Drilling with a number 78 drill. They keep breaking!

[car2]

Third/fourth the sensitive feed drill chuck. I've never been successful trying to use the quill with small bits (you can forget carbide bits).I use the sensitive feed fairly often in the bridgeport for under about .03 holes. I have two, one is an Albrecht brand sensitive-feed with a 0-3mm albrecht chuck, the other is a royal shank with 0-1.5 albrecht chuck. The 0-3mm is the most versatile since you can chuck 1/8" "PCB" carbide bits in it. The albrecht feed seems a little better made than the Royal; if looking at them on ebay, the Albrecht shanks have a smaller-diameter, thicker, black-oxide, feed-ring that you hold. They're a bit pricy ($200-ish, used with a chuck), but almost essential if you need to drill small holes on location (I've tried a couple of "sensitive drill presses", and aside from not being able to locate a hole in x/y like on the BP, still could not drill small holes with carbide bits with them; I have an old Dremel stand with the movable table that works better than those sensitive drill presses).

Also tweaked the spring on the Albrecht feed to just counterbalance the chuck such that the feel is even more precise, and easier to use.

I chuck the sensitive feeds in a (good) 1/2" collet in the BP, and use a larger carbide drill to spot the holes, then you can often use hss wire drills which are much more forgiving than carbide drills (especially running at a mere fraction of the speed that they would typically be run). On particulary fussy jobs (small and/or high aspect-ratio holes), I'll take a small brush with lubricant, and wipe off the drill-bit each time you "peck" it (yes, it's tedious, but usually successful with no broken bits). Cheers

(Hate those larger air-spindles, have to run a 5 hp compressor to power a dinky spindle, wear ear-protection, and they're still clunky and don't have but standard collets; probably still an issue with the lack of feed-control/feedback on a manual machine).

 

[rklopp]

This operation will go OK even at vastly sub-optimal spindle speed if you can control the feed rate and peck increments quantitatively. There's no need to stone the cutting edges, either, if you can rigidly control the feed rate in a way that keeps the drill from being sucked into the work. A feed rate around RPM*(drill dia)/64 should work, even at 1,000 RPM, though it will be a snails pace of 0.25"/minute for a #78 drill. Using the RPM*(drill dia)/64 rule I have drilled 0.008" and 0.006" holes on a manual mill at 3,400 RPM, but with shallow enough holes that no peck was needed. The mill had the capability to let me dial in a precise feed rate in in/min. Pecking will be very tough to do on a manual machine. CNC could do it.

Do you need the whole 1/4" depth to be 0.016" dia? If it's just an orifice, for example, you could drill most of the way with a much fatter drill and leave only a drill diameter's worth for the 0.016 drill.

 

[Illinoyance]

ask your dealer about a D bit or spade drill.

https://www.mscdirect.com/browse/tn...+round+drill&refinements=Drill+Bit+Size:0.016

 

[Milland]

https://www.mscdirect.com/browse/tn...+round+drill&refinements=Drill+Bit+Size:0.016

Almost $200 for 12 - ouchies...

 

[boslab]

I worked at a place that drilled 1/4” brass bars with a 20 thou drill, there were breakages btw, rpm was I think 17500 on the drilling machine ( a brush making machine) Titan drill, collet, the feed was sub second a hole, bad grind would wander the hole, the drill was solid carbide, it’s doable but low rpm is a killer
Mark

 

[Scottl]

The Dremel drill press attachment works well, and a variable speed Dremel would allow more reasonable speeds. Other option would be a sensitive drilling attachment for a drill press. These clamp in the chuck and have a sliding spindle controlled by a knurled disc you hold in your fingers. They give much better feel on tiny drills.

 

[kustomizer]

Almost $200 for 12 - ouchies...

Not only that but if you attempt to count them you stand a real good chance of not having them anymore

 

[Thunderjet]

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.

I drill holes like this all the time. In a bridgy spinning 4000.

You must spot the hole first. Just a solid tiny center punch will do, turned in your spindex to a point matching your drill point.

Then install your drill, after inspection on the point. Many bits this small are useless from the box, due to improper grinding on the point.

I use the quill and knee together. I set a stop on the quill and bring the table up until I just touch the spot, then I raise the table .005 and gently down feed the bit with the quill. Blow off the swarf raise the table and repeat as needed. If you watch the drill shank, you will see when the bit bends instead of drilling. When this happens, replace the bit and continue.

 

[Scruffy887]

I have done thousands of .016 holes in 360. I used to have them in the turret of a Mazak SQT 250 MS. VooDoo to make them work. There was a very special tapered reamer that came after the #78 hole. If that #78 hair drill broke it would take out the reamer.
I made a special tapered reamer just for brass that works without the #78 hole. Part is finished with a sensitive attachment on a tiny crap box store drill press, #78 cobalt PTD bit. Finally found a .125 shank #78 bit to do the job.

 

[Mike1974]

Harvey Tool

 

[Mcgyver]

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.

agreed, watchmakers drill holes a lot smaller than that and do so quite happily at 1500-2000 rpm. Speed just makes the job go faster, doesn't stop drill breakage.


add to that concentricity. A crap chuck will worsen things, collets are best. Look at how a Levin drill press or Servo drill press is set up. You can also spin the work and hand hold the drill in a pin vice - another watchmakers technique that works well because there is no run out if its not rotating.

The best device for sensitivity I've seen appeared in home shop machinist probably 30 or more years ago. Why? because of the brass counterweight. Build it with easy sliding fits and there is about zero force required to move it - unlike the various spring loaded devices. less forces acting on it = greater sensitivity. Its construction should be obvious from the photos - this is a great little tool! Can't remember the designer or I'd give credit where due.

Before I got a Servo, I would use a dumore speeder in a drill press. The DP is just a fixture in this case, a way to hold the speeder - turning off the DP breaker is a good idea. All to easy to reach for the green button by rote. the speeder gives good concentricity an they are not stupidly expensive used

brass, yes, remove the positive rake. tough to do on a such a small drill and I'm not sure its the problem in this size. Watchmakers would often make or buy a spade drill which eliminates the issue, if it is one. For sure it is with larger drills, just can't recall a tiny one being as grabby. maybe its happening and I can't feel it or may they ratio positive rake edge to chisel point is different enough to reduce/stop it (of maybe my memory has gone to shit...a viable option as well)

 

[Ron Hofer]

+1 on a Dremel drill press. It'll do, although a sensitive like Cameron works waaay better.

You're getting a lot of good advice here. I've had pretty good luck with 1/8" shaft carbides. A few years back, they were plentiful on Fleabay. Now, not so much, but you can still find them. All I'd add is--peck at it. Between pecks, look at the tip of the drill with a magnifier to see if any swarf collected in the flutes and use a soft toothbrush to remove it.

Ron