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Ideas of a beginner...

Posted by trapperjohn 
Ideas of a beginner...
June 23, 2017 01:19AM
I am really interested in engraving and cutting stuff for hobby DIY (making PCBs, small cases, logo engraving etc.) and would like to buy/build a laser cutter.

I've read a lot about laser modules, drivers etc. and people seem to have very different kinds of opinions about what's a "must" and what's a "don't" for laser cutters/engravers.

The really cheap lasers from banggood, Aliexpress etc. seem to be problematic (or last only for a short time), the expensive (often recommended) modules are out of my budget (or out of the budget I'd like to spend on this hobby).

What about the mid-priced modules from DTR? E.g. the 6W NUBM44 including glass lens and driver
[sites.google.com]
Will it cut (e.g.) 4mm plywood or (colored) acryl?

This would be about 200 Eur including tax and delivery when sent to Germany.

I'd like to buy an Anet A8 3D printer (about 150 Eur), add/print all the recommended updates for the A8 and then add the laser module and build a laser-proof housing incl. fume extraction etc.

As I have experience in DIY electronics but no experience in 3D printing or laser cutting, I'd like to know if this is a feasible way to go or if it is just a bad idea (and possibly give me some improvements winking smiley ) ...

Thanks,
Florian
VDX
Re: Ideas of a beginner...
June 23, 2017 07:30AM
Hi Florian,

if you're from Germany, then the "laser section" in the German sub-forum could be intersesting for you too winking smiley

[forums.reprap.org]


Viktor
Re: Ideas of a beginner...
June 25, 2017 09:31PM
Yes, thanks, I already found that group - my hope was to reach more people when using the int'l group (especially people who already use a NUBM44 for cutting) winking smiley
Re: Ideas of a beginner...
June 25, 2017 10:59PM
Have you tried building "Grovers dvd laser Engraver" ?
It would get you running.

I have a 1W Neje laser as a learning tool and after a bit of playing I can get it to engrave.
Based on the neje, I am now building a bigger cutting area sized engraver.
VDX
Re: Ideas of a beginner...
June 25, 2017 11:31PM
... I'm starting a local forums project "laserdiode-module with driver" in the German RepRap-forum and the (too German) forum "Peter's CNC-Ecke" - here the link to the RepRap-group:

[forums.reprap.org]


It's meant to build some laserdiode modules with fibercoupled 9Watt@975nm-NIR-diodes and a stable (spike-free) current driver, capable of up to 8,5 Amps (needed for this IR-diodes) -- but this driver can be set for smaller currents and used for smaller laserdiodes too. The "basic" driver type will use up to five parallelized LM317 and LM338 and is meant for pulsing/PWM modes only ... I'm actually reasoning, if/how to redesign my analogue operating OpAmp driver without interfering with my comercial drivers ...


Viktor
Re: Ideas of a beginner...
June 26, 2017 02:12AM
That sounds interesting - but I'm not sure if 975nm is a good starting point (for me). This is only for dark material, i.e. I guess it won't be able to cut wood, right?
Re: Ideas of a beginner...
June 26, 2017 04:03AM
So far I've read that the 6W laser is not really recommended for engraving/cutting due to its large beam - but which diode is currently worth a recommendation?

I found this shop in UK (Odicforce) which sells laser modules and driver bundles, e.g. 4.8W for less than 200 Eur:
[estore-sslserver.eu]
(not sure if this link works)



Quote


This 12v module has a driver with TTL Modulation to allow switching at up to 20kHz. Coated glass optics.

Wavelength: 450nm
9mm Nichia diode
Optical Power: 4800mW
Operating Voltage: 12.0V
Operating Current: 2A
Operating Lifetime: >1000hrs
Operating temperature: 10 - 40 °C
TTL Control: 20kHz @5V
Glass lens (OFL3-M)

This module has adjustable focus and optional TTL switching that can be used to control the power output (normally on full power, the TTL signal can be used to reduce the output power using PWM). 12V operation. Cooling fan. Suitable for CNC laser engraving etc. 4W+ will cut paper, thin balsa wood etc. and engrave wood. Standard 9 x 0.5mm thread lens allows alternate lenses to be used. Laser head has mounting holes pre-tapped.

