brand unit that needs a external air supply, you are correct.


#15

Yup…one really nice bonus feature of the GF. Most hobby lasers require a noisy external air source.


#16

@fablab_elpaso - thanks, that falls pretty much in line with my thoughts. It would seem reasonable to direct airflow so as to pull smoke, etc. away from the optics.

I have what looks like a Gast regenerative blower that puts out 27 cfm - would something like that be appropriate for the GF? I’ve no real feeling for how much air flow is required but that would probably be around 5-7 GF chamber changes per minute which doesn’t seem like all that much.

I hope that @dan isn’t too upset with back seat engineering.:slightly_smiling:


#17

Mike, The Gast is designed to draw vacuum. Way overkill for this.
A very nice blower BTW


#18

It probably won’t be standard glass since it is fairly opaque to CO2 lasers.


#19

Haven’t had the benefit of looking at the design. Still, cleaning a couple first surface mirrors vs. the simple wipe down of clear windows with a non abrasive cloth is probably a good decision for the less experienced. Though the windows might still have a delicate anti-reflectivity coating. Don’t know. Also, no alignment issues. More importantly the optics for the variable focus are also all enclosed. Those might have been difficult to clean without significant dissassembly.


#20

Yeah…but you can buy replacement mirrors from lots of places online for very little cost. Custom window housings will have to come from GF at whatever price they decide to charge for replacement parts (if they offer them at all).