Bright idea to cut thick acrylic.

[Neville Stewart]

I thought I had one but not actually. Using Lasercut 5.3 I changed the number of runs a cut would perform. Simple enough idea right? Well instead of running over the previous cut, the head moved over a few inches and started in another spot altogether. Is it at all possible in LCD 5.3 to run over the same vector and adjust the Z each time to cut deeper? I was messing about with .75 acrylic. Don't need to cut anything that thick but I was trying to get LC to act like it ought to. TIA Neville

[Dan Hintz]

Multiple cuts never works out well on acrylic... you need to pierce to get rid of the material through the bottom.

[Mike Null]

It depends on thickness. I generally use multiple passes with .25" and thicker with good results.

[Dan Hintz]

You're happy with the edge quality, Mike?

[Mike Null]

Dan

Yes, I don't perceive an edge quality problem. None of my work needs a polished edge. I've cut a good bit--some for high end signs and the customers were happy.

If I needed a polished edge I would charge for it and flame the edge or buff it.

[Dave Sheldrake]

The sensible limit on acrylic for a 100 watt DC glass tube is about 10mm Nev, 15mm will cut but VERY slowly. On the right hand side there is a #num databox, set that to 3 if you want 3 passes (you may need to scroll across in the layers box)

To get a good finish reduce your air assist pressure to around 5psi (or you will get striation lines on the cut)

A longer focal length lens may also be a good idea but to get real benefits you would need to go to a 4 inch focal length (and the resultant loss of power density due to the bigger spot size)

I *can* cut 20 - 25mm on a 180 watt but the time it takes is prohibitive as well as surface melt on the cut sides looking a bit *off*

One of my pet hates with Chinese laser vendors are the claims of what they can do "30mm acrylic on an 80 watt laser" while *technically* true (even a 1 watt mid IR diode will cut 20mm acrylic...eventually) they neglect to mention cycle times would be weeks not hours or minutes.

Gains are available by using:

Clean, dry air assist
A 1/-3 nozzle clearance ratio
High power DC tubes (150 watts +) (or Mid level RF tubes @ 100+ watts)
Top class Western made lens (II-VI Infrared or Rocky Mountain Instruments)
Good quality mirrors (Knights Optical, II-VI etc)
Beam profilers
Phase retarders

and so on, the gains are very small and often don't meet the cost of doing them in many if any cases.


the head moved over a few inches and started in another spot altogether

Make sure the "Immediate" box is checked when you start the job or it will start from a relative position not it's current position.

cheers

Dave

[Neville Stewart]

Excellent tips and points gentlemen, and in reality it was more about the SW than the machine but still very valuable. Dave what confuses me is that I had for example 3 passes checked in the box, but it tried to cut the paths just not on top of each other, similar to a profile step down on a CNC, so would checking the "Immediate" box, result in it doing what I intended? I rarely use the "immediate" option and hadn't really considered what's it's real purpose was.

[Dave Sheldrake]

Hiya Nev,

I tend to run a lot of repeat jobs on my machines so I always use immediate, when the job finishes and it returns to the start point I can just re-hit it if there has been any problems. Sometimes if you use absolute mode (immediate off) when the lasers re-datums the sensor switches can lead to the home position being different each time.

Try immediate on and if no luck set it to cut the vector once then when it finishes just hit start again.

If neither work then there is something else causing it that wil need more in depth investigation.

cheers

Dave

[Neville Stewart]

Yes that's what I did in fact end up doing. Just noticed you're in the UK, up late are ya :). Greetings from a Dubliner in Texas.

[Joe Pelonio]

I do that to get through 3/8" thick acrylic with 45 watts, just copy the shape once on top of itself in Corel and it cuts twice.

[Glen Monaghan]

I do that to get through 3/8" thick acrylic with 45 watts, just copy the shape once on top of itself in Corel and it cuts twice.

That's interesting. I thought it should do that, but never have tried it myself, although I just this afternoon wanted to do a 2nd pass engraving through a powder coat and so copied the bit map image on top of itself, but it only engraved once. I even tried making the copy a different color (red on white, and even red on transparent) than the original (black on white) and using color mapping, but it still only engraved the bit map once... Apparently bit maps work differently than vectors???

[Dan Hintz]

That's interesting. I thought it should do that, but never have tried it myself, although I just this afternoon wanted to do a 2nd pass engraving through a powder coat and so copied the bit map image on top of itself, but it only engraved once. I even tried making the copy a different color (red on white, and even red on transparent) than the original (black on white) and using color mapping, but it still only engraved the bit map once... Apparently bit maps work differently than vectors???

Yep... most packages will "flatten" bitmaps. It can also cause issues when you get into power clipping of bitmaps.