Drilling with a number 78 drill. They keep breaking!

[Laverda]

I need to drill some holes in brass using a number 78 drill which is .016" diameter. They are through holes and I am drilling a 1/4" thick brass rod held in a collet. The drill bits keep breaking! I have never used a drill bit this small. I am sure I am doing everything wrong. I don't have a small drill press, just a big 1950's Rockwell drill press that only spins up to 2400 RPM. Probably not fast enough. Although my Bridgeport will spin faster than this, it provides even less feel as to what the drill bit is doing before it breaks.

I am guessing I have the wrong machines to do this job? Drilling by hand is not an option as the holes won't be the size I need do to the drill moving around.

Spending money on the proper small precision drill press is not a good option for a one time job.

Anyone ever used one of the attachments that converts a Dremel tool in to a drill press as mine will spin up to 35,000 RPM? I don't have the attachment but may get one if it will work.

 

[MrWhoopee]

You need a sensitive drill chuck or drill press. That and much higher speed. In addition, the brass is a problem because it wants to grab the drill. The traditional approach is to dub a slight flat on the cutting edge. Not going to be easy on a drill this small. How did you get yourself into this mess?

Here's a reasonably priced sensitive shank. It will need a chuck.
Sensitive Drill Feed - -

 

[steve45]

Perhaps you could make a drill bushing. Even a small block of aluminum might work.

I've tried drilling small holes in brass and bronze. It can be challenging. Use lots of oil. Heat builds up very fast, so I'd run the bit slowly and peck at it and let it cool periodically.

 

[Bill D]

Is it breaking as soon as it touches the curved surface or is it after it goes in a little bit. I would think milling a flat spot to start may help.
Bill D

 

[Milland]

1) Quality drills. Don't cheap out.

2) Sensitive drill chuck/shank, held in the BP with a collet, not a larger drill chuck. And check TIR, if not good during initial use get a replacement, don't try to "tap it in".

3) Sensitive fingers - you need to develop the "feel" of how the drill is cutting, so you can apply the correct pressure and notice when the drill stops cutting so you can withdraw before breakage. This includes backing off just before breakthrough of the part.

4) RPM is the least critical aspect here, the above three points matter much more.

 

[jims]

Where are you located in Calif ? I will loan you a sensitive drill chuck if you would like to use it.
I’m near Sonora. [email protected]

 

[L Vanice]

Decades ago, a jewelry store owner mentioned that he had his wife do an outside job on one of his watch lathes that simply involved drilling tiny holes in small parts held in the headstock collet. The time per piece was less than a minute, and having the right machine let him quickly net a larger hourly rate than having her clean watches. The shop with the big machines was probably glad to pay someone with the skill and machine to do it for them. So that is one option.

If the brass is 360, you do not need cutting oil. You do need to prepare the drill bit, as mentioned before. One stroke on each lip with a triangular Arkansas or India oilstone is all it takes. And running the machine at high speed is best.

If the brass is 260, that is the root of your problem. Toss it and start over with 360. Look up machinability if you are not familiar with the term.

I have lots of watch lathes, so I know what can be done with them. I have a bunch of those sensitive drill chuck feeders, and they work, but you still need a high speed spindle to drive them.

Larry

 

[lazz]

Peck at the hole...

A sensitive drill is the tool to make this easy but it can be done SLOWLY.
Do not try to go thru the hole in one shot.
A little pressure then back off and do it again till you get thru the hole.

 

[Laverda]

1) Quality drills. Don't cheap out.

2) Sensitive drill chuck/shank, held in the BP with a collet, not a larger drill chuck. And check TIR, if not good during initial use get a replacement, don't try to "tap it in".

3) Sensitive fingers - you need to develop the "feel" of how the drill is cutting, so you can apply the correct pressure and notice when the drill stops cutting so you can withdraw before breakage. This includes backing off just before breakthrough of the part.

4) RPM is the least critical aspect here, the above three points matter much more.

OK, good info.

1. The drills I am using are Chicago Latrobe HSS made in the USA and are new.

2. Do they make collets this small? I don't have any that will hold a drill this small. I am using a Llambrich precision chuck to hold the drill. Run out is not supposed to exceed .0012"

3. I will try but the Bridgeport does not provide much feel.

4. What is the recommended RPM?

And finally, digging around in the shop, I found my air powered spindle for the mill. It can go to 30,000 RPM but still provides little feel what the drill is doing. Run out is supposed to only be a couple 10ths. It's collets don't go small enough either!

