Relation of power versus speed

[Brian Rodenz]

What is the relation of power to speed. If I were to raise the speed up 5%, what would I reduce the power by to obtain the same result? Is there a power to speed equation?

[Keith Colson]

Its pretty simple on a "basic level"

Say you cut some 3mm acrylic with 100% power and 10% speed then if you cut the power to half that e.g. 50% power then you will need to cut at half the speed to end up with a similar result. These numbers are all "about" equal in the cut result.

100% power 10% speed
50% power 5% speed
10% power 1% speed

Basically the slower you go the more power you get into the cut over time. OR the faster you go the more power you need. Does that help?

Thats for cutting, engraving gets a bit more tricky because the number of line per inch will change things a lot.

And to add more confusion you should be familiar with PPI pulse per inch. This can be good to set to a low number for some materials that are harder to cut. At the end of the day you experiment and get familiar with "your" machine as no two machines are the same.

Cheers
Keith

[Gary Hair]

If power and speed were linear then Keith's assertion would be correct, but since they are not, then he is not exactly right. And when you throw into the mix all of the various manufacturers and how they have implemented their controls things get even worse. So, to answer your question "Is there a power to speed equation?" - no, not a generic one that fits all lasers.

[Bert Kemp]

I think he asked the question wrong, if you increase speed you would need to increase power also to get the same result. At least thats been my experience, the faster I cut the more power I need.

[John Noell]

Not only are there machine to machine variables, but some materials seem to react differently when engraved or cut at diferent speeds/powers. You can usually say that if you go faster you need to increase power to get the same effect but that's about all, as there are a lot of variables. I could not cut clean holes in keytags made from dakua salusalu (a local hardwood) at any combination I tried with my 45 watt Epilog (even when the tube was brand new) but my Shenhui does it beautifully at 60% power. I figured 60% on a Chinese 80 watt has to be lower that 100% on a 45 watt RF tube, but who knows?

[Ross Moshinsky]

People overstate the differences between machines, especially on raster engraving. Speed and power are close to linear and the difference between an Epilog and Universal laser (for example) are not enough to talk about. Based on manufacturer spec actual speed, I bet I can guess workable specs on any material I've engraved for any machine. When I demo'd most of the major manufacturers, I found this was very much the case.

On vector cutting, I've found the ratios to be much different. 1% speed on one machine does not directly relate to 1% on another. Not exactly sure why cutting is so much different, but it is.

[Keith Colson]

If power and speed were linear then Keith's assertion would be correct.

I think you misread my post. I wrote These numbers are all "about" equal. I even put the about in big quotes. It certainly gets you within a percent or two from my experience.

[Gary Hair]

I think you misread my post.
Not at all. My point is that percentage of power and/or speed isn't necessarily linear, in other words, it may not be true that 50% power is truly half of full power, or that 10% power is 1/10th full power, etc., etc.


I wrote These numbers are all "about" equal. I even put the about in big quotes. It certainly gets you within a percent or two from my experience.
That's not been my experience and validates my point about every machine being different.

If your assertion is true then you could laser something with 100% power and 50% speed and reduce the power by 2% and speed by 1% and have the same results every time - I can guarantee you that won't be true, not all the time and for every machine.

[Dave Sheldrake]

It is linear but not in a linear way if that makes sense, LOTS of variables for any laser beam from materials absorption rates, liberated CO2 blocking the longer wavelengths (shorter frequencies), diminishing returns rate, reflective cancellation effects ,beam modes to name a few.

You would think that an ABC Laser running 100 watts will cut twice as fast at 200 watts, it won't, once you go beyond the rate that the material can absorb energy you get very little in the way of a return. If I hit 6mm MDF for example with 200 watts it will cut at X speed, If I run that at 2,000 watts you would think it would be 10x faster, it isn't, it's closer to 3 times faster as much of the power is wasted. Sometimes less is more, lasers generate carbon, carbon absorbs lasing radiated power like a sponge, if you use too much power you generate more carbon so reducing efficiency hence the reason a laser running at 70% power may cut more effectively than a laser running at 90% power.

Each measurable data point in and of itself is linear when taken as a single input but when combined with all the other contributing factors there is no realistic equation possible that can give you exact results.Heck even a 1 degree temperature change in ambient can make a difference to a laser source.


I can guarantee you that won't be true

Gary's right, even matched lab lasers don't give the same results when tested to extended degrees, you can pick two expensive resonators (like REALLY expensive) that make Synrad and Coherant look like junk and the results will be different even when they are sold in *matched* pairs.

