Drill bits modified for brass ?

[sparkey0151]

Seen a video on YouTube, of a guy re bushing a clock plate made out of brass and he mentioned the drill bits being modified for brass ? is there such a thing as i thought HSS are it, hes selling them for $5.

john

 

[dAz57]

Yes, you run a slip stone or very fine diamond file on the inside lip of the cutting face, basically you need a zero rake, a twist drill as standard will dig in and the brass plate as the drill breaks through to the other side, this can cause the part to catch on the drill and spin around.

I use metric drills in 1/10th mm steps for bushing since I don't use a bushing machine or the cutters, you can also buy drills in 0.05mm steps, so to drill a hole for a 3mm bush I'll use a 2.95mm drill, and all of my drills for brass have zero rake,

Run the slip stone parallel to the axis of the drill and take a few strokes off the cutting face, the drills will cut brass and cast iron without digging in.

 

[sparkey0151]

Thanks, just wondered what they where talking about, you learn everyday,

regards john

 

[glenhead]

It's called "dubbing" the bits, or making a set of "dubbed" bits. dAz57 described the process nicely. Here's what you're shooting for:


It makes a huge difference. As he said, I have complete sets of dubbed bits for brass. They also work nicely on bronze and aluminum.

Glen

 

[Kevin W.]

Very good explanation Glenhead, a picture is worth a thousand words.

 

[sparkey0151]

HI, is this on the very tip of the drill bit? if so im trying not to sound stupid, how would you get it to centre,

regards john

 

[David S]

John,

Check out click spring.

https://www.youtube.com/watch?v=pAngKHIZgyA

David

 

[MartinM]

Search Google (Images) for "Drill dubbing".
Lots of good pics and links to more technical explanations.

 

[glenhead]

HI, is this on the very tip of the drill bit? if so im trying not to sound stupid, how would you get it to centre,

regards john

Yes, it's at the tip. The sharp-angled edge goes from the outside clear in to the web in the center, and you want to make a flat all the way across, on both sides.

Glen

 

[Kevin W.]

Thanks David that is a great video, i like many appreciate seeing it done.

 

[David S]

Kevin I am not sure if you remember, but it was you that mentioned this more than a year ago, and I immediately went and got a limited set of HSS drill bits and modified them for Brass use.

So the thanks goes to you as well.

David

 

[Kevin W.]

Thanks David i remember that, been meaning to do this on a set of drills and never got to it.

 

[dAz57]

HI, is this on the very tip of the drill bit? if so im trying not to sound stupid, how would you get it to centre,

regards john

This is a pair of 1/2" drills, the one on the right is how they come, made to drill steel, if you attempt to drill brass with this even if you have the piece clamped in a vice on a drill press as soon as you break through the other side the drill will snatch and pull the quill of the drill down which can result in a broken drill and ruining the piece being drilled.

The drill on the left has had the cutting face ground to a zero rake, this will drill the brass cleanly and no grab or snatching, on smaller drills I don't even bother to clamp the part being drilled.

 

[sparkey0151]

Thanks David i now get it,

regards john