Q. re Z Offset & Z Steps Per Pass | Sliding Puzzle

I intend insetting some tiny neodymium magnets into 3 mm plywood – the magnets are disc shaped 2 mm x 1.5 mm deep. I need to get my head around the concepts of Z steps and Z offset in order to get an ideal hole which will fit the magnet without its bottom surface being too deep or causing the magnet to sit above the surface of the wood. I normally cut cleanly thru 3mm in 2-3 passes and my Z offset is set at 1.00mm and Z steps per pass is set at 1.5. I do not understand these settings so don’t touch them but on this occasion I need to work these to my advantage.

I know that 0.66 times the depth of the wood is the ideal setting for cuts on my Emblaser 2 but in this case I do not need to cut so I’m somewhat confused. How would you approach this so that I end up with holes which are exactly 1.5 mm deep? I will be using the array tool to make 4 lots of 16 holes. Obviously there will be some trial and error involved but I don’t know where to start as to how many passes and what to set the Z offset and Z steps pass settings. Presumably I will use Fill.

Any help and understanding of why these settings will be much appreciated.

Hi Elayne,

Great question!

It is important to understand that the Emblaser (like any non-specialist laser cutter) has no method of precise Z/cut depth setting. Cut depth is dependant on laser focus, power, speed and material properties, such as type, moisture content and density (which can vary across a sheet).

The Z controls available (Z Offset & Z Steps Per Pass) control the focus point of the laser in relation to the materials surface - not the physical depth of cut.

To obtain a depth of approximately 1.5mm I recommend using no Z Offset or Z Steps Per Pass on a Fill layer with 0.200mm Line Interval, to engrave a set of circles at 100% Power and varying the Speed setting (I’d start near 600mm/min). Then increase or decrease the speed as needed until the desired depth is achieved. You should only need a single Pass by the sounds of it.
You may need to clean out the area with a firm plastic brush or similar before inserting the magnet.

Alternatively depending on your application, you could cut through the material and use spacer to ensure the magnets are only inserted 1.5mm, then fill the back with a wood filler, epoxy, or even a 1.5mm thick material cut to fit.

I hope this helps, and please let me know if anything is unclear.
We’d love to see what your working on if you have a chance to share!


Thanks Lliam, that’s excellent help, just what I needed. I tried measuring holes with calliper but found it “iffy” and it doesn’t help that the magnets won’t arrive for 3 weeks or so (Xmas holiday break at factory).

I’m attempting to make a sliding puzzle but hope that magnets might be easier than constructing tongue-and-groove which would be too bulky.

You were spot-on with your numbers, Lliam. Confusingly the measures vary along a piece of laser ply but maybe the magnets height will too. For now I’ll settle with speed 524 (and remind myself to turn off bi-directional and cross hatch, which was confusing measurements).

I’d like to use one of your 2 alternate suggestions but they won’t work as I’ll also
be etching on the “back” side of the wood. Thanks once again for your help. Can you suggest what I need to return my Z measures to, for general cutting of 3mm?

Sounds like an interesting project, and I’m glad those settings were close!

I recommend applying the Material Library settings when switching back to cutting, which will set everything including the Z-Offset.
For 3mm Poplar Ply the Z Offset in the Library settings for ‘Line’ is: 1.5mm (IN).

I give up, I admit defeat!:confused:

I’ve worked on my concept of a magnetic sliding puzzle for several weeks and have come to the conclusion that I can’t create a good working copy which I’d be happy to give as a gift. The magnets work and the tiles work but alas there is too much friction when sliding the tiles to make the puzzle seamless. Now if only I had a 3d printer …… .

Back to the drawing board.

Oh no!

Have you tried applying some wax to the sliding faces?

I just use a cheap paraffin candle and apply liberally, then dust off. This helps a lot and might work for you…

Hey Elayne,
If you are interested, send over a puzzle to Darkly and we will have a look at it and see whether we can give you any suggestions.
Our team has lots of experiences with projects and may be able to help you resolve this.


Hi, Domenic and Lliam - thank you for your offer of help with my Sliding Puzzle. I’ve compiled this Lightburn file from 95 different saves (1.68 GB) as I have the somewhat neurotic habit of saving my changes as I go. I hope I haven’t left anything out or duplicated one of my design errors in your version.

My original intention was to create a 15 sliding puzzle, operate it with magnets instead of tongue-and-groove and glue a coloured photo to the front and cut it into tiles but smoke staining proved impossible to clean up from the tiled photo’s edges so it was back to the drawing board. The next effort was to convert the photo to an image and etch it to the front and also glue a coloured photo onto the back. (it is a composite my daughter asked me to create) I imagined I could scramble the tiles before I gave the gift to her and that she could refer to the glued photo for clues if needed.

At some point I decided to change from 16 to 25 tiles, then later I swapped back to 16 tiles but during this phase I made errors in placing the magnets. When I created an amended file and tested it I overlooked allowing for the width of the frame in my magnet position calculations so those pieces had to be scrapped, too. On and on it went, then I decided that the brown etchings on small tiles wouldn’t be distinct enough so set aside the puzzle and went down the rabbit hole of testing baking soda on the laserply. The black etchings looked good but stained the wood an unpleasant yellow colour. Abandoning that idea I moved on to borax and although it changes the laserply to a creamy yellow, it seems to be my best compromise. I’m not happy with it and tested borax on eucalyptus ply, too, but that just looks yucky.

