Thread: HELP, Drilling Acrylic Blanks

Originally Posted by HazzaB

I have a piece of Sheoak that I am going to make a pen for me, when I find out how to drill the 82mm hole. (I am going to make a jig tomorrow and try drilling from both ends, on some scrap material )

My drill press has an ever shorter throw (closer to 50mm ) but the way I get around it when drilling long blanks is to drill down until I reach the maximum throw. Then, leaving the drill bit partially inside the hole to keep the blank centred, I move the drill press table upwards until the end of the drill bit reaches the bottom of the hole I just drilled. Then I can effectively drill a further 40 - 45mm, which is usually more than enough for the lengths I need. I suspect drilling from both ends will almost always end up in some alignment problems, especially if the blank isn't quite even.

First thing comes to mind , are you spraying with water to lubricate and cool the drill bit with acrylic, most essential to do so. Also I find a well sharpened HSS drill bit with a normal grind will work better on acrylics as the brad point design tries to break up the shavings differently than a standard drill. EG instead of a long curling shaving coming up the flutes it tends to break up into small pieces and clog the drill causing more friction and heat which then tries to expand and bond with the hole you are drilling ,bang ! as you found out, slow the drill down in speed as well to cut cooler. With the longer hole you can drill as far as the travell allows ,then either release your drill in the chuck ,and lower it a bit into the hole and continue drilling bit by bit as you have already, or you can release the blank and lift it up into the drill and retighten it in your vice and continue drilling ,clearing the shavings as needed. If your table has a winder that makes it easy as well just lift the table when you reach depth with the drill stopped, Start the drill again to align the hole which it should do no problem,nip up the table clamp and continue the process, Not really advisable to drill from both ends as very hard to get both holes concentric ,can be done though.
Hope that gives you some ideas to try at any rate hehe, good luck with it all.

I can not add any more to what was said. But reiterate. Get rid of the brad point bit. Not good for acrylics. The ideas about drill with a short throw is right on. Slow is the key when drilling acrylics and back out of the hole to remove the shavings. Cool the bit. I happen to use Denatured alcohol to cool my bits. That stuff is cold. Also have a back up piece under the blank when drilling.

I have to disagree about drilling speed. I drill at 1800 rpm with no problems. A parabolic bit is the best choice, but standard 135* bits work just fine. I also drill on the lathe at the same speed.

I agree about not using the brad point bit for acrylics. I was using them for a while until I discovered that the brad point would actually deflect the bit a little when it first entered the blank, then it would straighten out when the rest of the bit entered the blank. The end result was a perfect, tight hole at the bottom of the blank, but an oval hole at the top that would cause blow outs when turning.

I haven't had any problems since switching to a standard HSS twist bit.

In addition to water cooling, don't use a sharp drill!

Acrylic is best scraped, not cut.

Google for drilling acrylic if you want angles and diagrams, but I used one of those diamond plates to take the sharp edge off a brand new drill (about 5 or 6 strokes of the plate), and keep that bit purely for drilling acrylic.

No more blowouts!

Cheers,
Andrew

Originally Posted by arose62

In addition to water cooling, don't use a sharp drill!

Acrylic is best scraped, not cut.

Google for drilling acrylic if you want angles and diagrams, but I used one of those diamond plates to take the sharp edge off a brand new drill (about 5 or 6 strokes of the plate), and keep that bit purely for drilling acrylic.

No more blowouts!

Cheers,
Andrew

Well this is a new one, never heard that before.

I drill my PE cast ersins all the time. I had troubles originally with blow outs, but some tips from the forumites and I'm having no problems at all now, even with a 13mm bit.

As said above, follow the tips for long hole drilling, moving the table up as you go, works fine. Water cool as you go. I use brand new, sharp enough to chop up your fingers (DAMHIKT) standard HSS twist drill bits and they work perfectly.

One tip no one has yet mentioned. Ensure your blank is about 2cm longer than needed and do not drill through the bottom. Drill far enough to get the tube in and then say 5mm - 10mm more, then go back to your sander/bandsaw etc and cut through the end of the blank to open the hole up. Drilling right through the bottom is one of the major sources of blowout.

Russell.

PS. I was drilling slow. they guys said go faster, so now I drill flat out (about 2000rpm I believe) and as long as you,re water cooling, it works like a charm.

Russell.

Hey Guys,

Thanks for the replies, I will take it all on board and see where we get this arvo.
Had not even thougt about cooling the bit. I also will try thenot drilling through the bottom trick. I will let you know tonite how things went,.

I owe, I owe so off to work I go

Thanks again

HazzaB

For those who've never heard of modifying the drill bit to suit the material, here are some links:

http://www.plasticsmag.com/features....sue=Sep/Oct-01

http://www.bertram31.com/proj/tips/drill_acrylic.htm

http://www.hawkfish.org/snailman/acrdrill.htm

Once I modified my drill bits, I found I could drill out the bottom (into a sacrificial piece) with no more blowout, and no going to the bandsaw to chop the end off the blank to expose the hole.

Cheers,
Andrew

Something hard to get used to (at first) is that you can drill pretty quickly through the
first part of the blank. But the further in you get, the slower you have to go. Cooling the
bit and blank is essential, especially since some plastics will 'explode' when over heated.
Cooling the bit doesn't mean backing it out for 2 or 3 seconds, you need to wait for a
while and let it cool down. If you spray water on the bit and it boils, imagine what it is
doing to the blank. The last 3 mm might take longer than the first 30mm did.

Also, you need to be careful drilling in a lathe chuck, since you're compressing the end
of the blank. Once you drill into this part, the chuck can crush the blank because there is
no more material in the end of the blank to support this compression.

Think of an egg shell .. as long as the egg is whole, you can apply quite a bit of pressure
to the center of the egg without a problem. Break the egg in half, and it will no longer
stay together when you apply pressure to the very same spot.

One little thing. Why raise the drill table each time then lower again? Drill as far as you can, then lay a piece of flat scrap under the blank & resume drilling. I've drilled acrylic blanks with a 7mm bradpoint bit since I started 4 yrs. ago & have yet to blow one out. Use a soda straw & drip water in the hole after clearing hole. Only time I won't drill all the way thru is when holding in a chuck. There's nothing backing it up.

Get a small squeeze bottle of water and keep the bit and hole wet while drilling, you won't hurt the bit or the blank.
Try drilling a pilot hole first...drilling large bore holes in acrylic is tough to do, so start small and then use progressively larger bits till you get to your final size...say start with a 7mm, then a 9mm, then finish with the 10mm.
Don't use brad points, use good quality twist drills.
Brad point are great for wood, but lousy on plastic.
If I am drilling all the way through an acrylic piece, I glue a small piece of masonite or thin scrap wood to the bottom of the blank, so the bit dosen't blow out the plastic when it cuts through, it blows the scrap wood instead...then simply band saw off the scrap wood.
As for drilling a long bore in a blank, a lot depends on your vice...I use a drill press vice with the drill table turned on its side...I can drill most of the way through, then bump the blank up some and finish.

Originally Posted by Mobil Man

One little thing. Why raise the drill table each time then lower again? Drill as far as you can, then lay a piece of flat scrap under the blank & resume drilling.

Some are using jigs that attach to the table, so this might not be an option.