Grinding Twist Drill to drill brass.

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Years ago I had to enlarge the holes in a couple hundred brass parts on the lathe. I bought half-round drills. They worked perfectly. No tendency to pull into the work.
 
Search Amazon and such for slow twist drill. You seem to scrape brass more than drill it. I have managed to get a hold of some slow twist and they are great for brass. Just don't have a sharp edge like you normally have
 
You need zero to slightly negative rake for drilling brass - particularly when enlarging a hole.
You can simply break the edge of your standard drill - you only need to break 0.1-0.2mm of the edge to the required rake 0° to -5° and it works fine - also you then don't have to grind back very much drill when resharpening it for normal use.
 
Bronzewing said:
Search Amazon and such for slow twist drill.
Click to expand...
I always thought slow twist had more to do with the flute helix angle & vacating chips optimized in different materials. Are you saying these things go hand in hand in a commercial drill? My own experience is that unless the rake is altered at the cutting edge, it almost doesn't matter what kind of flute occurs behind it because the grabbing has already started to occur.
 
ClickSpring has a good video on this:

I picked up a used (empty) drill index at a tool auction a while back. When I need to drill brass, I modify the required drill bit and then save it in the index for future use. Do this and eventually you will build up a collection of "brass" drill bits that you usually use.
 
The way to avoid resharpening is to build up a set of "Brass Drills". Generally i like a slightly wider break, maybe as much as a half mm. "Brass" Drills are also useful in other grabby materials, in fact I first learned of this mod when working in Lexan and other plastics. A set of well maintained "Brass" Drills can be very useful if a person works a lot in these sorts of materials.

Ken I said:
You need zero to slightly negative rake for drilling brass - particularly when enlarging a hole.
You can simply break the edge of your standard drill - you only need to break 0.1-0.2mm of the edge to the required rake 0° to -5° and it works fine - also you then don't have to grind back very much drill when resharpening it for normal use.
Click to expand...
 
Omnimill said:
I'm not very good at hand sharpening drill bits so I wish you could buy them specifically for brass... :D
Click to expand...

You can buy straight flute bits. These are made for brass and copper but are expensive. My grandfather had a set that I am sure he got from work. They look like chucking reamers. I did a search and found that Grainger has sets from 1/16" / 1/2" for only $718.00.
There is info on you tube on dulling the flutes so the drill does not grab on brass.
If you need to drill large holes in copper than a step type bit does this very well. I needed to drill 1-3/8" in copper . I bought the bit at Harbor Freight for about $20.00. They may be called " Unibit". You get 2 step bits ,narrow one probably goes up to 7/8" or so and the larger bit goes to 1-3/8".
I have a new set of drills that I have not yet modified for brass. The flutes are stoned dull . They work good for brass and still drill steel too.
mike
 
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