Darkly Labs Community

Cutting 6mm MDF - a possible solution

I have been struggling to cut 6mm MDF, even though I have done it previously.  It was cutting only 5.5mm through.  

I had the bright idea of changing the support thickness setting from 10mm to 9mm.  I still have a few spots where it does not cut all the way through, but it is much more successful.

 

By the way, does this suggest that I need to recalibrate the machine?  

Hi Stuart,

I don’t recommend setting the  Material value away from the ‘as-measured’ values. The Calibration assumes you are using the correct values, so any deviance will likely negatively affect the output.

The Support  value should be 10mm if using the silicon mats.

_ —- Note: The above two paragraphs were edited on 26/04/21 to correct an error stating both values should be ‘as measures’ - this is incorrect. —- _

Cleaning your Focus Lens and re-running the Focus Calibration  is always the first thing to try if cutting is not working as well as it has in the past.

LightBurn includes a way to offset the laser, and also step the laser down with each pass, which sounds like what you are tying to achieve. You can find more information on using these settings here: https://lightburnsoftware.github.io/NewDocs/CutSettings-Line.html

If you do not see these setting, you are likely in ‘Beginner Mode’, which you can turn off via the Settings window.

Unfortunately, MDF is very prone to absorbing moisture from the air over time, which can make it harder to cut. This may be a factor also.

Please let me know if there is anything else I can assist with.

 

Best regards,

 

Lliam

Customer Support Team

D A R K L Y    L A B S

d a r k l y l a b s . c o m

Thanks Lliam

I have cleaned the lens and have worked out that I need to re-run the calibration.  Maybe the calibration will do the job.

Interesting that you say the “measured” values for the support, as I have never measured that.  I think I do need to.  My solution simply assumed that it is less than the standard 10mm.  Since it worked, first with a setting of 9.5mm and then better with the setting of 9mm, it is worth checking more thoroughly.  I did measure the material.

I have already tried playing with the Z offset and step settings in LightBurn.  I found that:

  • A Z-Offset of 1.5 mm worked better than 3mm

  • A Z-step per pass of 0mm worked better than 0.25mm, which worked better than 0,5mm.  I think I did this after I changed the Z-Offest to 1.5mm but even so, this is counter-intuitive.

  • Playing with these two settings did not fix the problem.

  • With a support thickness value of 9mm, a Z-Offset of 3mm and Z-step per pass of 0.25mm, which I got from the library (E2_5W_MK1), worked better than the 1.5mm / 0mm that gave better results otherwise. 

I am aware that different pieces of “the same” materials can behave differently.  For instance, MDF that is lighter in colour actually cuts much more easily than if it is darker. To deal with these differences, I typically first cut a small test shape (circle / square / hexagon / octagon) and change settings as necessary to get the cut to work on the actual piece of material being cut.  Even this is not always successful.

For one thing, I am frequently successful at cutting the small test shape, but then unsuccessful cutting a larger piece.  My thinking about this has always been that there is less time with the small cuts for heat to be dissipated between passes.  To overcome this, I have progressively slowed my feed rate (2mm/sec or 120mm/min has become my standard for MDF).  This has helped, especially at 3mm thick, but does not solve the problem at 6mm thick.  I have occasionally tried even slower than that, but I am nervous about how slow I can go before I overheat the material. I do sometimes see burnt edges on the cuts with slower speeds.

The other interesting observation from cutting test squares is that the vertical lines cut quite successfully, but the horizontal lines do not.  When cutting hexagons and octagons, the lines 30° from vertical seem to cut, but 45° do not.  I have also seen this on a large piece where I cut half of an 18-sided polygon about 240mm in diameter.  The two segments on the end of the “curve”, which where closest in angle to vertical, cut through on both sides.  However, the horizontal centre segment and the two segments adjacent to that, on both sides, did not cut through.  I really have no explanation for this.

Oh. one thing I have not mentioned yet is number of passes.  4 is the standard for 6mm MDF and there seems to be no benefit from any other number,either as part of the planned cut or as additional passes after the first set of cuts has completed and failed. 

The bottom line is that the machine is perfectly capable of cutting 6mm MDF so I need to find settings that work consistently, even on large pieces and long cuts.  Being successful at small test cuts but then unsuccessful on larger work pieces is both a waste of time and material.  I have done more than enough of that and I am over it.

Any other suggestions you have will be gladly welcomed.  I will let you know if the lens calibration works. 

Thanks for your help.

Hi Stuart,

I’ll try to answer a few of the points from your post I can answer immediately, and will get back to you about any remaining points in the next few days.

You are right, I did mention the ‘measuredSupport and Material values. This was misleading, and I apologise for that. The Support value is assumed to be 10.0mm by the software and this is ‘baked in’ to the Focus Calibration -  meaning any deviance in the actual mat thickness is compensated for during calibration. As such you should always use 10mm if you are using the silicon mats.

The Material value should be as measured, as this will ensure the focal point is at the correct height. I’ll put a note in my original response to reflect this incase someone else comes across this.

The difference you noticed, based on the direction of the cut can be easily explained. Laser diodes, due to the way they operate, produce a long rectangular beam. The lens assembly in your Emblaser is specially designed to make this beam as square as possible, before it is focused down to a point by the focus lens.

Despite the laser appearing as a circular point/dot, the power is still more condensed along one axis, giving a very slight difference in ‘apparent-power’ between the two axis. The Focus Calibration wizard in LightBurn 9.19 and later has some compensation for this.

 

Small tests often perform better than longer cuts as you have described, due to the reasons you listed. Warm material is easier to burn/vaporise/melt than cooler material. I recommend testing a longer line in the horizontal direction to gauge the performance of your settings, if possible.

 

We find that 200mm/min is a safe minimum speed. Below this, the likelihood of burnt edges increases.

6 Passes is usually the maximum worth attempting, and burnt edges will decrease the effectiveness of the laser on subsequent passes. The Air Assist can help to reduce this.

 

4 passes on 6mm MDF is impressive! We recommend a maximum of 3mm for MDF, but it sounds like you are close to getting successful cuts. You may find the newer library settings of use for comparing settings: https://darklylabs.zendesk.com/hc/en-us/articles/360002746596-LightBurn-Materials-Library

I’ll be back in touch soon regarding the other points.

 

  • Lliam

Good Day Lliam

Well, calibrating the laser was effective.  It easily cut a 15 x 15 mm test square with the following settings

Power = 100 %

Speed = 120 mm/min  more about this below)

Passes = 4

Support = 10 mm

Material = 6 mm

Z-Offset = 1.5 mm (In)

Z-step per pass = 0.25 mm (In)

Air Assist = On

It did not do quite as well if I either increased the speed to 150 mm/min or the Z-Offset to 3.0 mm (In).  I had to break the squares out, but this was easily done.

However, it did not cut a 115 wide x 15 mm high rectangle with those settings.  I increased the number of passes to 6 and it almost cut through - I was able to break the rectangle out, but with quite a lot of effort needed.

Regarding speed, I have had little to no success over the years attempting to cut at 200 mm/min.  I can do 150 mm/min for 3mm pine ply, but need 120 mm/min for either 3 or 6 mm MDF.  I will try speeding up again with the recalibrated laser, perhaps with additional passes too.

One thing I did notice with the squares and rectangles was that the top horizontal edge  (only) cut at an angle of about 5° from the vertical.  Is that normal?