Engraving On a Contoured Surface

[James Rish]

I have a 30w fiber laser that my wife and i bought from a former employer of hers. He sold it shortly after purchasing it because he did not find the EzCad program to be an easy addition for his employees that were currently using Corel based software. To my understanding he purchased the laser from G. Weike. It has been a pretty good learning curve for me from figuring out how to convert logos to a file that could be read by EzCad (DXF) and then hatch filled for a nice looking engraving, to learning how to use the rotary attachment and split mark settings to engrave text on cylindrical objects (but no luck with logos for the issue of the lines showing up as stepper motor rotates). Ive read here that im not the only person with that problem.:mad: My issue that I bring to the table today is that of engraving on a contoured surface. I am starting to do some work for a friend that wants to incorporate laser engraving into the motorcycle industry. He is starting his own shop so I am engraving his logo onto some different parts as sample pieces. The piece I am working with now is a derby cover.

391538(not sure why picture is inserting upside down).

When I engraved this first test I engraved in continuous mode and adjusted my focal height while it was engraving just to get the image on the piece and go from there. It did not turn out horrible but it is not consistent all the way across as I would like, and more detailed logos at this size would show more blemishes from doing it this way. Then I went on to break up my engraving space in to focal sections that I found to be good for this piece with the contour that is has. As you can see by the circular sections around the logo. My idea here was to break apart the logo in to these four sections and attempt to engrave them one section at a time while adjusting the laser head to the appropriate focal height in between sections (Not sure if this would work either). The problem that I ran in to here was after importing the sections of the logo in to EzCad they would not hatch properly since the lines in the logo were broke apart, even after regrouping the sections back into a single object it still would not recognize the lines as being conjoined. That leads me to my question about lenses, I do not know much about them but I am willing to learn.

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This is what I am working with for a contour. There is about a 6mm drop from the center point to each edge of the engraving. Which is right on point with my over all change in focal height when I created the circular sections on the cover. I have read that there are lenses that can increase the over all engraving area. My question is will the lenses also increase the depth of field or focal depth that you can engrave within the central portion of the engravable area. So if I got a lens that could increase the engravable area to lets say 11" square then is it possible that within the 4.75" that this logo takes up could it handle a drop of 6mm in contour?

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Here are images of the lens that I have now, like I said I don't know a whole lot about lenses and how the work so any advice and tips are much appreciated.

[Kev Williams]

That 160 lens as printed on the lens is around a 110mm lens 'as advertised', which is the approx working area- roughly a 4" square... that's a great lens for high detail in small working areas, but definitely not conducive to varying focus distances. My laser came with a 150mm (210mm as printed on the lens) which gives me around 6.2" of workspace-- I bought a 220mm (310 printed on the lens, I think) from an ebay seller for $100, and I've been quite happy with it, I can actually engrave a 12" area diagonally with the thing. Also, the longer path gives you more leeway in the focus distance-- but not a whole lot. You're 'drop' on that cover is somewhere between 3/16" and 1/4", so at best you're having to split the focus at around .1", or approx 2.3mm-- that may be a bit tough. As for manually focusing on the fly, that too is best done with a longer lens, because as you move the focus point, you're also changing the dimensions of the engraving; the farther from the lens the work gets, the larger the engraving gets... so what was engraved at first focus will likely have a shadowed engraving as your focus distance changes...

Also note, the longer the lens, the less power density of the beam. With my lens, worst case is typically having to engrave a bit slower...

Short version, engraving variable height items is going to be tricky with a static-focus machine. Active-focus machines (not sure the correct terminology ;)) are available that can focus on odd shaped items. Once you get familiar with the machine you have, you can decide if there may be enough money to be made to cover the cost of machine that will engrave your odd parts :)

[Trey Tull]

What about one of the 3d fibers?

[Kev Williams]

that's what I meant by 'active focus', they're referred to as '3D' machines?

[Jeff Watkins]

Check out the Depth of field calculator below. Just like in photography, the larger focal length the greater depth of field. My f290 (200x200 work area) lens gives about .25 inch depth of field. The f160 is a razor thin dof but great for deep engraving or light cutting.