It's part of the reason I look at these "expensive materials databases" as guides (pointless guides) as all they can really give is a start point to work from.

cheers

Dave

[Gary Hair]

It's part of the reason I look at these "expensive materials databases" as guides (pointless guides) as all they can really give is a start point to work from.

My "settings guide"? 100% speed and 10% power. Adjust power up if you don't get the desired results. If you reach 100% power and still don't get the desired results, then decrease speed. If you get to 1% speed and still don't have a good result then it's just not going to work out. I guarantee that anything that is laserable with a co2 will fall between my suggested starting point and the "give it up" point. Thank you, you're welcome, please send money to the address shown below on your screen.

[Dave Sheldrake]

Thank you, you're welcome, please send money to the address shown below on your screen.

$1,500 a year isn't it Gary ;) the checks in the mail :)

cheers

Dave

[Paul Phillips]

My "settings guide"? 100% speed and 10% power. Adjust power up if you don't get the desired results. If you reach 100% power and still don't get the desired results, then decrease speed. If you get to 1% speed and still don't have a good result then it's just not going to work out. I guarantee that anything that is laserable with a co2 will fall between my suggested starting point and the "give it up" point. Thank you, you're welcome, please send money to the address shown below on your screen.

Ha! more likely you'll be sued by ULS for stealing their secret proprietary formula! :D
Dave, you're the one who should set up a website for tech support and training, the info you give away here is priceless! Many thanks!

[Dave Sheldrake]

Dave, you're the one who should set up a website for tech support and training

I have Paul :) been running a laser support forum for the last 3 years :)

I don't do much these days on physical call-outs, it's getting harder and harder, the biggest problem is not knowing what you are going into, a quick example...went out to see a chap who was having laser problems. All I had been told was "it's suddenly stopped firing"

I asked the usual "What has changed or has been changed" and was met with the usual "Oh nothing,it just stopped working"

Do you keep it clean..."Yes, spotless"

Turned up 150 miles away to find the machine was indeed spotless, mainly because it had been cleaned with a pressure washer inside and out!

If you know what you are facing and people are totally honest, tech support and servicing is easy...sadly it's not uncommon to find what you arrive at bears no relationship to what you have been told ;)

These days I don't do call outs anymore (mostly due to time constraints) but I still run a tech support forum for people who are struggling :)

cheers

Dave

[Gary Hair]

because it had been cleaned with a pressure washer inside and out!

Looks like tomorrow is suddenly free, I was planning on a bit of "maintenance" but maybe now I'll rethink my strategy...

[Richard Rumancik]

I would modify the following:

100% power 10% speed
50% power 5% speed
10% power 1% speed

to read:

100 watts power 10 ips speed
50 watts power 5 ips speed
10 watts power 1 ips speed

This would give you the same energy per inch (10 watt-seconds/inch travel) in each case. This is probably a closer approximation, but of course, most of us do not know the true wattage output nor the true speed so this is not actually useful in practice.

Although 10 watts at 1 ips might be theoretically the same energy/unit length, the quality of the cut might not be satisfactory compared to using 50 or 100 watts. As others have said there are other effects going on when applied to real materials.

I think that people read too much into the meaning of % power and % speed. If you just think of them as numbers with no units (like a volume control on a radio) then you will be on the right track. I have concluded with my laser that trying to create these relationships is not useful as neither power or speed (as a %) are linearly related to the actual power or speed. The laser manufacturers have clouded the issue by pretending they are.

Brian, best to use Gary's method: "100% speed and 10% power. Adjust power up if you don't get the desired results. If you reach 100% power and still don't get the desired results, then decrease speed."

Of course you might have a better guess as a starting point, but the process is iterative, not mathematical. Forget about equations as it won't work for these types of laser systems. Furthering the Volume control analogy, if the radio is not loud enough, you turn the knob to the next number till it sounds right. On your laser, if it doesn't cut, turn up the heat. Just don't read too much into the numbers. I wish it were more scientific than that but unfortunately it isn't.

[Paul Phillips]

Dave, that's great, can you please PM me the name or link in case I ever need your help?
Wow, pressure washed the laser huh? That's one way to get it clean I suppose. :eek:
Reminds me of a story my PC repair instructor told us about an old farmer looking guy in overalls who came into his repair shop with a PC that had been making noise then it "quit working", upon opening the case he saw that the guy had used almost a quart of oil on it to try to get the fan noise to stop, needless to say it fried the whole MB, good times!