View Full Version : Wood cutting inconsistancy...not all the way through

Joseph Tovar
11-07-2010, 3:10 AM
Why are my cuts inconsistant..

I'm trying to cut some 1/4" Birch and I'm having so many issues cutting all the way through. I thought it wouldn't be that difficult, but it seams that about 97% of it cuts fine, but there are several areas that don't cut all the way through. It takes to long to cut all the uncut sections with an exacto knife and it causes more buring to run a 3rd pass.

It's a 50W ULS and I'm running it at 95%P 5.5%S 500PPI with 2 passes. Shouldn't this be enough? Also, why is it that some parts cut and others don't? Is it because certain parts of wood are harder than others, or because of the orientation of the cut...going up/down version left/right?

Any tips for cutting 1/4" Birch?

Michael Hunter
11-07-2010, 5:12 AM
Ply is very inconsistent and this is probably the reason that your cuts are variable.
Among the problems are glue pockets, voids, overlaps in the inner layers, changes in the density of the wood veneers .... etc.

My current settings for ply are set at over twice the power that I originally used, and I still get occasions when the ply is incompletely cut.

I only do one pass as this gives the cleanest edges.
Because of the difference in the way the settings are measured I can't be sure, but is looks as though my 60W Epilog is cutting faster at less power - it might be worth you testing with a higher PPI setting to see if it helps.

Michael Simpson Virgina
11-07-2010, 6:22 AM
I have cut 1/2 Popular nicly with my 50Watt. As well as some 1/8-3/16 exotic woods with good results.

For birch ply 1/8 is easy to get consistancy. When you get above that the glue in the ply becomes a major factor. Also with thicker woods because of the shape of the laser beam its hard to get a two pass.

Try focusing haulf way into the board and doing it. If the glue chars up then a second pass wont be as effective as a single slower pass. Make sure you are using air assist to keep the charing down as well.

When all else fails move to a different brand. IE if you puirchased it from Home Depot then try some from Lowes.

If its not a real large project try some of the 1/4" hobby ply from your local craft or hobby store. This cuts pretty consitant.

Mike Null
11-07-2010, 6:26 AM
If you have a hertz or frequency setting I would increase that to double what you have tried.

Focus down into the wood slightly. Keep the Exacto handy.

Joe Pelonio
11-07-2010, 9:38 AM
I use birch ply from Michaels, Ben Franklin and some larger pieces that I got from Rockler. With 45 watts it almost always cuts in one pass at speed 6, 100% power and frequency 600. When I have had issues was only warped pieces that were out of focus in spots. The only wood I've bought at Lowes and HD is 1/4" Oak. That cuts well but is almost always cupped. If you don't need the strength try using Basswood, that cuts like butter.

Richard Rumancik
11-07-2010, 12:11 PM
In my experience with 3 mm birch plywood, the main reason for imperfect cuts is knots in the internal veneer layer. In my case, the parts are small and I usually just reject the problem parts, and build it into the cost of the job. If you can't permit rejects for your project (larger parts, for example) then I think the only solution would be to look for a higher quality plywood that does not have internal knots. However, the normal grading classifications generally refer to the appearances of the faces (the best normally available being grade B with no football patches.) If you go into aircraft grades perhaps they will be more rigid with the quality of internal layers. But it may be a trade-off between shipping special plywood across the country as opposed to accepting some scrap. And your "special" plywood won't necessarily reduce scrap to zero.

Voids don't usually cause a cutting problem, but may be reason for rejecting the part depending on how it is used.

If the internal layers are patched, that would be the best. When you hit a hard knot on an internal layer, re-lasering won't help much as it will carbonize and then the laser will cause sparks and smoke with little cutting. I usually don't have good success salvaging parts with a knife so usually just scrap parts that did not cut through.

Joseph Tovar
11-07-2010, 8:25 PM
Hi all,

Looks like a few of the techniques sure helped out. I think the biggest was refocusing half way down. This eliminated a lot of the charring near the bottom and it seams to be cutting in one pass with a bit higher settings...100P, 4.0S, XXXPPI.

What I'm not sure about is the PPI setting. I thought that a higher PPI setting would give me a more throrough cut since the laser will pulse more often so the pulses are overlapped? But then I read in one of my training manuals that a lower PPI is preferred for wood:

*500 ppi is average for cutting
*For wood cutting use 200 - 300 ppi for less burning of the edged
*For acrylic cutting use 1000 ppi for polished edges

Joe Pelonio
11-07-2010, 9:26 PM
Yes and no on the PPI, lower reduces the dark color (char) on the edges, but then higher cuts through better. Pick which is more important, and whether it can be sanded. I find that if it's being finished people like the darker contrasting edges.