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  1. #1

    Join Date
    Feb 2021
    Posts
    8

    Machining Plastic Sheets

    There isn't a category for plastic on this website, so I guess I'll post here for now.

    I have a CNC router (Shapeoko 3) that works well. I would like to machine stuff from thin sheets of plastic (<3mm thick). I'm trying to machine stuff that is 1.5mm or 1.6mm thick.
    I do know of the tape and super glue method and it does work quite well. What I noticed however, is the amount of time needed to set everything up. Putting the tape on the work surface, putting tape on one side of the plastic sheet, then placing superglue to adhere them together.
    It does a great job at holding the piece while machining but because of the amount of time it takes to set it up, I'm curious of alternative methods of mounting the plastic sheet. I'm aware of the vacuum option but a lot of the pieces I make has a lot of holes (some stuff I made has more square-shaped holes than material, haha).

    Are there alternative ways to mount the plastic sheet onto the work area that's faster than the glue and tape option?

  2. #2

    Re: Machining Plastic Sheets

    Are you doing full cuts or are you doing 3D features?

    EDIT: I'll just add, under the assumption you are just doing full cuts (2d contours, pockets, holes). In that case, you can just affix sheet down with button head screws to a spoil-board. Yes, it will result in as much as a 0.020" variation in the height if you get a bow in it at some location, it will be of course up to you to make sure you aren't causing gross deformation by overly tight screws or not enough of them. At work on our router we use a high density PVC foam for a spoil-board, it's under $50, full size for the router table, and we use it for many hundreds to thousands of cut parts before replacing it. We don't bother facing, it's already incredibly flat new and the facing time isn't worth the savings for us. We just start cuts 0.025" over the part model and cut through to -0.035" under the part model, when programing the CAM. The spoil-board gets chewed up over time, but between materials we airblast clean it and if necessary give it a quick pass with an orbital sander. That's it. We cut plastic, lots and lots of 5140 and 6061 aluminum, and some 1000 series steel and 416 stainless on it.

    The strategy for complete cutout (zero tab) parts, is to drill holes for fastening (we just bore-mill drill with the same 1/8" 1-flute carbide endmill we use for everything except plastics and wood, which we pull out the 2-flute 1/4" for sometimes). It's rare that we have a part without holes because it's mostly for brackets, sheet metal parts with bends, acrylic that we'll bend on a heated bender, etc. After drilling the holes, we use at least 2 screws in those locations to fix it 'internally' to the spoil-board, then cut the remainder out (make sure you will clear the screw heads!).

  3. #3
    Member
    Join Date
    Jan 2005
    Posts
    12862

    Re: Machining Plastic Sheets

    Quote Originally Posted by brainy19 View Post
    There isn't a category for plastic on this website, so I guess I'll post here for now.

    I have a CNC router (Shapeoko 3) that works well. I would like to machine stuff from thin sheets of plastic (<3mm thick). I'm trying to machine stuff that is 1.5mm or 1.6mm thick.
    I do know of the tape and super glue method and it does work quite well. What I noticed however, is the amount of time needed to set everything up. Putting the tape on the work surface, putting tape on one side of the plastic sheet, then placing superglue to adhere them together.
    It does a great job at holding the piece while machining but because of the amount of time it takes to set it up, I'm curious of alternative methods of mounting the plastic sheet. I'm aware of the vacuum option but a lot of the pieces I make has a lot of holes (some stuff I made has more square-shaped holes than material, haha).

    Are there alternative ways to mount the plastic sheet onto the work area that's faster than the glue and tape option?
    You can make a vacuum table or use vacuum pods, these are easy to make, this is what commercial machines use mostly as well as many Hobby guys

    Thin material you have to use small holes in the vacuum pod or it can distort the material that it is clamping

    https://vacuum-cnc.com/en/
    Mactec54

  4. #4
    Registered
    Join Date
    Nov 2013
    Posts
    1349

    Re: Machining Plastic Sheets

    Hi,
    I use double sided tape to hold down sheets like that. My spoil board is polycarbonate and double sided tape sticks well provided its spotlessly clean.
    This works best when the parts have enough area to be retained by the tape, and the bigger the area the more secure the part is held.

    I also use this for thin sheet metals, .020 brass for instance. If trying this you need to flood cool the brass otherwise the heat from the cutting cause the
    adhesive of the tape to soften and the part moves.

    Quick, cheap and easy.

    Craig

  5. #5

    Join Date
    Feb 2021
    Posts
    8

    Re: Machining Plastic Sheets

    StrawberryBoi, for your info, it's mainly 2D cuts for now, but I may expand into 3D cuts eventually.

    Everyone's feedback is interesting tho, so I'll probably just have to test different methods and wee what happens. Thank you everyone!

  6. #6

    Re: Machining Plastic Sheets

    Awesome, I look forward to hearing how things go. I do 3d cuts in foam, but I can fixture with the screws because the button heads bite into the sides of the foam and make anchor points.

    If I was going to do anything over an inch thick I'd have to figure something out. Truthfully I'd just use the VMC I have access to instead.

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