I bought a APC 4.0", 101.6mm in September and have just had time to install and test.
Problem? It will engrave but won’t cut. I used variables of focus length from substrate as well as different speeds and power. I have always cut with one pass. This lens makes no difference between one or many passes, the engrave is the same depth. I have it set for “Line”, it only engraves.
Replaced with my 2.5" lens using my original settings, I have perfect cut.
The lens is glued into the tube from APC and obviously has a lens contained but I have no idea what value lens is.
I haven’t contacted the company as yet. Wanted to see if someone has an idea.
Ferg
I have contacted APC, haven’t gotten a coherent answer from them yet. Lol
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APC is sending me a new unit. I think the nozzle end of the tube has been glued into the extension tube unintentionally. I tried two wrenches, the two parts will not seperate.
A 4" lens has twice the best focal spot size of a 2", so energy density is reduced by a factor of 4. That’s due to a limitation of physics of a diffraction-limited system, which it should be.
The benefit is the expansion of the spot diameter when moving away from the focal point is reduced by a factor of 2. You need to know the beam diameter entering the lens to determine more details there.
However, this is not helpful in most cases, as you’d just focus on the top of the material.
The ONE case where I know to recommend 4" lenses is for foam.
Reason is complicated- lasers actually only cut the first 2mm or so, then convert to a thermal gas lance to cut deeper. The fact that the beam’s spot doesn’t expand as much by the bottom of 1/4" plywood is irrelevant because the beam is gone in that first little bit.
Foam is uniquely different in that it recedes and usually will not support a tight channel to contain the thermal lance. The laser goes much further into the material and expands too much. I have a very powerful laser that does 1/2" wood easily, but 1/2" regular crosslinked PE foam required surprisingly slow speeds to cut and the edge was not very straight. With no channel to form and contain the lance, the beam never converts and is expanding too much by the bottom of the foam.
In that one case- foam- the 4" lens will help enough over a certain depth that the worse focal spot size is worth it.
Is your cone getting hot? The one other thing that can cause loss of performance is the beam clipping on the cone, which is more likely with a longer lens since usually the cone is placed further out with the same size orifice. Angular errors create proportionately worse lateral offset error of the orifice so it’s easier to accidentally clip it.
In all cases of clipping, the AA cone tip will get notably warmer, so fire it a few seconds- like 5 sec is plenty- and touch it immediately after stopping. If the beam isn’t clipping it shouldn’t have a noticeable temp rise.
Thank you and I checked the cone to see if it was heating up. Warm but did not get hot.
Sounds like some clipping may be occurring. And on a 60W, clipping say 25% of your power will not be as obvious as clipping 25% of the power on a 150W laser. You may need to play with alignment to get all the beam out.
But, fundamentally, I wouldn’t actually expect better cutting from the 4" on plywood and acrylic. I’d expect worse. 4" lens helps on foam and other materials which cannot form a channel to contain the lance.
Danny,
I have had time to use and adjust the 4" lens with great results on 3mm plywood with mdf core. I do a ramp test with the high end of the ramp about 3 1/2" off laser bed. I am getting a fine line from 15mm to 18mm. I like to set the FL near to 16mm maybe a little more. Warped material is always a problem, have been adjusting the setting over the section of ply that is tight to laser bed. Purposely used material that may have as much as 2mm “hump” in the middle. I am getting excellent results over the entire surface. Running two exhaust fans with between 35 and 40psi air assist. Main fan is a 16" spray booth unit with an axial 16" fan drawing from the laser cabinet.
BTW: I fine tuned the M2 and M3 to get the beam straight through nozzle.