Author Topic: Need help with grey scale and 5.5W laser  (Read 1120 times)

danlsam

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Need help with grey scale and 5.5W laser
« on: January 10, 2018, 09:45:48 AM »
Hello,

I am looking for advice on how to get good gray scale images using a 5.5W laser. I have been using T2Laser since before Christmas and trying quite a few tests with speed and changing the minimum and maximum power levels. I have been getting images that range from looking like wood that has been pulled from a fire pit or ones with just a faint scorching. I am not sure what is going on but even using Velocity mode usually starts a fire.

I have an A3 size eBay clone that came with the EleksMaker Mana SE board (now flashed to Grbl 1.1e) and a really nice EleksMaker Blue laser module with a control board that has both a TTL and PWM input connector as well as a weak laser button for focusing and another button to switch between the TTL and PWM inputs. I am pretty impressed with this module except for the focusing, the threaded barrel was a little loose and needed a few layers of some Teflon tape to snug it up. (Please refer to the attached pictures.)

I have been using Midwest Products Craft Plywood that is available at my local Menards store because it has a consistent surface, closed grain and is inexpensive, I am fairly certain that it has a birch veneer on the top and bottom.

So the question is: What am I doing wrong and how can I fix it? Is the laser overpowered and 8 bits (0-255) is not enough dynamic range to burn a gray scale picture? To test that theory I have a 2.5W laser module on order that is currently somewhere between here and Hong Kong and is expected to arrive the beginning of February. In the meantime I am open to suggestions and I am especially looking for someone that has had good results with a 5.5W laser.


Thanks for your time,

-Dan
Never optimize a bad algorithm.

wild.bill

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Re: Need help with grey scale and 5.5W laser
« Reply #1 on: January 10, 2018, 11:03:49 AM »
Hello,

I am looking for advice on how to get good gray scale images using a 5.5W laser. I have been using T2Laser since before Christmas and trying quite a few tests with speed and changing the minimum and maximum power levels. I have been getting images that range from looking like wood that has been pulled from a fire pit or ones with just a faint scorching. I am not sure what is going on but even using Velocity mode usually starts a fire.

I have an A3 size eBay clone that came with the EleksMaker Mana SE board (now flashed to Grbl 1.1e) and a really nice EleksMaker Blue laser module with a control board that has both a TTL and PWM input connector as well as a weak laser button for focusing and another button to switch between the TTL and PWM inputs. I am pretty impressed with this module except for the focusing, the threaded barrel was a little loose and needed a few layers of some Teflon tape to snug it up. (Please refer to the attached pictures.)

I have been using Midwest Products Craft Plywood that is available at my local Menards store because it has a consistent surface, closed grain and is inexpensive, I am fairly certain that it has a birch veneer on the top and bottom.

So the question is: What am I doing wrong and how can I fix it? Is the laser overpowered and 8 bits (0-255) is not enough dynamic range to burn a gray scale picture? To test that theory I have a 2.5W laser module on order that is currently somewhere between here and Hong Kong and is expected to arrive the beginning of February. In the meantime I am open to suggestions and I am especially looking for someone that has had good results with a 5.5W laser.


Thanks for your time,

-Dan

For the technical details it's not TTL or PWM. TTL is a voltage and PWM is a modulation technique.

The TTL laser's have a PWM signal on the  control line to set the power level of the laser,
and the NON TTL laser's use a PWM signal on the power line to control the intensity of the laser.

For a grayscale image the first thing I do is determine what speed I need to move at to get the black (255) to the level that I want for the material that I am trying to etch. Once you find that speed anything slower can cause it to burn. We have now set a bound for the upper level.

Then you can play around with the low levels to get the proper range.

Another thing that I have found is that some of my laser's are not linear so I do not get a smooth range. So to get good linear gray scale I load the image into Photoshop (or you could use GIMP) and use curves to adjust the image. I push the dark range down and the light range up some.

Without applying the curve if I printed the grayscale test on the system that I use most - 50% to 100% were almost the same. Using my other laser the grayscale test was close with no adjustment. They both us a 2.0W TTL laser.

There is no magic button, just a lot of testing until you find what works for you laser.


Laser: was an A3 2.0w TTL L6 Z axis now 2'x3'
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danlsam

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Re: Need help with grey scale and 5.5W laser
« Reply #2 on: January 10, 2018, 02:57:18 PM »
Hello and thanks for the reply.

Yes, I understand the difference between the two different ways to control the laser module and I have wired up cables to try both modes, they really shouldn't label the new laser module inputs "TTL" or "PWM", TTL is a voltage level and PWM is a modulation technique that in this case runs at TTL levels. It makes it very confusing to look up any information for the operating parameters.

I have been using both the circular test chart and a gray scale step chart for my tests, I also wrote a grbl file that draws lines at different speeds and power levels just because I got tired of doing them one test at a time. I use both GIMP and Paint.NET when I need to manipulate a graphic.

What I have tried so far is running from 4000mm/min down to 800mm/min in 200mm/min steps and changing the power levels from 255 down to 96 in 16 step increments (I have not done all of the permutations because some are obviously not going to work). Needless to say I have done a considerable number of tests and I have gone through a good sized pile of wood to do them. Nothing has been very satisfying so far.

From what I have been reading in the forums it appears that the vast majority of people that have been successful are using lasers that are 2.5W or less (not counting the CO2 gas laser group). It would be nice to hear from someone with 5.5W experience, their answer might just be that it can't be done.

