ULS air assist maxing at 10-12 psi, normal?

[John Tolman]

I recently setup a new VLS 3.60 with the air assist option. I purchased a GAST DOA-P707 (http://www.drillspot.com/products/35711/Gast_DOA-P707-AA_Compressor_Vacuum_Pump) from the ULS distributor I purchased the system from that also came with an oil catch and desiccant dryer.

The manual specified that the air source should provide 50-60 psi at 2.5 CFM. Surprisingly I was only getting 10-12 psi with the regulator opened all the way. I spoke with their technician who told me that is not good and proper, but then when they got back to me after speaking with the other tech, they told me that it is normal and that's how their systems run. I am re-reading that portion of the manual on manual air assist, it specifically says 50-60 psi at 2.5 cfm, and yet that spec list I linked to above says that at 50 psi it is only rated for 0.25 cfm. In fact, it doesn't look like it's possible to get 2.5 cfm at any pressure.

So, will I find 10 psi adequate for most jobs (currently I'm using it on corrugated cardboard, thin wood and G10—the only material that I'm really concerned about having enough air from an equipment safety perspective). Can someone confirm for me that this is just an underspec'd compressor? If that's the case I'll have to see if they will take it on return, and purchase an adequate unit from somewhere else. If that ends up being the case I'm sure I can find some posts on recommended units for this system. I'm not too thrilled about the idea of having an underpowered system that while maybe adequate most of the time, may jeopardize my optics or lead to poor cut quality. I noticed I have a slight amount of char on corrugated cardboard that rubs off, as opposed to samples I got from the vendor which were absolutely clean. This could just be coincidence or non-optimal cutting settings.

One last thing, the desiccant filter takes a small amount of desiccant (a cup or two) but it would be nice to have a second set so I have no downtime when I need to reactivate it in the oven. Grainger sells a replacement set for this Wilkerson filter but it's $60. Seems steep for a little desiccant but maybe I have a poor concept of the cost of silica gel. If someone has another source of equivalent silica gel that'd be great.

BTW, this is my first post but I've been reading these forums over the years in envy. I'm pretty excited to finally have a laser cutter to play around with myself!

[Scott Shepherd]

We have a shop compressor that can give us much more than we need for the ULS spec's, but I can tell you that I keep the pressure around 10-15psi on our PLS 4.60 on almost all work we do that requires air. I've not found any use for cutting anything yet that requires or does better with 40-60 psi of air running through it. Maybe it's out there and I haven't run it yet, but I've run a ton of various materials and 10-15 seems to work just fine.

[Dan Hintz]

I keep mine set to around 10-15, like Steve, and mine comes from a chop compressor, as well. 10-12 is usable, but it's not what is advertised and should be remedied.

For desiccant, you can buy quart containers for around $10-15.

[John Tolman]

Thanks for the replies. I'm not sure what to do at this point, I'll have to think about it. I spoke with ULS tech support and they are telling me that although at this underpowered state the machine is safe, I won't get optimal improvement on cut quality with some materials. That somewhat contradicts what I've read around here as far as what pressures ULS users typically use.

I contemplated just getting the ULS compressed air unit until they told me the price—no thanks. Hence I wonder if I am better off just sticking with this unit that may be perfectly fine for everything I'll be cutting and it wasn't *that* expensive.

[Scott Shepherd]

This probably won't come across quite like I mean it, but with all due respect, most people in tech support in all laser manufacturers have never run lasers for a living. Many of us probably have more hours in front of a laser than most tech support departments as a whole.

40-60PSI into a cut isn't going to do much other than make the cut cool faster. If you're cutting thicker material, you don't want to cool the cut before it's finished cutting. You'd actually reduce the depth you could cut with a laser if you cranked the air way up. You'd be cooling the cut and it wouldn't work. You need enough pressure to blow the debris out of the kerf while cutting, not to cool the material rapidly to stop the flow of the cut.

That's just my opinion.

At one point we were cutting a lot of 1/2" thick acrylic. We tried just about every pressure available and it ended up less than 20 psi on all test and production we did.

You don't use it with raster engraving too often, so high pressure there would only blow debris back into the cut, which would be bad. I honestly can't think of when I'd want really really high pressure. Again, the application may be out there, but I've never seen it. I think you're perfectly fine.

[Zvi Grinberg]

I also recommend to keep the pressure at the lower range.
I saw customers who used too high pressure and their air assist piping suffered severly.

