I’ve found that using a laser cutter to make diffusers out of 0.5mm white polypropolyne (PP) sheet can be quite tricky. It’s a material that melts very easily and it’s difficult to get smooth edges.
I recently had some diffusers made from 0.25mm PTFE (Teflon) sheet in White Opal (Translucent) and it cuts much cleaner on a laser cutter.
I installed the PTFE diffuser and it seems to work fine. My question for the forum is whether there is a specific reason why 0.5mm PP was used, and if there are any potential issues with using 0.25mm PTFE for the diffuser?
Which way round are the two materials in the photo? [Edit, opening the photo shows a caption, PTFE on the left, PP on the right]
The important thing for the diffuser is that it should have no directional dependence and no positional dependence. Things like PTFE plumbers tape that was used sometimes on v6.1 have a structure that is aligned with the tape length, which is likely to have an uneven directional scatter. This does not fill the NA of the lens equally in all directions. This is also a reason not to use a 3D printed diffuser. Most sheet materials are more uniform, although some do have a directionality from the production process.
With a uniform sheet, you then need enough scattering so that the light coming from the diffuser does not really depend on the shape of the light source. That means that we probably want it to look white rather than translucent. In your photo the dark/light grain of the wood is visible through the left hand diffuser. Of course, if it is too thick and scatters too much then there may not be enough light for the image.
So in answer to your question, an appropriate type of PTFE sheet should work, but we have not tested any. PP was selected because it is available and works. I punch through the screw holes using a 2mm pin punch and a blank LED PCB as the backing and template.
I got reasonably ok cuts by playing with the laser settings (going somewhat fast (50mm/s) with a slight overcut and just enough power to cut through), but the edges still curve up a bit. The sheet also tends to curve up while cutting, last time I did it I used a large piece of acrylic with a hole approximately the size of the grid of diffusers to hold it down all around the piece.
Cutting PTFE can generate some nasty fluorine compounds which might cause damage to the laser cutter (also humans), but with a 0.25mm sheet it’s probably fine.
Before I started selling kits I did buy some thinner PTFE and some other plastic sheet as the PP sheet loses a ton of light, but the PTFE was too thin (0.1mm I think and somewhat translucent), before testing the other sheet I decided it’s better to go with what is in the instructions. But if we can find a material which works as a good diffuser but loses less light that would be great.
I ran into the same issues. Even with optimal settings, the PP sheet still melts and curves up a bit. For the whole sheet curving up, I even tried sticking it down to some MDF (also to a metal grill) using double-sided tape (also tried glue stick), but that just left a mess when burn marks transferred onto the PP plastic. I like your acrylic weight idea!
I would be happy to send a couple of folks in the UK a 0.25mm PTFE diffuser who wants to try them out for free? Just send me your address via DM.
I introduced the PP sheet as a way to get around other more hacky methods. The original reason was that I already had some and it worked.
I have found a leather punch works well for the sheet. I haven’t tired this for the diffuser as I don’t have a 14mm punch. But I have used a 15mm punch with success for making little round labels. I’d think it could be really quick to do then have a jig to drill a number of them. It seems like a case where traditional tools may be more successful than digital ones.
Evil Jeff sells 14mm punches:
I am sure people who pay taxes sell them too!
But I have nothing against PTFE if it illuminated evenly
With tuned laser settings the warping isn’t that bad in my opinion. The edges are lifted by around 0.2mm, which shouldn’t cause issues with mounting and it’s far from the optical path. One side is always more flat.
