dull number drill bits

[BETAQDAVE]

    I've been having problems with numbered drill bits sized 67 to 80.  While they seem to have no problems drilling wood, it appears that metal is another thing all together.  Are they just dull or not made for drilling metal? Is it possible to be sharpened or just discarded?  Some bits from the same brand new sets are good while others can hardly make a dent in soft brass even after prolonged drilling time.  Perhaps it's just a question of getting what you pay for.

[kurtvd19]

Dave:

I make it a practice to anneal brass before working with it.  Didn't used to do this for drilling but after I started doing it before drilling things went much easier.  I am not a machinist so there will surely be other answers.

Kurt

[vaddoc]

Dave, I have very little experience but I have always struggled to drill brass with steel drills and had the same issues. However, using Tungsten carbide with my drill press, no issues at all.

[mnl]

The answer is somewhat both, you need a quality drill, but then you also need the proper technique. Prolonged drilling is not a good thing, it means that you are rubbing, not drilling, and the tool is work hardening the material you are trying to drill. There is also a chip load, how much the drill cuts every revolution, but we will leave that for now. Every metal has a recommended cutting speed. For brass it is between 150 and 300 surface feet per minute (sfm).

 

Take for example your #60 drill. It is 0.040” diameter or 0.125” circumference. To get 150 sfm you need to turn the drill at 14,400rpm. There are a few drill presses that can do this, Electomechano made some very nice ones, and others have as well. But very few people have them, so chances are the drill will be turning much slower than optimal. For this you need what is referred to as a sensitive drilling machine, one where it is easy to feel how the drill is feeding, because it is important it cuts all the time. If it rubs then the piece work hardens and it is all over. 

 

Brass is more difficult that steel in some ways, because the flutes of the drill try and dig in which can snap the drill. One larger drills it is typical to dub the flutes to reduce or eliminate the rake. It will stop the drill from digging in. That is easy to do on a larger drill, very difficult on a #80.

 

You also need a pretty good drill press to do this. A quality chuck is essential to hold a small drill exactly on center and not wobble.

[Bob Blarney]

As mentioned directly above, cutting speed is very important. Usually I find Dremel tools to be weak, but in this case it may be the best tool available to you.  If it can be fitted into mechanism similar to a drill press, then so much the better.  I made such a thing using linear bearings and precision drill stock and acrylic blocks (it's really ugly but it works), and I lower it down on to the stock with my fingers to feel how it's drilling.

[vaddoc]

Very interesting info Mml

 

I recently had to drill some difficult holes. The photo shows 2mm brass rod, with a sleeve made from 3 mm tube soldered around it, so a pretty solid thing. The hole going through is 0.8 mm, this is 0.03 inches. I used the TBM 220 Proxon drill press (8500 rpm) and cheap chinese carbide drills and they drilled through in no time. Still I broke 2 drills to make 8 pieces but this was me not keeping the piece securely. The Dremel goes up to 33000 rpm but I doubt I would be able to drill with steel bits

[wefalck]

There is brass and there is brass. Some types of brass machine well, others tend to smear when turned or catch drills.

 

There are special brass drills with a steeper helical angle and differently ground tips, but I don't think they are available as 'numbered' drills. Watchmakers traditionally use spade drills or 'Eureka'-drills. Spade drills one can make oneself. Eureka-drills have straight flutes and tend to be very expensive these days. Both types of drills don't catch easily, but due to the absence of helical flutes need to be lifted out frequently to clear out chips.

 

 

[mnl]

4 hours ago, vaddoc said:

Very interesting info Mml

 

I recently had to drill some difficult holes. The photo shows 2mm brass rod, with a sleeve made from 3 mm tube soldered around it, so a pretty solid thing. The hole going through is 0.8 mm, this is 0.03 inches. I used the TBM 220 Proxon drill press (8500 rpm) and cheap chinese carbide drills and they drilled through in no time. Still I broke 2 drills to make 8 pieces but this was me not keeping the piece securely. The Dremel goes up to 33000 rpm but I doubt I would be able to drill with steel bits

 

 

The carbide drills are much harder than HSS so they won’t have as much trouble with work hardened material. Carbide is also much more brittle than HSS so if your setup is not completely rigid the drills will snap as you observed. The work requires a rigid machine, a secure piece, and some sort of center pricked and aligned so the drill stays straight. 

[Bob Blarney]

this might be interesting:

 

 

[BETAQDAVE]

    His solution on the video has one drawback that is hard to overcome.  The bits are so small you would need a microscope to see what you are doing to modify the cutting edge.  However, for the larger size bits it would be useful.

[mnl]

That is what is referred to as “dubbing” a drill. Almost mandatory for larger drills in brass, especially if you like to avoid excitement. It is probably not feasible in 0.040” and below even if you’d have fine enough abrasives. 

 

This discussion has prompted me to pull out my copy of George Daniels book Watchmaking and review his comments on making small drills. I will have to pick up some small drill blanks the next time I order from McMaster and give them a try.

[wefalck]

The watchmaker spade drills bits I mentioned above have zero rake. Watchmakers used to forge them from oil-hardening steel, file them to shape, harden them (watchmakers are very familiar with hardening small pieces), and then grind and hone them. They were meant for reciprocating Archimedes hand-drills and cut in both directions. However, they can also be used in electric drills and, of course, in the lathe.

 

I have a small butterfly-shaped jig (the correct name escapes me for the moment) for honing drills on an Arkansas-stone. It holds the drill bits in a collet and presents it to the stone at the correct angle. I never actually used it, I must admit, but I think it could be used to grind the zero rake onto twist drills.

Edited April 6, 2020 by wefalck

[mnl]

The easiest blanks to source are M2 which is considered to be an oil hardening steel, although for such a small section it will cool before it can make it from the flame to the oil. Daniels shows a pointed form for nonferrous and and rounded form for hardened steel. Drawing the temper will also be interesting.

 

I plan on using my pillar drill as it is easy to get 300-500 rpm that he recommends for brass. It also has a very sensitive feed. It has a Albrecht chuck that holds down to zero.

[Maury S]

News to me department...I always thought slower speed was for metal and higher speed for wood.  Next time I'll turn up the revs!

Maury😀

[RussR]

On 4/4/2020 at 2:35 PM, kurtvd19 said:

Dave:

I make it a practice to anneal brass before working with it.  Didn't used to do this for drilling but after I started doing it before drilling things went much easier.  I am not a machinist so there will surely be other answers.

Kurt

Kurt,

What method do you use to anneal brass and not burn it up?

Thanks,

RussR

[kurtvd19]

Heat it until it is an even red color then drop into water.  How to apply the heat is dependent on the material thickness.  Photo etch - a candle flame is adequate.  Thicker brass can handle a torch - don't get it too close when it is thinner.  Most of the time I use a butane torch - closer for thick stuff farther away for fine.  I also use my Smith Torch (propane/oxygen) at times.

[Gaetan Bordeleau]

On 4/4/2020 at 3:23 PM, BETAQDAVE said:

hardly make a dent in soft brass

just like a knife that cannot cut;

sharpening is possible or may be  buy a better quality