However one additional point should be considered. I
In general higher pressure compressors (off the shelf at relatively low cost) have larger tanks for buffering compressed air.
Using compressors for air assist is usually for long time periods. There are jobs that take a full hour or more.
You might want to give your compressor some rest during the job, and avoid overheat. Stronger units with larger tanks would be more comfortable in such conditions.
There are of course several types of compressors, some can work continously. But they also vary in price.

[John Tolman]

Hey Scott, I get what you are saying about the limited experience of tech support, and from my limited experience would agree with the exception of maybe one person at the distributor. That's reassuring that you never go over 15 on your system and have no issues. I'm content with keeping this unit and if I move it into a larger shop with a compressor with a large tank I'll consider switching for convenience.

Zvi, this pump does get pretty hot if I'm cutting for more than 15 or 20 minutes but I usually don't run it constantly longer than that, mostly so I don't load up the desiccant faster than necessary. I can't find a rated duty cycle for the pump anywhere, but maybe I will look some more.

[Dee Gallo]

John,

I always use a mere 10 psi - which is what Epilog recommends in the manual. It has proven to be enough, since it only has to blow away smoke, small flames and tiny particulates. I suspect that having too much pressure will cause a few possible problems, like maybe moving your substrate in addition to slowly eroding the small tube directing the air. If it's anything like an airbrush's white metal, air flowing over it can wear the metal away. 10 psi will not bother it.

I've had tiny pieces of paper, cardboard and even veneer fly around from the air flow, which can get in the way of things. More pressure would increase that likelihood.

I would do some tests to find out where the optimum settings are for avoiding as much char as possible, such as ppi, rather than rely on air assist to do that. And learn to accept that sometimes you just can't eliminate all char.

cheers, dee

[Robert Silvers]

My compressor's regulator seems unreliable at lower pressures (much below 40 psi). My plan is to set the compressor to 50 psi and then adjust the volume with the needle valve near the lens.

[Dan Hintz]

My compressor's regulator seems unreliable at lower pressures (much below 40 psi). My plan is to set the compressor to 50 psi and then adjust the volume with the needle valve near the lens.

Make sure it's designed for that pressure. I think on many ULS machines the tube starts popping off around 60psi. Sounds like you need a better external regulator rather than beating up the on-board one.

[Scott Shepherd]

Make sure it's designed for that pressure. I think on many ULS machines the tube starts popping off around 60psi. Sounds like you need a better external regulator rather than beating up the on-board one.

I don't know what people are cutting with that much air. I run 3-15 psi on both our lasers and don't see any benefits from higher pressure. In fact, Synrad recommended like 1-2 psi for cutting thick acrylic. Honestly, there is little need for that much air. I'm not saying there isn't a need for it for some application, but with all the things I've run over the years, I've never had super high air pressure on anything.

[john banks]

We do a lot of oak cutting and use 30 PSI and elongated cones to bring the coaxial air assist close to the wood so we don't have to mask or sand, or in fact just trash the piece to a charred mess if we use say 15 PSI. 3HP compressor just about keeps up on about 50% duty cycle.

[Scott Shepherd]

We do a lot of oak cutting and use 30 PSI and elongated cones to bring the coaxial air assist close to the wood so we don't have to mask or sand, or in fact just trash the piece to a charred mess if we use say 15 PSI. 3HP compressor just about keeps up on about 50% duty cycle.

How thick of oak are you cutting? I've cut stacks and stacks and stacks of various plywoods, etc, and I'm not getting charred edges on anything. Maybe you are the exception I mentioned. Charring typically comes from too high a ppi.

[Robert Silvers]

PSI does not tell you how much air. If you run it through a tiny needle valve it is not much air.

[Dave Sheldrake]

If someone has another source of equivalent silica gel that'd be great.

Bob Martin cat litter (kitty litter) is good silica, very pure and turns green when wet :)

Pressure / volume is less important than efficiency for air assists, as John said (Hi John) close to the job and a small exit hole is far more important than huge compressors.


. Charring typically comes from too high a ppi.

Chinese lasers my friend, no adjustment available for ppi :(

cheers

Dave

[Scott Shepherd]

Chinese lasers my friend, no adjustment available for ppi :(

cheers

Dave

Learn something new every day! I did not know that.

Knowing that, let me change my answer- crank up the air :D

[Robert Silvers]

When engraving you can set the dpi in the Y direction, but not X. I don't know what the native X resolution is.

[Scott Shepherd]

When engraving you can set the dpi in the Y direction, but not X. I don't know what the native X resolution is.

