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How to keep wood flat?

I’ve been trying to cut 3mm plywood and for the most part it works fine. The problem I run into is that when the wood bowes in the middle, the focus gets off and it doesn’t cut cleanly everywhere.

 

What are people’s solutions to keeping their material flat?

Hi Adam,

I realise this may not help you, but we basically only use really flat plywood. We have a supplier that supplies very good quality wood, which arrives almost perfectly flat… We keep it sealed in airtight plastic bags until we use it to prevent moisture affecting it.

If there is a slight bow, we can usually eliminate it by placing some metal bars along the edges which don’t interfere with the laser head movement.

The Picengrave team clamp their wood down to prevent movement and possibly keep it straight, but this is a custom base they have made and suitable mainly for engraving and not cutting.

I would also be interested to hear how other customers have resolved this problem.

Domenic

I have a piece of particleboard on top of the aluminum base with threaded inserts (similar to https://www.grainger.com/category/hex-drive-thread-inserts/thread-insert/fasteners/ecatalog/N-8nx)  that I put in the board so that some oversize washers will hold down the edges of plywood. I have the focus set so that the laser guard will just pass over the top of the washers. 

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Good solution Thomas.

What thickness of plywood would this be effective in keeping straight?

 

Nice. So did you have to adjust the laser higher to pass over the washers?

I have the height of the laser adjusted so the guard will pass over - it’s still not particularly high, the washers are only 1-2mm thick. I also have the plywood propped up on some 1x2 scrap pieces as well as shims for the washers so they’ll be level. 

 

That’s awesome, how thick of wood can you cut?

I haven’t tried anything over the 3mm birch plywood, which I have cutting in 4 passes usually after dinking around with the focus.

The holder design isn’t elegant - it’s the first draft solution come up with while standing in the hardware aisle looking at the selection of parts. 

Cool, I am having trouble with 3mm birch plywood which I think is caused by the wood not being flat.

I use a base board that is cut larger than the imaging area. The base board just sits on the aluminium base of the Emblaser and is removed from the Emblaser to screw/unscrew my 3mm ply/mdf.

On the baseboard I have screwed in a series of button head screws that the ply sits on. This allows airflow under the work for more efficient cutting.

Around the perimeter I use the same button head screws to hold the work in place and simply place the whole lot on the aluminium base and align for cutting.  The mounting screws are outside the imaging area so I never have an issue with the laser guard catching the screws.

I do a lot of cutting, as you can see by the base board, and after trying lots of ways to hold material down, I find this works great for me.

Cheers

Daryl

 

I use a base board that is cut larger than the imaging area. The base board just sits on the aluminium base of the Emblaser and is removed from the Emblaser to screw/unscrew my 3mm ply/mdf.

On the baseboard I have screwed in a series of button head screws that the ply sits on. This allows airflow under the work for more efficient cutting.

Around the perimeter I use the same button head screws to hold the work in place and simply place the whole lot on the aluminium base and align for cutting.  The mounting screws are outside the imaging area so I never have an issue with the laser guard catching the screws.

I do a lot of cutting, as you can see by the base board, and after trying lots of ways to hold material down, I find this works great for me.

Cheers

Daryl

I bought a 1 meter steel bar (about 2x1 cm) and cut it into 3 small pieces with a handsaw. Unless I have to cut a whole sheet with a lot of detail, I can usually manage to place the bars on the wood in areas that I know the laser head will not move across.
It also helps to either remove the final G28 command from the gcode file (DO NOT REMOVE THE M5! or the laser will not turn off) or replace it with something like G0 Y0 to move the head to the side/top/bottom without going diagonally back to 0,0

Specifically with plywood I moved to pre-staining them with a water-based stain. Not only can the wood be clamped back into a flat form while damp, a darker stain also increases heat absorption and let’s me cut 3mm birch at about 525-550 mm/min @3 passes instead of 500 using the 4W laser with the G2 lens on a aluminium honeycomb grid.