Plexiglass + holesaw = broken plexiglass?

Discussion in 'Workshop Tips and Secrets / Tools' started by Jonny C, Sep 23, 2019.

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  1. Sep 23, 2019 #1

    Jonny C

    Jonny C

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    Hi all, I need to cut a circular hole in a 1/8" thick plexiglass canopy in order to fit a latching mechanism. The hole diameter is 1.5".

    I've only got one chance at this and I don't have an offcut on which to practise!

    Has anybody tried this? Is it even possible?

    I can drill a pilot hole with my plexiglass drill bit so that's no problem. But the moment the holesaw itself makes contact I'm concerned that however gentle I am the plexiglass is going to crack. The teeth on the standard holesaw just don't look right for plexiglass. How about a diamond holesaw for glass/tiles - or would that just clog up?

    Thanks for any suggestions (I suspect I know the answer: don't even think about it!)
     
  2. Sep 23, 2019 #2

    Hephaestus

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    Template and plunge router. Get a proper plastics bit.

    Hole saw you're huge risk of cracks/breakage
     
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  3. Sep 23, 2019 #3

    pictsidhe

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    Buy a sheet of 'scrap' from your local bigbox
     
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  4. Sep 23, 2019 #4

    BoKu

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    Step one is to ensure that the acrylic is at least 70 degrees F (21 C). Cold acrylic is much more prone to cracking when drilled or cut.

    Step two is to obtain a collection of acrylic scrap to practice your cutting and drilling techniques. You say you don't have one, and that's fine, but I would stand down until you can get one.

    For the holesaw pilot hole, use an acrylic bit of the appropriate size.

    For the holesaw blade, I would recommend against using a standard toothed one. Instead, I would use an abrasive grit blade such as one of these: https://www.mcmaster.com/4194a16. I would turn it as slowly as possible. But again, try it on a scrap before using it on your flight article.
     
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  5. Sep 23, 2019 #5

    D Hillberg

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    1.5" steel tube. heat to cherry red = nice hole trim with Dremal tool.... no cracking
     
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  6. Sep 23, 2019 #6

    BoKu

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    Try it on scrap first, and cool it down to minimum service temperature to see what happens. Thermal cutting operations like that often lock in stresses that result in cracks later in service.
     
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  7. Sep 23, 2019 #7

    Dana

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    I've cut plexiglass with a holesaw with no problems. Spin it real slow so it doesn't melt the plastic.
     
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  8. Sep 23, 2019 #8

    narfi

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    I wonder if you could get an affordable unibit that size?
     
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  9. Sep 23, 2019 #9

    Aerowerx

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    Keep in mind that a standard hole saw isn't that precise as to the diameter, because of the saw tooth kerf. That abrasive one looks like it might be a problem.

    If you need "just about" it would be OK, but if you need a nice fit measure carefully before cutting no matter what type of saw you use. And certainly buy some acrylic to practice on (You spent how much on your plane, and you are worried about buying a small practice piece?)

    I wonder if a Forstner bit would work? They are more precise than a standard hole saw.
     
  10. Sep 23, 2019 #10

    Hephaestus

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    Why I recommended the template and router above.

    Drilling flat Plexi/acrylic/polycarbonate is fairly easy. But start throwing curves into it and that big honking holesaw starts getting wierd pressure points and it gets a little wonky. Even irregularities in sheets makes for funky cutting.

    Clamping a template (front and back) on, saves those little vibration spiders. Then it's just a 1 or 2 flute plastic upcut bit and cut slowly and carefully.
     
  11. Sep 23, 2019 #11

    Jonny C

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    Brilliant responses, thank you.

    I've just bought a 2 inch unibit online - didn't know they were available that large. I'm also going to buy an abrasive hole saw to see which works better.

    I'll get some sheets of plexiglass too to practise on. Hopefully it'll be similar enough to the canopy to give a good idea how well it cuts.

    I'll test versus the standard holesaw bit and report back with pictures in a week or two.

    Might get plastic router bit too - sounds like a better way of trimming the edges than using a mini angle grinder disc...
     
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  12. Sep 23, 2019 #12

    TFF

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    I drill as many 1/8 holes inside the line of the hole to be cut as I can fit. Cut the little bridges between the holes. Then smooth with dremil. Don’t use a hole saw.
     
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  13. Sep 23, 2019 #13

    BBerson

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    Break though is when it cracks. Might want to be careful, or cut the last bit by hand with a Dremel or something.
     
  14. Sep 23, 2019 #14

    bmcj

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    Just to be sure, you’re talking plexiglass, not Lexan (polycarconate), correct?
     
  15. Sep 23, 2019 #15

    Angusnofangus

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    I have made numerous holes in plexiglass using garden-variety bi-metal hole saws, no problem. The advice previously given to do a couple of samples is right-on. Get a feel for it before committing to your final piece. You most definitely not get an exact size. a 1 1/2" holesaw
    will give you a hole that is close, but that's all.
     
  16. Sep 23, 2019 #16

    Jonny C

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    Yes, this one is 1/8 inch plexiglass.

    I'm going to try a few of the methods suggested and see which seems least likely to shatter my canopy!
     
  17. Sep 23, 2019 #17

    poormansairforce

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    On vinyl siding and plastics we run our saw blades and hole saws in reverse.;)
     
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  18. Sep 23, 2019 #18

    Rik-

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    My wife owns an acrylic window company (automotive, marine and *****)

    I'd never touch it with a hole saw if it's thin material. I do not know the shape of the panel but if you could use a router to plunge through it and then use a jig to enable you to route to the contour of the jig it would be safest.

    Afterwards equally important is to debur the opening. Sharp edges are a stress riser.

    Else a drimel tool and patience with a steady hand, a file and no strong forces as it can crack if abused. Poly-carbonate is just soft so it can absorb a bit more abuse.
     
  19. Sep 23, 2019 #19

    D Hillberg

    D Hillberg

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    YEARS AND YEARS & NEVER HAD ANY ISSUES,,,
    JUST A LOT OF WEIRD LOOKS WHEN THEY SEE HOW IT'S DONE WITHOUT DRILLING.
    Soldering irons for screw holes. when plastic is hot all stresses are removed, burs and excess Dremaled off...
    Routers, high speed saws, plastic drills, vacuum molding all work . . .
     
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  20. Sep 24, 2019 #20

    Sockmonkey

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    My two cents is that buying the right tool for a tricky job is usually worth it even if you only use it once because of the amount of aggravation it saves.
    Cent number two is cut slow and let the saw teeth do the work. Pretend the handle is covered in powdered glass. Trying to muscle it doesn't get it cut faster.
     
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