#!$%!! Mylar

[Dave Vigness]

Okay guys, I've answered a lot of questions, time for me to ask. Is Mylar just a royal PITA to work with?

She got a little pack of Mylar, thankfully only 10 12x12 sheets, for me to practice with. The package says 10 Mil, my micrometer puts them at .25mm. I'm on an 80W China Red with 6445G controller. My power curve is more like a quarter circle, and my tube puts out something more like a halo that a dot when doing my focus tests. I do get a nice sharp dot on the thermometer though.

Did a quick stencil she just had to have with some guess work on the settings. It came out, but the edges were a little rough. Got around to running some actual test squares. All, and I mean ALL, of the edges are nice and yellow. Even the edges that cut are not the cleanest. I'm getting in the neighborhood around 15% power at 80mm/s and slower. My bottom end on this laser for card stock is 12%.

Here's the weird part. My Y cuts are fairly clean and straight, but don't go through all the way. My X cuts, while they do go through, are pretty scruffy. Everything was a bit scruffy doing 10mm squares. Bumped up to 20mm squares and that's where it becomes much more noticeable. The squares that don't drop out, are hanging on the clean Y lines, and the ugly X lines are free as a bird. I'm running low air assist, not blasting it like I do for MDF, but not just the bypass I use for engraving.

Oh yeah, and I JUST went through alignment two days ago. I'm going to check again in the morning. But Damn...

Thoughts, hints, tips, rolling laughter?

[Jeffrey Aley]

In the research that I've done, there's an awful lot of different stuff that's referred to as "mylar". So let's start with that - what material do you have?
Is it true Mylar - a registered trademark for a polyester film made by DuPont? Or is it Duro-lar, or "drafting mylar", or something else?

I just bought some Duro-Lar, but I haven't cut it yet.

[Dave Vigness]

It's a milky white sheet, nice and smooth. The Amazon listing says Mylar made from premium PET. I'm not a big fan of PET and the laser to begin with. And of course she listens to what I tell her about materiel... LOL Been down this route with rubber stamp material. Nothing in the add says anything about laser compatibility.

I can just see the wheels turning in her mind when she read the description - compatible with most cutting machines. If cutting by hand, we recommend a heated stencil cutting tool

[Gene Uselman]

My power curve is more like a quarter circle, and my tube puts out something more like a halo that a dot when doing my focus tests.

This seems like the place to start to me. A halo is often the beam hitting the edge of the nozzle and would affect one axis more than the other. I use the anal thermometer for a quick check to see where your beam is in the nozzle opening. Power curve like a quarter circle doesn't seem normal either. Sometimes more power and more speed can work on different materials [have never tried Mylar] and for cutting I always use lots of air pressure to clear the cut.

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anal thermometer2.jpg

[Dave Vigness]

Sorry gene, I get the halo right out of the tube. It's a QC EFR reject with a KH label on it. I get a decent dot on the thermometer. Once the tube warms up a bit I do get a spot out of the tube, but cold I get a halo. Russ suspects an incorrectly mounted partially reflective mirror, but admits that's just guesswork. I get decent power out of it, and reasonably sharp cutting on other media. Even card stock cuts nice. The lower power curve is practically vertical. The power graph Russ sent back looks more like a quarter circle than a normal power curve.

Going to check alignment and clean mirrors and lens' later today or tomorrow depending on when I can break free of my current projects. The thing that bugs me is I have never had anything but a nice straight line for my X travel. I don't even have the mirror / stepper conflict, they are at opposite ends of the gantry. It would have to be some healthy vibrations to transmit all that way across to upset the #2 mirror that much. The idler is right there, but that would be a stretch to get vibrations from that. I'm using a modified version of Russ' #2 mount, but the base plate on the gantry is twice as thick. The mirror stands a bit higher, but only about 10mm.

The squiggle does seem to be more noticeable at slower speeds. 90- 95mm/s and you have to look real close. 70 - 75mm/s and they are readily visible to the naked eye for my 14 - 15% power tests. But yet up at 20% it is noticeable all the way up to 175mm/s on both X and Y. Granted those were 10mm squares, not the 20mm I did on the last test.

Hell, I even 'fixed' my skew error... mostly. I was out a little over 2mm. Loosened one of the belt tensioners and jumped a tooth on the drive gear. Went from a little over 2mm out in the PITA direction, to about .4mm in the 'good' direction. I won't be running off the top of my material as I go across any more! That would be the only good part of when I have to replace a tube. I will be able to get to the set screws on the drive gear and true up that last .4mm