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HELP! I'm at a loss!

Its like my laser runs out of steam… 

I did about 5 x 3cm circle tests on a new piece of 3mm bamboo ply - found out the following settings were the best: 4 passes, 240mm, 25.5 height (as i now use a bed of nails instead of the silicone mat). The circle cut really well and slid out with only one tiny piece catching. So I thought this was the best setting to follow. I then tried those settings on a bigger scale - just to cut lots of shapes. But i made the mistake of moving my piece of ply after the job without checking first… NOTHING had cut through (I pushed some through and it was a mess!). I did the job again with fewer shapes and carefully checked to see if it needed more passes when the job was done. After the first 4 at 240mm, I did 2 more at 220 and then one last one at 200… 7 passes and it barely cut through.

Why when doing a bigger job do the settings differ to my test? Same piece of ply. 

*I don’t think my air assist is working properly - could this be causing such extreme results? 

I’ll attach some pics. Thanks in advance for your help! :) 

 

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Hi Katherine,

From my experience with 3mm ply, I have an “overkill”-setting (something like 3-passes at 180mm/min), and a “should cut it most of time”-setting (2 passes, at 240mm/min), and you may notice there’s a big gap in between. So there is certainly some variance, but not as extreme as yours.

Anyway, my first guess would be your bed of nails. Are you sure that it is completely flat? A slope would definitely mess up the laser focus.

Secondly, if the bed is correct, then the plywood itself may be bent/bowed. In my experience, it is very hard to find a 3mm 30x30cm piece that is completely flat. If you lie the plywood on a flat surface, does it lie flush on all side? It’s very common for me to have one side raised by 1mm. Was the test piece done on a piece of plywood that is slightly raised?

 

 

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Hey Daniel,

Thanks for your reply. I’m pretty sure my nail bed is ok, as a good portion of the nails are straight.

And from working with this piece of bamboo it seems as if it holds its shape a lot better than my normal ply (which bows as the job progresses).

Another thing that confuses the situation is that I’ve successfully done a few jobs on my nail bed using the normal ply (not bamboo) with settings like 3 passes at 180… maybe I should just try 4 passes at 180 on the bamboo and see if that works - maybe my ‘blitz/overkill’ setting - but I need something!!

Oh and all my tests were done on the same piece of bamboo ply.

Can I ask, what do you do to keep your ply from bowing mid job?

Thanks :slight_smile:

Hi Katherine,

Not sure if I can help, may be a task for Domenic as it could be any number of things.

As Daniel said the cutting can be affected if the height isn’t just right. I often use small but dense objects to hold my plywood in place and flat. (e.g. marble noughts and crosses)

Also you said you have been cutting MDF, Domenic recently posted about the sideaffects of cutting MDF and the cleaning precedure required to bring the lens back to full health. Perhaps use a mirror to check your lens for debris. But don’t try cleaning it without the proper tools.

Also humidity can greatly affect cutting settings however it is unlikely to be that significant particularly in a short period of time.

If you are concerned the laser is failing, or cable running to the laser is faulty, a good way to test it is by running the calibration gcode on a piece of paper and on the silicon mats. If the results have changed significantly from last time there could be an issue and it is best to lodge a support ticket. 

Also a firmware update may help reset the air-assit if you think that is the issue. With regard to the air assit, ensure it isn’t blocking any laser light. I have had issues in the past when I accidentally jogged the laser head too far down. When I homed it again the air assit nozzle sprang back but not far enough and blocked part of the laser light reducing performance. Now I just have the nozzle seated as far back as possible.

Hope this helps a bit,

Jeremy

Hi Katherine,

I second what Jeremy suggested about retesting the machine, and I also think that this lens cleaning tool will be a must have. 

I don’t weight down my plywood/MDF. For MDF, I have plenty of them cut into 30x30cm pieces and I stack them up (must be about 10 kgs) and when I’m doing a cut, I pick one from the bottom, so it’s pretty flat. However, as you may have noticed, even a flat piece may start bowing as you heat up the sheet.

I noticed that in your pic, the problematic cuts are the ones near the large teardrop shapes, whereas the circles on the corner seems fine. If I had to cut something like that, I would probably do the two large shapes with an extra pass, then break the plywood to two pieces and cut the smaller circles. Having two smaller pieces means it’s less likely for either one to be bowed. 

By the way, what is your pass height setting? I cut 4mm ply in 5 passes at 180mm/sec (that’s actually an overkill) with 0.5mm pass height. It’s just another setting I played around with.

G’day Katherine,

 

I can only echo what the others have said. I’ve been cutting ply for 2 years with the Emblaser 1 before I got the Emblaser 2 and I’ve found the overwhelming causes of grief are bowed ply (even 1 mm of bowing, which can be unoticeable when you put the ply down on the laser bed can cause issues). The Emblaser 1 didn’t have the silicone mats, so the bowing was more apparent. I used to tape the ply down on the  metal base, but it would still pop up and cause issues. Its very frustrating because you don’t know if its cut through or not until you pick it up and turn it over, and if it isn’t, you can’t put it back down in the same place to give it another go! To be safe, I always up the passes and/or  reduce the speed when using doubtful ply.

To minimise the warping issue I cut the ply down to the minimum size needed for the job, and always do a small test cut in the bottom corner to make sure that it cuts cleanly.

