How to Modify Twist Drills to Make Them Safe for Use in Plastics and Brass

[george wilson]

It WAS in the 70's,Tom!!

 

[jamie76x]

What I am getting at is that when you stone the edge of your drill flute, you are taking rake away... Not dulling it.
You are doing the right thing but not expaining the mechanics of it correctly. You are taking the rake away with the stone and that is the correct thing to do. Im not bashing you, just throwing out some info

 

[Tom Griffin]

What I am getting at is that when you stone the edge of your drill flute, you are taking rake away... Not dulling it.
You are doing the right thing but not expaining the mechanics of it correctly. You are taking the rake away with the stone and that is the correct thing to do. Im not bashing you, just throwing out some info

Sorry, I misread your emoticon. :LOL:

There actually is a method where you grind the bits on the side of the wheel that produces a bit of negative rake over a larger area, but it's difficult to master by hand. What I am doing is literally chamfering the cutting edge just enough to break the sharp edge. I guess you could call it negative rake as well.

Tom

 

[kevin]

Good tip and a nice video. Rather than buy a full set of drills just for "dulling" I would say to get an empty drill index, modify the drill bits as you need them, and save them in the index. That way, you'll end up with the set of drill bits you actually need.

Here's a good set of links on drilling and machining plastics (scroll down to "Plastics"):

https://sites.google.com/site/lagadoacademy/useful-links#info-other

 

[Tom Griffin]

Good tip and a nice video. Rather than buy a full set of drills just for "dulling" I would say to get an empty drill index, modify the drill bits as you need them, and save them in the index. That way, you'll end up with the set of drill bits you actually need.

Here's a good set of links on drilling and machining plastics (scroll down to "Plastics"):

https://sites.google.com/site/lagadoacademy/useful-links#info-other

Thanks.

Yes, that's exactly what I do. I have a box of old drills to pull from as needed. There's no set-up involved so nothing is lost making them one at a time, as needed.

Tom

 

[Oldnbroek]

I made an interesting discovery the other night while I was drilling some quarter inch copper plate. I had just broken my last bit in that size, and was forced to regrind the stub of the tiny joker. I wound up putting a really steep point angle on it, almost 60 degrees, and it worked wonders! Located instantly without walking and didn't grab on break through which was the original problem. Just my 2 cents.

 

[kwoodhands]

I was in a shop that sold audio equipment years ago. One of the things on display was a clear plastic speaker cabinet they had made. It was high priced. The guy said it wouldn't be so expensive except for all the plastic they had broken while drilling the holes. I made him a drawing of how to grind his drill bits for drilling plastic. I'm sure he found it useful if he made another plastic speaker cabinet. I grind a vertical edge on the cutting edges of the drill bit,similar to what you are doing,but I don't put a negative cutting edge on the drill.

The cutting ability of the drill doesn't seem to be affected when using it in a machine. Might really be noticed when using it in a hand drill.

I have several old brass drills. Their flutes are ground just like regular drills,except they go straight up the drill's body,not spiraled like a normal drill bit. I'm not sure if these are made any more. They look sort of like those old straight fluted drill bits you used to get inside the wooden handles of egg beater drills,but more carefully made,and of HSS.

I really don't see why anyone would want a transparent speaker cabinet ! You could see the speaker,and all the messy wiring,too!

I have a dozen or so drills with straight flutes made for drilling brass.Inherited them,tried to buy more to complete a set.
If they are sold I can't find them.I bought an import set of 29 drills that I made into drills for brass by dulling the sharp flutes.There is a website that shows how.Spade bits work very well in sizes above 1/4" diameter in plastic.

mike

 

[Bill C.]

I would suggest adding negative rake to the lips. This will cause the drill to push instead of pulling up as it cuts. Also put a piece of plywood under plastic to give it all the support it needs. If you are drilling Lexan plastic you shouldn't have to many problems. Plexiglas is trickier, it will chip when it breaks through. Go online and search for the plastic you are using.

 

[Steve_Cole]

I often find when drilling thin brittle plastics a sacrificial piece of plywood above and below works every time.

Sent from my Nexus 6 using Tapatalk

 

[kevin]

For what it's worth, I found straight flute drills at the link below - no idea what they cost. Straight flute carbide drills are easily found, but they cost a fortune. I just use the method of "flattening" the cutting edges of regular drills; I picked up an empty drill index at a flea market, and whenever I need to drill plastic I modify the required drill bit and then save it in my "plastic drill index" for future use.

http://www.ohiodrill.com/straight_flutes

More links to machining plastics here (click on the link and scroll down to "Plastics"):

https://sites.google.com/site/lagadoacademy/useful-links#info-other