Hi there, First time poster, and hopefully soon to be owner of a 1500 x 1500 Ooznest. I basically want to start a little business cutting some products out of something called Stokbord/Ecoply (as well as maybe a few HDPE/aluminium/ply bits and pieces but that’s another issue) Stokbord is “a recycled Low Density Polyethylene (LDPE) plastic. The recycled LDPE plastic is reprocessed to form a homogenous section of solid LDPE which is extruded through a die, calendar rolled, cooled and cut in a single process.” I was wondering if anyone had experience of cutting it? It has a melting point of 110C/230F. I’m not engraving it, merely cutting out a few fairly simple shapes and drilling some holes. And it would be in 12mm, maybe 9mm and 18mm as possible future options too. I wanted to ask as I don’t want to invest in a machine if my hoped for material won’t cut nicely. It’s also really hard to get samples of the material where I am and I haven’t got any yet either… Basically I’m curious about any advice, in terms of end mills, cutting speed/direction tips etc. Never used a cnc before. Just been teaching myself Fusion360 to create my designs and learning as I go. Thanks
Haven't cut much plastic, and what I have cut has mostly been urethane, which is extremely tolerant of cutter geometries, so salt to taste. For LDPE I'd go polished parabolic single flute, high positive rake- like a quality aluminum end mill, but single flute low helix (straighter) instead of three flute high helix (twistier), pretty much. I'd worry more about the workholding than the cutting, honestly. How do you intend to hold large sheets of it down across the entire section to stop it vibrating? Vacuum is usually the go-to for that kind of thing, which isn't too difficult to DIY but not cheap with the very large aluminum plate required. Some dedicated sheet processing mills use rollers attached to the gantry or ball bearing presser feet on the spindle, too. That's an option. Plastic can be much grabbier than wood though, so it's not like just throwing a sheet of birch in, clamping the edges and walking away. I'm sure someone somewhere has processed this exact material though, I'd search around.
Ah thanks for the reply. As I'm new to this I hadn't fully considered vacuum yet as it's another complex thing to work out. But it was a future goal. So it would just be basic hole clamps etc to start. The finished dimensions would be approx 840mm by 400mm, and 400mm by 400m, and 400mm by 350mm Ah thanks for the single flute etc tips. I did do a bit of searching but wasn't sure how much LDPE resembled HDPE and acrylic etc to cut. Especially as it might be a bit thicker than most often gets cut.
As far as hold down goes, I've had a to a few larger pieces of acrylic. I used some small pieces of double sided duct tape spaced out under the plastic, and it worked out really well.
I cut HDPE all the time. I would assume LDPE is similar since it is also a plastic that is easily machined with similar properties. My endmill of choice is a two fluted endmill with straight flutes which are commonly available everywhere router bits are sold. Here is an example with 3 flutes Straight 3 Flutes Solid Carbide End Mill 1/4" Nano Shield. With "twisty" endmills like o-flutes, the plastic spirals up and wraps around the endmill more. With the straight flutes the chips are short and easily removed via the dust boot. HDPE cuts like butter. It is my favorite material to machine because it is easy and rarely do I have issues with it sticking to the endmill. I cut at about 2500 mm/minute with a depth of cut (DOC) of about 1/2 the diameter of the endmill I am using. For example, a 6.35 mm endmill would have a 3.175mm DOC. Those straight flute endmills work well with acrylic and I have successfully use smaller 3.175mm ones with aluminum if I need a smaller hole drilled. For work holding, I like to keep it simple. If I have holes to drill, I clamp the piece down and do the drilling tool path first. Then I screw he work piece down using some of the newly drilled holes and remove the clamps. Then I cut the part out of the stock. This way I do not need holding tabs. If the stock piece is a lot larger than the part, I will leave the clamps on the off-cut and just remove the clamps near the part I am cutting out. For smaller pieces of plastic, I use the painters tape with super glue method. Put painters tape on the spoilboard, put painters tape on the bottom of your part, then smear superglue on either surface of tape and glue the taped pieces together. I put a weight on it for a few minutes. Once it has set up I can cut the part without clamps or tabs and the part will peel off with no issue. It is Poor man's thin double sided tape. I can cut all the way through the part without damaging the spoilboard with this method. Picture of what I mean.
Yep, this is what I was gonna suggest- plenty of holes in those designs to add additional hold downs. Might be worthwhile, if you're making a lot of them and constant screwing into the spoilboard would destroy it, making more of a fixture system with stops and known G53 offsets for ensuring the holes are in the exact same spot every time within a reasonable margin of error, so you can add insert nuts to your spoilboard to use machine screws instead of wood screws. The tape method is great for onesie-twosies, but I wouldn't want all that work and waste for production. Anyway, fixtures and pallets and all that good stuff have been figured out by the machining industry. Just gotta adapt them to individual use cases.
Thanks about the mill recommendations, cutting speed and DOC details. That's great. As is making dedicated jigs, had been down so many rabbit holes looking for people's clamping setups I hadn't yet made the leap to making dedicated jigs yet. Think I'll go ahead and order a 1500x1500 machine then as if HDPE cuts so beautifully I imagine Stokbord should be fairly similar. Many thanks
