I remember my dad showing me this drilling brass trick more than 30 years ago. And who better to show you, other than the guys on the Home Model Engine Machinist forum because they really know their stuff when it comes to tricky machining jobs. Here is what Deanofid had to say about an easy way to modify a standard metal HSS drill bit to easily (and safely) drill holes in brass…
Brass has a tendency to grab the sharp edge on drill bits. Bits for brass, whether drill bits or turning bits for the lathe are supposed to have a zero rake cutting edge. That way, they will not grab, and, it’s simply the proper tool bit geometry for brass.
I keep an extra set of drill bits just for brass. All ground as shown below.
This is how a stock drill bit looks on the end. It comes to a very sharp edge where the bit cuts metal (arrow). That same sharp edge that cuts steel so well will also dig in hard in brass and suck the bit into the work.
To take that sharp edge down, you run the cutting edge of the bit along a honing stone. The idea is to make it flat, which is no good for cutting steel, but cuts brass very well, and stops the grabbing problem. Run the bit in the direction of the arrow towards you, honing in only one direction. It usually takes 3-5 strokes to get the sharp edge off and condition it for brass cutting. (I realize the arrow has two heads, but hone the bit in only one direction.)
When you are done it will look like this. The shiny part you see is where the sharp edge has been honed down flat. It only takes a very small flat to be effective. No more grabbing.
Thanks Deanofid! I hope that this is useful for you, I know I got into trouble the first time I tried to drill brass before my fathers old advice made a ‘too late’ return into my head. And me the son of a fitter and turner, oh the shame of it…
Here is a great video showing exactly how to modify your drill bits from clickspring over on yoootooob!
Stay well
Ian
Comments 6
What is the best cutting angle of twist drill used for drilling brass material workpiece ?
Author
Hey Roshan,
Well, I just file regular HSS twist bits to create a flat ‘milling’ type edge, so they are usually around 60 degrees,or 120 across the flutes. Often though straight fluted bits are used to further reduce ‘grab’. Here are some at 118 degrees with straight flutes… https://www.fine-tools.com/messingbohrer.html.
Hope that helps and good luck with the project 🙂
Ian
i have a 50mm deep hole x 25mm diam to drill into brass, any clues?
Author
Sorry Russell, that’s a real big hole! I’ve not even seen any metal bits that big. There are large stepped drill bits, but they are no good for a blind hole. Depending on the size and shape of the object the only way I’ve done this is on a lathe…
Sorry I don’t have a magic bullet Russell!
Cheers
Ian
I clamped some 4 or 5mm thick UPVC behind a brass sheet and drilled a 5mm hole having drilled a 1.5 and then 2 mm pilot. There was a bit of a ridge at the back – easily filed off.
Author
Stepping is one way to minimise the ‘pull’ of a standard twist bit in brass, but honestly, try filing a small flat on a spare drill bit. You’ll be amazed at the difference; it sort of ‘mills’ the brass instead of ‘shaving’ it off in spirals. Also, it does depend on the brass thickness, thin stuff up to 2 or 3mm isn’t likely to scare you too much!
Many thanks for contributing Frank!
Ian