how to drill brass without drill grabbing?

[Aquarius21]

Hi, while watchng MIT's great machine shop video on drilling (#2) the instructor
mentioned the concern about a regular steel drill grabbing brass while drilling.
One internet suggestion was to file a flat on the flute to reduce grabbing.

Any suggestions as I would rather not toast a drill either. Do people buy
a separate set of drills for brass? Does one bolt the vise to the drill table?
Drill in a lathe? Your advice is welcomed as the cost of messing up a block
of brass to make the cylinder block for the rotary valve 2 cylinder engine
would be disenheartening ( and to fetch another piece of brass would mean
a hour drive to the city as there are no local suppliers.)

Thanks for helping in this, Quincy, Nova Scotia

 

[rake60]

I have a friend who insists on resharpening every drill bit after each use.
I do not do that. I resharpen every drill bit BEFORE each use.

If the material is aluminum, the bit goes through the Drill Doctor and it is
used as is. If the material is steel, the cutting edges get a few light laps
with a stone to remove the burr after resharpening.
For brass I don't resharpen the bit at all.

Rick

 

[mocaquita]

Removing the positive rake of the cutting edges works good. You don't need much of a flat on there. Also, the smaller the drill the less flat you need. I use a grinder on bigger drills and just stone the little ones.

Dave

 

[Deanofid]

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've put up this bit of info a number of times, but might as well put it up again, since it's a fairly common question.
FWIW, I do 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.


On the same brass cutting subject, HSS tool bits need to have NO grinding done on the top of them for brass;

I think the pics are self explanatory, but just ask if not.
Hope this is of some use.

Dean

 

[Aquarius21]

My thanks for the very helpful replies and pictures! It makes me realize that I should have a separate set of drills for brass even as I would have separate lathe bits for turning brass. My thanks! Quincy