Cutting Delrin .125" Thick

[Ernest Saldana]

Guys, I am having a problem with melting while cutting delrin that is 1/8" thick. There part I am cutting has a series small teardrop shaped holes that tend to stick together due to melting. I can poke out most of them, but I end up losing about 20% of the parts because some of the holes are fused at the cut line. I have tried many different setting. Currently I am using the following:
Pinnacle 40W Laser Engraver
DPI = 1000
PPI = 200
Speed = 1.5%
Power = 35%

Any suggestions?

Ernest

[Doug Griffith]

Your PPI seems low. How about using air assist to "blow" the melted material out of the kerf. Try cranking up your psi.

Cheers,
Doug

[Angus Hines]

The power sounds low and the PPI low.

I cut 1/4" Delrin @

100% PWER
.09% speed
1524 PPI or the highest you can go before getting the auto setting of X which sets it to match your DPI

When cutting plastic or Acrylic you want the laser to fire as many times as it can to prevent the preforation effect you are describeing.

and if you spped and power settins are wroking try these setting starting by increaseing the PPI only at first then adjust from there.

Also, make sure you have your air assist on HIGH. to help blow the plastic slag through the cut.

Hope that helps.

angus

[Kim Vellore]

I have my settings at home but I remember the PPI=5000 and speed =1% I had the power adjusted so it does not fuse together, I dont remember that number. I am sure it will be different for you because I use a 1.5" lens and 45 watts. I got clean cuts like acrylic.
Kim

[Ernest Saldana]

Thanks for your help guys. I can't believe that all this time I had the valve for the air assist shut off. The parts are coming out a lot better. Still a little bit of fusing but loss of parts is 0%. I turned up the DPI and PPI plus I increased the power to 40% and lowered the speed to 1%. I will keep trying to tweek the settings but much improved. Thanks for the heads up on the air assist.

Ernest

[Brian Robison]

I'd increase the power to 100% and raise the speed.

[Gary Hair]

Thanks for your help guys. I can't believe that all this time I had the valve for the air assist shut off. The parts are coming out a lot better. Still a little bit of fusing but loss of parts is 0%. I turned up the DPI and PPI plus I increased the power to 40% and lowered the speed to 1%. I will keep trying to tweek the settings but much improved. Thanks for the heads up on the air assist.

Ernest

Just for your own reference - DPI has nothing to do with cutting but PPI does.

Gary

[Gary Hair]

1524 PPI or the highest you can go before getting the auto setting of X which sets it to match your DPI

Sounds like you have a GCC/Pinnacle/LaserPro - if so, then the "X" setting gives you a continuous pulse, at least that's what the manual states. It's funny though, because in the driver itself "X" is equated to "Automatic" which would make sense that it matches the DPI.

Anyone know what it really does?

Gary

[Michael Hunter]

A layer of masking tape on top helps prevent the plastic melting alongside the cut line and another layer on the bottom stops any smoke and mess sticking there.

Works well for nylon and delryn - and even better for really soft plastics like HDPE which spoils very easily.

[Martin Reynolds]

I spent some time measuring this. At 1524 and below, the laser varies the pulse rate with the speed of the head. This way, the energy density in the cut remains constant even if the speed changes (which it does). My measurements show that this mode delivers about 70% of power that you get in X mode.

In X mode, the laser is on pretty much continuously. I don't know if it is pulsing or not, but that's another question. In X mode, the laser is at 100% all the time. As the laser slows (a lot) for curves it is difficult to get the power right on designs that have curves and straights.

[Mike Null]

Martin

I was under the impression that PPI was a linear measurement. Am I wrong or are you saying that in a different way?

[Martin Reynolds]

PPI is indeed a linear measurement, but the laser head does not run at constant speed. So the pulse rate on the laser has to vary continuously to maintoan constant PPI.

Above a certain pulse rate, the laser power becomes pretty much continuous. On my laser, that is the X setting. It puts out about 50% more power than a constant PPI setting, but the balance between curves and lines is tricky.