Greyscale image burning in to wood

Mostly Printed CNC - MPCNC Your Builds
#1

This is kinda of a show and tell thread. I have been working the last week or so to get grey scale images looking good in woods like birch plywood. I have had several people express interest in purchasing pictures done this way.

I have the NDB7875 laser running at 2 amps. I also have the G2 lens and the 3 element lens… So far I have learned that it appears the G2 lens is too powerful and does not allow as good of grey scale resolution as the 3 Element lens which also has small dot when focused properly.

I was using nice smooth not very grainy birch from Michaels (local craft store) and I was getting decent results using 3000mm/min at 100% power. I could only achieve good results printing from SD as it appeared the Repetier Host could not keep up.

What I am interested in is seeing what people source images look like and what the finished product is. It seems to me that a fair amount of tweaking of the image contrast/brightness and gamma levels are needed.

#2

Not there yet but will be trying this soon as well. Are you running it in PWM instead of TTL? Also assuming this is with PEP5… have you seen this thread;
http://www.photonlexicon.com/forums/showthread.php/20162-CNC-Laser-Engraving-8bit-Shades-of-Grey-445nm

They move from a 1W 405nm laser in the first posts to the 6W and around to a few others, post 143 shows some settings on the M140 at 2W that may… ahem … shed some light on a starting point.

http://www.photonlexicon.com/forums/showthread.php/20162-CNC-Laser-Engraving-8bit-Shades-of-Grey-445nm?p=330672#post330672

#3

I am using PWM, PEP5 and I2G.

He says they are using 70IPM which is about 1778mm/m which is a little more then half of the feed rate I have had to use to get good results. I have had to use between 3000 and 4000 mm/m as I2G has as defaults for leather/wood. My acceleration is set to the default 400mm/s2.

I was reading some posts yesterday about peoples setup (not on mpcnc) and they were talking about having their acceleration set to like 8000 or higher. I had tried 1500mm/s2 but that did not seem to really make whole lot of difference.

#4

Does anyone printing or lasing err lasering… using a laser use higher then the default 400 acceleration for X and Y?

In my adventures to make laser engraving a sustainable side business for me I am wanting to do images (photos) on wood I have come across people using extremely high acceleration settings like 8000 or higher. I am pretty sure that is not possible on this machine using only Nema 17s. Plus I am running a 5’ axis which adds more moving mass then normal laser machines too.

I am just wondering if I am over thinking this too much and perhaps the issue lies in the contrast/brightness/gamma settings of the picture. I generally adjust the image so it look nice on the screen… The result is nothing like the screen usually.

#5

Just a thought. Why not just make a short Z that’s just big enough to hold the laser? Aren’t these things mostly fixed focus anyway? Maybe give it whatever travel the tool holder mounting plate gives, and do any bigger adjustments with a thicker backing plate under whatever you’re cutting. You could then do away with the Z motor and just put a locking knob on top. Should save quite a bit of weight and let you move faster. When you want to do the router thing, just unscrew the laser carriage off, and screw the taller router z assembly back on.

#6

Ohhhh, good idea!

#7

Maybe more eyes can help me out here… Attached is my result. I am close. But what am I missing.

The file comes from PEP5. I have my power range 20-255 speed 3000mm/m. Pixel size is 0.1mm. There are these wierd patterns that are not in the original image.

I think i have the power and speed pretty close but it is not nice and clean and focused like I see on PEP5s website.

IMG_0255.jpg
IMG_0255.jpg3264×2448 1.16 MB

#8

The ringing could be a lot of things. I think most common is from your accelerations being high, or your machine being very tall. How far down is your laser hanging? As always you should raise your material up to the gantry as far ass possible to minimize this.

Could be loose belts but usually not. A cool trick is to zip tie your zip tie…it takes the spring out. Shown in the pic.

IMG_20161126_104857.jpg
IMG_20161126_104857.jpg3075×3848 1.26 MB

#9

My results are getting better. I am pretty sure it is not loose belts. The are quite tight.

I have slowed it down a bit to 1800mm/min and that seems to have eliminated the ringing. I also printed and added another mount bracket the the laser holder. I am using your laser holder vicious. With just one it seems to be a little wobbly and prone to vibrating. I am trying another pass at 2400mm/min to see what it looks like and hopefully increase the depth of colour.

#10

Well I got one good… image out of about 40 tries. This is frustrating AF.

One thing that seems to be causing problems is in the software I set the speed to 3000mm/min (No speed overrides or anything set up) When it does normal movements it moves nice and quickly but when it gets to when it is burning it slows way down making everything too dark. I have tried upping the speed, lowering the speed, playing with acceleration a bit, jerk but nothing seems to keep it moving at a constant speed which is what I am expecting to see. Are my expectations wrong. I watch videos on youtube and their heads move at a constant rate.

What gets me is the 1 time I got a good result I save the file. I re ran the exact same file last night on the same material (mdf) and got totally different result.

I am engraving directly from SD card. so USB speed is not an issue. It does not matter whether i create the file with PEP5 or Image2GCode results are the same.

Is this some thing that needs a firmware tweak? Is this beyond the limitations of this machine?

#11

Jason it seems a firmware issue…
Look here
https://www.v1engineering.com/forum/topic/image2gcode-engraving-how-to-improve-it/

#12

Have you tried the firmware change?

#13

If you want to give it try, turn the acceleration way way up and the jerk as well. Turn the accel to 5000, and the jerk to like 10.

Let us know how that works out.

I do it the other way. I use slow speeds and just turn the laser down. I haven’t really noticed the difference between 256 levels and 128 in burnt wood.

#14

I tried a jerk of 20 and accel of 1500 i think but just from the panel, not sure if that affects the current running job, or do I need to do it prior to starting the job. I will try playing with the actual firmware and see what happens.

I could tell the difference in the depth that it burnt… 256 burning noticeably more the 127.

#15

Hmm… maybe I am an idiot. Was just reading another thread about focus size.

Now I dont have a J Tech laser but I assume the diode is the same. He is saying that the 3 watt has a focus dot size about around .23mm. I am using a pixel size of 0.5mm in PEP5. I also tried 0.1mm which is what I do my mirror engraving. I never considered the laser lines overlapping… Perhaps my problem lies in my pixel size? I am going to try 0.2mm and see where that goes. It should end up close I would think.