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

[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

[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.

140461405.jpg

[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.