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Cheap Chinese Laser Cutter

experiences with a Chinese laser cutter

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FlyinFlynn11/01/2020 12:14:14
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122 forum posts
85 photos

They are.

There are at least two ways of doing this... the first would be to manually edit your gcode file by searching for M03 and replacing it with M04, there would normally only be one instance at the start of the file -or- you can edit your post processor file to automatically edit the gcode file as it is being generated.

What software are you using to generate the gcode? You will most likely have had to choose a post processor with your software to specifically use on a laser machine, if you look with notepad or notepad+ in the header section of the post processor file you are using you can stipulate using M4 instead of M3. For example, here is the header section of my post processor file that I modified for use with my laser..

begin HEADER

"G17"
"G21"
"G90"
"M04"
"G0X0Y0Z0"

This will set the plane (G17 sets XY plane), metric (G21), absolute positioning (G90), dynamic laser power (M04) and go to set zero position if you are not already there.

All mode changes ( S for power and G1, 2 or 3 for motion mode) will all then use dynamic laser power. you should also find either an M05 or a M02 in the footer section to ensure the laser is turned off at the completion of the gcode program.

There is an explanation of how to adapt a post processor for laser use here

Edited By FlyinFlynn on 11/01/2020 12:15:35

FlyinFlynn11/01/2020 13:18:56
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122 forum posts
85 photos

Perhaps I could explain that better....

there are some parameters that need to be passed to the controller before it can start processing the cutting data, there are typically added to the gcode by a piece of software called a post processor. There will be a different post processor for every cnc machine (well almost all). So in my example the 'header' adds some instructions before the cutting data and the 'footer' adds some more at the end of the cutting data. you could add these instructions manually just by editing the gcode file, or I guess some software might give you the option to tell it what those parameters are so it can compile the gcode with them (LightBurn for example does this I believe, but LightBurn is specifically written for lasers and not general cnc machines so some of the parameters are not needed to accommodate a laser, so it is easier to just specify those that are needed and not bother with a post processor)

3dpburner is another where you specify the header and footer parameters and the software compiles the gcode file with them included in the correct places

3dpburner.jpg

I hope that makes it a bit clearer

adrian garnham12/01/2020 16:01:55
19 forum posts

Hi FlyinFlynn

I have designed and built a cantilever type laser cutter similar to yours.

I am using an arduino, cnc shield and 5W laser the same as Geoff Gardiner used in his build.

For software I am using Inkscape (with the laser extension) to create the gcode and Universal Gcode sender to control the steppers and laser.

I haven't turned on the laser yet (too scared lol) but have been playing around with carriage movement, homing etc and noticed that the carriage doesn't seem to be moving the correct distance. I've obviously not set the steps/mm correctly.

I noticed in your previous post .... "The 80 steps per mm is correct if you are using a 1.8 degree per step motor set to x16 and a 20 tooth gt2 pulley

360/1.8 * 16/40 = 80 degrees per motor revolution/degrees per step * microsteps/ mm per pulley revolution"

I am using the motor and belt combination above but could you shed some light on how to set the microstepping to x16 ?

Andy Joyce12/01/2020 17:18:02
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155 forum posts
28 photos

Adrain

Use the $$ command to ascertain the settings you have at the moment. Then try adjusting $100 and $101 to 80 which should work if you have the same pulley type that I have.

Andy

adrian garnham12/01/2020 18:29:48
19 forum posts

Thanks Andy

Do I have to set the micro stepping as well ?

FlyinFlynn13/01/2020 11:58:12
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122 forum posts
85 photos

Adrian. your microstepping will also depend on which stepper driver you are using. The two common (and cheaper) drivers are known as A4988 and DRV8825. The A4988 was the first type to be available and can manage 1/16th microstepping, this is achieved by fitting all 3 of the jumpers under the driver. The later DRV8825 can manage 1/32 microstepping, which is also achieved by fitting all 3 links under the driver......so....assuming you have the 3 links fitted you either have 1/16th microstepping (with a A4988) or 1/32th microstepping (with a DRV8825).

