View Full Version : Boring Acrylic rod?

Doc Nickel
08-09-2007, 05:53 AM
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.


08-09-2007, 08:45 AM
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.

08-09-2007, 09:41 AM
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.

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

08-09-2007, 10:58 AM
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.

08-09-2007, 11:15 AM
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

08-09-2007, 01:42 PM
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

08-09-2007, 01:56 PM
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

Doc Nickel
08-09-2007, 08:25 PM
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...


Rookie machinist
08-09-2007, 08:42 PM
Just curious, clear paintball gun barrel??

Doc Nickel
08-09-2007, 09:33 PM
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 Nickel
08-09-2007, 09:45 PM
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.


08-09-2007, 10:05 PM
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.

08-09-2007, 10:12 PM
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.

Rookie machinist
08-09-2007, 10:55 PM
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:(

08-09-2007, 11:44 PM
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.

08-10-2007, 01:42 AM
OK Doc, what you got your hands on is acrylic, it can be turned, bored or drilled to whatever size your heart desires.

As others have allready stated, it WILL melt if the tool tip gets TOO HOT, use anything that will keep the tip cool, even straight water from a squirty hand bottle/ pump will do that job. Just keep it cool and get the swarf out of the hole as quick as you can.

The best way to attack it, is to put a smaller drill down there first, then use just a piece of MILD STEEL with a ground up tip on it as a boring bar, it's real easy to turn this stuff. Get a good finish inside the tube without too many scratch marks, slow to medium feed, but watch the heat build-up, if needed, use the emery cloth on the end of the stick trick, to get out the rest of the turning marks.

Once you've got the hole to whatever size you wanted and it's got a good finish inside it and then want to polish the inside, no wucken furies, go get some AUTOSOL aluminium polish from any where you can lay your hands on this stuff, this stuff is used for polishing mag wheels and comes in a handy tube just like toothpaste, even comes out of the tube just as thick as toothpaste.

Autosol? what the hell you say, well, all you got to do is get a bit of old "T" shirt and wrap it around the end of a sturdy piece of stick, apply the Autosol to the rag, turn the lathe on to about 1000/1500 RPM's and shove the stick up the tube. Use this just as you did the emery stick, the in and out motion, you know, you can even see the polishing start to happen from the Autosol, right before your very eyes.
Remember that polishing with this stuff does create heat and by now you will know what heat does to acylic, be carefull and it won't be long and the inside will BE as smooth as glass. Even do the outside and all your mates will think you got a glass barrel, don't tell 'em any different and they will be amazed.

As for threading it, well go right ahead, just treat it like metal and it will hold a good thread form. If you try and thread it TOO slow, it will chip bits off, not cut like swarf, keep the revs up around 300 and be quick getting the tool out before you crash it. Do not take too big a bite with the threading tool either. It can be tapped as well, interesting watching the internal thread form.
Make sure that the threading tool is TOOLSTEEL sharpened so the edge will cut you, DO NOT use threading inserts, as they are just not sharp enough to create a good clean thread form.

How do I know this, well, I use acylic on the models that I build and this method is used to make bull-lights and headlights for the models. People look at the finished items on the model and DO NOT even think about it, as it looks SO real. Even use acrylic for some set-up jigs, when I got to make multiples for the models.

Try it, you will be absolutely amazed at the finish you can get.
Don't use acetate or acetone near it at all this just softens the surface and crazes it and it looks like crap, avoid the flame as well, it will just burn if left in the one spot a micro-thousands of a second too long.

regard radish

08-10-2007, 01:54 AM
They're going to need embedded blue LED lamps coupled to the trigger. Definitely.

Doc Nickel
08-11-2007, 08:48 AM
Thanks Radish, that was very helpful.

I haven't had much time to experiment, but I spent a few minutes tonight trying a few cuts. As you said, slow feed, sharp tools, good polish.


I broke out my block of white rouge and a new buffing wheel, and it worked great. Polishes easier than aluminum. For the bore, since it was short, I used a pressed cloth buffing wheel on a ubiquitous Dremel arbor, with the same white compound. Didn't get rid of all the turning marks, but as you can see, made it pretty clear.

The "bubbles" are leftover from my earlier attempts to flame polish. :D

I definitely want to try a barrel, but I'll probably have to make an extended-reach drill for it. I have long, smaller drills that I can pilot bore with, and boring in from both ends should help minimize wandering, but it'll probably still be tricky to get a straight, consistent-dimension bore.


John Stevenson
08-11-2007, 09:22 AM
I made some drill bits for double ended boring machines that put the hole down standard lamp columns.
Instead of reinventing the wheel we looked at what the Victorians used and modified their idea's.

These machine are like a lathe with a driven headstock and a large bearing tailstock. The column is held in two inverted cone chucks, one either end and driven at about 1,000 rpm.
The drills, which are stationary, are air fed thru the headstock and tailstock bore and limit rods hit switches to prevent one drill hitting it's mate.

They continually feed and get rid of the chips as they go thru, more later. It can get 'interesting' if the column has an internal burr or shake you can't see as the drill runs off centre and comes out the side of the rotating column which then rips the drill out it's holder and proceeds to whack everything in sight :rolleyes:

We used to have the drill made at the local sheet metal works.
We would supply them a piece of thick walled hydraulic tube about 1/2" diameter and they would put it on the folder and press a vee into the tube so endwise it looked like Packman.
We would then braze a tipped spade blade on the end and seal the end up.
Then two small holes were drilled thru the braze into the hollow tube.

This was fed air at 120 psi and this blew the chips back along the Vee in the tube to clear the chips.
They worked very well, usually the drills were about 20" long allowing us to bore about 36" to 38" is one pass in about a minute per piece.


08-11-2007, 09:59 AM
Righto, now I got your attention, try this lot for even better results.

Use a new acrylic rod that you aint touched yet, as your going to play around with just the outside of it.

This time into the lathe again and start to use the good ole wet and dry with a bit of water as lube, start with about 600, then go to 1000 and if you can find it go for 2000 grade, jewellers use this stuff, it leaves a finish on clear acylic like opaque milk. By doing it this way there are virtually no deep scratches left AT ALL.
Then into it with the AUTOSOL on a bit of the ole "T" shirt, use as many revs as the lathe can kick out. I use a Unimat3 for this job as it gets about 4000 RPM's and the finish is just like a clear mirror if you do it right.

As for the inside bore you gunna do, just use the same system again to get that glass look to it.

Jewellers rouge does work as you found out, but not as good as Autosol.

Sir John has come up with a doozy of an old method for drilling deep holes, I'd look into that one.

regards radish