Tuesday, July 15, 2014

Techy Tuesday - How to Make Holes in Things

Most people right now have those Looney Tunes-style question marks over their head.  "How to make holes in things?  Uh... with a drill and bit?"

Before you can answer that question, you need to know what the hole has to be for, how perfect it needs to be and what material it will be in.  Sunday, for example, I needed a hole to clear a 3/8" bolt, through 1 3/4" thick hardwood.  A portable drill is the right answer here; I started a pilot hole with a small bit (between 1/8 and 1/4") and then finished it with a 7/16" bit.  Yes, deliberately oversized to allow some adjustment by jiggling the reloading presses while I set them in place.  Ask a carpenter and this is the answer you'll get.  It's the right approach for a very wide range of problems. 

Ask a machinist and you'll be told that holes drilled with a drill bit in a drill press are never circular and never straight.  Drill bits wander as they go through the work piece.  For a hole that needs to be more circular and straight with a precisely sized diameter, machinists will use a boring head and boring cutter on the milling machine and gently feed the cutter into the work.  Many use a pilot (undersized starting) hole to locate the feature and a boring head to enlarge to just about size, followed by a reamer to achieve the final size.  A high quality, "heavy metal" or "big iron" boring head.  A set of reamers sold like a set of drill bits.  Sherline's miniature version is here:

That idea of starting with smaller bits and working up to bigger ones is universal.  It will get your through lots of problems in the shop.  Another thing to do is "peck" with the drill, advance the drill no more than a couple of diameters and then pull it back to help clear chips.  Keeping the waste out of the hole helps the process.  (Peck drilling is so important, it has its own command in CNC instructions).  If you're drilling metal, a cutting/cooling fluid like a light oil can keep the bit from getting too hot and getting duller.   

Chances are you've seen (or even have) a set of standard sized drill bits like this.  But what you have to drill a deeper hole than those?  Longer drill bits are available, like this set.  Longer drill bits wander even more than short ones, but if it's the only way to cut a hole to pass a wire, you have to do it.  Easily found twist drill bits get you up to a half inch holes.  Spade bits for wood get you even bigger; over an inch.  For larger holes, most people transition to a hole saw.  Hole saws cut out a waste plug in the middle of the material and get you to even bigger holes, but usually not in very thick materials.   For large holes in thin sheet metal, I've seen many people recommend these step bits.  I've personally never used them as I don't do much sheet work.  In my early ham radio days, when more people homebrewed their radios, a set of Greenlee punches for punching holes in metal chassis was absolutely da bomb.  I've used a nibbler to cut out 1 1/2" holes for a pair of meters and almost lost the use of my hands from muscle fatigue!  I've seen a nifty video of a power nibbler driven by your electric drill; that would be the way to go. 

Need to cut a hole in a granite counter top?  You need a diamond drill bit or diamond hole saw set.

We could go on, but I'll cut it here.  People have been making holes in things for a long time and a lot of clever solutions have been developed.  We really haven't touched on making holes that aren't round.   And we haven't even gotten near the topic of drilling a long piece of steel into a barrel without the bit wandering through the sides!


  1. I could call this one "Things I Learned from My Father When I was 10 years Old".

    Dad was a Tool and Die Maker.....

  2. Dang! and I thought this was going to be a shooting post!

  3. juvat - I almost started this with a line about "other than bullets". To be honest, I thought I left it in. Must have edited it out and forgot.

  4. I kinda like them Forstner bits. Mmm hmm.


  5. Forstner bits are really a good approach for a lot of problems. They're essential for relatively flat bottom holes that need to not go through the wood or whatever.

  6. I use the step drill bits for putting holes in my bulkhead in the shack to feed bulkhead connectors (SO-239s) through. I start out with small straight bits, switch to step drill bits to clean material away that would wear out the Forstner bits (material is plywood), and then finish off with the Forstner bits which nicely follow the pilot hole.

    Square holes:


    Extra Bonus machinist goodness, a nice club, and a sometimes very good newsletter.
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    73, Jim

  7. More rounder! holes Fast! in purty thick steel - rotabroach or similar. Big diameters too!