PCB drill bits???!!!???

[Beo]

PCB drill bits are going to break. Maybe an quality drill press will greatly increase the longevity, but these things don't like cross-force/angles/twist. I have a drill press, unfortunately without a laser guide, and trying to line up the center and the longish pull distance of the lever really slowed down my progress. My choice was to buy a bunch of bulk resharpened bits, and use a dremel with the hand held flex shaft extension. By bracing my palm, I could punch well centered holes at a fast clip, with only occasional breakage. Half the time, the breakage would be mid-bit, and I could still use it to punch more holes. Maybe a laser pointer on a drill press would make the difference in speed.

By the way, I have all my dimensions for eagle design, pcb and box drill hole sizes for various components. I'll try to find that sheet and post to this thread.

Travis

[Beo]

After checking my notes...
Here are the values I use for Eagle and PCB drilling:

inch      mm   Type                              Drill Bit
0.03150   0.8   IC's, Resistors, Capacitors, small Diodes            68
0.03937   1.0   Transistors, large Diodes, TrimPots, Dip Switches, Wire      61
0.05512   1.4   PC Mount Pins: Pots, Switches                  54
0.08661   2.2   Solder Lugs: Pots, Switches                  44

For Box drilling, I use these values in general:
3/8      I/O Jack
5/16      3mm LED (w/o bezel)
15/32      3PDT
1/2      DC Jack
Pot      9/32
Toggle   1/4

I use a step drill bit and then a reamer for clean circular holes. I also use a hole measure to double check, especially for unusual parts. (e.g. cheap jacks compared to switchcraft/neutrik have different sizes I think). Usually better to stop with the step bit early and use the reamer if close.

[duck_arse]

@ mark - usage - "I got some mods from k....... that I thort were pretty naff. I tried 'em in my gargle-blaster, and it caught fire, fell over, and sank into the swamp. so I told him to naff off"

- or - to paraphrase the Standells in "sometimes good guys don't wear white", 'You think those guys in the white collars are better than I am baby, then naff off'. and something about a haircut

[Mark Hammer]

LOVE that tune by the Standells!    I mean, first of all, ya gotta love a band that names itself after its equipment (we have a well-respected band in town called the "Hilotrons"), but it's the dramatic pause between the line "So tell your momma and your papa", and "Sometimes good guys don't wear white", that really makes the tune.  It's the punk equivalent of David Caruso reaching up to take off or put on his shades before uttering a comment.

[italianguy63]

It's the punk equivalent of David Caruso reaching up to take off or put on his shades before uttering a comment.

OK Mark, now you've done it -- (totally OT)....

David Caruso-- OK.  I don't get it.  There is zero bad-azz or cool about David Caruso..  I know it is TV.  I really DO party in Miami too..   But, David Caruso is the guy we used to beat up at the school bus stop for his lunch money.  He's just "comic relief" on CSI.

MC

[Mark Hammer]

No exaltation on my part.  I just turned to it as a familiar and relatively current (is the show still on?) example of someone inserting a pause to make a subsequent statement appear more important.

My late best friend Lenny used to use a cigarette-flick in the same way: "So I told him...(ash flick)...go f*** yourself".

[italianguy63]

I get it (pregnant pause)--

I think it is called "over acting" sometimes too..  LOL.  David Caruso.  You bust me up!   

Happy New Year!!

[davent]

No exaltation on my part.  I just turned to it as a familiar and relatively current (is the show still on?) example of someone inserting a pause to make a subsequent statement appear more important.

My late best friend Lenny used to use a cigarette-flick in the same way: "So I told him...(ash flick)...go f*** yourself".

[GGBB]

Carbide is brittle. #70 bits are tiny. A wobble of a few 1/1000 of an inch will break them.

I've done a few hundred holes so far with a #70 carbide in a cheap bench drill press with more than a few thous wobble.  Perhaps the lower speed helps (~3000 RPM), or the fact that I use a light touch to hold the PCB down flat and keep it from spinning but let it move horizontally with the bit.  Or maybe I'm just lucky.
--
I find most components typical in pedals fit #70.  For off-board wiring or thicker leads like on power diodes I use #65.  For some board-mount things like molex connectors I have a #60 but it rarely gets used.  Going with a bigger bit for everything give a little more fudge room with the precision of your hole placement - helpful with ICs, sockets, box caps, and anything that has non-flexible lead spacing.

[R.G.]

You have good hands and good luck. 

Small drill bits need to spin FAST or fed very slowly. This is a consequence of there needing to be only very small "bites" taken on each revolution. An edge can only cut so deep before something breaks. This is easy to see with something big, like a knife. If you cut into wood with a hand-held knife, not-very-deep slices are easy, but if the blade digs in deeper, you can't make it cut any more and eventually more force breaks the blade.

With a rotating drill bit, the cutting edges are knife edges. How deep they cut depends on how fast the bit is fed along its axis. In a hand-fed drill press, you can't control that, only the force you place on the bit along its axis. How deeply the bit's knife-edges cut per revolution depends on the axial force compared to how fast the knife edge moves around the rotation. If the bit is hardly moving, the axial force makes the bit dig in and cut deeply. If the bit is spinning very fast, each revolution cuts away a thin shaving, not a deep chip. Bits also break when they dig in too deeply and the rotational force exceeds the ability of the bit behind the knife edges to hold together, and the bit snaps in torsion, not in axial bending.

There is an ideal rotational speed for each combination of drill bit diameter, knife edge geometry, material being cut, and axial feed speed. In the PCB industry, bits in the #65-#80 range are usually run at about 8000-10000 rpm, sometimes faster, so the bits slice off thin shavings, not chips. It's hard to get high enough speeds in a hand-fed drill press, but you can compensate by feeling the feeding force and being very gentle. Hence my comment about "good hands".

[GGBB]

Not sure about good hands - I just try to be very careful and go very slowly - I take more than a full second to pass completely through the PCB. 

[stallik]

+1 on the 1 second rule.
I inherited an old pin chuck drill which I attached to a home made drill press with a couple of cable ties. Lateral movement can be measured in inches if I pull the bottom end of the drill about but once aligned by putting the drill bit into the "vertical" hole it remains reasonably stable. I work slowly and have never broken a hss drill bit. Must be really lucky

[R.G.]

I work slowly and have never broken a hss drill bit. Must be really lucky

HSS is very much more forgiving of lateral movement and bending than carbide. The problem with HSS is that you only get about 50 good holes and maybe 100 total holes before the bit is so dull that you're abrading a hole through the fiberglass, not cutting. Thin HSS bits will bend enough to take up the lateral movement and misalignment.

Carbide bits will drill thousands of holes before getting dull, but they are almost completely intolerant of bending.

[davent]

If someone would market a carbide bit with a 3/32"-1/8" shaft length we could all reach those 1000 holes but that'd be poor for business.