Best settings for dithering on anodized aluminum for DSP

leonarddyoung
Posts: 4
Joined: Thu Mar 30, 2017 12:55 pm

Best settings for dithering on anodized aluminum for DSP

Postby leonarddyoung » Fri Apr 21, 2017 12:17 pm

Hello, Need a little guidance. Im having a hard time getting the settings correct on my light objects DSP 7 upgrade I installed on my k40 laser. I etch very detailed images onto anodized aluminum. On the stock k40 M2 board I could just send the dithered image to the laser and it would etch them perfectly. I dont not use bitmap image conversion but rather dithering i create myself. Ive uploaded a few examples of the work Ive done with the stock k40 nano board. Im not getting nearly as clean of etchings using the exact same files on the dsp however and could use alittle help understanding why. What is the best way to dither an image for maximum detail for the DSP controller? Right now i use a resolution of 1000dpi. Any help is greatly appreciated.
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SWMS
Posts: 125
Joined: Mon Jan 06, 2014 4:28 am

Re: Best settings for dithering on anodized aluminum for DSP

Postby SWMS » Sat Apr 22, 2017 1:15 am

In your image editor resize the image to the size you need it.
Resample the dpi to match the dpi you are engraving at (1000dpi)

Convert it to grey scale to get rid of the colour.

Convert it to black and white or 8 bit bitmap. ( depends on what the software calls it)

Choose half tone and tell it he number of dots to use

I prefer to use Corel Draw for all this. It's dead easy and you can select the type of dithering. ( floyd steinberg) seems to work pretty good.

Inverse the image for aluminium.


Note it might be worth working out your dot size based on the lens you are using for this then divide that into 1 inch.

Build log has an optics calculator for that here..

http://buildlog.net/cnc_laser/laser_calcs.htm

I am a metric person so that would be something like 25/0.02. Isuspect you will find you can't get 1000 of your dots into an inch. Your steppers might not be able to increment by 1000th of an inch anyway. So, you are engraving at a resolution too high for your laser and losing money as you can get the same quality from a lower resolution and it's faster. You'll never see the difference.

Currently I suspect you are over engraving. Think of trying to draw a picture with your finger in lines by putting some ink on your finger and drawing a 1000 lines in an inch. You will get over lap.

Apparently our self build lasers max out on resolution at around 400- 500 dpi ( I am not sure of the truth in this )

Once you have worked out your maximum resolution do all the above and...

Change the scan gap as close you can to match the maximum resultion your laser can do.

For instance if your laser dot size max resolution is 172 dpi use the scan gap for 175 dpi.

Before you do this you might want to make a small black box bitmap and engrave at a really wide scan gap so you can see the lines.

If they don't match up you need measure the difference go into the settings and adjust the engraving backlash offset ( I think it's called that )

try engraving again.



This page is great for explaining this it appears to be down at the moment tho!

http://www.engraversnetwork.com/support ... ppi-laser/

The invoice is in the post I probably saved you quite a bit of money in the long run ha ha.
Last edited by SWMS on Sat Apr 22, 2017 1:37 am, edited 3 times in total.

SWMS
Posts: 125
Joined: Mon Jan 06, 2014 4:28 am

Re: Best settings for dithering on anodized aluminum for DSP

Postby SWMS » Sat Apr 22, 2017 1:16 am

By the way...

What power is your laser?

leonarddyoung
Posts: 4
Joined: Thu Mar 30, 2017 12:55 pm

Re: Best settings for dithering on anodized aluminum for DSP

Postby leonarddyoung » Tue May 16, 2017 12:01 pm

Its a 40w k40 with a dsp upgrade dropped in.

leonarddyoung
Posts: 4
Joined: Thu Mar 30, 2017 12:55 pm

Re: Best settings for dithering on anodized aluminum for DSP

Postby leonarddyoung » Tue May 16, 2017 12:13 pm

Im also using the stock 12mm 50.8mm lens that came with the k40 and have the scan gap set to .03

leonarddyoung
Posts: 4
Joined: Thu Mar 30, 2017 12:55 pm

Re: Best settings for dithering on anodized aluminum for DSP

Postby leonarddyoung » Tue May 16, 2017 12:57 pm

another quick question man, If i get a z bed and get a a new lens thats closer to the material will the dot size go down?

Techgraphix
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Joined: Fri Jan 20, 2012 1:39 pm
Location: Appelscha, the Netherlands
Contact:

Re: Best settings for dithering on anodized aluminum for DSP

Postby Techgraphix » Wed May 17, 2017 2:31 am

A lens with a smaller focal distance has a smaller spotsize. Widening your beam (with a beam-expander) will also reduce the spotsize.
To play with some data, i attach this excel-sheet:
Lasercalc.zip
(6.32 KiB) Downloaded 17 times


Kees

SWMS
Posts: 125
Joined: Mon Jan 06, 2014 4:28 am

Re: Best settings for dithering on anodized aluminum for DSP

Postby SWMS » Sun Jun 18, 2017 7:58 pm

If you put the bed closer to the lens without getting a lens with a smaller focal point the opposite of what you think will happen will happen.

The dot size will be larger.

If you cut a cross section through a laser beam it looks like a sand timer. First it's large, then is small at the focal point for a certain depth, then it gets large again. Currently you are in the small, sweet spot. Moving the label up moves it into the large zone. Moving it too far down does this too.


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