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Polyethylene (PE) — melts badly


#1

I was just wondering what specifically you mean by “melts badly” with respect to Polyethylene on the Custom Laser Cutting materials page.

I was hoping to get some very thin (0.05"-ish) adhesive-backed plastic to laser cut and engrave into a faceplate for a PC-104 computer case, but all McMaster stocks in the right color and thickness with adhesive backing is Polyethylene.

Thanks,

-Adam


#2

Hello,

In general, the laser centers itself on the lines you draw in your file and usually burns away about 0.005" of material from either side of the line. With polyethylene (PE), the laser might take off closer to 0.02" of material from either side of the line for sheets around 0.05" thick (possibly even more for thicker sheets).

The cuts in PE usually have a lip or ridge to them, and very long, thin strips in a part will melt or warp. Thin, sharp, acute angles also tend to melt and warp. If you care only about the holes that are left in the plastic (and not the pieces that fall out), then even though the part itself might come out gnarled or warped, the hole left in the material might look acceptable.

If you like, you may email us your design and we can let you know if laser cutting it from PE would work.

If a different thickness of material is acceptable, then johnsonplastics.com has 1/32" acrylic-based, adhesive-backed plastic that comes in a variety of colors. You can see them by following these links in their online catalog:

Engraving Products / Plastic / Rowmark / ADA Alternative / 1/32" (second 1/32" option in the list; part numbers end in “A” to indicate adhesive backing)

They can also apply an adhesive on other materials for you, in which case you can look at their 1/16" and 1/8" offerings as well (you would have to call them for pricing and lead time). Note that you would need to select a laser-safe material (look for a thunderbolt icon at the top of the catalog page).

- Candice


#3

After reading this is it just all polyethylene that melts badly because there are three different types of polyethylene. The three that I can think of is LDPE, HDPE, and UHMW. Do they all behave the same?


#4

I tried some 0.062" thick UHMW polyethylene, McMaster #7701T214 (on my university’s laser cutter, not through Pololu) and it came out really nasty with melty edges, just like Candice described.

From now on I’m sticking with the A’s: ABS, Acrylic, Acetal…and kApton.

-Adam


#5

I just found some leftover laser-cut pieces of the UHMW PE sheet:

For reference, that hole is 0.375" diameter. Yuk!

-Adam


#6

I hate acrylic with a passion. It’s the only plastic that I can think of that can shatter into tiny little pieces if you look at it the wrong way. Kapton is a funky material. The only time I’ve used it is when I needed a tape that doesn’t melt into oblivion when bombarded with UV rays. That leaves Acetal and ABS. Acetal/Derlin is a nice material used a lot as bearings and ABS is the same durable material used in plumbing Legos. The only problem is that I know ABS comes in other colors other than black and white.
EDIT
I saw your other post after I wrote this.


#7

Yeah, I try not to use Acrylic for structural parts, but it comes in so many pretty translucent colors! If only you could laser cut polycarbonate without releasing all that pesky chlorine gas!

-Adam


#8

I would like to reiterate on my last post that I actually own the little plastic rover kit that Pololu sells. For small applications acrylic works out just fine but I wouldn’t go larger than that chassis. Just out of curiosity you mentioned Kapton. Have you ever used it for anything?


#9

I only cut kapton once actually. I was making little insulating spacers (out of Acetal) for a tiny sensor board that had to sit recessed in an aluminum part. These boards each had a little surface-mount capacitor about the thickness of the plastic sheet I used for the spacers, on the spacer side, so there needed to be a clearance hole cut, but it still needed to be insulated from touching bare aluminum. I cut out all the little capacitor holes, then laid kapton tape down over them and cut out the other holes and edges. It worked really well.

If I ever need to make a flexable laser-cut part I’m totally trying kapton first though.

-Adam


#10

I only cut kapton once actually, but I felt it belonged on the list. If I ever need to make a flexable laser-cut part I’m totally trying kapton first.

I was making little insulating spacers (out of Acetal) for a tiny sensor board that had to sit recessed in an aluminum part. These boards each had a little surface-mount capacitor about the thickness of the plastic sheet I used for the spacers, on the spacer side, so there needed to be a clearance hole cut. Of course, there still needed to be some insulation behind this hole, to keep the capacitor leads from touching bare aluminum. I cut out all the little capacitor holes, then laid kapton tape down over them and cut out the other holes and edges. It worked really well.

-Adam