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Machining Lexan

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  • Machining Lexan

    I need a pistol grip for several projects that I have in mind. It needs to be light weight, fit my hand well and be able to hold 4 AAA batteries and at least one switch. I designed a grip using CamBam and cut the prototype on my CNC mill.

    Machining Lexan (polycarbonate) comes up here from time to time, usually when somebody has tried with poor results. The "secret" to machining polycarbonate is simple. Avoiding the generation of excess heat is the prime objective to achieve a good finish. Two main considerations apply: Run the cutter at the lowest practical rpm while taking the maximum chip load possible. The other is to use the sharpest tooling available, preferably a new cutter to avoid friction caused by a dull edge. This applies equally to CNC or manual machining of the material. When using larger cutters cooling in the form of continuous compressed air is essential and it also clears chips well.

    Here is the current project:










    I find Lexan takes paint very well if the paint is extremely fast drying so that it doesn't have time to attack the plastic. The best I have found for this is Krylon extra fast drying enamel, the kind that is labelled "dries in 10 minutes or less".

    A short video of the machining action is here:

    1 MB
    http://ixian.ca/video/lexancnc.wmv
    Free software for calculating bolt circles and similar: Click Here

  • #2
    Nice machining, Evan - I'm impressed.

    Batteries? Pistol grips? Laser guns! :-).

    - Bart
    Bart Smaalders
    http://smaalders.net/barts

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    • #3
      no coolant?

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      • #4
        This could have been done with a scrollsaw.But if you have expensive toys I suppose the expensive way is best.A lot of work for a $0.50 cent handle but wheres the fun in buying.Alistair
        Please excuse my typing as I have a form of parkinsons disease

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        • #5
          Originally posted by Alistair Hosie
          This could have been done with a scrollsaw.But if you have expensive toys I suppose the expensive way is best.A lot of work for a $0.50 cent handle but wheres the fun in buying.Alistair

          Scroll saw would work on the outside, indeed, but inside is a little
          trickier... won't be much room for batteries then...

          - Bart
          Bart Smaalders
          http://smaalders.net/barts

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          • #6
            Sorry, no scroll saw. It's not just pocketed but there is an interlocking lip all the way around that is .1" thick and .1" deep. positive on one side and negative on the other.

            As for a 50 cent handle, not here. We don't even have a craft or hobby shop in this town.

            Beanbag, no coolant. It's running at maybe 300 rpm and cutting at 10 ipm with a 4 flute carbide cutter. Small cutters radiate the heat away faster than big cutters because the ratio of surface area to mass goes up the smaller the cutter is.
            Last edited by Evan; 10-17-2009, 03:59 PM.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              Thanks Evan,
              I certainly have experience machining it poorly. :-(
              I will give your ideas a try once I get the spindle working properly on my Mill. (Thats a hint to Sir John)
              Dave

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              • #8
                Evan

                If you can heat the polycarbonate after painting you can increase the dissolution of the solvents, and other paints may work. The difficult part will be heating without a film forming, cause then you'll get pinholing and surface abnormalities.

                For the actual machining, it helps quite a bit to use a blast of compressed air as coolant. The other thing that works really well with polycarbonate is router bits. That's all we used on the trim robots (pulled the pieces out of the mold, then held ran them across a router bit to trim the sprues)

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                • #9
                  I think somebody mentioned that Simple Green works well as a lubricant/coolant.

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                  • #10
                    We are at the show at the moment and the small KX1 is making Lexan patterns for another guy to make sand castings in brass from.
                    We are doing loco nampletes and such like.

                    We are running 3mm 3 flute carbide at 6,000 rpm and 600mm /min for clearing and engraving the letters at 7,000 rpm and 800 mm / min with single flute engraving cutter, again solid carbide as we get free tooling.

                    We are running an airbush compressor with one of these drip feed oilers in the line to provide a crude form of mist lubrication although it is more like missed

                    [ Not forgot your spindle Dave and Arturo has been contacted ]

                    .

                    I'll get some pics tomorrow when we get into the hall, Don't think it's been quite as busy as last year but still have 3 more show days to do.
                    .

                    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                    • #11
                      I use router bits all the time and not just on plastic. Carbide corner rounding bits work just fine on aluminum.

                      That's what I used to round all the corners on the 4th axis tailstock.

                      Free software for calculating bolt circles and similar: Click Here

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                      • #12
                        Re: Lexan

                        Evan...That's what, 1" sheet? That used to be pretty pricey stuff a few years ago. Did you find a deal on it or buy it from a regular plastics supplier?
                        I am always looking for good suppliers and sources.

                        Nice job on the handles. There are just some things a cnc really does a great job on.
                        Jim (KB4IVH)

                        Only fools abuse their tools.

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                        • #13
                          That's 1/2" sheet. I get it for free from a local shop that uses a lot of it to replace the windows in heavy logging equipment. It is worth about $100 per sq foot but any pieces smaller than a couple of sq feet are useless to them as they won't fit anything and there aren't any other uses for that thickness in those sizes. They could recycle it but a lot of what they have is the scratch resistant grade. It has a layer of much harder plastic on both sides and that makes it unrecycleable.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #14
                            I use router bits all the time and not just on plastic. Carbide corner rounding bits work just fine on aluminum.
                            I also use them all the time on my mill, they also work just fine as a form tool on the lathe.

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                            • #15
                              I bought a 2' x 2' of lexan for a project at work. I had this idea that I could shear it.

                              Well, I could but since the shear comes down at an angle, it rotated my stock and cut it at an angle. The shear also left an A shaped edge.

                              So I switched to plan 2, I ran it across my table saw to cut it to size. I got a decent edge using wood working speeds using a carbide tipped blade.

                              Sure doesn't seem like you should have problems with this using metal working equipment which tends to be a bit on the slow side when compared to ww equipment.

                              Clutch

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