Drilling Bronze

[petertha]

I just use a few passes on a stone, usually not as severe as in the above attached images.

I'd have to go back to the video, I thought he said 0.2mm (~0.008"). I blued mine so I could see the shine of new metal as I stoned the flat. I suspect I'm right around that width, maybe a tad less. Kind of curious to try now.

The other thing I heard is: don't use drills on brass that were used on steel. I'm not clear on why exactly. Not sure if its a play on words that really means 'steel lip geometry' vs. 'ideal brass lip geometry' ie. just keep some separate drills for soft alloys, or it has to do with something else. I only have one set so violated that. But I expect to do more brass work so may well keep them in a dedicated box because grabbing is no fun.

Sidenote. I have a few HSS drills in .375-.625 range, uncoated, very sharp. I just bought them as loose stock. They did the grab/dig on 6061 aluminum where I have never had that issue on my normal silver/deming ?sp? drills. That particular lip profile had a funky grind, looked like a shallow positive arc vs. a straight flat. They work great on steel but could feel they wanted to suck the drill in. I'll try & rig up my camera on a magnifying glass to show.

 

[Technical Ted]

On the stock sharp drill, yes by grab I mean the drill pulled & screwed itself into the material & kind of stuck there within the bore.

I haven't tried my dub drills yet but was almost wondering if the first say 0.2" of the spiral cutting part of the drill should be similarly treated? Nobody mentions that, only the conical cutting part, so I assume no.

If the drill is pulling in then I would do like others have suggested and dub the cutting edge.

The sides of the drill don't (or shouldn't anyways) do any cutting. On a properly sharpened drill, all cutting is done on the end.

Ted

 

[Technical Ted]

The other thing I heard is: don't use drills on brass that were used on steel. I'm not clear on why exactly.

I think this is going on the same line as where I suggested only using very sharp drills when drilling materials that close in around the sides of the drill and seize up on the sides. I have seen this with some types of bronze (there are a lot of different flavors). Some are really wicked to drill. Drilling steel first would dull them up some and cause issues. I've heard some suggest to only use brand new drills on materials that do this for the same reasons.

Ted

 

[francist]

I agree with the "no oil" others have mentioned. With something that makes fine chips like cast or bronzes the oil just tends to combine with those and make a slurry which is hard to evacuate.

Having said that, I was working on a job once where I was hand-tapping about thirty 3/8"-16 holes in 360 brass blocks. It was a new tap, and a good one, but about halfway through each hole the tap would start to squeak. Eeeh-Eeeh-Eeeh-Eeeh ..... as I wound the tap in. Drove the mechanic in the next room to madness, so much so that he got a radio from his truck to drown out my squeaking. I let him suffer through it, but afterwards it was starting to get on my nerves a bit too. A very light wisp of cutting oil from an almost-dry acid brush onto the tap worked miracles. No more squeak, the tap wound in smoother, but there was not enough oil to gum things up. I do it all the time now (except when the mechanic guy comes around next...

-frank

 

[EmilioG]

You could use wax to tap and that squeek is normal when tapping brass. You can power tap on a mill at low speed if you have reverse.
I don't see a reason for not using drills that have been used on steel to drill brass, as long as the lips are dubbed and the drill hasn't seen a lot of use..
I keep a set of non-ferrous/plastics drills in a separate index and they're all hss bright un-coated. BoeLube is great for tapping. There are wax stick lubricants as well. Drilling/tapping brass dry works too. I also make sure I buy ground taps, mostly Guhring, and make sure they're sharp. A dull tap is worthless. Plastics: I mainly use 60° DP angles and carbide dagger drills., but you can use dubbed twist drills with no problem.

 

[kd4gij]

I do not dub my drills. Good sharp drill and feed it as fast as it will cut all the way through in one shot. And I have done that with a 2 1/2" drill.

 

[Silverbullet]

I use to run lots of brass and bronze , first never step drill the holes , start with just a dimple then right to your largest diameter for drilling . Reaming is fine or boring after. Had a very good old machinist teach me that during an apprenticeship learning turret lathes and the set ups.

 

[EmilioG]

I do not dub my drills. Good sharp drill and feed it as fast as it will cut all the way through in one shot. And I have done that with a 2 1/2" drill.

I've drilled brass w/o dubbed lips feeding fast and hard, peck drilling. It was hot or miss, so I just started dubbing the lips. Thin material may present a problem with sharp drills. I didn't want to chance it.

 

[mikey]

Another vote for going to the main drill after spotting to avoid grabbing. I don't "dub" my brass drills, either; I just don't pilot drill and that makes all the difference. You just need to use enough pressure to keep the drill cutting and it goes right through. I use a tiny bit of DoAll wax stick lubricant like Emilio said when tapping brass; I actually just touch the tap to the stick and no sticking or noise.