Hi There,
Maybe I’m being a little naive here but if I select from, Parameters, Wood 3mm Cutting, would you expect the laser to cut through 3 mm of wood in one go or would it need a number of executions in order to complete the cut. Assuming I have not altered any of the other machine settings.
Cross your fingers… once. BUT, depends upon optical alignment, condition of laser tube (deteriorateS just sitting there… slowly, but they all do), wood hardness/gluing products, humidity of wood, … you get the idea. In general, if you have a fresh tube, perfect optics, and use select wood/products their proposed settings are often a little too powerful and I find I need to dial it back, sometimes a surprising amount. Let anything be off and you’ll have to up the power, lower the speed or some combination with perhaps a second/third round. Two CAUTIONS: 1. Their defaults allow for max 60% power… I’m advised max laser tube life and longest “good” cutting occurs if you never exceed 50% power. I think they are right. Not that 60% won’t last long enough but tubes are expensive. 2. I always throw in a couple extra layers before my project with random boxes, ellipses, etc ., with a few different settings to see if I get the desired results before it turns to my project. I can pause/abort if my couple cutouts aren’t giving me good results. I leave those layers in for future uses as there is surprising variance from identical products. That works only if you have extra boarder material but it sure helps to have some practice results on the exact same material as your production run. That is more important if cutting than engraving. 3. (I know, I said “two”… live with it) I’ve found often that 2 executions at 30% power and 20 mms is better than one 50% power at 10 mms (example’s here) from that standpoint of less charring, more certain cuts, etc. So, take their presets as serving suggestions, get a small notebook, and experiment and record your results.
Thanks Merge,
As I understand it then the Parameter setting should work, on a good day with the wind behind you sort of thing.
If they don’t then look at other factors that control the quality of the operation, like mirrors etc.
I’ve noticed on most test runs using the Parameter settings that the actual burn path is not complete so I take it that the mirrors might be off, I have cleaned them. So I’ll have to get the spanners out I think?
Jomacot.
Works well for me, but as Merge says, it does depend heavily on the wood. I find that plywood is very unpredictable but, the more you pay, the more likely it is to cut well. The cheaper ply seems to have huge glue pockets inside, and the laser just doesn’t cut it. I find out after making five or six passes, then giving up and breaking open the charred mess to see what’s inside. The barrier is so impenetrable that the wood can be heavily charred above, yet untouched below!
When aligning the optics… I do it slightly different. I thought it would help to “level” the tube (a step they wait until you get to the third mirror) early… I’ve learned you can’t move that up and do it earlier unless you are already close to a good alignment. When I check mirrors 2 and 3 I first take a shot at the tape in the first position (like for mirror 2, at position A). Before I put the tape on the opening before the mirror I mark it as “A1” (for my first attempt at “A”. I also use a pencil and put write on a crosshair that I try to tape pretty close to the middle of the hole. Precision of the cross hair is not critical but you want a reference later for when you compare the hole to where it would have been desirable. This tape I place with the long edge of the tape vertically with respect to the machine. After taking the pulse at “A” I leave that tape on and put another tape marked “C1” (for my first shot/attempt at position C) again with a hand drawn cross hair approximately the horizontal and vertical centerline. This tape I place with the long edge horizontally to the machine. I then take the pulse at position C. Now I have an overlapping set of tapes where I can easily distinguish the shot at position A from the shot at position C and by marking them A1 and C1, A2 and C2, etc., I can see my progress (as I remove both tapes at once and tape them to the bottom of the cover glass. I’ve found that after a couple or three attempts I draw a freehand crosshair that is pretty straight/90 degrees and I am able to place it very close to the center of the portal to the mirror. Having the line of a half cozen or even more tape pairs at position A, C MidLeft, MidRight, MidMid (or however you want to label them) is very helpful. Moreover, you can observe the “type” of the hole at the different positions. Twice as I’ve gone through this process I would find I started with a really nice round hole, that as I continued and got further away from the laser tube would become an oval and even resolve into 3 smaller holes vice one large hole. (That is a good indication your tube is almost dead). If you’ve aligned optics 6 or more months ago, the current recommended process is somewhat different and probably better. I’ve also done my best to try and have ALL the holes light up somewhat close to the centerline of the mirror and just slightly above the vertical center. If I can get very close to identical holes at A, C, MidLeft, MidRight, and MidMid I feel better than if my A is a little low/left, the C is high and right, the MidMid is somewhere in between but the MidRight is different from everything before it. It takes a little longer but I’m much, much happier with what appears to be a much more consistent burn/results. And, while you/we are at it… do NOT forget to ensure that your honeycomb table is level. A 3mm difference in focal length from one part of a burn to another will really muddy up your results. If you are not level you have to remove the rubberized timing belt and adjust each of the four corner tray supports. That is also tedious, but worth it.