The second issue is the quality of the ply. Poor quality ply like Bunnings has very variable qualities, even within the one sheet. The glue and the wood aren’t necessarily uniform across a sheet which can cause issues  This can affect both cutting, and rastering a surface image. To illustrate this, here are two raster images, both done on opposite corners of a 900 by 1200mm Bunnings ply sheet, using the same laser settings and they came out quite differently. (I’m not sure what the white bits are on the left hand image, they aren’t there in teh actual item - I think my camera went  a bit wierd!)

Thanks guys for your replies. 

I read Domenic’s post about MDF after I had made my bed of nails out of it! Dammit. But I haven’t used MDF for cutting yet - just nail bed, so I’m not sure of the impact. Good idea about doing another calibration with the silicone mats. The first time i did it I’m sure 1.5mm was the best result, but when I’ve added this to the height of my new nail bed it hasn’t been the best result - which has totally confused me!! Its all looking like the height is the issue, and whether there is a slight slope in my bed or maybe the ruler I have been using is out slightly. 

The bamboo ply I’m using is from Plyco, so I’d hope its good quality.

Thanks heaps for the tip on file layout - the reason i did it this way was to eliminate wastage, but if its adding to the problem, I’ll separate for sure. 

So, back to the drawing board this morning. I’ll remeasure everything and retest & recalibrate. I’ll also look into a firmware update for my air assist. And hopefully I’ll be back with some good news! :slight_smile: Thanks again. 

Ok, so I carefully measured different points around my nail bed and the ply is sitting unevenly - but I’m not sure whether this is from the nails being uneven or a slight bend in the ply or both. The bamboo ply is a lot more rigid than a normal ply and it doesn’t seem to ‘sink’ into any dips if you know what I mean. And the unevenness is only about 1/4-1/2mm, with most measurements being 24mm. 

Without running the calibration test again, I know - I’m so impatient, I tested the new piece of ply and 25mm height 4 passes at 180 worked really well… so I tried it on my larger shapes and found there was clearly big inconsistencies with the height across the shape.

Here are 2 photos: the first one before i moved the ply to show the variation of cut - the top of the teardrop looks a lot cleaner than the bottom - near the edge of the ply, I’m assuming a height thing; and the second photo shows 3 shapes : 1. is an outsourced laser cut piece of the exact same design, this is what i am trying to achieve. 2. is the front of one of the pieces i have just cut and 3. is the back of on i have just cut. (I sanded both 2 & 3 to try and flatten some edges and reduce the burn marks). The backs are very wonky, and even though they were ‘mainly’ cut through, it wasn’t a clean crisp cut. 

More questions: 

Could this unclean cut be due to my busted air assist? (currently trying to solve, ticket open)

Can you please post photos of your work to help me with my expectations?
I want to know if I can strive for a clean cut, front and back, like the shape 1. in the above photo. Sanding doesn’t worry me, its the wonky/unstraight underside of the cut that does. 

Thanks again! :slight_smile:

Another question… I was using the silicone mats logo side up - but when i was looking at them again this morning, it would make more sense if they were logo side down so the smoke can escape easier through the gaps. Which way around are they supposed to be? And do you agree, would it be an idea to try it the other way? 

The silicone mat should be used with the logo side down. I remember reading this somewhere (maybe the starting guide?). I generally have a very clean cut. The only problem is the burn marks at the bottom due to the laser cutting through. Here is a picture of 4mm ply (pine, I think), done with 5 passes at 180, 0.5mm or 1mm pass height.

Can I get 100% clean cut? Not always. Sometimes I still have to bring the knife to it.


(that’s an overkill setting). 

Thanks Daniel!! ok great. Well, clearly I was using the mats wrong! Oops! Thanks for showing a photo… good to align my expectations. I’m sure it’s all achievable, I just have to modify things slightly. 

I just did a job with 3mm poplar ply, and it cut a treat. I did have to put an extra pass over it, but that was it. (not my brand). A little bit of sanding to reduce burn marks from top, and that was it. 

Hi Katherine,

I’ve tried with and without and cutting with air assist definitely reduces the browning of the top surface. I posted a picture here at 23:26 last night, which shows the outline left from cutting out shapes (to the right of the portrait).  Thats the  top surface and being waste I haven’t cleaned it  but there is  little to no brown discolouration at all.

Looking at the picture you posted of the two teardrops, in my experience the wider smokey lines towards the bottom of the right hand tear drop is usually an indication that that part of the ply is a bit closer to the laser (ie warped up or not placed evenly on the base). 

Finally to reduce the chipping on the underside unless the grain pattern has to lie in a particular direction I try to align the long surface of  whatever I am cutting to the direction of the grain, this minimises the amount of cutting that goes across the grain, which is where the chipping usually occurs, ie I’d have rotated your teardrops by 90 degrees, unless there was a reason for having the pattern running across them.  Hope this bit makes sense!

Wow Chris, there is nothing on the top! My air assist isn’t doing its job. I think you are right. I might tape my ply down or weigh it down somehow and see if that makes a difference. I tried to tape it on the 300mm length, but didn’t do it on the 500mm length (the side where the marks are). And I can see your point about rotating my shape 90 deg to get it flowing with the grain more, but unfortunately I have designed my pendant specifically so the grain runs in this direction. I’ll attach a photo so you can see the final result… keeping in mind these are double sided so having nice cuts on both sides is critical. (they have a coating of resin on top which makes them glossy)