Drill bit sizes for PCBs

Discussion in 'General Electronics Chat' started by SPQR, Nov 11, 2012.

  1. SPQR

    Thread Starter Member

    Nov 4, 2011
    Hello all,

    About two months ago I started making PCBs again (based on Bill Marsden's thread regarding the thermotransfer method - excellent!).
    One of my difficulties was finding the right size drill bit to use. I couldn't find any "standards" on the web, and didn't find any "general recommendations".

    I drilled a few holes, and most were fine, but a few were too small, and a few too large.

    So, I figured, what the heck! I'm a neurotic, why don't I do a little project that would help me, and perhaps someone else.

    So I went to Harbor Freight and bought three of their mini-cases of carbide bits (recycled from other users). With a spreadsheet I went through all the boxes and recorded the sizes in inches and mm.

    By eyeball, I picked a few of the larger sizes that might work for my hobby PCB's. Using an extra piece of PCB, and using those eight larger sizes, I drilled three holes for each size.

    A picture of the PCB is attached.

    Then, using my "pile of parts", I put each wire through the hole that it fit "best" in, then on the same spreadsheet put an "x" in the sizes that worked for that part.

    The spreadsheet of drill sizes and part hole sizes is attached.

    What I've learned is:
    Resistors, disc caps, small diodes, ICs, transistors, reed switches, DIP switches, encoders, PCB relays, DIP sockets, LEDs and SIP resistors will all fit fine in any hole greater than 0.0292".

    Odd capacitors - 0.0394 or greater
    Large wire diodes - 0.0394 or greater
    small PCB switches - 0.0360 or greater
    large PCB switches - 0.040 or greater
    2N3771 TO-3 - 0.0595 or greater
    Molex KK connectors - 0.036 or greater
    7809 - 0.036 or greater

    So probably what I'm going to do is use 0.033 for most of my holes, and 0.04 for the larger stuff like switches.

    Any thoughts from the experts?
    What do all of you do about hole sizes?


    NB: I couldn't upload the Excel file, but I changed it to pdf and uploaded that.
    Last edited: Nov 11, 2012
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    Excellent post. I've always taken a guess when buying these things too. and my memory always fails me what I used before. I guess I should make notes.

    But it would be good to get advice from our more experienced forum members. Once we get a nice chart going, perhaps it should be added to the making PCB threads to act as a reference.
  3. Wendy


    Mar 24, 2008
    Last edited: Nov 11, 2012
  4. SPQR

    Thread Starter Member

    Nov 4, 2011
    That is a nice kit - it contains the sizes that would cover most of the stuff I mentioned.
    I can't see whether it is carbide or not - I've read that non carbide bits get eaten up like crazy.

    Of course the downside of carbide is:
    If you drop one, it will break.
    If you don't use a drill press, it will break.
    If you drop the whole box, they all will break. (been there, done that, got the T-shirt).
    If you touch the tips of the smaller ones, they will break.
    If you don't speak to them nicely, they will break.:D
  5. Wendy


    Mar 24, 2008
    Main thing is have a good drill press, as I mentioned in my article. If you have such a drill press they will last.
  6. nerdegutta


    Dec 15, 2009

    I opened the attachment, and I saw 0.0031mm drill size. "WOW" I thought, "that's really tiny."

    Are you sure 0.0079inches are 0.0031mm?

    I drill my PCB's with 0.7mm 1mm and 1.5mm drillbits. Res, caps, doides with 0.7mm. Headers and some switches with 1mm and 1.5mm. Mounting holes with 3 or 3.2mm.

    Great job, btw! :)
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Most standard 1/4W axial resistors had lead thicknesses of about .022" ballpark. I always spec'd a hole of about .031" for all those.

    Half W axial resistors were maybe .032" so I used an .040" hole.

    Other components you just have to clamp the calipers on the leads and then go up about .008" from there to get the hole size.
  8. t06afre

    AAC Fanatic!

    May 11, 2009
    The conversion factor is 1 inch is equal to 25.4 mm. So your table is not correct. I post the correct table here
    For a hobbyist I see no point in going lower than a 0.8 mm hard metal drill bit. The lead of a standard 1/4 watt resistors is 0.6 mm. A standard TO-220 package use 1.02 mm legs. Here is my recommendation for the hobbyist then using hard metal drill bits 0.8mm,1.00mm,1.2mm, and 1.5mm. For other dimeters use a standard HSS drill bit. Then using HSS drill bits. You should always drill a pilot hole with the hard metal drill bit
    • test.pdf
      File size:
      46.8 KB
  9. Wendy


    Mar 24, 2008
    Actually I etch the pilot holes, along with the Dremel drill press it has been good enough. The big hitter is eye wear, I used magnifying headgear with built in LED lights, as my eyes are just not good enough anymore. The alignment is critical (of course).
  10. MrChips


    Oct 2, 2009
    Yes, etch the pilot holes to help center the drill bit.

    I think I use 0.035" carbide drill for all holes (have to check) to handle everything from resistors to IDC connectors except of course larger mounting holes.
  11. SPQR

    Thread Starter Member

    Nov 4, 2011
    Thanks very much!
    Yes, I used the wrong conversion factor on some of them as noted above.
    All of the bits except one had their measurements in inches.
    Last night I did another PCB and used the 0.033" for resistors, IC's, LEDs, and the 0.04" for the microswitches and the Molex KK connector.
    They worked perfectly!

    For now, I use my PCBs by just placing them on a table and hooking them up to 5V (I'm not sophisticated enough to put them inside something that works!:)). On each corner I put a nylon 4-40 screw and nylon standoff, so I etch a "hole" in each corner (a large pad) and drill it out with a 1/8" drill bit.

    So I think at least from my perspective, the hole size issue is solved.
    Hope it might help another hobbiest.

    Thanks for all the excellent comments!