Now, what I don’t know but intend to experiment with someday is how does one go about cutting a 5mm, an 8mm, and a 10/12mm thick workpiece? The ideal focal length is 12mm from the bottom of the focus lense housing to the workpiece. But what if I’m cutting an 8mm workpiece and it take 2 or 3 passes? Should I raise the table the 2-4mm after each pass to keep the ? Anyone have experience with this?
In theory, cutting a thicker workpiece requires a lens with a longer focal length so you can keep the beam relatively narrow over a greater vertical distance. In theory. In practice, you could raise the bed slightly for subsequent passes, but you’ll have to allow for some the outer edges of the beam hitting the uncut upper surface. Increasing the focal length helps to reduce this effect, but I have an inkling — i.e. I haven’t had this confirmed, nor taken the time to calculate it myself — that the beam waist is a little wider with the longer lenses. That means a slightly thicker kerf, and slightly lower power density so you might need to go a little slower.
Hi Merge,
That’s a lot to take in so will need to read and inwardly digest and have a check later.
One thing I forgot to ask. When I cleaned the mirrors I remover the focus lens as per instructions but neglected to see which way up it was placed in the holder. Concave up or down?
Interesting PT… I’ll also investigate someday. Once the laser went through the focusing lens I simply assumed it was of constant width for 20mm, 30mm or more. I’ll try your thinking out and let you guys know what I find.
The beam’s longitudinal profile is (ideally) hyperboloidal after it passes through the lens. See here: https://en.wikipedia.org/wiki/Gaussian_beam
There’s a diagram half-way down, captioned “Gaussian beam width”.
If you don’t get much fun from that sort of article, think of the beam (after the lens) as being conical. As you may have have noticed from the burn profiles while aligning the mirrors, the beam’s cross-section isn’t quite symmetric (i.e. it doesn’t have the same Gaussian intensity distribution across all diameters) so all this has to be taken with a grain of salt in any case. At the least, my beam is definitely not Gaussian.
Jomacot: yes, it does make a difference which way you set the lens. The criterion here is really the focussing gauge block which has been predetermined by Flux. Probably best to try the lens each way and see which burns the smaller, more concentrated dot.
Some easier-to-interpret diagrams here, showing how the beam is shaped by lenses: https://www.thorlabs.com/tutorials.cfm?tabID=BA49B425-F85B-4549-8C1A-F111DDBB9099
PT… thank you… seriously, that helps. I believe we have a “Plano-Convex Lenses” although I did not take the time to study what I believed was the flat side of the lens. Just for grins… I spent 15 months receiving, putting together, working with Flux to run down 5 major issues that took months (sometimes my fault) to troubleshoot and I’m now on my third tube; replaced mother and daughter board; circuit patch panel in the back; 4 wiring bundles/cable sets including the camera cable (twice0; camera; etc. Flux provided all the replacement parts (although I’ve bought a 4th tube as my ready spare). I “believe” (fingers crossed) I finally have a machine that lives up to its billing. I’ve done a few things that may be worth consideration. First, if you’re in North America and buying tubes/other BeamBox (BB) parts use the US source and not from Asia… cheaper, faster, no customs wrangling. Second, I bought (at my expense) a replacement focusing lens (a plano-convex) to replace the original which appeared “mottled” to me. I was told it was OK, no reason to insist it was not, but I’m really happy with the small beam I currently get and never had in the previous 15 months. They are cheap. Third, I also bought a new honeycomb table since the one that came with the machine was pretty beat up… as a function of all the maintenance I subjected it to. It also had gotten quite black/dirty with all my testing/practicing and i didn’t think it was necessarily dissipating the heat as much as I would like. Rather expensive. I intent to take the old one out and pressure wash it, soak it in detergent (if necessary), and determine the degree of flatness across every dimension. I’m glad to have this spare. Fifth, I almost always place 3 or more approx 3/32" to 1/8" wood pieces under my workpiece under the theory that the little bit of distance between the workpiece and the honeycomb tray MAY keep the workpiece and underside of the workpiece cooler/less charring. Somewhere else I wrote about indicators that I had cut through a workpiece (as opposed to a deep embossing) (smoke/soot traveling across the top of the workpiece… engraving; smoke/soot traveling under the workpiece implies I have cut through the material.
