Cutting thicker materials with a diode laser

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Downunder35m
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Joined: Sun Aug 16, 2020 5:32 am
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Cutting thicker materials with a diode laser

Post by Downunder35m »

If you just started your new hobby you might use thinner materials or manily some nice engravings.
But once you are a bit sick and tired of buying coaster and other small items you really need to be able to cut out your creations.

Let's start with a short and not complete list of materials.
Great for cutting is all soft, natural wood, especially the resin free varieties.
Balsa wood might cost more but is almost a joy to cut.
If you make your own models from it you know what I mean.
Plywood and MDF is the next thing people might try.
And both come in many different grades and varieties.
So called laser ply has a much more even inner filling and it also uses glues and binders that work much better for a laser than the formaldehyde based versions from your home depot.
Articial wood designed for laser use should be prefered over the cheap alternatives.
Plastics....
While there are some that work great there is always the problem of color and actual composition.
Keep in mind that things burn away and the created fumes are the same as when burning it with an open flame.
PVC for example is really bad as it release chlorine and other rather harmful things.
Other plastics release even more volatile chlorine compounds that turn into acid in the presence or humidty - ruining things in the room quickly if the extraction is not 100%.
So pay attention to what the plastic is made of before trying ;)
Acrylic is quite nice, expesially in black or a matching red/green color.
Clear or translucent though and you are basically lost....
Paper, even craft paper isusually not an issue, except for the unaviodable smoke.
Carboard though can sometimes be a real pain.
The remains of a cerial box is great for quick cutting jobs but the colorful printed side is really nasty.
You really should aim for carboard that is plain on both sides and without and prints or protective films to keep the product fresh.

Ok, having said that I guess you know how good or bad the stuff cuts you want to cut.
Means you get the job done but might be interested in ways to do the same clean cuts in thicker material.
You might think going from 1mm ply to 3mm is only a matter of increasing the power and if in doubt pass count accordingly.
Far from it...
Going from zero to cutting power might seem to happen instantly but in reality there is a slight delay.
Some modules are better here, some are worse.
Either way it means that when a cut starts the output power will still slightly increase.
As result the beginning of this cut is often less deep than the rest.
If then the drawing is not optimised for the laser and a ouline to cut is split into different segments with the laser jumping back and forth....
Some might kown the frustration when it is always those fine corners that seem to stay stuck and prevent the release of parts....
There is options to address this issue ;)

If you are a Lightburn user you will find all the options I mention in there.
If in doubt check the great online manual and tutorial videos for it.
For the rest out there you might have to seek through the menus and options or improvise a bit.

1. Adding a lead in and a lead out....
When cutting through thicker or really thin materials you often want to prevent these visibly thicker burn areas at the start and end of an outline cut.
Using the lead in/out feature means the laser starts outside the cut and for those extra few millimeters it builds up to full power and speed.
Especially on fine paper cuts it can amke a huge difference.
For thicker matrials you will learn to value the fact that where the actual cut starts the power will already be identical to the rest of the cut.
The lead out does a bit of the same but I only use for paper jobs as the overburn at the end is usually not worth mentioning.

2. Pause / Trough hole function.....
With this feature you make the laser head pause the movement at the start of a cutting line.
For example:
You do a test with the head stationary and it takes 4 seconds to burn a hole through the material.
Adding a 2 second puase should then be enough in most cases to ensure the cut will also be all the way through at this point.
It does make no sense though to combine this with option one...
Best used for thick materials that reuire a lot of passes to get through.
With a good air assit it can often reduce the required pass count significantly.

3. Perforation / dot mode....
Especially for paper and carboard creations you want to keep in place it is great feature.
Define outline cuts as a perforation line with a mm or so between the cut that is not cut.
But for thicker materials it can be helpful as well.
Especially if not plastic.
A perforation of let's 0.5mm on / 0.5mm off effectively reduces the overall power by 50%.
On the other hand if you use a high output power for this cut it means that the material where the laser is off still burns away from the heat indicuded in the surrounding area - especially with a good air assist.
Of course the speeds have to be cranked down accordingly but it can often result in much cleaner cuts with far less soot and ash produced.

Speed Vs power....
This is my last point for today but a rather vital one.
If you make a comparison of how long it takes to cut through thicker material you will find there is not really much difference at all.
A single pass at 75mm per minute might take as long as 4 passes at 300mm/min.
But while the first literally burns through it the second can vaporise more material.
Meaning the air assist can remove the burnt material easier.
Considering that the build up of black coal and ash is a good insulator despite absorbing the laser enrgy really well....
Thick is a relative terms and directly relates to the optical power you have at your disposal.
Do a greyscale box test as a relief engraving.
You will that you can get the same depth in various settings.
But the appearence will be different ;)
The ideal speed and ideal power should be what removes the most material with the least amount of charring or discoloration ;)
Creating small test bagdes for reference is time consuming, frustrating and a waste if you don't have off cuts - I KNOW.
But it is well worth it if you do those jobs a lot as it will save you a lot of time later on.
Plus you get cleaner looking results.
Exploring the works of the old inventors, mixng them up with a modern touch.
To tinker and create means to be alive.
Bringing the long lost back means history comes alive again.
Downunder35m
Posts: 630
Joined: Sun Aug 16, 2020 5:32 am
Location: Australia
Contact:

Re: Cutting thicker materials with a diode laser

Post by Downunder35m »

Depending on what software you use the mentioned features might not be available or available in a slightly different type.
Check it out anyway and experiment a bit with these little known features.

But what to do if Lightburn is too expensive and your software is quite basic?
There is no reason you have to stick with what came with the machine...
Laser GRBL should work just fine once properly configured.
And some programs do work fine with other machines....
If it speaks GRBL there is always options ;)

Not just the materials we use require a learning curve...
Cutting thick materials should mean your files support the job.
Not always though will you see how a seemingly great ouline is cut in one go, no matter how hard you try to optmise things.
I still struggle with this part a bit but there is a cheat that you can try.
We have quite a bunch of online tools now to opmise layouts for laser cutting - free ones I might add.
Upload you "mixed up" drawing and in return you get something with all parts in a layout reducing the waste and required sheet size.
Most of these tools "mess up" the original file in terms of all those created lines.
Means if you used the right tool all you cuts will be continous without the head jumping all over the place for small line segments here and there.
I tried it with a few jobs and got time savings between 30 and up to 60%...
Exploring the works of the old inventors, mixng them up with a modern touch.
To tinker and create means to be alive.
Bringing the long lost back means history comes alive again.
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