Because I will glue the photo onto the back of the BASE, the magnets need to be inset from the reverse side first and thanks to Lliam’s help (600 speed), I settled on 524 speed and found that the magnets set in without too much protrusion. Alas, when it came to glueing magnets on the back of the TILES and after remembering to first etch the image onto the front, my settings no longer pertained - those damned magnets sat proud of the holes regardless of multiple attempts. At this point I was running out of magnets and had to wait for another shipment and when I finished THAT one, the magnetised tiles not only looked messy (borax creates soot and the sliding of the tiles exacerbated the mess) but I had incorrectly reversed the poles on a corner piece. Drat!”

I knew I will have to redo the front tiles piece but in the meantime taped the frame on and tested the action of sliding the pieces. Sadly, it doesn’t feel like a sliding puzzle and wouldn’t be good enough to give as a gift. Lliam has suggested testing waxing but I’ve already chucked the pieces. If you are able to come up with any alternate suggestions I will be eternally grateful but otherwise have set aside the project as something I will try one day if/when I buy a 3D printer. In the meantime my aim is to set aside any 3d printer pennies for an Emblaser 3, long delayed with supply constraints.

Sorry this is so long-winded, just trying to explain my frustration.

Many thanks, as always.


SLIDER PUZZLE - reconstructed for domenic - h.lbrn (3.11 MB)

Hi Elayne.
Apologies for taking such a long time to check your file.

There seems to be a problem with it as it opens with nothing in it.

Can you please check and re-post it here OR email it to help@darklylabs.com

SLIDER PUZZLE - reconstructed for domenic - h.lbrn (3.1 MB)

let me know if this doesn’t work and I’ll resend to help desk
SLIDER PUZZLE - reconstructed for domenic - h.lbrn (3.1 MB)

That opens for me now. thx.

Let me have a look at it and I’ll see if I can get you some advice.

Hi Elayne,

Apologies for the delay in replying.

I have chatted with a few people at Darkly about your project and we are very impressed with how you have gone about trying to achieve your project.

We agree that the toughest thing you are trying to achieve is having the parts sliding smoothly (or at all). This is not easy, as your tests have shown, especially with wood.

A tongue & groove method may work, but it is a complex thing to do and have working smoothly.

I know this is not what you want to hear, but have you considered not having the puzzle need to slide? Instead, treat it as like a jigsaw puzzle where the parts are placed in the right area and held there by magnets?

Maybe someone else in the community may have some better suggestions.

Thanks for the suggestion, Dominic – yes that seems the only sensible alternative. In the meantime I have engraved the image on a round cutting board and as it is a gift for my daughter I guess she will be happy with it.

I may try doing a puzzle as you suggest as I hate admitting defeat. LOL

Hi Elayne,

I’m sure your daughter will love the cutting board!

As mentioned, we had a chat about this yesterday and where really impressed with the amount of effort you put into your projects!

I had a think about the sliding puzzle concept overnight and came up with a proof of concept design. It is fairly simple and should scale well - though may not be exactly what you are after.

The design is 4 layers thick. So for 2.5mm Eucalypt ply, it would be 10mm thick.

Essentially each piece is a square top and bottom, with an offset square between to provide the ‘tongue’ and ‘grove’.
The frame has the same offset distance applied to the middle layer and has an added ‘base’ layer.


  • Add some chamfers to the tabs on the middle layer to aid in alignment as pieces are being moved.
  • Add a thin layer <0.2mm, (card perhaps) with all sliding areas removed, to give some additional clearance to the sliding parts.
  • Remove alignment holes in top layer, or add a finishing layer with the puzzle image.
  • Add wax to all sliding faces.
  • Use Eucalypt ply, for its smooth hard wearing surface.

Note: You will need to glue at lease some of the final pieces with them installed in the frame.

Here is an image of the ‘solved’ and ‘scrambled’ states. For a 3 piece puzzle, there are very limited moved, difficulty will scale with design. I suspect a 9 piece design would be a good minimum complexity.

File attached for reference. Let me know if you have any questions.

20220301_slidding_puzzle_proof_of_concept.lbrn2 (37.4 KB)

Lliam this sounds incredible! You may have solved my dilemma. I’m presently working on 3 separate projects so can’t get to this for awhile but will download your test files and get back to you in due course.

Thank you once again for all of the time you put in to helping me. If you are anything like me, you hit the pillow and then try to solve it in your head. Hours later …… :sleeping:


p.s. what are your “chafers”? I only know of cooking pot and insects


Yep, thats how it works!

Ah, that was a typo - it should read “chamfer”. I’ll edit that to avoid any future confusion.


Keep us updated if you ever get back to this!

Chamfer, of course! My first knowledge of chamfers was in the early 1950s when my father would let me play with a tool which I dragged along the edge of a 2x4, scratching it with an embedded nail so that a chamfer line was formed. Ah, dim memories.


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If you make this from our 1mm Eucalypt the final product will end up 4mm thick.

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…… at long last and thanks to both Domenic’s encouragement and enthusiasm, and Lliam’s excellent plan and suggestions. Thank you to each of you.

My aim was to make a hand-held sized sliding puzzle and incorporate a composite family image but because of the size constraint (each tile is only 18mm x 18mm) there is very little definition in the image, although I’m sure that someone with greater image-processing skills could do a better job. As is typical for me, it took several attempts before I had a working version and I’m actually glad to have finally finished with it.

Lliam’s suggestion that it would need plenty of candle wax before it would budge proved correct and kids’ birthday candles were an ideal size to apply to the tongues and grooves. Additionally, I hit upon the idea of cutting a separate slippery layer from a face shield and glueing it above the base but below the tiles. That improved the friction enormously. Lining up the tongues accurately was proving tricky until I created a glueing jig which suddenly overcame this issue.

I was given a numeric sliding puzzle 67 years ago and treasured it - I certainly never imagined that one day I’d be making a personalised one.

Working version ———- SLIDER PUZZLE for KT.mp4 - Google Drive

Happy lasering!

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