High speed problem (Denim engraving)

[RobotEyes]

Hello.
I'm using gearbest 5.5W machine.
with t2laser  (so far the best tested software)
The goal is to etch / engrave images on Denim!

I understand that  high-speed is need for this purpose (raster mode);
so I changed the firmware parameters (Jtech 0.9g)
with maximum speed 50000 ($ 110 = 50000) and it seems to work,
the problem is that at the edges slows down the movement again with the laser on,
so... it cuts the edges.
I tried to leave a white border around it, but is ignored.
the only way I've found is to put two vertical bars far from the image
and mask it with aluminum foil.

How can i start slowing down after the image (laser off)?
I tried to increase acceleration, no results.
Any suggestions for the best setup on Denim is welcome,
it is the main destination of my new laser.

Currently i use speed 25000, power 127, 2-4 pass

My setup is as follows:

$0=10 (step pulse, usec)
$1=25 (step idle delay, msec)
$2=0 (step port invert mask:00000000)
$3=0 (dir port invert mask:00000000)
$4=0 (step enable invert, bool)
$5=0 (limit pins invert, bool)
$6=0 (probe pin invert, bool)
$10=3 (status report mask:00000011)
$11=0.020 (junction deviation, mm)
$12=0.000 (arc tolerance, mm)
$13=0 (report inches, bool)
$14=1 (auto start, bool)
$20=0 (soft limits, bool)
$21=0 (hard limits, bool)
$22=0 (homing cycle, bool)
$23=0 (homing dir invert mask:00000000)
$24=25.000 (homing feed, mm/min)
$25=500.000 (homing seek, mm/min)
$26=250 (homing debounce, msec)
$27=1.000 (homing pull-off, mm)
$100=80.000 (x, step/mm)
$101=80.000 (y, step/mm)
$102=80.000 (z, step/mm)
$110=50000.000 (x max rate, mm/min) (Previous $110=500.000)
$111=3000.000 (y max rate, mm/min)
$112=500.000 (z max rate, mm/min)
$120=2000.000 (x accel, mm/sec^2)  (Previous $120=200.000)
$121=10.000 (y accel, mm/sec^2)
$122=5000.000 (z accel, mm/sec^2)
$130=200.000 (x max travel, mm)
$131=300.000 (y max travel, mm)
$132=200.000 (z max travel, mm)

Thanks to All....... Carlo

[Zax]

Hi Carlo, and thank you for the endorsement of T2Laser.

The problem you are seeing is due to the acceleration and deceleration combined with the high feed rate (speed).

I wouldn't recommend those speeds or acceleration as you are likely to lose steps and get jagged results, but if they work for you, that's great.

The time it is taking your machine to slow down and speed up is causing more burn in those areas. Generally you want to balance the speed and acceleration for engraving to keep a nice constant power density, of course this requires lower power (a slower overall result but better quality).

So, what can you do?

1. Turn off the "Skip Blank Lines" setting in T2Laser and ensure you have some white space around the image. This will move those acceleration/deceleration areas to beyond the image when the laser is off.

2. Use diagonal engraving, it is using both X & Y so the result (the hypotenuse if you think of a triangle) is a faster acceleration and you can reduce the travel speed slightly.

3. Run a much slower speed and reduce the laser power  ok, but I had to suggest it

[RobotEyes]

Hi ZAX,
Tks for rapid response....

Was so simple...... turn off skip blank lines,
my misunderstand, i intended totally empty line.......

Using this option acceleration in no more so important
100 mm/sec^2 is adeguate.

First usable test seems promising....
Attached some test:
Speed : all 30000
1 -> power 64 scan horizontal 1 pass
2 -> power 64 scan diagonal    1 pass
3 -> power 32 scan horizontal 1 pass
4 -> power 32 scan diagonal    1 pass
5 -> power 32 scan horizontal 2 pass
6 -> power 32 scan diagonal    2 pass
7 -> power 64 scan horizontal 1 pass gradient box, grey scale

Seems that my laser is not very linear, (test 7)
but i've to test more.

To avoid step loss I increased a little the motor current.
I added a little radiator over the motor controller chip.
I've to look at motor datasheet to see the max current
(I suppose 1A or little more)

For what i understand, with Denim I need to burn only surface,
so... low power, high speed, several pass.....

In any case, if someone has experience in Denim engraving is welcome.

Tks, Carlo

[Zax]

Yes, you are bleaching the demin and removing the pigment from the cotton. The "trick" as you say is to do this without damaging the fibers, or you end up with an entirely different result.