Here are the two 'truth tables for the two drivers showing which jumpers need to be inserted to set the microstepping. Low means no jumper fitted and high means jumper inserted. You can see that fitting all 3 jumpers in both cases gives you the maximum that each driver is capable of achieving.

A4988

a4988.jpg

DRV8825

drv8825.jpg

There is a calculator here to work out the steps per mm value you need to get the correct distance moved.

adrian garnham13/01/2020 13:26:48
19 forum posts

FlyinFlynn

thank you. I have A4988 stepper drivers. I have fitted jumpers to all 3 pairs of pins on both x and y (I am not using z at the moment) and changed the steps per mm to 80 ..... everything is now OK

I produced my first test square on cardboard by running the program and manually turning the laser on and off at the corners etc. I haven't figured out how to get the cnc shield talking to the laser yet (my laser is this one **LINK** 

Martyn K13/01/2020 14:01:46
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5041 forum posts
3677 photos

Hi FlyingFinn

Many thanks for your help. I have established that my controller does not accept the M04 command. Unfortunately. M04 was introduced or fixed (I think) with GRBL version 1.1f. Unfortunately, my firmware is at 1.1e...

Modifying the gcode, replacing M03 with M04 resulted in the laser simply running at about 20% power, it didn't change in intensity and it didnt even mark the wood.. .

I have sort of got round it by putting the corners on a different layer and running them at reduced power, not totally satisfactory but I am not getting any fires now...

Martyn

FlyinFlynn14/01/2020 12:00:45
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122 forum posts
85 photos
Posted by adrian garnham on 13/01/2020 13:26:48:

FlyinFlynn

thank you. I have A4988 stepper drivers. I have fitted jumpers to all 3 pairs of pins on both x and y (I am not using z at the moment) and changed the steps per mm to 80 ..... everything is now OK

I produced my first test square on cardboard by running the program and manually turning the laser on and off at the corners etc. I haven't figured out how to get the cnc shield talking to the laser yet (my laser is this one **LINK**

The laser you have has a single 3 wire connector, those 3 wires are labelled + - and pwm. The + and - are the 12volts supply to power the laser. The third wire (PWM) goes to cncshield Z+ pin, along with a common ground wire to the ground pin next to the Z+ pin. You could use the 2 pin connector next to the 3 wire one...it is labelled - PWM + for ground and signal, and then not use the third wire in the 3 wire connector (they appear commoned on the PCB)

I assume you have been getting the laser to come on by tapping the pwm wire from the 3 pin connector to +volts?. Normally the spec would be +5v for the PWM so be careful if you are using +12v. The spec has

Input Voltage DC12V (+,-, PWM/TTL) + DC5V (PWM/TTL,-)

(whatever that might mean?)

Martyn - I believe M4 was introduced with v1.1 so I think it should be working with 1.1e. Do you have a screenprint of your gcode where the laser comes on at about 20% that you can post? I wonder if it has to do with the speed of cut you have set, if the carriage never gets to it's full speed the laser will never get to full power, especially for short runs with low acceleration.- just a thought.

adrian garnham14/01/2020 12:43:00
19 forum posts

FlyinFlynn

thank you for your answer (comprehensive as always ) There is a small switch on the laser controller which dims the laser for setup purposes. I have been switching that on and off.

Martyn K14/01/2020 16:18:05
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5041 forum posts
3677 photos

Thanks FF

See below..

