Foolproof, Easy, Drill Bit Sharpening for Acrylic

If you have ever drilled acrylic with a standard twist drill you've probably noticed that it is less than ideal. The angle is too shallow and the drill bit tends to break out the backside and chip the material. Here is an easy way to put a much steeper angle on the bit that leaves both flutes the same length (on center) and gives you a ridiculously sharp edge (where it counts).

Disclaimer:
 

• I am about to show you a few things that are definately not safe / OSHA approved.
• Try this at your own risk.
   
• If you blow up a grinding wheel or burn yourself or in any other way damage yourself, anyone else or your tools or equipment, you've been WARNED!!!
   
• So anyone who feels like leaving safety related comments, please leave them only if you have a safer way of doing this.  I already know it is dangerous.
   

That being said...On to the show! 

Step 1 Tools needed...

You'll need:

The drill bit you want sharpened (of course)
A small (high speed preferably) electric hand drill
A bench or pedestal grinder

Comments

[sschoemann]

If you read my post to another poster earlier on in the thread you can tell I've done a lot of acrylic work. I'm going to have to give this a try!
As for a safer way, I used to have a trailer bearing that fit on the keyed Jacobs chuck of the black and decker I have ( green body too,,,) that allowed me to grab the chuck with some amount of safety ( it had a wide press fit race)

[waldosan]

in my experience drilling into acrylic when using a bigger drill bit caused it to want to crack. did you notice if this way of sharpening the bit solved that problem or toned it down? also i thought that drill bits had a temper in them, won't setting them against the grind wheel make them lose it?

[qualia]

again about the temper, have a container of water or other non-flammable coolant handy to cool the bit every now and again between grinding, that way you wont get it past the steels critical temperature

[Mikey D]

Excellent quetions! The angle on the drill bit solves exactly that problem. because it gradually enlarges the hole it minimizes the cracking problem.

If you need a larger hole than you have a twist drill for, a spade or paddle bit will also work. It however does not leave such a smooth finish inside the hole; but a small drum sander on a "Dremel" type tool can solve that. Also the spade bits with "spurs" on them work better than the flat ones.

Concerning the temper in drill bits: They should be hardened (from the factory) that's why they will shatter or snap rather than bend. If you grind slowly (lightly) and don't burn (blacken the steel) you will be just fine.

Thanks for the comments!

Mikey

[grunff]

That's really neat, thanks for posting it. I'm going to give it a try. Instead of holding onto the rotating chuck (!), I think I'll use my drill's handle, which clamps onto the collar just back from the chuck.

[daftcloud]

my shop teacher puts some type of burr deal on the end of his, and it seems to cut fine. He also uses the bits for brass too.

[Mikey D]

Ideally drill bits for brass should be sharpened at a 155 degree angle. The point is almost not a point but is 25 degrees from being flat. This is because brass is a verry "grabby" material and likes to hang onto cutting tools and bind them up.

I'd like to see the "burr" to which you are referring. Cabinet makers put a burr on a flat (or sometimes curved) piece fo steel and call it a cabinet scraper. It leaves an exceptionally fine finish that needs little or no sanading.

Thank you for the comments

Mikey

[burnerjack01]

While the danger is just a "fact of doing business", an excellent rule of thumb is " objects in motion tend to stay in motion". Yeah,so? You ask? Well, If you realize the "plane of motion" and keep your body away from said plane, anything which strikes you has already scrubbed off considerable speed and energy by being the result of a ricochet and not a direct hit. Still not ideal, but less is, well, less.

[Mikey D]

I guess I reflexivly stand out of the "line of fire" whenever I use a grinding wheel. Great point though - thanks!

[Jayefuu]

Interesting! And very well illustrated :D

[Mikey D]

Thank you Jay

[bgipson1]

this also works on fiberglass maybe a little
less angle fiberglass dulls bits fast
learned this method 20 years ago
works great is it safe yes as long as
you not a total goofball

[fegundez1]

i wonder if an abrasive stone would work also. good idea now i can use the el cheapo bit set i have in the junk drawer!