Forums/Tutorials/Laser Cutting Tutorials & Tips

Avoid warping issues with plywood

Josh Judkins
posted this on March 17, 2011 10:10

Getting superb results from thin plywood and bamboo.
A guide by Yana Skaler - originally posted to the Ponoko Blog.

Every now and then we come across P3 design files that are so densely populated with designs that we marvel at the super efficient use of space. It is fantastic cutting something that will generate minimal waste. However, there can be a downside to adding so much detail onto a large sheet.

Sometimes a sheet of material may not be very flat when we get it from the manufacturer. This is seen most commonly in 2.7mm/0.106" bamboo, 5mm bamboo (NZ) and other thin plywood. Unfortunately this is the nature of material. The inherent tension in the grain of the wood and the way it is constructed means the panels can warp between the factory they were made in and the Ponoko shop.

Additionally, dense cutting and engraving generates heat build up, which can cause the sheet of material to warp during cutting. This can adversely affect the quality of the cutting, engraving and has the potential to damage the machine. This is most apparent on thin materials like leather, styrene and bamboo. So why is warping so detrimental to cut quality?

The laser is set up to cut flat sheets of material. Before each job it is focused to to the top of the material for a given thickness. For example, if a sheet of 3mm/0.118" acrylic is being cut, the laser been is set to focus on that thickness. If a sheet of 9mm/0.354" MDF is cut afterwards, the beam needs to be refocused to accommodate the extra thickness.

The laser can handle variations in focus of +/-2.5mm. Once it gets outside this the laser beam becomes wider (less focused) and this results in a thicker cutting line and ill-defined engraving.

Here is an example:

This is a side view of 2.7mm/0.106" bamboo ply P3 on the laser bed, and as you can see, it’s not very flat, as often happens with thin plywood and bamboo. This sheet is to be cut into 1xP2 and 4xP1.

The numbers show the order in which the cuts were made.

You can see that cut 3 is thinner and nicer (because it is more in focus) than 1. Why? Because when the sheet got cut in half (cut 2) it was a lot flatter for cut 3.

So how does this affect you?

Sometimes we need to pre-cut the material into smaller pieces to minimize the warping and produce better quality results. If you have a plywood P3 packed with detailed designs, especially ones that have engraving, there are a couple of options at your disposal to get the best results.

One option is arranging your designs on smaller material sizes, like the P1. It might mean paying a slightly more for the materials, but you will end up with consistent, quality results.This is a great option if you have multiple small, jewelry like items.

Another option is creating channels of space that can accommodate additional cutting lines. Unfortunately, this means that you will be sacrificing a little design space, and producing a tiny bit more waste, but this modest compromise will ensure a higher degree of awesomeness in your products. This might be a good way to go if you have bigger more irregular objects that don't quite fit on a P1.

Here’s what we are talking about. The example below is too dense to cut into smaller pieces:

Whereas this example shows room for us to pre-cut the material to flatten it.

So if you are into hardcore detail, give your designs some breathing room and take a step closer to laser cutting perfection when working with thin plywood and bamboo.

If you are unsure about how to layout your designs, contact us, we are always happy to assist with advice.

 

Comments

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Denis Bohm

What is the minimum channel space that you suggest?

March 29, 2011 17:28
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Josh Judkins
Ponoko

Hi Denis!

The main function of the channels is to allow for vertical and horizontal cuts - the actual cut line is likely to be a maximum of 0.25mm or so - so allowing a couple of mm for your channel should be a-okay.

Cheers!

March 29, 2011 18:02
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Mark Schafer

Does this mean there is a way for us to order the lines in our files so the sectioning happens first ?

April 01, 2011 02:38
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Josh Judkins
Ponoko

Hi Mark,

Unfortunately there is not a guaranteed way to order which lines will be cut first, this is done programmatically by the cutter software. It does tend to do a good job of cutting interior details before cutting outer lines, however.

These gaps in designs for ply are more for our use in case we need to cut the sheet up prior to making to avoid warping. Naturally we avoid doing this unless absolutely necessary, as it provides an added layer of time, complication and room for error.

I hope that helps to clarify.

April 01, 2011 08:04
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Ben Carney

Would the same apply to P2 sheets as well or do you not find as big a warping issue with P2 sheets?

June 08, 2011 15:40
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Josh Judkins
Ponoko

Hi Ben - great question!

If you're using this sort of material, it's ideal to leave channels in a similar fashion on a P2 just to be safe.

As a rule, though - we run into this most with P3 sheets. =)

June 08, 2011 15:41