What's your opinion on these?
VDX
Re: Ideas of a beginner...
June 26, 2017 04:20AM
... for engraving and cutting plywood I'm using the blue (445/448nm) 2W and 3,5W modules from Lasertack - [www.lasertack.com]

The 6W-diodes have a bigger and more elliptic beam, so problematic to focus on a small spot.

The fibercoupled 9W@975nm-IR-diodes are pretty good for dark or black materials, but will have trouble with bright or translucent/transparent ones ...


Viktor
Re: Ideas of a beginner...
June 26, 2017 11:05PM
The Lasertack modules are quite expensive compared with the modules from DTR or Odicforce (the ones I linked above). I thought about getting one of these and possibly buy the laser driver from Lasertack for analog modulation: [www.lasertack.com]
VDX
Re: Ideas of a beginner...
June 27, 2017 12:21AM
... this is a pretty good and reliable driver.

For higher currents he's testing one of my drivers with up to 10 Amps current winking smiley

Here is an image of this 10A-driver (on top) compared to a new design with up to 30 Amps continuous output or upt to 100 Amps pulsed!!

[forums.reprap.org]


Viktor
Re: Ideas of a beginner...
June 28, 2017 11:04PM
Finally I decided to order a 3.5W NUBM05 in 25mm copper module and G-2 glass lens from DTR. Divergence / beam size seems to be okay for my purpose ... I'll see ;-)

But first I have to wait for the Anet A8 and become familiar with it...

Recommendation for the best bang-for-the-buck laser driver with analog modulation (the NUBM05 has a max. current of 3.5A)?

The Lasertack 4.5A driver for about 60 Eur ($68)?
Re: Ideas of a beginner...
June 29, 2017 05:58PM
Why not get driver from DTR?

If they don't sell compatable drivers then they can't be very good

8A blackbuck 8 amp, modulation input, thermal cut off -- sounds good?

confused smiley
VDX
Re: Ideas of a beginner...
June 30, 2017 12:27AM
... is there some experience or output signal measuring with the DTR-drivers?

In my experience all drivers with buck-DC-DC-converters driven with >3A produced spikes and transients ... sometimes with up to 300% of the set current!!!

Here two images showing the signal whille ON/OFF switching - it's measured across a shunt resisitor with 0,1 Ohms, so calculate the drawn current by 10x the showm voltage:



... in detail:




-- especially the "under-shoots" when switchin OFF will kill the diode pretty fast sad smiley

Viktor


Viktor
Re: Ideas of a beginner...
June 30, 2017 11:35PM
I could not find any info or recommendation for these drivers - most of DTR's drivers seem to target laser pointers etc and not cutting/engraving

I found at least some recommendations for the Lasertack...
Re: Ideas of a beginner...
July 03, 2017 05:26AM
Short question: Can I feed the driver's analog modulation input with PWM signals from a microcontroller? Or does it have to be a "real" analog voltage (e.g. PWM plus resistor/capacitor)?
VDX
Re: Ideas of a beginner...
July 03, 2017 08:21AM
... if it's a common analogue input with 0-5V range, then you can PWM it ... with a 0-10V input you have to use a transistor or OpAmp to rise the voltage.

If it will do as you expected, depends on the bandwith (or time resolution) of the driver - my controllers and drivers works with up to 500kHz (can tune it up to 2MHz) ... a slow driver with e.g. max. 5kHz bandwith will show a different behaviour ...


