Laserscript user forum

Hi all!

I am experiencing a lot of wasted money and time with inconsistent cutting of 3mm (mainly coloured) perspex I cut a full (A4) sheet on my LS3020 with on average 22 separate items per sheet at a speed of 10 and power 75. However, when I come to press out the finished article roughly 30% have cut OK and come out and the rest have not cut through and are wasted.

I check the focus at a mid point before starting. I have tried increasing the heat in increments up to 85 but this just seems to cause the perspex to fuse back together and end up with the same result. If I cut one large single object I can usually push out the finished product albeit with some filing needed where the edges fracture slightly.
Can anyone offer any advice please?

I am currently having to do a second cut at speed 15 power 45 to ensure I cut through but this is very time consuming and heats up the perspex with cloudy marks that take some removing with the IPA solvent.

Should I let the perspex cool before attempting to push out the items or is this best done warm do you think?

Any advice would be sooo welcome!

Best regards, Richard. Puffin Design

You should be looking at one pass at around 14mm/s at 60% if I remember correctly. I would check the alignment and condition of the mirrors and lens and even do a ramp test to make sure you are focusing correctly. Are the parts are failing to drop out in a specific area?

Best
Dave

Hi Dave - thanks for that.

When you say "cutting at 14mm/second" is that the same as setting my speed to "14" on my LS3020 please? The failed cuts seem to be random over the A4 sheet - I can't see a particular pattern.

I have cleaned the lens on both sides and a manual test of the laser fires as near central as I can tell. I would be grateful if you would you explain what a "Ramp Test" is please? The machine is very new so hopefully nothing drastic is wrong!

Best regards, Richard

I have just cut another sheet of 18 keyrings on A4 3mm yellow perspex at a 1st cut of 10speed/75% and 2nd cut of 20speed/30% and interestingly the cut nearest "Datum" almost didn't want to come out - but was persuaded to. However the perspex now seems very soft and even using a microfibre cloth and IPA Solvent, doesn't want to clean up fully.

I would second what Dave says. 3mm acrylic is pretty much our standard material, and (allowing for the different tube in our 6090), his suggested settings tally with what we use.

The ramp test is very simple - just cut a simple shape over and over from, say, 10mm below where you'd normally focus, raising the focus a little each time until you have found the "sweet spot" where the width of the cut is narrowest. Then measure between the workpiece to a convenient point on the cutting head. I usually then cut out a square of acrylic that size and stick it on the keyring with our machine's keys (otherwise, I guarantee it'll get thrown away as "scrap" before long!). You can then repeat the same thing with different power settings and speeds to find the sweet spot for those too.
It's a bit time consuming, but you shouldn't have to do it too often - once for each new material you want to cut is usually enough.

Couple of other things worth noting...
- It seems a bit perverse, but turning UP the power isn't always the right thing to do if your parts won't pop-out. Firstly, it gets the plastic hotter around the cut, so it's more likely to sink back into the cut and fuse back together. Secondly, too much power can sometimes cause the plastic in the cut to change its properties - forming a kind of hardened barrier at the bottom of the cut that prevents the laser going right through. A Brucie Bonus is that you save on electric bills and your laser tube will last longer!
- Get yourself a thermometer and check the temperature of your cooling tank (Assuming you have one, I'm not familiar with the 3020) - it's a pretty good guide to how hot the tube is running. Once the temperature gets above about 20-25degrees, the laser loses it's efficiency, and you'll get much less power than you asked for. When we added a chiller to our 6090, the difference was amazing - from trashed workpieces after only half an hour, to utterly reliable cuts running continuously for a full 8hr shift. If money is a bit tight, get yourself some wine cooler blocks, stick them in the freezer overnight, and add those to your tank at the start of a job!

All the best
Steve

Agree with Steve - turning the power up is not always the solution. The 3020 is a great starter machine and tuned nicely will give you speed equal to a 60w.

Ramp test explained by Tweakie

Check also how you are focusing and how level the bed is - there should be a post or two here that explains it

Best
Dave

Thanks to everyone for the very comprehensive and detailed replies. Just one thing - I am still not clear on is the speeds quoted ie xmm/second. My LS3020 has software driven speed increments which seem to be on a scale of 1 upwards - does this equate to mm/second - ie if I input a speed of "10" does that equate to 10mm/second?

Once I know this I promise to keep quiet - for a bit!

Cheers, Richard

Hi Richard, yes it is mm/s

Best
Dave

Hi Richard.
I use the 3020 I have had it for about 18 months now.
I cut 3mm perspex most of the time with no problems (touch wood)
I set my amps at 4 and a speed of 5 with great results. This might be a bit slow for you but most of
time i am not in a hurry. Like in an earlier post save on power and laser life.

If the cut parts are fused at the end of the cutting, then maybe not enough extraction. As extraction cools the material when it sucks the air passed. I cut with card under the acrylic and quite a bit of liquid is absorbed and there is a fire risk, whereas without the card underlay, no problems. The manual does say to lay card under. When you lay the card in it does suck to the table. Proof of the extraction.