What is % Speed

[ron ateah]

I need help defining percentage speed as it relates to my laser. My lasers speed is define by setting mm per second. Most of the posts on this forum is in percentage. 10 or 20 % speed for instance across many manufactures and sizes of lasers. Rarely if ever defined in mm or inches per sec. what is the actual speed in ipm or mm/sec of 100% speed. Can anyone give me a rough idea

Thanks in advance

[Richard Rumancik]

Which machine do you have?

%-speed is what the programmer who wrote the driver decided it was. It is often not linear at all. They might as well have dispensed with the % designation (and just called it Speed/ 0-100) because calling it a % makes people think there is some proportionality involved when there is little.

It is similar to a volume knob that is labeled 1-10. We don't really know what volume level 5 is until we set it to 5 and test if it is satisfactory. If not, we tweak. Same with your laser.

For a lot of mainstream lasers, the % speed is (roughly) a percentage of the maximum RASTER speed. So you might find that if doing a raster plot, that at 50% speed it takes twice as long as at 100% speed. Notice I said might. Don't expect exact linearity.

When it comes to vector cutting, it is is usually more ambiguous, as many laser manufacturers don't tell you the maximum vector speed. (That's because it isn't as impressive.) You will only achieve maximum speed on a long stroke, one which is aligned with the x or y axis. With a short stroke, it can't get to maximum speed even if you command it to. That's because the carriage needs to accelerate and decelerate at the ends. It ramps up, stabilizes at maximum velocity, then ramps down.

On my GCC machine, the maximum vector speed is probably about 30% of the maximum raster speed. So if I tell it to go 40% speed it will likely max out at 30 speed anyway. So don't get misled if you do not see linearity with vector cutting. Also, with vector cutting, you may have lots of twists and turns, stops and starts so the maximum velocity may never be reached. It is just ramp-up and ramp-down on each segment. So I could command 20% speed, and find no difference at 10% speed, because the laser can't actually get beyond 10% due to the nature of the file.

I can't say that this applies to your machine as I don't know. But it probably has the same issue with vectoring as you can't fight the physics. You can tell it to go faster but that does not mean it will.

I would say trying to read too much into the speed setting is usually an exercise in frustration.

[ron ateah]

Thanks Richard

Here is my issue - i am using cermark to laser mild, stainless and alu and i am finding it is taking far to long. I have a 150 watt 3 by 5 foot shenhui laser. The best raster speed and any power is 50 mm/sec at an ideal power setting of %50 and line scanning at 0.05 mm. any faster at any power the cermark material wipes off. I have set up matrix of speeds and powers and that is my sweet spot. I do 2.5 by 4 inch plot and that takes 19 min to complete. That hurts. I have got a reoccuring job that is 12 by 6 roughly and that takes more than 2 hours. That really hurts. I have talked to the manufacture and they to have no idea what the actual speed i should be running but they are surprise with the length of time it is taking.

[Richard Rumancik]

Well, since this machine is quite different than mine I think I have to defer to Rodne and those that have a similar laser as to what settings are likely to work.

[Mark Sipes]

Cermark list the procedure of 100% power at 25 % speed as the proper setting for their material. It takes 19 minutes to do a 2.5" x 4" area at 500 dpi !! Wow !!!! Shoot me now! It sounds like a setting of 150w at your 25% speed should cook the Cermark on. You need to determine what your speed issues are... according to my rough calculations if 2.5" @ 500 = 1250 lines so 4" x 1250 lines = 5000 inches / 4.4 in/sec = 19min = 1140 sec and that takes into account accel and decel at every point, and you say that is at 75w ( 1/2 150w) My 25w runs at 87 in/sec at 100% and 25% that roughly 21.75 in/sec . You definetly have a speed/power issue.....

[Gary Hair]

Cermark list the procedure of 100% power at 25 % speed as the proper setting for their material.

That's not quite accurate Mark. They suggest that you start with 100% power and a speed setting equal to your power, so for a 25 watt machine you would be correct that a 25% speed setting would be the place to start. For a 150 watt machine that would be 150% speed... so much for guidelines... I would start with full speed and run a power grid from 20% power up to 100% in 5% increments. There must be a setting in there somewhere that will work. With 150 watts you will likely never use full power unless you are trying to mark gold.

Gary

[Scott Shepherd]

I don't find their settings work for Trotec either (due to it's faster speed). Speed is a relative term, as mentioned above, and a slow moving 80w laser is a lot different than a fast moving 80w laser. So I honestly have no idea how that chart works. I've found their guidelines to be utterly useless.

[Rodne Gold]

Use a much bigger stepover , 0.1 to start with , that will cut job time in 1/2 , 500 dpi cannot be resolved due to spot size.

[ron ateah]

That is interesting. What is my spot size roughly? Is it some what dependent on the lens. I have lost track but i think i am using a 70 mm lens. Cermark recommends 500 dpi. but if the spot size is larger than 0.05mm then what is the point. O.1mm spot size seems large.

Lastly how do you add your signature and equipment to the end of your posts?

[Richard Rumancik]

A 2" FL lens (50mm) will usually result in a .005" spot size. I'm guessing a bit but with 70mm you probably have more like .008" spot size (.2mm).

A setting of 500 dpi results in a .002" (.05mm) dot pitch as you noted. With a .2mm spot size you can't really take advantage of 500 dpi as the spot is too large. A .2mm spot might work for some things but the edges of graphics will not be very sharp. Also the energy is not concentrated enough to make the Cermark stick. I think you should consider a lower FL lens - say 2" or 50mm or smaller. The ratio of the area of a .005" spot to .008" spot is quite significant.

It is okay to use a dpi which allows for some dot overlap as it will make the edges of a graphic sharper.

[ron ateah]

Richard - that is really helpful. I think i have got a 30mm lens kicking around i will give that a try. thanks much

[Rodne Gold]

30mm is very short , your depth of focus is very critical with this lens .. any small deviation can result in loss of energy density and thus bad results.
Even with that lens , my suggestion is to start at 0.1 stepover and work downwards from there. You don't seem to be doing small and very fine logos etc , your jobs are large so you can afford to "lose" resolution
Also , with an 80w RECI and a 38mm lens , I have been able to engrave DIRECTLY to stainless without cerdec, albeit slowly , worth a try with your 150w
We have an issue with the internet , seacom cable is cut , so I cant find the thread but you can search for it , I think it's buried in the sticky thread re Chinese lasers.

With cerdec , I suggest you also turn your air assist way down or even off as it cools down the material and can often blow off small flakes of the cerdec...

[Mike Null]

We are assuming your solution of Cermark is correct. If you are mixing your own you could well be mixing too thin or too thick for optimum adherence.

[Richard Rumancik]

30mm is very short , your depth of focus is very critical with this lens .. any small deviation can result in loss of energy density and thus bad results. . .

Yes, maybe a bit short, but he should not have trouble getting a "flat" (parallel) surface over such a small area. And the way I see it even if the spot is a bit out of focus it will still be way smaller than the .008" or so he is getting now, and it is not like he is short of power. Worth trying it at least to get more data.

[Mark Sipes]

Here is my issue - at my sweet spot , I do 2.5 by 4 inch plot and that takes 19 min to complete. That hurts.

Is there no more to this issue than spot size ??