As a side note has anyone experimented with changing the maximum laser power to 1000 and the Grbl $30 limit to 1000, will that change the PWM modulation at all and give me greater control over the power range? I will have to do an experiment unless someone already knows the answer.


Thanks,

-Dan
Never optimize a bad algorithm.

ggallant571

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Re: Need help with grey scale and 5.5W laser
« Reply #3 on: January 11, 2018, 02:34:39 AM »
The native resolution of the hardware that does the PWM is 8 bits or 256 increments. The 1000 is just math. I had a 5.5W for a year (went snap, crackle, & pop) and the delivered power was anything but linear. Good repeatability. Did the various combinations of speed and power with different materials. Found that 1200/120 and 900/90 were good numbers for slate and 1200/30 was good for most woods. Have switched to 1.6W & 2.5W modules and think the results are much better for wood & mirrors, poorer for slate.

The faster you burn the more the effects of acceleration will be. I think laser mode in the 1.1 firmware is designed to compensate.
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Finiousfingers

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Re: Need help with grey scale and 5.5W laser
« Reply #4 on: January 11, 2018, 05:17:42 AM »
I use that same circle template that you have in your post for greyscale.
But I find that 5.5 is to hot for most wood stuff. When I want to burn wood I downsize to the 2.2 and it burns much nicer.
I know you should be able to dial it down to the right temp but its fickle and demoralizing for me to keep getting my butt kicked by a laser module.

So I use the 5.5 for slates and cutting and the 2.2 for woods, and the .5 for the neighbor cat, jk jk

MarcusJ

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Re: Need help with grey scale and 5.5W laser
« Reply #5 on: January 11, 2018, 06:13:57 AM »
I suspect that the material is playing a part too.  The Midwest birch is still pretty soft.  If you can find some oak or maple veneer, give that a try and see what your results are like.

danlsam

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Re: Need help with grey scale and 5.5W laser
« Reply #6 on: January 11, 2018, 02:25:58 PM »
Hi and thanks for all the good feedback,

I am responding to the different posts in no particular order:

ggallant571:

I should have looked at the Arduino Nano specs before I started digging around in the Grbl code, the PWM pins (3, 5, 6, 9, 10 & 11) are only 8-bit, I would have saved some time figuring that out.

Now that I have tried it I do find that being able to set the power range from 0-1000 makes it easier to work in percentages of full power and let the code scale it to an 8-bit range.


MarcusJ:

I tried oak, the species I used had a very "open" grain and liked to start small fires and leave the grain pattern, it was not pretty. I need to get my hands on some hard maple, cherry or hickory, they all have a "closed" grain and are harder than the birch I am using right now and might tolerate the power better.


Finiousfingers:

I am glad that someone else has come to the same conclusion that 5.5W is pretty hot and not really suited for gray scale engraving. Black and white or dithered can work if you mess around but there just isn't enough dynamic range in 8 bits to be able to dial down the average power. I imagine that your 5.5W did not even break a sweat working on the slate.


New information:

I am glad now that I ordered a 2.5W module, I will just need to be patient until it arrives.

From what I was reading on the Grbl 1.1 web site the new code uses the M4 spindle command to dynamically adjust the laser power based on the current speed. It has it own strengths and weaknesses and I am not sure if the T2Laser G-Code incorporates it yet or not. Zax could answer that question when he gets back from his vacation.

-Dan
Never optimize a bad algorithm.

Zax

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Re: Need help with grey scale and 5.5W laser
« Reply #7 on: January 14, 2018, 06:21:05 AM »
T2Laser has supported Dynamic Laser Power since it was available, in fact I was probably the first to include it.

danlsam

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Re: Need help with grey scale and 5.5W laser
« Reply #8 on: January 14, 2018, 05:03:05 PM »
Welcome back from your vacation, hopefully it was restful.

Which mode setting makes use of the M4 command? I have been looking through the *.nc file I have been creating and I see the use of the Grbl 1.1  M3 Constant Laser Power Mode, but I have not found the T2Laser mode setting that invokes the use of the M4 Dynamic Laser Power Mode. Or have you implemented a "Dynamic Laser Power" mode that works across all GRBL versions?

-Dan
Never optimize a bad algorithm.

Zax

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Re: Need help with grey scale and 5.5W laser
« Reply #9 on: January 15, 2018, 05:50:12 AM »
You just enable the menu option, that it (of course it does require Grbl 1.1 firmware).

danlsam

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Re: Need help with grey scale and 5.5W laser
« Reply #10 on: January 15, 2018, 02:14:06 PM »
I am going to guess that there isn't some weird data coupling from the T2Laser Controller dialog back to the main program that affects the G-code generator and that the setting causes some on-the-fly post-processing that does the M-code translation to an M04 command as needed because I do not see an M04 in the sample files I just created.

-Dan
Never optimize a bad algorithm.

Zax

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Re: Need help with grey scale and 5.5W laser
« Reply #11 on: January 16, 2018, 06:16:24 AM »
The G-code you see on screen and is saved is "standard", the post processors do change the code before sending and can do many things including enable the Dynamic mode. So yes, there's some hidden magic!

The reason for this is simple, it allows the user to save the generic G-code, and use it on a different configuration machine or send it to someone else and their post processor would change it to their system requirements.

T2Laser has the option to save the actual post processor output (Save Machine G-Code) but it's currently restricted, this is useful for people that run their machine by SD card, WiFi, BT or some other non-USB method.