; LightBurn 0.9.07
; GRBL-M3 (1.1e or earlier) device profile, current position
G00 G17 G40 G21 G54
G91
; Cut @ 1800 mm/min, 80% power
M8
M5
G0X-21.5Y16.69
M3
G1Y0.66S800F1800
M5
G0X-10.8Y-1.36
M3
G1X-1.84Y-0.1
M5
G0X0.26Y0.01
M3
G1X0.6Y0.04
M5
G0X-0.3Y-0.02
M3
G1X0.01Y2.72
G1X-2.55Y0.26
G1X-0.01Y-3.13
M5
G0X-0.65Y-0.04
M3
G1Y-2.19
G1X11.36
G1Y2.89
M5
G0X3.3Y12.08
M3
G1Y0.66
M5
G0X-10.79Y-1.36
M3
G1X-1.84Y-0.1
M5
G0X0.26Y0.01
M3
G1X0.6Y0.04
M5
G0X-0.3Y-0.02
M3
G1X0.01Y2.72
G1X-2.55Y0.26
G1X-0.02Y-3.13
M5
G0X-0.65Y-0.04
M3
G1Y-2.18
G1X11.36
G1Y2.88
M5
G0X4.54Y20.44
M3
G1Y0.66
M5
G0X-10.8Y-1.36
M3
G1X-1.84Y-0.1
M5
G0X0.26Y0.01
M3
G1X0.6Y0.04
M5
G0X-0.3Y-0.02
M3
G1X0.01Y2.72
G1X-2.55Y0.26
G1X-0.01Y-3.13
M5
G0X-0.65Y-0.04
M3
G1Y-2.19
G1X11.36
G1Y2.89
M5
G0X3.3Y12.08
M3
G1Y0.66
M5
G0X-10.79Y-1.36
M3
G1X-1.84Y-0.1
M5
G0X0.26Y0.01
M3
G1X0.6Y0.04
M5
G0X-0.3Y-0.02
M3
G1X0.01Y2.72
G1X-2.55Y0.26
G1X-0.02Y-3.13
M5
G0X-0.65Y-0.04
M3
G1Y-2.18
G1X11.36
G1Y2.88
M5
G0X-25.93Y1.21
M3
G1X-0.03Y-0.34
G1X-0.1Y-0.31
G1X-0.16Y-0.28
G1X-0.2Y-0.25
G1X-0.25Y-0.2
G1X-0.28Y-0.16
G1X-0.31Y-0.09
G1X-0.34Y-0.04
G1X-0.33Y0.04
G1X-0.31Y0.09
G1X-0.29Y0.16
G1X-0.24Y0.2
G1X-0.21Y0.25
G1X-0.15Y0.28
G1X-0.1Y0.31
G1X-0.03Y0.34
G1X0.03Y0.33
G1X0.1Y0.32
G1X0.15Y0.28
G1X0.21Y0.25
G1X0.24Y0.2
G1X0.29Y0.15
G1X0.31Y0.1
G1X0.33Y0.03
G1X0.34Y-0.03
G1X0.31Y-0.1
G1X0.28Y-0.15
G1X0.25Y-0.2
G1X0.2Y-0.25
G1X0.16Y-0.28
G1X0.1Y-0.32
G1X0.03Y-0.33
M5
G0X-10.95Y0.17
M3
G1X-0.04Y-0.42
G1X-0.13Y-0.39
G1X-0.19Y-0.35
G1X-0.25Y-0.31
G1X-0.31Y-0.25
G1X-0.35Y-0.19
G1X-0.39Y-0.12
G1X-0.42Y-0.04
G1X-0.41Y0.04
G1X-0.39Y0.12
G1X-0.36Y0.19
G1X-0.3Y0.25
G1X-0.26Y0.31
G1X-0.19Y0.35
G1X-0.12Y0.39
G1X-0.04Y0.42
G1X0.04Y0.42
G1X0.12Y0.39
G1X0.19Y0.35
G1X0.26Y0.31
G1X0.3Y0.25
G1X0.36Y0.19
G1X0.39Y0.12
G1X0.41Y0.04
G1X0.42Y-0.04
G1X0.39Y-0.12
G1X0.35Y-0.19
G1X0.31Y-0.25
G1X0.25Y-0.31
G1X0.19Y-0.35
G1X0.13Y-0.39
G1X0.04Y-0.42
M5
G0X-1.05Y-9.79

FlyinFlynn15/01/2020 12:08:54
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122 forum posts
85 photos

As you are using Lightburn you could flash GRBL 1.1f onto your controller. Unfortunately I am unable to install Lightburn again to see if it has a firmware update feature as my free trial period has elapsed. Re-flashing is easy enough though with an external flash program, if you wanted to.

