Depth of field issue

[Aaron Reimer]

I was working on a customer's paintball marker the other day, and I seem to have come across one that is impossible to get the full design into a field of focus that will burn the anodizing. Is there another type of lens that I can get that will keep the beam coherent for a longer distance? I'm using a cheap chinese 40w CO2 engraver. As you can see from the picture, the top ridges of the milling are rising out of the field of focus and the frame is too low to get a good burn. Any help would be appreciated. Just to clarify, I do not have a motorized table, but a ghetto tray that I put cd cases underneath to position the height. Most of my work so far has remained largely in focus, but this was way out.

[Joe Pelonio]

I've done a few jobs with irregular shapes where I ran a part at a time, stopping to refocus, but nothing like that with multiple compound curves.
It sounds like a good opportunity for the laser manufacturers to invent an autofocus tool that changes the focus as it goes based on bouncing a beam back to determine the distance. I'll be anxious to see if anyone has any ideas.

[Aaron Reimer]

The picture is a little deceptive too... there's at least 0.5" difference between the tallest point on the milling and the grip frame. Unfortunately I don't have it to measure anymore as it went out in the mail today. And yeah, a machine with an automatic refocusing as it went up and down around the curves on a gun would make my life hugely easier, as about half my business is on paintball guns. Flipside is that my laser only cost about $1500 and I'm sure that something equipped like that would have me in debt until 2020.

[Mike Mackenzie]

The Universal systems can change focus by color already. If i change the color of my graphic to eight different colors I can change the focus on the fly.

The other option to try is a 2.5 inch focus lens or even larger. The larger the focus distance the larger the depth of field however you also will lose some detail as your spot size gets larger.

[Michael Kowalczyk]

See if you can get a 4" lens for your laser. Mine was under $400.00 but it opened up a lot of doors and pens. I can laser 2 lines on a pen with good results.

Just get a 1/2" dowel from one of your local suppliers to practice.
Make a jig to hold it in place. Be sure to make a notch for the pen clip for when you feel confident enough to do the real thing.

If you plan on doing a lot of the paint ball stuff or see opportunity knocking with the many possibilities a greater depth of field will allow you to laser with great results, maybe you can justify it.

After having my Trotec for over 5 years, and keeping current with the software, I just found out that I have these little things called "Markers" that I can place anywhere on the table and save it as a template. I place the markers to correspond with my jig/fixture and am able to drag my text over and it will either snap left, right or center. What a time saver and it is extremely accurate. By making a jig/fixture with multiple slots for the pens or other items and then putting corresponding markers on the template, I can engrave several pens at the same time as long as they are fairly close in diameter and species. (Acrylics and Corian pens are a different beast but can be done.) I also found this feature that allows me to run the laser to trace out the outline of the file to quickly check if it is centered correctly without the laser energizing.

Sorry if I rambled on but just like Pringles, "once you pop the top, you just can't stop" or something like that.

Hope something I wrote helps and ...

[Aaron Reimer]

Hey, that's some great information. I'll have to take a look at trying to find a 4" lens. As for my software, Moshidraw just doesn't have much to work with. I can't even pause and pick up in the middle of a job; if I stop it, it goes back to the beginning.

[Scott Shepherd]

You can also try to focus a little deeper into the work, trying to split the difference some. That's way deep for it to work, but you can probably take it down 1/8" or so and get a little more. I'd try it before I did anything that mattered.

[Peck Sidara]

Aaron,

A longer focal lens would help, as would focusing in the middle of the high and low points. Another option would be to do a 2nd or 3rd pass (be cautious as it may cause the image to lose some of it's detail/resolution).

[Aaron Reimer]

Right... so I've basically got this:

on my laser. Would I need a different attachment, or can I just drop a different lens into it?

[Scott Shepherd]

Not sure, but it looks like that photo shows the wrong end of what we'd need to see. That's the mirror end, I think.

Go to the people you got it from and see if they offer any different lens. You'd want something larger than what you have.

[Dave Johnson29]

Right... so I've basically got this:
on my laser. Would I need a different attachment, or can I just drop a different lens into it?

Aaron,

Tip it up the other way and take another pic for us. That ring at the bottom should screws out. It will then have a plastic washer, the lens and another plastic washer. Measure the diameter of the lens.

Get a longer focus lens as Mike suggests. You need to find the focus you have so when the thing is running try and pause it and measure from the bottom of that lens holder to the thing you are marking. My guess is it will be around 1-3/4" which would make the focus 2" with the lens about 1/4" up inside the holder.

Go to someone like http://www.laserresearch.net/ and get a longer focus ZnSe lens in the correct diameter. Your laser probably has a Plano Convex type so a 3" focus will probably give you a depth range of about 1/2" with tight focus.

When you first take the old lens out, use a tissue to hold it and rub it gently between your finger and thumb. One side will be convex and the other concave or flat. Make sure you put the new one in the same way up.

Oh, one other thing, "coherent" is what the beam is before it gets to the focusing lens. After the lens it is convergant.