There are several calculators like this but good is a simple one that gives everything you'll need. If you don't know your beam diameter (coming out of the fiber source) just used the default.

https://www.controllaser.com/resourc...us-calculator/

[Kev Williams]

Wouldn't it be nice if there were some simple lens 'filters' that would compensate for convex or concave objects. I mean, there's several lenses within a fiber lens, and part of their job is to compensate for the longer beam length at the outer edges- My big lens spans over 10" across, and the straight-down-from-the-center focused beam-path length is almost exactly 14"... however, the focused beam-path length from the center of the lens to 5" away from center is 14.8"-- That's quite a difference, nearly 3x the depth of field distance! If you could just add or subtract the compensation with a simple lens adapter, doing those derby covers would be pretty much automatic! ;)

[Bill George]

I can't help but believe that someone hasn't added a stepper motor and a automatic adjustable height control to keep a laser in focus over a object that varies in height. Even using off the shelf components for say $500 or less?

[Gary Hair]

I can't help but believe that someone hasn't added a stepper motor and a automatic adjustable height control to keep a laser in focus over a object that varies in height. Even using off the shelf components for say $500 or less?

There is way more to it than just focusing the beam by raising or lowering the bead (or the galvo head). Unless you are lasering a single spot the size of the beam itself, directly beneath the lens, the beam exits the lens at an angle and you would have to compensate for that angle every time you increase or decrease the distance from the part to the lens. You might be able to find hardware to do this for relatively nothing, but finding someone to create the software would cost a fortune, if you could even find someone with that ability.

[Kev Williams]

"3D dynamic focusing" I guess is one term- This machine would definitely do curved derby covers will little problem-


https://www.youtube.com/watch?v=HluJk-5mF1A


-- what I don't know, is if the focusing is software based (part dims entered by the user) or hardware based (fully automatic focusing)..? Seems software based, which is fine, but full-auto focus tracking via sonar or infrared (?) would be the bomb! :D

[Mike Null]

This company in Japan builds lasers and also components which will do what you want. Bring $$$$ Look at their MD-X series.

www.keyence.com

[Kev Williams]

The 3-axis 355nm UV laser on their website looks interesting--

[Matt McCoy]

Not a solution, but somewhere in the ballpark:

https://www.lightobject.net/autofocusoptin?__s=sjsechktenmepzh4gegq

[Bill George]

I know its possible because years ago when I had my PlasmaCAM it had THC that followed the height of the metal being cut. At the time I had a Hypertherm 380 and it and other like it had a circuit that measured in millivolts the amount of current being used in the cut and correlated it back to torch height somehow. For the most part it worked.

[James Rish]

Thanks everyone for the tips and good information. Yea it would would be nice if there was a quick cost effective fix to this.

[James Rish]

Jeff, you say that with the f290 you get about .25" depth of field. I'm guessing that as you move from your center point that number will decrease. Have you played with it to see what kind of contour it can handle?Or do you know until about what diameter away from the center point it can hold that kind of depth of field.

Thanks

[Jeff Watkins]

Hi James, you know I haven't tested the outer limits of it. I have done >2in logos/lettering on a couple tumblers. I used the Project Mark to keep it from stretching the sides out. When I did my tumbler test I ran a .25in by 3.5in wide hatch to see where the engraving stopped. I figured that I could comfortably do a little over 2in wide logo on a 30oz tumbler.

For your Derby Cover I would form a piece of foil over it and then use a sharpie to black it out. Try a low power and high speed pass and see what the extents of your lens is. Maybe try focused on the center then drop it a little so the center is still clearing along with the edges of your logo. You'll get to a point that focus is too low and the center will start suffering.

[Kev Williams]

nothing like real world testing :)
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this was simple enough-
The lines are 6.1" long, about the max for my 150 lens. This is just a simple ramp test, and not only does it show the- I'll call it "usable depth of field", it's a great way to find your dead-on focus point...

I shimmed the right side of the plate right at the edge of the lines, the left side is flat on the table.
top lines are shimmed 3/8", middle are 1/4", bottom are 1/8".
I focused as close as I could to the actual plate center.
I did a cross hatch at 45 and 135 degrees, .08mm spacing-
the top of each pair was run at 100% power,
the bottom of each pair was run at 40% power
speed 1500, freq 35.

While there IS quite a bit of focusing leeway- I was surprised the 1/4" version engraved edge to edge at 100 power- the low power lines show that, even with only an 1/8" rise, there's substantial power loss at the far edges. Since I focused in the middle, this means the drastic losses begin at less than .060" from the prime focus point, which isn't a whole lot of free play...