Electrox marking outside of marking area.

[Joe Hillmann]

This is mostly a question for Matthew Knott but I figured I would put it up as a forum question rather then as a private message because it may help someone else as well.

I was using my Cobar laser and after I started marking the part I looked at the computer screen and realized the text went about one inch outside of the marking area on the screen. Since I had already started it I decided to let it run. When the part was done the area that was outside of the marking area was as good as the area that was in the marking area.

With all that said I can get to my question. Is there any risk to the machine by going to far outside of the marking area? I assume at some point the part will be to far out of focus to mark which will ruin a part but I am more worried about possibly damaging something inside the galvo head if I go to far out. The reason I ask is in the past I have had to break a part jobs because they were just a bit to big to fit in the marking area and when those jobs come back up I would like to run them as one if I know the only thing I am risking is the part and not the laser.

[matthew knott]

Hi Joe , the answer depends on if you have a dsp galvo board, I think all cobras did have so you 'should' be ok marking out off the area, on older machines it was possible to bang the galvo mirrors together and even break them ! What you see on the screen is not truly the marking area, it's just a visual guide set in the software, your lens size sets the maximum marking area (and scan angle of galvos) in your test program's on the controller you should have a program called max grid, run this on a price of black paper and it will draw the maximum area. What you find as you reach the extremes is first the power drops off in the corners and next the mark will be truncated. What I mean by this is all the marking that is outside of the area is done at the hard extreme so it wrecks the part and also you should get a value out of field error. So if you tried to mark say a 500mm circle you would end up with a 220mm square ish shape. Let me check is you have dsp first but as long as you do then you can do no damage and you can play and find your own extremes, you can always get a bigger area than Electrox specs ! One way to tell if you have dsp is when you turn the control key on your red laser light should dance around drawing a pattern as it tunes the galvos then after 5 seconds it stops, another is to look on the pendant screen and it will tell you the dsp version! Hope that helps !
Matt

[Joe Hillmann]

When I first hit the laser start button but before hitting the laser button the red light marks the edges and a cross hair in the center. That means I have the DSP and the mirrors can't damage themselfs?

[matthew knott]

In theory yes, I say in theory as they can physically touch and it's software protection but you are just as likely to break it in general use as marking outside the marking area! Measure the height from the the bottom of the galvo head (where the lens screws in) to the focus point and tell me the result and I can calculate what the maximum area should be! There's a good chance your software has not been set correctly for the lens and you might be able to have a bigger marking area, also what size is the marking area ( diameter of the circle on the screen) cheers

[Joe Hillmann]

The marking area on screen looks to be about 8 3/4 inches in diameter and the focal length looks to be pretty close to 12 3/4"

[matthew knott]

The marking area on screen looks to be about 8 3/4 inches in diameter and the focal length looks to be pretty close to 12 3/4"
Ok so you definitely have a F254 lens as the focus is about 323mm, and 8 3/4 inches is about 220mm and to be fair that is getting close to the limits of the engraving area, the power start to drop at the edges anyway. I try not to go any bigger than a 220mm circle, but as you have found you can go a bit bigger.

Try marking a 220,225,230,235mm circle and see what it does, its quite interesting and it will show you what happens when you go out of field.
Also worth noting that if you have offsets in the controller this does not move the maximum area over, ie you cant mark a 220mm circle and off set it 20mm, you will start to lose some of the circle.
cheers
Matt

[Joe Hillmann]

Thanks Matt, I really don't plan on pushing it too far, it is just in the past I have had jobs where one section of the engraving was just a bit out of the marking area so I would break it up into two jobs. Next time I will see if I can run it as one.

[matthew knott]

ALWAYS do a dummy run, it's a good way to wreck a part :)