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Machining Acrylic

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  • Scishopguy
    replied
    Cutting Plex

    If you are making parts from a solid block of acrylic and need to square up the piece before other operations, you can fly cut the part with good results as long as you grind a generous radius on the tool bit. Also use a diamond hone to get the cutting edge nice and sharp. Best results for cooling and chip removal is by compressed air. Graft a quick connect fitting to an small valve and set it up in a magnetic base on your table, aimed at the vise. Works like a charm. Speeds and feeds similar to aluminum work just fine. Practice up on some scrap and you will get it dialed in in no time.

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  • Evan
    replied
    Sounds the same to me.

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  • beanbag
    replied
    Originally posted by Evan
    The secret weapon in this case is a 1/8" spin saw cutter.
    Is that the same as a "downcut" endmill used in CNC wood routers? Similar to a normal end mill except that the spiral pushes the chips down.

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  • dalesvp
    replied
    To avoid climbing, chipping and break-out I clamp the sheets between two pieces of wood. Drill through them all at once. Same goes for drilling very thin metal sheets in which case clamp between two thicker pieces of metal.

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  • strokersix
    replied
    Modify your cutting edge on drill bits by grinding zero or slight negative rake on the cutting edge. You will be amazed how much better this works in acrylic.

    Similar to cutting brass.

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  • Black_Moons
    replied
    Ah ok, my dyslexia strikes again.

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  • Evan
    replied
    Polycarbonate doesn't have a tendency to shatter when drilled, it's almost impossible to shatter. Acrylic sure does though and will climb up the drill bit unless it is clamped down.

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  • Black_Moons
    replied
    I also read just the other day that plastics like polycarb like to shatter when drilled when braking through the back, apparently allmost directly related to the drill angle as lower angles (More of a point) make it grab more when it exits, and you should probley use 130+ degree point drills.

    Not sure if this applys to acrylic, but its something to keep in mind if it starts cracking on you during drilling.

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  • Evan
    replied
    Sorry about being slow on this but I wanted to show something special that will probably be of interest.

    Acrylic is brittle and has a bad tendency to climb up the bit following the flutes. One answer is to use a carbide burr with straight flutes for edge finishing. After that you may need to wet sand and then to get a glass clear finish use methylene chloride for chemical polishing. To treat an edge put a little on a rag and give the edge a very fast wipe to wet it. ONLY DO IT ONCE. If it doesn't work well enough WAIT 10 minutes before doing it again or you will ruin the work when the rag becomes glued to the piece.

    WARNING: Methylene cholride is toxic and should only be used with very good ventilation and while wearing rubber gloves. It will dissolve most plastics in very short order and it doesn't have a strong enough smell to warn you when the concentration is dangerously high. It is flammable and extremely volatile. It should only be kept in a metal container with a well fitting and sealed cap.

    THE SECRET WEAPON FOR MACHINING ACRYLIC

    It is impossible to make this cut with an ordinary endmill:



    The secret weapon in this case is a 1/8" spin saw cutter. They have reverse spiral flutes and press the work against the table instead of lifting it. I use an upside down hard faced dining table placemat with a thin cork backing as the work surface as this makes an excellent non skid and non marking surface for machining acrylic. By the way, HSS spin saw cutters are relatively cheap.

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  • small.planes
    replied
    tct - tungsten carbide tipped.
    Sorry, common abbreviation so I didnt expand it.
    A plain HSS (High Speed Steel ) bit will probably work to, but TCT will last longer generally.

    Dave

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  • dlsinak
    replied
    Originally posted by small.planes
    try a tct rounding over cutter in a wood router.
    Thats how we used to do it for riot shields, tho admittedly thats polycarbonate.
    Dave
    What are you referring to as a tct cutter? Is that a brand or style of cutter?

    Thanks, Dennis

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  • small.planes
    replied
    try a tct rounding over cutter in a wood router.
    Thats how we used to do it for riot shields, tho admittedly thats polycarbonate.
    Dave

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  • motorcyclemac
    replied
    I believe you can machine it by conventional methods and then dunk the part in acetone to clear up the white machine marks. This should leave you with a clear finish just like the unmachined parts.

    You will likely want to use a cutter that employs a good chip breaker as I believe it strings pretty bad and creates a rats nest when lathe turned. I would seek to keep feeds and speeds out of the area that would encourage melting.

    I have alwasys machined acrylic by the seat of my pants.

    I am sure Evan can give you some accurate feeds and speeds.

    Cheers
    Mac.

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  • Tony Ennis
    replied
    Har, Evan will be all over this. I believe he does 'chemical polishing' on acrylic.

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  • dlsinak
    started a topic Machining Acrylic

    Machining Acrylic

    I'm sure the topic has been discussed before, but being search challenged I have not found any discussion on methods including cutter speeds and feed rates to get a decent finish when machining acrylic.

    I am looking to radius the edge of an acrylic sheet so it will require a minimum of polish for a smooth edge. Any suggestions on this?

    Thanks, Dennis
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