Bit confused PT. Looking at the Thorlabs document I would say it would have to have the concave side down.
Anyway, I’ve checked the mirror alignment and the beam is hitting the second mirror almost on the edge. and testing it with the carriage at the rear and front shows the dots are coincident. Not sure how I can bring the dot to the centre of the mirror as I cannot swing the first mirror round to move the dot as the beam is obviously parallel with the guide rails.
When checking the third mirror the dot is again almost on the extreme left looking into the mirror but I can correct that by moving the whole print head to towards the rear of the Beamo.
I’ve not been able to test the adjustments as had other work to do, not related to this task.
Page 56 of the BeamBox User Manual says, at the bottom in reference to the focusing lens… orange acrylic lens: “ When putting back the lens the curved side should face up and the flat side should face down.“ By “curved side” they mean the convex (bubbles out) side… there is no convex side to the focusing lens. If I’m wrong… please correct me.
Hi Merge,
Well I’ve taken out the lens again and carefully laid a straight edge across both faces and as far as I can tell the lens has both a convex and concave surface, admittedly the deviation is very small, but I am certain that is the case.
So referring to the Thorlab info I would say it’s a Positive Meniscus lens so my guess would be that concave side would be at the bottom, unless I have misunderstood things.
Page 56 in my manual refers to the water in the laser tube. The only reference I have to the lens is on page 54 and is related to cleaning, but there is no reference to which way up it is to be replaced in the lens housing.
I think you have a Beambox, mine is a Beamo, so maybe that is why there is a difference in the manuals?
Fair enough. I’m not able to discern any concaveness (is that a word?) in any of the three focusing lenses I have. Yet, I’ve seen several references like section 3 at https://lasergods.com/laser-lenses-optics-and-focus/ indicating there is a convex side and a “flat” side. My physics optics class from 44 years ago led me to believe that making one side convex, while the other side concave, doubled the work instead of simply grinding/polishing an additional curve into the convex side… at least for the type of focusing the laser requires. Moreover, grinding/polishing the convex side is easier/cheaper than concave work. All that said… put the side that bumps out (convex) “up“ in the lens holder. Think of light “waves” coming down… the outer edge of the wave will hit the higher middle of the lens first and bend the rest of the wave towards the center of the lens (or, in our case, towards the focus). I had problem trying to discern a difference between the convex (subtle) and concave or flat side so I also wanted to share a quick way to tell the difference by laying the lens on a flat surface and see which side would wobble when poked with the finger (that’s a technical, industry term and technique); that would be your convex side. Somewhere I thought I saw someone saying to INCORRECTLY to put the concave (or flat) side up. I simply wanted to correct that and help get the orientation correctly. Sorry about “p 56” reference… that was to the Beambox manual found at:
https://cdn.webshopapp.com/shops/290919/files/329306044/beambox-manual.pdf
Plano-convex lenses actually produce a bit less geometric aberration than symmetric convexo-convex lenses do. It takes a bit of effort to demonstrate this; the thin-lens approximation erases the difference.
It’s been a fair while since I took optics, too. I think I remember that the convex side faces into the parallel beam, and the flat side goes with the conical beam; this way both surfaces contribute to the refraction. Not sure whether my memory should be trusted, though.
If you’re worried (as you should be) about damaging the lens surface by feeling or rocking to find the convex side, try looking at reflections in it. For the focal length used in the Beambox (about 5cm) my gut intuition has me expecting reflections off the convex side to look noticeably bigger than off the planar side.