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  • Boring Acrylic rod?

    Through no fault of my own, I wound up with forty-eight of these:



    They're 1" OD, 14-/34" long, with about 12-1/2" of solid rod between the drillings. They're out of an old wide-format automated film developer, so whatever the material is would have to resist some semi-nasty chemicals (though still water-based.) I'm kind of assuming they're Acrylic, but what else could they be? Lucite?

    Anyway, being an unrepentant paintball lunatic, my first thought of course was to bore and thread one for a barrel. Firing pressures are minimal, no rifling, etc.

    So how would one bore it, first off (needs to be roughly 11/16"- between .680" and .690") and second, how would one repolish the newly-bored hole back to as close to glass clear as possible?

    I need at least a good six inches- eight would be better- of proper bore. The rest can be overbored if necessary (it's common in PB gun barrels, makes 'm quieter.) I'd prefer a full foot of good bore if I can get it.

    Should I try making a "D" reamer or single-flute drill out of a chunk of 11/16" drill rod? I've got some 8" and 12" drills up to 1/2" for a pilot bore.

    I'd rather not have to buy a 12" 21/32" drill bit and a long-shank 11/16" reamer, if I can help it.

    Doc.
    Doc's Machine. (Probably not what you expect.)

  • #2
    It's probably acrylic. Acrylic is rated resistant to photographic solutions. To bore deep holes in plastics I use a spade bit. You want minimum contact area of the tool to the work to avoid building up too much heat. A spade bit also allows plenty of room for chips.

    Another trick that works is to take a regular long bit and grind the OD down starting about .25" from the business end and leaving a full OD collar every couple of inches to keep it on track. It's all about friction and heat. I'm not sure about acrylic but with most plastics you can use alcohol as a coolant. It evaporates quickly and so carries away a lot of heat.

    Acrylic can be flame polished after working to obtain a crystal clear finish.
    Free software for calculating bolt circles and similar: Click Here

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    • #3
      Originally posted by Doc Nickel

      So how would one bore it, first off (needs to be roughly 11/16"- between .680" and .690") and second, how would one repolish the newly-bored hole back to as close to glass clear as possible?

      Should I try making a "D" reamer or single-flute drill out of a chunk of 11/16" drill rod? I've got some 8" and 12" drills up to 1/2" for a pilot bore.
      Doc.
      Doc:
      The single flute reamer is a good idea. The bore will have to be extremely finely finished in order to obtain anything close to glass clear finish.

      Use a lap with progressively finer grit and then cotton buffer with jewellers rouge to diamond paste.

      Flame polishing is very tricky on a long bore. I'd more than likely try to rig up something like a heat gun (aka paint stripper), with reducer adapter to long copper tube drilled radially ...

      NOTE: you want to control the temperature very carefully otherwise you will get bubbles forming which will really spoil the finish
      Last edited by bob_s; 08-09-2007, 09:52 AM.

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      • #4
        Seen a episode of How's it Made shown them making screwdriver handle on a auto feed lathe. They came off a milky color and then dipped them into a vat of acetone finished up crystal clear. You could try that with a cut off.
        Wow... where did the time go. I could of swore I was only out there for an hour.

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        • #5
          Similar to what Tinkerer mentioned, I've "polished" small repaired areas of plastics by gently (and quickly) brushing with a wet brush of solvent bonder which is primarily MEK. Whichever you use, it will QUICKLY soften the entire surface of the part so it should sit (or hang) for a few hours before handling, longer if you're gonna do anything further to it. Den

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          • #6
            Boring Acrylic rod?

            For the "science boys" I drilled a lot oc cast acrylic rod for various projects. I found that if you use WD 40 for a cutting fluid and flood the cutting tool you will get a near mirror finish. As Evan says, it is heat buildup that dulls and spalls the finish. You need to remove the chip as quickly as possible also. The drill chips come off soft and hot but harden up almost instantly.

