Edge Charring of Wood Based Materials when Vector Cut

According to my laser manufacturer's sales blurb, wood is the most commonly used material for vector cutting.

If that is so, then am I alone in getting the following results ?

I have conducted hundreds of tests on many types of wood based materials - plywood, medium density fibreboard (mdf), hardboard and cardboard, with thicknesses ranging from 0.6mm to 6mm.

The majority of these materials leave a loose, sooty deposit (charring ?) on the cut edge. Handling the cut pieces leaves black marks on the end user's hands which is clearly unnaceptable. Even some materials sold as suitable for laser cutting don't cut cleanly.

The settings of the laser system driver software, the focus distance, the use of air assist, the use of nitrogen assist, the use of a honeycomb grid, other means of supporting the material and increasing the extraction air flow rate all have had little or no effect on the results found.

The species of wood(s) used to manufacture the product only seem to affect the effective cutting speed, presumably because they have different densities and different amounts of natural resins.

The type and amount of glue (adhesive) and/or resin used in the manufacture of the materials tested is the only thing which seems to make any significant difference to the amount of soot produced.

Before I ramble on about the different types of glue, speed of cut, etc. does anyone else have any thoughts on this subject ?

As I am from the UK, some of the terminology used to describe the materials may be different to that used in the US.

Not sure what brand of laser you have, but when vector cutting wood or paper you'll want to set the PPI or Frequency to a low number, such as 400 or 500. The default (2500 on Epilog) is too high for wood and causes a lot of char.

Wood will always char somewhat, but with woods like alder, cherry and maple I can keep it down to a dark brown edge by keeping the frequency low and using just enough power to make it through the material.

The glues in plywood and MDF will always char more than pure wood.

I agree with Dave. My vector cutting is limited to 1/8" plywood and 1/8" to 1/4" cherry. A charred edge is a reject. I don't mind making two passes to keep the charring down if necessary.

Basswood is another that cuts cleanly. In many cases the wood does look good with the contrasting darker charred edges, you simply wipe the loose black off and spray the whole thing including edges with a clear finish.

I cut alder for BUSINESS CARDS regularly. They cut clean and look great. One thing I have learned the hard way, if you want good cutting results from your laser, you better have your optics clean. 500 dpi is also correct for wood in general. I have so far, only used woods that have a finish on them. I can clean any tar or residue off with isopropyl alcohol.

I have always had charred edges when cutting wood with my Epilog Legend 35 watt laser. The new Xenetech 60 watt we purchased last December at CNU shines at vector cutting wood, it leaves a very light brown edge on alder. I haven't had the time to try other species.

I wonder if higher powered machines have an advantage when cutting wood, not just the thickness but the edge quality as well.

.

Dave and Mike. Thanks for your replies.

My laser is an Epilog Mini with the optimum PPI, power, speed, focus, number of passes etc. set for each type of material.

These are determined from a large number of tests and each material requires different parameters.

I cut 12" by 18" sheets and, as far as I know, pure wood is not available in sheets as large as this, apart from veneer which is to thin.

All my tests relate to man-made materials such as plywood and mdf and involve cutting hundreds of pieces from each sheet. Each piece has an area of approximately one square inch .

I have a found that a few of the materials I have tested do not leave loose soot which comes off when handled.

They do darken the cut surface ( charring ? ) but that is expected and acceptable.

What I am interested in is the differences between the common materials which produce soot when laser cut and the uncommon materials which do not.

I suspect that it depends more on which type of glues are used than on the species of wood.

I have a 100 watt laser. With it most woods up to about 3/4 I only have a brown edge. With my 35 watt I get a lot of charring.

As the speed of cut can be faster with a higher wattage laser there should be less after-burning of the wood/glue/resins which should, in theory, leave less soot on the cut edge .

Has anyone carried out comparative tests on this ?

In my case, using a 35W laser, I have found that some plywoods and one type of mdf do cut successfully without leaving any soot on the cut edges.

What is basswood and is it available in 12" x 18" sheets ?. Maybe basswood is known by a different name in the UK ?

Unfortunately cleaning is not possible in my case as printed paper is laminated onto a wooden substrate before cutting and the use of any liquids would mark the paper.

This business of the higher-powered lasers charring less has me thinking. It's starting to sound like the problem is that the beam continues burning the edge in the just-cut region because it is moving too slow.

Maybe the right answer is multiple passes at very low PPI settings, like maybe 100-200, allowing the material to cool before the beam comes through again. Of course that assumes there is some way to offset the pulses on subsequent passes to miss the "holes" left by the previous pass.

The higher power manifests in more complete vaporization and less heat affected zone
Think of burning a hole in a piece of paper with a BIC lighter vs a propane soldering torch , both can do so , tho the soldering torch will have a much cleaner hole.
The other limitation with a low powered laser is the power density above and below the focal point , due to low power there isnt enough when the lens is out of focus to promote clean vaporisation - ie less power in the same area as the more potent laser.
Evacuation and air assist should be optimised to try keep resins and products of vaporisation out the way.
There is not that much upside to lasering thicker wood products , most of these can be done better using overhead routers or very much more potent lasers than we talking about here. (500+w)
In the time I have used lasers , I have come to the realisation that wood cutting is fraught with difficulty but wood engraving is a doddle.

The laser does cut Formica very well and lasers it equally as well , so what we often do is use laser cut/engraved wood grain formica cladding on cnc cut supawood or just pasted back to back or on laser cut acrylic , to simulate wood products.
We also used to have sheets of light density fibreboard (ldf) veneered with real wood veneer either side and use that - my 25w lasers used to cut 6mm (1/4") with no problem. They had a tendancy to warp however - the full sheets that is , and ended up bowed on the table. Hence the erzatz wood direction - easier to control , sometimes cheaper , weather and heat resistant and so forth finishes are often better as well.

Rodne

Many thanks for your reply to my posts.

I understand the reasons why a high power laser can cut faster and therefore cleaner than one with lower power and agree with you that wood cutting is fraught with difficulty.

My laser tube is, however, rated at only 35W and I have to work with the system I have.

I have found, so far, a few types of plywoods and one type of mdf which cut with clean edges and no soot, even at this low power.

Cutting the mdf produces a lot of airborne resin which causes contamination of the surface and very quickly clogs up the extraction filters. I have overcome the surface marking problem but it cuts very slowly as one would expect from such a dense material with only 35W of power available.

Cutting the plywoods is nearly twice as fast as the mdf, with clean, light brown edges and the airborne resins are minimal.

The best of these is a light-weight, almost white, 3 ply, plywood which is 2.38mm (3/32 inch) thick but of unknown origin. I guess it is from the Far East.

It is an ideal material for laser cutting but my problem is specifing and then finding a supplier of this particular plywood.

I use a similar but thicker material. It is 3 ply, 3mm identified as Baltic birch and I believe, imported from Russia. We call it 1/8" though it is slightly less.

My supplier is a member of this forum.

John,

MUTR, as you quoted on the recent Maplex question by me is a supplier of 4mm baltic birch here in the UK.

I've also sent you a mail with further information.