I haven't tried with the diode laser but it works really well with CO2 wavelength, no damage and very white results.

Also try diagonal or rotate the demin so the laser isn't going along the threads, this helps a lot.

[Lob0426]

The maximum speed of the Nano is 35,000, according to @Chamin, the developer of GRBL. My particular machine started making "grinding" sounds after 12500. Probably belt slippage. I did not test X all by itself however.

I would worry that you will cause excessive wear to your X axis with those speeds. Keep an eye on the wheels to see if they begin to have grooves scored into them. And look for the inside of the run becoming shiny. The belt might stretch so keep an eye on tension also. All those parts can be replaced.

Richard

[RobotEyes]

Unfortunately I have to suspend the tests,
Seems that t2Laser is the only software which pilots laser power.
(With gbrl controller do not definitely successful)
and having to change the controls PC in little time I can not buy it,
(will not work on the next PC)
and 10,000 lines of gcode not allow to make anything useful (the maximum a rectangle of 10 x 20 mm).

Then. goodbye.

@Lob0426
I've not tested if setting 50.000 mean really 50.000 speed. (is not easy to measure with chronometer)
but is very difficult that belt can slip,  Seems step loss of motor; easy to solve increasing motor current.
In this case is better to paste a dissipator on controller chip.
I've a lot of experience in 3D printer design (mechanically similar).

Carlo

[Lob0426]

The 35000 is the maximum cycles possible from a Nano controller.

You were using 50000 max speed and 2000 acceleration, to fool the planner into moving faster where it slows down then speeds back up due to accel/decel. GRBL was designed for CNC use, not Laser or 3D printing. So it slows drastically before direction changes to prevent breaking tools. Lasers do not need these protections, though you still need to control inertia, during the direction change to keep accuracy, i.e. not rounding a square corner. In 3D printing you are limited by extrusion speeds, generally under 150mm/s. Lasers can run in thousands of millimeters a second, depending on their power.

Try this instead;
#define MINIMUM_JUNCTION_SPEED 50.0 // (mm/min) was 0.0   in config.h
Or higher, Then recompile. I have just started playing with this. I tried 20 and it noticeably sped up.

Belt slip in this case is a mechanical issue not a stepper issue. You cannot run the belts tight enough, in this design, too stop this at real high speeds. These machines do not run the tension that the 3D printers do. My printers run three times the tension than the laser uses.

I hope you will find a solution that works for you!

Richard

[RobotEyes]

Although I love T2laser, yesterday I started to write my own controller.
At the time I wrote the part for manual Jog and parameters setup ($nn=xx) .
Strange behavior, however, appears on my machine.
(Exactly as with t2laser, so I think to the firmware)
Movements  turns laser on (low-power, but not always) and don't turns off anymore.
I tried to send commands by terminal but nothing changes (So it's not my sw)
Even in tests with T2Laser, moving from home to start position of the job sometimes "cut" the fabric.

A simple G1 X10 Y10 F1000 moves the carriage, but with laser on.
To turn it off is not sufficient a simple M05; I have to send M03 followed by M05.

At the moment I do the movements with M03 S0 G1 X .. Y .. F .... M05,
but it seems very bad.

It also happens to someone else?

Tks, Carlo

[Zax]

T2Laser has a solution for that, it's in the settings menu (M30 end command).

It has side effects that I have documented on the forum previously but it will solve your problem, and you can add that command to your controller program.

[RobotEyes]

Thanks for the reply ....
The M30 command (and M2) effectively reset the pwm,
but (as you sayd) also resets arduino, and this I do not want that.

I coded the manual movements as M03 S0 G1 Xnn Ynn Fnnn M05,
At this point I added a command to replace S0 with Sxx, to draw lines manually.

For the scanning from bitmap (almost finished) I will add M03 S0 G1X0Y0Fxxx M05 for the home return.
For DXF GCode, or otherwise vector mode.... i do not yet arrived.

I wish you a good w.e.
Carlo

[RobotEyes]

My software now works......

see:
http://benboxlaser.us/index.php?topic=598.0

Carlo

[RobotEyes]

Hello everyone
After a few days of vacation I gone back to work to the laser controller.
The portion of denim etching works,
The velocity is limited by the speed of the serial port, considering an average of 23 characters per point and a resolution of 0.2 mm the maximum speed is 5-6,000 mm / min
The results is shown in the photo below. and it appears acceptable to me.
Now I'll do some tests on other fabrics such as microfiber and scuba.

I consider this thread closed and continuous here:
http://benboxlaser.us/index.php?topic=598.msg6954#msg6954

cheers
Carlo