Power and speed settings

[Jim Reinhard]

I am new to this and trying to learn about settings for speed and power.

Will 50% power and 50% speed get the same results as 100% power and 100% speed.
also if dpi is dot per inch and ppi is pulse per inch .Then do you get different results changing them , such as 400 dpi 200ppi the same as 200dpi and 400ppi

[Craig Matheny]

Jim welcome to the site you will find a ton of great people here. It would seem to reason that going from 50% pwr and sp to 100% power and speed would accomplish the same thing but being the speed has increased then the head has to move further to slow down and can take longer you just have to try different things on your unit. On my Epilog we use freq and DPI the higher the freq the faster the unit fires but the cooler the pulse if that is clear. With DPI you can take a circle and run it at 75 DPI and it will be jagged raise the DPI and it will smooth out just like a photo the hight the DPI the smoother the cut or engraving. With that said raising them to high will have an adverse affect just like if it is to low. There are some guys that have the same brand unit and they should jump in soon and really clear this up for you.

Again Welcome and Good Luck

[Jim Reinhard]

Has anyone used the settings calculator at laserbits to get speeds and power setups?

[Richard Rumancik]

The short answer is . . . .there isn't a short answer.

In an ideal world P50/S50 would be the same as P100/S100. For raster engraving, I think it would probably be a reasonable relationship.

For vector cutting, over certain ranges, it would also be true. Say you are cutting acrylic at P2.8/S100. You would probably have similar results at P1.4/S50. But there are certain things the way the driver works that may make the relationship invalid at certain points. Also the old Mercury had a threshold at S2.9 where it automatically went into continuous wave mode (no pulsing) so if your relationship crossed this line it might be invalid. I don't know if the Mercury II retained that algorithm. Also, for vector cutting, if you keep doubling speed and doubling power, you might get into a speed setting that the motors can't really can't accomodate. For example, if you vector cut cardstock at P50/S15. Then you try P100/S30. It might not be able to achieve a speed of S30 for vector cutting (even though it may accept the settings.)

But doubling of settings is probably rare; we might boost speed 10% and power 10% and expect similar results.

For most lasers (GCC included) ppi is pulses per inch along the cut path. Epilog calls it frequency but it is the same parameter. PPI does not apply to raster engraving. So they are not really related; the ppi sets the pulses for vector cuts and dpi sets the resolution for filled shapes or bitmaps. If the file is a vector file only the dpi setting should be ignored (and vice versa) although I have heard of a few strange anomalies as well where a dpi setting DID affect cutting. It shouldn't.

In Craig's answer he refers to a circle - he is referring to a rastered circle here, not a cut circle. A filled raster circle will be subject to a dpi setting. A cut circle will be affected by the ppi setting.

[Mike Null]

Epilog does quite a good job in their manuals of explaining settings. http://www.epiloglaser.com/downloads/pdf/mini_helix_dec_2009.pdf

What they say is applicable to most laser engraving and particularly their section on DPI is worth reading. One of the things about dpi that is difficult for many to understand for example is that 600 dpi is not twice 300 dpi but actually 4 times 300 dpi. On many materials the higher dpi can be very detrimental to the engraving while on others it may produce the desired result.

[Richard Rumancik]

I took a look at the Helix manual Mike linked to. Some interesting info there. I also came across this comment:

"Because there are many factors that influence the time it takes to engrave or cut a
given image, the Speed settings were designed to be reference numbers only. The
Speed setting scale of 1% to 100% is not linear – i.e. 100% speed will not be twice as
fast as 50% speed. This non-linear scale is very useful in compensating for the
different factors that affect engraving time, but using speed to predict a jobs
engraving time is not practical.

The Power settings are linear – i.e. 50% power is half as much as 100% power."

This reinforces the point that I was trying to make earlier in that there a lot of things going on that are not readily apparent, and of which the operator has no control. The programmers of the driver and motion system have added their own algorithms to make the overall system behave "better", but it means that you can't make a lot of assumptions about doubling or halving speeds. Logic says 100% speed should be 2x faster than 50% speed but the Epilog programmers have decided to apply a non-linear relationship. Off hand I don't know why but it was probably to balance out some other non-linearity. But it makes the definition of % speed somewhat meaningless.

You will probably find different manufacturers have various ideosyncracies of their own built into their drivers and firmware.

[John Noell]

And to add to the confusion, it seems that if the dots (pulses) are really close together (esp. in something like acrylics), the point where the beam just hit may still be molten when the next pulse fires - and if it is close enough to keep the first point hot longer you get a smoother melt. If the dots are far enough apart, each pulse is unaffected by the others. I can definitely say that 50/50 and 100/100 has given me different results on many materials.

[Jim Reinhard]

thanks ,Good tip on the eplog manual.Lots of good reading.