Assuming your GRBL has $30=1000 then all looks good, that gcode produces a series of straight line cuts interspersed with non-cutting moves at a reasonable speed and intensity. I cannot see any reason why an M4 command should not work, although I don't understand what the flood coolant command is doing there (M8) - anybody know?

LightBurn uses M05 and M03 to turn the laser on and off as well as G0 for rapid moves and G1 for cutting moves, I think these M commands are superfluous as the G0 will prevent the laser from operating during rapid moves. The software I use just uses G0 to move without cutting and G1 to move with cutting so it only needs to specify M04 once at the beginning of the job and M05 at the end. I'm not sure of the reason why LightBurn does this as it increases the size and complexity of the gcode file ....anybody know?

FlyinFlynn15/01/2020 17:07:59
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122 forum posts
85 photos

To answer my own question it appears that -

>>>>>>>M4 / M5 commands shouldn’t be necessary between cuts because G0 is a non-cutting move.

This is only true for grbl 1.1f/g.

Martyn K15/01/2020 21:22:35
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5041 forum posts
3677 photos

Thanks for that flyingfinn. I still need ťo update the firmware and retry. I'll try and get that done this weekend.

I have photographed some of the modifications

The obvious one is that I have reduced the width of the machine do that the cut width is now 250mm. The beams were cut from the front and the plastic legs moved to the side. This has given me a nice manual home with the laser Pointing within the cut area at 0,0.

dsc_1480.jpg

You can see from this photo there is a piano wire rail. This is to help prevent the cables falling on the bed. It has made a big difference. I am going to add a second rail above the controller and laser psu.

The tool is screwed down to a piece of 400mm x 1000mm conto shelf board and my sacrificial panel is 12mm builders ply screwed to that. There are two guides that I push the wood into to locate consistently.

dsc_1477.jpg

A small £4 fish tank aerator is fitted at the back. This provides more than an adequate supply of air to diffuse the smoke. It will also blow away any small waste that has been cut as well.

dsc_1478.jpg

The pump is held in place using double sided sticky pads which damp the vibration nicely. The feed to the laser head is by clear pvc tbe using a swinging arm. The final feed is length of brass tube with the air outlet about 6mm from the laser focus. You can see this in the first photo. The arm is 10g piano wire in a brass tube bearing located in a home made 3d printed support.

The little pump claims to be 1.5 l per minute output.

Simple mods but it is now much nicer. Reducing the width and screwing it to the baseboard have made it much stiffer.

Martyn

Andy Joyce17/01/2020 16:46:41
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155 forum posts
28 photos

Flynn, do you find air-assist improves the cut quality? If so what flow rate are you using.

Andy

Martyn K17/01/2020 17:17:37
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5041 forum posts
3677 photos

I am not actually sure what air assist is. Can someone clarify please?

Thanks

Martyn

Andy Joyce17/01/2020 17:39:29
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155 forum posts
28 photos

Air directed over the laser cutting point to blow away smoke and ash.

Martyn K17/01/2020 22:53:21
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5041 forum posts
3677 photos

Thanks Andy

That is what I thought. I seem to get a cleaner cut with no smoke present. I think the smoke will be diffusing the light.

Martyn

FlyinFlynn17/01/2020 23:17:23
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122 forum posts
85 photos
Posted by Andy Joyce on 17/01/2020 16:46:41:

Flynn, do you find air-assist improves the cut quality? If so what flow rate are you using.

Andy

I have a small 1.8litre per minute aquarium pump. I cannot say if a bigger pump would be better, it seems to blow away the smoke and dust, but you do need to get the nozzle very close to the laser spot. a desk fan also does the job, but from further away! I haven't really done enough to be sure what is best in the air pump department.

Andy Joyce20/01/2020 18:56:22
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155 forum posts
28 photos

Made an offer on a 35l/min pump on flea bay, so will advise if it makes an improvement.

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