DPI and PPI are 2 totally different things on a Western system.

[john banks]

With RDCAM you can effectively change PPI (based on time rather than distance, with control over mark and space but if you know the speed you can still do it) but all it does is reduce the effective power in all our testing. Must be a function of the glass tube that if you turn off the TTL signal to the power supply on a given duty cycle you just get less effective/average power whereas on an RF tube you seem to store up the energy that would have been deployed and release it in discrete pulses? I know some on other forums said they got results from it on Chinese tubes, but we don't. The TTL signal is correct as proven by slowing it down so you can see the pulse macroscopically (quicker than getting an oscilloscope rigged up), but the effectiveness isn't there on our setup and it was a pointless/abandoned exercise to optimise this way for us.

The oak we cut is 1/4" thick with characters with curls that are only about the size of the thickness of the wood, so many of the features in the fonts are say a fifth or even a tenth as wide as the depth of the cut. To avoid overdoing it you do have to check detail areas and font choice. Biggest issue has been some batches of oak that crack across the grain, we are about to experiment with some 1/3" thick sheets that seem stronger.

For sure, cutting 1/8" thick materials doesn't matter so much, but we hardly have to mask or sand things and seem to get results on wood our customers keep coming back for.

The demos we had of RF tubes cutting our wood also benefited from lots of air pressure and flow to avoid charring. Tiny compressors were universally rubbish for our application.

We had some results from making the cone exit smaller, with careful alignment so that the coaxial jet was narrower, but you reach practical limits easily even if you use the laser to make its own hole through an acrylic end cap on the cone, eventually we would melt it and it would drop out, so lots of airflow and pressure and an opening about 1/8-1/6" (can't remember exactly) or so in the end of the cone which has an extension to get it near the wood works for us.

[john banks]

Hope I'm allowed to post a picture that contains no commercial references. This oak is 1/4" thick. It comes out the machine like this with no masking and just the occasional bit of sanding on the back. If another machine would do this through PPI with little air it might give us flexibility with future machines as although our present machine is busy and very profitable, a faster engraver may be useful, but I always thought the big cheap Chinese machine would always be our cutter.

The nice thing with 30 PSI is that the little bits of wood clank onto the bed with a most satisfying noise and with the power (actually speed - we use full power) set to threshold to just but virtually always cut through the back is lovely, 99% as good as the front. We also get far superior results with slatted black finned table rather than honeycomb which chars the back, different to what most experience it seems.

273093

[Robert Silvers]

DPI and PPI are 2 totally different things on a Western system.

You mean DPI and PPI are different from each other on a Western system, or DPI and PPI are different on a Western system than on a Chinese system?

On my Chinese system, it only refers to "scan gap," which I can convert to DPI in the Y axis.

[john banks]

Scan gap or DPI is for rastering.

PPI is for vectoring. The controller pulses on-off rapidly, typically a few kHz on Western machines whilst it is vectoring what in your artwork is a continuous line or curve.

[Scott Shepherd]

I mean PPI is pulses per inch and dpi is dots per inch. Two completely different things. You can pulse 200 pulses per inch on a 1000 dpi image if you so desired.

[john banks]

If you did 200 PPI on a 1000 DPI image (which is rastered) and you weren't varying the power by grayscale information, then you would only be able to see 200 DPI (horizontal) resolution on the workpiece? Is the control mechanism the same, just turning the laser on and off according to bitmap information filtered through a 200 PPI gate? If so, the PPI setting would be void when considering rastering?

[Robert Silvers]

I mean PPI is pulses per inch and dpi is dots per inch. Two completely different things. You can pulse 200 pulses per inch on a 1000 dpi image if you so desired.

I see. I thought you meant points per inch. Pulses per inch is actually what I would call DPI.

[Scott Shepherd]

I see. I thought you meant points per inch. Pulses per inch is actually what I would call DPI.

DPI is the resolution, PPI is the number of pulses the laser makes. Two totally different things.

[Robert Silvers]

DPI is the resolution, PPI is the number of pulses the laser makes. Two totally different things.

DPI is physical hardware resolution. In this case each dot cannot be a grey value. So you need many more dots if you are reproducing a photograph than pixels in the original image.

If you have a photo at, say, 300 Pixels Per Inch, then you really want about 1200 DPI hardware to dither or screen each pixel into a cluster of dots that looks like that value.

So DPI is also the number of pulses the laser makes because each pulse of the laser makes a dot. They should have used the term DPI, as it is fitting and was already existing.

