Laser cutting thick materials

[Sterling Wong]

Hi all I dont remember if ive ever asked this but is there a manual technique or free software to manipulate the laserachine to cut thick materials with a flat edge?

I have been told by representatives that they sell software to do this but it is too expensive just to do a few small jobs

Im only able to laser cut materials up to 1/8 thick without getting too much of a slanted edge

Id like to be able to cut plexiglass 1/4 inch and up with the flattest edge possible

[Sterling Wong]

I have also tried lowering the focus after each pass but the results are not very nice
It seems the edges on certain sides get "shifted" to another direction

[Joe Pelonio]

The only way I have found is to cut on the laser, hit with the router, then flame polish. Fortunately not needed that often. CNC is better for really flat edges.

[Gary Hair]

I have also tried lowering the focus after each pass but the results are not very nice
It seems the edges on certain sides get "shifted" to another direction

That means your beam is out of alignment, adjust it properly and the problem will either go away or be minimal.

[Rich Harman]

Here's what I do. Focus on the surface, go slow enough to cut cleanly through in one pass.

What happens if you cut too fast or with not enough power? The top edge of the cut is open and the bottom is closed. The laser makes a valley. Cut just a tiny bit slower and you will open up the bottom making the cut complete, but the bottom kerf will be tighter than the top - making for slanted edges. Slow down some more and the bottom of the cut will open.

Having a good alignment is necessary, as is knowing exactly where your focus point is. I cut things up to 3/4" with visually vertical edges. You can pick up nearly any random scrap in my shop and stand it up on it's edge.

[Sterling Wong]

Ok so you guys are saying a software isn't necessary to laser cut for example a 3/8 thick plexiglass?

I understand it wont be as flat as machining it but as long as it doesn't come out slanted

[Rich Harman]

Ok so you guys are saying a software isn't necessary to laser cut for example a 3/8 thick plexiglass?

I understand it wont be as flat as machining it but as long as it doesn't come out slanted

Well, that's what I am saying, I cut 3/8 frequently with edges that at least to the naked eye, appear vertical. I don't know what 'special software' would do for you. Water jets for example can angle the cutting stream to solve angled kerf problems - if they have an articulated head. Maybe some lasers do this too - but they will be very, very expensive machines. Maybe Dave has one???

[Ross Moshinsky]

I do find dropping the focal point about 1/6 - 1/4 into the material has benefits on thicker material. I also find thicker to be proportional to power. On my 30W, I'll focus into 1/4" acrylic a little. On my 60W, I won't do that until going 3/8" or thicker.

I do agree with power of cut. Don't just barely cut through. If it needs 100 power and 10% speed to barely get through, give it 100% power and 8% speed or maybe even a little slower. Also one pass is often better than many.

[Rich Harman]

I've also found that a 2.5" lens works best for cutting, for me. The depth of field is longer so small variations in distance don't matter much. In all my experimenting I haven't found the 2" lens to cut noticeably faster. I did find that the 4" lens cuts slower but does not give me any benefit over the 2.5" lens - except maybe for cutting thick foam, which I've only done once, and I'm not sure that I used the 4" for that anyhow.

[Keith Winter]

I think it might be your lens and/or speed Sterling. Guessing since I don't know your lens size, but if you're getting a slant either your lens is not big enough, you're out of power (or too fast), or out of focus. It is very likely one of those variables. 60 watt machine should be able to cut 1/4". Try a bigger lens or slowing it down.

[Keith Winter]

Rich how you like Shenhui, and your 130 reci z6? Guys in china said the 130w and 150w reci tubes are not as good as the 80w in quality. Any truth to that or is the salesmen just trying to sell me what's on his lot?

[Rich Harman]

Rich how you like Shenhui, and your 130 reci z6? Guys in china said the 130w and 150w reci tubes are not as good as the 80w in quality. Any truth to that or is the salesmen just trying to sell me what's on his lot?
If you don't need the power of the 130W then I would go with the 80W. I really like my 80W Reci. It has shown no signs of losing power. The 130W is okay, haven't had it that long so can't comment on it's longevity. I only got the 130W because I do mostly cutting and the extra speed means more money.

[Kev Williams]

nothing speaks like pictures... ;)

I did this just now just to see--

I just cut off the corners of a piece of plex, and a piece of butternut wood.
The plex measures .711" thick, the wood measures .736" thick.

Both cuts were 1 pass, 2mm per second, 80w RECI, my meter said exactly 20mA at 80% power, 2" lens.

Check out the cuts. It's not so much that they're angled, but curved!

I'm not surprised at the curved cut of the plex. But I am surprised that the shape
of the cut of the butternut is almost identical to the plex cut?

Is an actual STRAIGHT cut thru 3/4" material possible? I would have to say, with an 80w RECI, nope...


315624315623315625315626

[Sterling Wong]

Im using the standard lens that came witg the trotec. Not sure what it is but probably a 2.5

And yeah plexiglass for example i usually dont do one pass to go through
I go slow speed low power several passes so i dont get the smudge or foggy residue

Ill have to try the one pass method

[Rich Harman]

Is an actual STRAIGHT cut thru 3/4" material possible? I would have to say, with an 80w RECI, nope...


Look at my photo from post #5, that is 3/4" oak cut with an 80W Reci.

http://www.sawmillcreek.org/attachment.php?attachmentid=315610&d=1394092531

[Dave Sheldrake]

Well, that's what I am saying, I cut 3/8 frequently with edges that at least to the naked eye, appear vertical. I don't know what 'special software' would do for you. Water jets for example can angle the cutting stream to solve angled kerf problems - if they have an articulated head. Maybe some lasers do this too - but they will be very, very expensive machines. Maybe Dave has one???

Even on the Mitsu there is still problems with very thick material brother :( the depth of field controls most of it and given the nature of the gaussian curve of the beam it's always a fight when it comes to thicker stuff :( The Mits have swapping cartridges that have all the optics in them to cope with most stuff but get to inch material and it still bends :(

5 axis will do it like you say...but that's in the lottery money sort of price range

[Mike Null]

In my opinion Joe Pelonio has the best solution for a perpendicular edge.

[Bert Kemp]

This may be true but for those of us that don't have a router table and flame polisher other methods need to be tried. Personally I try not to do anything over 1/8 and I work mostly with wood so if I need thicker I cut 2 and glue them together, that keeps things pretty sq on the edges .


In my opinion Joe Pelonio has the best solution for a perpendicular edge.

[Mayo Pardo]

If you want to try the multiple pass method, the Trotec Job Control software has a way to automatically adjust the focus (raising the bed) after each pass...