Viktor
Re: Ideas of a beginner...
July 03, 2017 09:45AM
Bought the Lasertack with 4.5A max - i.e. feeding the input with a 5V Arduino PWM (less than 1kHz) should do the trick.. that would be nice ;-)

Now I have to look for a controller firmware which supports Laser and 3D printing at the same time. Most seem to target only one of them (e.g. the Marlin branches).
VDX
Re: Ideas of a beginner...
July 03, 2017 10:48AM
... I'm doing both, 3D-priting or laser-engraving, with Marlin4Due - you can use the step-pulses of the extruder for "pulsing" your laser too winking smiley


Viktor
Re: Ideas of a beginner...
July 03, 2017 10:13PM
I'm not sure that I understand how this works ... I've seen G-codes M3/M4/M5 to control laser power, but most tools seem to just use G0/G1 and provide laser power via the 'E' parameter. Doesn't the controller firmware have to know that its controlling a laser and not the extruder anymore? For 3D printing, the 'E' parameter describes the length of filament between start and end point - so when using this as laser power, the parameter describes the number of pulses between start and end and not an absolute power value (e.g. 0..255)?

My planning was to use an unused PWM port of the controller to provide laser power modulation - but re-using the extruder pulses as you suggest would be a lot easier... Are the stepper drivers on (e.g.) a RAMPS board able to generate step pulses with such a high frequency?
VDX
Re: Ideas of a beginner...
July 04, 2017 03:13AM
... I'm adjusting the laser-power mostly by the pulse-length (either externally per potentiometer - or per software, setting an analogue output), not with varying the current.

The effective power results then from the set power (mostly full power) and the pulses count (pulses per mm) and the pulse-length (5 to 30 microseconds for engraving, 200 to 400 microseconds for cutting).

Depending on the used machine the "pulses per mm" value is either a fixed hardware setting (400 pulses per mm with my converted CNC-mill) or I can define it while importing the file ...


Viktor
Re: Ideas of a beginner...
July 04, 2017 05:16AM
I.e. if laser power and pulse/mm is fixed, the variable pulse-length defines the cutting/engraving speed (and vice versa)? For example 400 pulse/mm, 30 microsec/pulse means 400*30 microsec per mm = 120 millisec per mm = 8,3mm per second?
VDX
Re: Ideas of a beginner...
July 04, 2017 06:23AM
... no, the engraving/cutting speed can vary -- I'm engraving with up to 100mm/s and cutting with down to 2mm/s ... it's only defining the averaged power along the path.

If you set your driver for e.g. 3,5 Watts (with the 3,5Watt-diode) and 5 microseconds pulse length with a pulse-ratio of 100 pulses per mm, then you can drive with 10mm/s or with 100mm/s and receive the same result winking smiley

The relation between pulse-width and speed is only there, if you use long pulses for cutting -- then you have to reduce the max. speed, so the pulses won't "overlap" ...

Edited 1 time(s). Last edit at 07/04/2017 06:25AM by VDX.

Viktor
Re: Ideas of a beginner...
July 04, 2017 10:25PM
But shouldn't the results differ? When running with 10mm/s, during a pulse of 5 microseconds the laser would 'touch' 0,00005mm. When running with 100mm/s the laser would touch ten times this distance (i.e. less power on a certain spot). Or is this negligible?

Nevertheless, I expected the laser to run continuously when PWM'ing the analog input (i.e. the laser driver sees the PWM signal as analog reference for current adjustment and does not power off as long as the pulse frequency is above a certain threshold).

Would PWM + low pass filter work? Or might the capacitor have negative effects on engraving (e.g. delay when switching off)?

Edited 1 time(s). Last edit at 07/04/2017 10:25PM by trapperjohn.
VDX
Re: Ideas of a beginner...
July 05, 2017 01:28PM
... with constant PWM and varying speeds you'll get burned edges, as the averaged power will be different for different speeds too.

To avoid this you either need to change your power setting with varying speed (what's a pretty hard to accomplish task), or change the pulse generation to a "geometric" representation - this is done with speed-independant "pulse per mm"-approaches ... e.g. for the extrusion of plastic with the common FDM-heads ...


Viktor
Re: Ideas of a beginner...
July 07, 2017 01:28AM
Received the laser module from DTR, fortunately without any customs problems



Now I have to wait until my safety glasses arrive. Won't try it before... ;-)
Re: Ideas of a beginner...
November 16, 2017 11:15AM
Quote
trapperjohn
Received the laser module from DTR, fortunately without any customs problems



Now I have to wait until my safety glasses arrive. Won't try it before... ;-)

Have you had this running yet? It looks like a good option cost wise.
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