[Scott Shepherd]

DPI is physical hardware resolution. In this case each dot cannot be a grey value. So you need many more dots if you are reproducing a photograph than pixels in the original image.

If you have a photo at, say, 300 Pixels Per Inch, then you really want about 1200 DPI hardware to dither or screen each pixel into a cluster of dots that looks like that value.

So DPI is also the number of pulses the laser makes because each pulse of the laser makes a dot. They should have used the term DPI, as it is fitting and was already existing.

Robert, you're incorrect on this. DPI and PPI and two unique things that have nothing to with each other. Might not work like that on your machine, but on mine, they are two very different things and PPI is NOT the same thing as DPI. PPI is not resolution, it's the number of pulses per inch the laser pulses.

[Robert Silvers]

Robert, you're incorrect on this. DPI and PPI and two unique things that have nothing to with each other. Might not work like that on your machine, but on mine, they are two very different things and PPI is NOT the same thing as DPI. PPI is not resolution, it's the number of pulses per inch the laser pulses.

DPI is also the number of pulses the laser makes - not according to your user manual it seems, but according to the rest of the world.

I am not talking about your machine or my machine. I am talking about graphics arts industry standard terms for decades.

[Dan Hintz]

DPI is also the number of pulses the laser makes - not according to your user manual it seems, but according to the rest of the world.

I am not talking about your machine or my machine. I am talking about graphics arts industry standard terms for decades.

Let's try a different tack...




If I set the laser to 600ppi and engrave at 300dpi... the laser will fire twice for each engraved dot.



You can only take the graphic arts industry analogy so far when talking about laser material processing.

[Scott Shepherd]

DPI is also the number of pulses the laser makes - not according to your user manual it seems, but according to the rest of the world.

I am not talking about your machine or my machine. I am talking about graphics arts industry standard terms for decades.

As someone in the graphics business, I can assure you I know what DPI is. DPI and PPI are NOT the same thing on the laser. Not sure how many different ways I can say it.

[Robert Silvers]

Well, it would be more clear it you acknowledge that your laser uses the term PPI in a way that laser printers use DPI - which is physical burns per inch.

[Scott Shepherd]

Well, it would be more clear it you acknowledge that your laser uses the term PPI in a way that laser printers use DPI - which is physical burns per inch.

I would if it were the same. However, the 2 are completely different. I'm not going to argue about it. I've been running lasers for 6 years straight. I know how they work. I have nothing to prove. If you think they work different then so be it.

[Dan Hintz]

Well, it would be more clear it you acknowledge that your laser uses the term PPI in a way that laser printers use DPI - which is physical burns per inch.

It's impossible to acknowledge something that isn't correct...

[Robert Silvers]

It's impossible to acknowledge something that isn't correct...

1200 pulses per inch can lay down laser burns at a maximum of 1200 little burns per inch. Agree or disagree?

1200 DPI for a laser printer can make a maximum of 1200 little black dots per inch. Agree or disagree?

If you agree to both, then his laser is using "pulses per inch" to mean DPI. So far no problem, except that it is being abbreviated as PPI, which is a graphic arts term that means pixels per inch, and has another meaning - because pixels usually don't map to dots one-for-one.

His laser should just call pulses per inch by the already accepted term used by laser printers, DPI. Why don't they? Probably because it would confuse people who don't know the difference between the graphic arts terms PPI and DPI - so they picked something different. And again, it would not be a problem except it is name-clashing with the other PPI.

[Dave Sheldrake]

A 1000 DPI image engraved at 1,000 PPI
A 500 DPI image engraved at 1,000 PPI

are the differences not obvious?


Probably because it would confuse people who don't know the difference between the graphic arts terms PPI and DPI

Or confuse those who know as much about Particle Physics as I know about dog food.

cheers

Dave

[Scott Shepherd]

Robert, you do not understand what you are talking about. The original comment was made by me in regards to wood charing while cutting. When vector cutting, mainstream lasers give control over the pulses per inch, also displayed in Hertz on some machine. You can send a file over at 1200 DPI all day long, but if you dial the Hertz down, it pulses at that rate. If I sent a 1200 DPI file to my Universal, I can open job control, change the PPI to 10 and it will look like stitches. It will be 10 pulses per inch on a 1200 DPI file. I can, on the fly, while it's running, dial that PPI to 1000 and it'll be 1000 pulses per inch.

We don't make this stuff up, it's how our livings are made and we use the stuff every day.