 

[drylakemachine]

I've got a rumored hispeed and a mecaanico. I am in the elmirage area if you want to try one. If it works we'll discuss $
Jim

 

[dgfoster]

Second post says it all. High speed is not needed. Dubbed-off cutting edge is needed. Do the job in a lathe with a sensitve chuck. The drill breaks because it is a coomon drill bit sharpened for common material---steel. Its cutting edge is too steep for soft brass and it dives into the work piece and jams and breaks. THe sensitive chuck allows you to feel the pressure on the bit and allows for rapid pecking to clear chips. Having a blast of air right at the entry point to the hole allows rapid clearing of ships with each peck. There was a recent thread in the last week showing how incredibly easy it is to make a sensitve chuck. Won't work in a mill though unless you chuck and spin the work and have the sensive chuck pointing at the work and stabilized in a bored chunk of steel (instead of the tailstock on a lathe) clamped to the table.


https://youtu.be/PqU5wS0J4MU

Denis

 

[jims]

OK, good info.

1. The drills I am using are Chicago Latrobe HSS made in the USA and are new.

2. Do they make collets this small? I don't have any that will hold a drill this small. I am using a Llambrich precision chuck to hold the drill. Run out is not supposed to exceed .0012"

3. I will try but the Bridgeport does not provide much feel.

4. What is the recommended RPM?

And finally, digging around in the shop, I found my air powered spindle for the mill. It can go to 30,000 RPM but still provides little feel what the drill is doing. Run out is supposed to only be a couple 10ths. It's collets don't go small enough either!

You don’t use the Bridgeport handle to feel the cut . The feel is in the sensitive chuck . The chuck slides down by a ring held by your fingers . And you feed down feeling the cutting action with your fingers. If you look on eBay you will see the chuck and the ring you feed drill with.

 

[Milland]

OK, good info.

1. The drills I am using are Chicago Latrobe HSS made in the USA and are new.

2. Do they make collets this small? I don't have any that will hold a drill this small. I am using a Llambrich precision chuck to hold the drill. Run out is not supposed to exceed .0012"

3. I will try but the Bridgeport does not provide much feel.

4. What is the recommended RPM?

And finally, digging around in the shop, I found my air powered spindle for the mill. It can go to 30,000 RPM but still provides little feel what the drill is doing. Run out is supposed to only be a couple 10ths. It's collets don't go small enough either!

Sorry, what we've been calling a sensitive drill chuck is like this: LittleMachineShop.com Sensitive Drill Feed and 1/8" (3 mm) Keyless Drill Chuck (3790) - - Amazon.com
where the drill chuck itself is mated to a keyed, spring-loaded spindle in a larger drive arbor. The arbor is usually 1/2" OD, that's what I'm suggesting goes into a collet, not a larger drill chuck. Don't over-tighten the collet, you'll collapse the hollow arbor onto the drive spindle.

If you have a loose Llambrich chuck or don't mind removing it from its current arbor, you can buy just the sensitive adapter and use your chuck on it (as long as the JT is correct). Again, make sure the TIR is good, if need be separate and mate again, sometimes you'll luck into a better concentricity.

I actually don't get too exercised about dubbing small drills, it's the larger ones I'll mod if working in brass or acrylic. A small drill like a #78 really doesn't have much "wedge" or torque capacity for me to be concerned. At least, it's not been an issue when I do it...

On small/thin brass I just go with either the max speed of the mill, or even less. I'd prefer a slower top speed with a sensitive drill just so it's a little safer for me to work with. Even at just ~3600rpm, you'll still go through 1/4" brass pretty fast with a little practice.

 

[1yesca]

it would be nice if you had one of theses

 

[camscan]

ask your dealer about a D bit or spade drill.

 

[crossthread]

I had to drill a very small hole in a brass nozzle (#80) not long ago and ran into the same problem. I don't do this very often at all and could not justify the cost of a sensitive chuck. I cut a 3" piece of 3/8" tubing I had laying around and stuck it in the tailstock chuck. I then put the drill in a pin vise and shoved the tail of the vice up in the tubing. This was to keep the whole thing straight. I was then able to slide the pin vice out of the tube with my fingers and only using the knurled portion of the pin vice for friction, I was able to drill the hole without breaking the bit. Cost little or nothing if you have a pin vice.

 

[DrHook]

Damn, thought I would go all day without learning something new... I found one of those in a drawer at work and never knew what it was for.
That is why I come here.

 

[Larry Dickman]

2. Do they make collets this small? I don't have any that will hold a drill this small. I am using a Llambrich precision chuck to hold the drill. Run out is not supposed to exceed .0012"

try using a carbide circuit board drill. They all have 1/8 shanks

 

[Human]

I thought ramping up the spindle to 20k and dialing a holder for the job using a similar size drill and mat on deep holes could have worked, I end up sending out the job to specialized tooling hours before officially going insane.

Not trying to discourage here. It's that thing... when you lose contact with physics(sound, vibrations, force, feedback, etc) on those large machine-tools it's never a good day

 

[MrWhoopee]

One more suggestion, do it in the BP with the quill locked and feed up with the knee. No feel but much more control than with the quill.

Also, are you trying to drill without spotting? Drill point walk will kill you with a drill this small.
Circuit board drills with a minimum flute length might be worth trying.