Lens Focal Points

[Chase Mueller]

If my understanding is correct, different lenses have at least slightly different focal points, right? The nature of my job has me putting logos on 1.5" diameter AA pipe, and more often than not, I get the usual complaint of "The client wants it bigger". After I fight the urge to reply with "That's what she said." (I watch The Office too much :p), I have to explain that I really only have about .56" at most to work with before I hit what I call the "Drop-off point", so if they want it bigger, they need to provide a different logo. I'd like to see if I can change that and am wondering if a different lens would increase my focal point in any noticeable way to try to compensate for the drop off point. I believe I have the standard 2.5mm lens.


So A: Am I right in thinking a different lens would give me a wee bit larger area to work with?
And B: Would I need to change the carriage head or is it as simple as order a new lens and just swap it out?

All I'm really trying to accomplish is to make the customers a little happier by showing them we care and to appease the sales staff. Plus showing the higher ups I care enough about my job to even try to offer a solution to this minor inconvenience can't hurt.. right?

[Mike Null]

It seems to me that the easiest way to give your customer a quality engraving is to get a rotary device. I doubt that a lens change will produce results that you like.

[Chase Mueller]

It seems to me that the easiest way to give your customer a quality engraving is to get a rotary device. I doubt that a lens change will produce results that you like.

I would love to add a rotary, but unfortunately, it's production and I have to run 11 at a time, so no choice there.
I'm not expecting a huge difference, just something to appease people at least a little bit. If it's not possible or even worth it, oh well. Just figured I'd at least give it the ol' college try.

[Dave Sheldrake]

What effective diameter is the part?

[Chase Mueller]

What effective diameter is the part?

If you're asking what engraves evenly, it would be the top surface of the pipe that I'm marking, and can only mark about .56" of it at max, and that's seriously pushing it. Deactivated door locks so we can slide our jig through the machine completely, and have to raise it with cardboard and what I assume are rubber gaskets. Definitely ain't perfect, or pretty, but it works acceptably enough I suppose.

[Kev Williams]

What is AA pipe? As in, are you using Cermark or not? (I'm assuming Cermark, but shouldn't matter that much actually ;))

Correct me if I'm wrong-- You're going around the circumference of a 1.5" diameter cylinder, but only spanning .56" across?
Assuming this is correct, I drew this up:
382616
At .56 across a 1.5" diameter, your total focal range is only .054"-- even with a 2" lens you should be able to expand on that- If you extend the length to .675", your focal range is .08". If you focus at top dead center then raise the table .04" you'll be dead even within the range. The pair of LOGOLOGO's show the difference in size, it's fairly substantial!

If you can't do this with a 2" lens, a 2-1/2" or 3" should handle the .675" span easily. You may have to slow the machine down a bit to compensate for power loss due to the longer lens, but it should be very doable. And I think it may be doable with a 2" lens, you just have to be sure to dial in the focus :)

[Chase Mueller]

What is AA pipe? As in, are you using Cermark or not? (I'm assuming Cermark, but shouldn't matter that much actually ;))

Correct me if I'm wrong-- You're going around the circumference of a 1.5" diameter cylinder, but only spanning .56" across?
Assuming this is correct, I drew this up:
382616
At .56 across a 1.5" diameter, your total focal range is only .054"-- even with a 2" lens you should be able to expand on that- If you extend the length to .675", your focal range is .08". If you focus at top dead center then raise the table .04" you'll be dead even within the range. The pair of LOGOLOGO's show the difference in size, it's fairly substantial!

If you can't do this with a 2" lens, a 2-1/2" or 3" should handle the .675" span easily. You may have to slow the machine down a bit to compensate for power loss due to the longer lens, but it should be very doable. And I think it may be doable with a 2" lens, you just have to be sure to dial in the focus :)

AA= Anodized Aluminum. I should have clarified, that's on me. No cermark.

What you drew up is spot on yes. I cant raise the table any, we don't use it. We have a sliding rack that goes through the machine, and if I raise it any more, the middle won't mark, and I assume it's because it gets too high for the beam to fully form its hourglass shape before it hits the pipe. But that's just a guess, so if I'm wrong please say so LOL. I need to verify that it is, in fact, the 2.5 that came with it. But I'm almost certain it is.

[Kev Williams]

you should ramp-test the lens and find it's true focal point...

If you're not familiar with ramp testing, what works for me is to take some anodized aluminum or laser trophy metal, about 8" long is fine, 1/4" to whatever width is handy- set the left edge on the table and the right edge put a shim under it, 1/4" to 3/8" or so to make a slight uphill ramp. Set the lens to focus approx in the middle of the ramp- Now set up to run a vector line across the length of the ramp, speed around 30% or so, and start with power very low. Run the line across the ramp... Ideally, you want to end up with just a speck of a line to a 1/2" long line ONLY that engraves- if the line is much longer than 1/2", reduce the power and/or the speed to reduce the length it engraves-- When satisfied, you now know the center of that line is your lens's prime focus point. Now place your lens head dead center within the line, and cut a piece of scrap plastic or wood or whatever that fits perfectly between the bottom of the lens housing the metal- it's now your new focus tool. Then measure it, write it's length down somewhere, and make copies of it! :)

Once you do that, if there's any way you can adjust the focus to around minus-.030" (or .8mm) from the TDC of the tube, you may find you'll have a bit more variance :)

[Chase Mueller]

Thanks Kev I'll give that a go!