            Another approach is to use an air jet to flood the cutting area with compressed air. This leaves a smooth but somewhat cloudy finish. That you could probably wash out with acetone and get the finish you are looking for.

            Good luck
            Jim (KB4IVH)

            Only fools abuse their tools.

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            • #7
              Hold the alcohol!

              Dear Doc,
              You can use alcohol as as tapping fluid for acrylic, but that's only because of the minimum heat produced.
              If you use alcohol as a coolant, withthe heat from any boring, you will create massive crazing throughout the thickness of the material, making it useless and dangerous for a paintball barrel. (Don't ask how i know? :-)
              As suggested, WD40, or Inox would do well for this
              Richard in Los Angeles

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              • #8
                So just a quick dip in acetone will clear up the surface? Might have to try that... How badly does that affect sharp corners and the like? Two things I'd like to try making have fairly fine threads, 20 and 32TPI- I suppose the acetone would probably melt those, or round them off enough to not fit the mating part?

                Though I could machine, acetone-polish and then do the threads as the final step...

                Doc.
                Doc's Machine. (Probably not what you expect.)

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                • #9
                  Just curious, clear paintball gun barrel??

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                  • #10
                    Acetone's a no-go. All it seems to be doing is giving me jillions of microscopic surface cracks. Looks like a slighty-more-frosted surface to the naked eye, but under magnification it's an array of extremely fine surface crazing.

                    Doc.
                    Doc's Machine. (Probably not what you expect.)

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                    • #11
                      Originally posted by Rookie machinist
                      Just curious, clear paintball gun barrel??
                      -Sure, why not?

                      Max pressure at the ball, in most PB guns, is 90 PSI, and by the time the ball's moved it's own diameter, which happens in just a couple milliseconds, the pressure's halved and falling rapidly.

                      There's no rifling to worry about, the ball's a loose fit- you can blow one through with lung power alone- and material, by way of things like expansion, droop, or surface friction, is essentially irrelevant. A paintball gun barrel is basically just a smoothbore tube.

                      The aftermarket, of course, hypes and promotes "stepped bore" barrels, lots of porting, muzzle brakes, and all sorts of other trinkets and bells and whistles. But after two decades in this biz, and having tried everything from brass barrels to carbon fiber, to stainless, to hardchromed to plastic, and rifled, stepped, grooved, gain-twisted and drilled with every imaginable combination of "porting" you can think of, I'm firmly of the opinion that none of it does crap, except the porting which makes the shot a little quieter.

                      Doc.
                      Doc's Machine. (Probably not what you expect.)

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                      • #12
                        Sorry Doc:

                        I should have warned you about using any aromatic solvent on acrylic.

                        Solvents like acetone and ether are used as the base for acrylic glues.

                        Years of helping my father construct acrylic jewelry displays has convinced me that mechanical polishing is the best way to treat acrylics, but must avoid over-heating the surface. It is just a very slow, time consuming process.

                        Flaming works well on outside surfaces, as you have more precise control of the temperature, because you can control where the flame touches, but with an internal bore that is very difficult. Flaming still requires a very fine mechanical preparation of the surface.

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                        • #13
                          Hold the alcohol!


                          I haven't tried alcohol on acrylic but I use it on other plastics. It will depend on what type of alcohol is used as the properties vary a lot. I use straight ethanol which is available here as rubbing alcohol. I expect isopropanol or especially methanol would have a different effect.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #14
                            Those will be bad a$$. Post some pics when ya get one done. I have not played in years. SC village is about and hour from where I live. I miss playing, but I sold all my gear, and I dont have the spare time I used too

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                            • #15
                              I've helped two instrument makers setup lathes to drill long straight holes in exotic wood (flute bodies).

                              The best way we found to do the drilling was with a long oil hole drill. Instead of pumping cutting fluid through the drill we used compressd air.

                              Of course, for Doc the cost of the drill would be the killer to that method.

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