Wednesday, May 16, 2012

Four Holes Enter, Two Holes Leave: Making a 1/8" Mortise with a 1/8" Drill Bit

When teaching people that are making their first hollows and rounds, Larry Williams advocates using gimlet bits to start the mortise for side escapement planes. He demonstrates this on his video. He and Don McConnell have taught this to a countless number of students who have executed the method successfully.

Much to Larry's chagrin, I use a drill press.

There are several issues with drill presses and drill bits. The biggest of which is dealing with a drill bit that skates around the top of your angled plane billet before wandering through a seemingly random and inaccurate progression. These issues are exaggerated with the thinnest drill bits (i.e. 1/8")

So, how do you make a 1/8" mortise with drill bits that are 1/8"? Here's how I make the mortise for a #1. (Again, this is a supplement to Larry Williams' Lie-Nielsen produced DVD.)

I start by marking the top of the mortise. 

Mark the angle that the wedge will ultimately lean on the back of your stock. This line is drawn from the blind side of the top of the mortise to the blind side of the mouth.

 Using a hand drill and drill bit that is 3/32" I make a pilot hole in the center of the marked mortise. (Use a nail set, awl, etc. if you are initially uncomfortable with making slight adjustments.) 

Go ahead and make three more.

 Once you are comfortable that the holes are centered in the mortise change the drill bit to 1/8". Widen the holes while approximating the angle.
These pilot holes, which are now 1/8", will prevent the thin bit from skipping around on the top of the plane billet when starting the holes. 

Then it's on the the drill press.

This is our final goal from the drill press. There are four holes up top. Usually you will only get 2 or 3 on the bottom.

I take the time to make four holes because the mortise chisel is then two strikes of a mallet away from being through.

The result:

I was off by 1/128".

Any time I use the 1/8" bit I make more than two holes. I make four for the 1s and 2s because the mortise is only 1/8". I make three pilot holes with 3-6. With those planes, after the drill press, I use a 9/64" or 5/32" bit in my hand drill to widen the holes.

The process seems like there are a ton of steps. The whole process--from starting the pilot holes to walking away from the drill press--will take me 5-7 minutes for a pair of planes.

Additionally, I only make these pilot holes when using a 1/8" bit. I always, always, always mark the angle of the leaning wedge on the back of the billet to make certain the jig is correctly aligned. It's quick.


  1. Wow, thanks again for sharing some of your secrets. This information is much appreciated. I have done the gimlet thing and its quite a bit of work digging out the mortise.

    A couple questions: is the 1/8 bit in the drill press appears to standard point drill point but of extra long length. Any other details?

  2. It's a standard point bit that was, I think, originally 12". I ground about 4" of it off.

    I originally started drilling only two holes. Then moved to three. Now 4. Clearing the mortise that starts with only two holes is difficult. It often turns into a frustrating rendition of The Sword in the Stone. Even getting a float, especially a new float that is also 1/8" before any sharpening, into the mortise with these thin mortises can be VERY difficult and time consuming. Taking the time for those other holes is highly beneficial with anything smaller than a 3/16 mortise.

    I should have stated (since the title of the post referenced it) that since you are using a flexible bit the holes tend to converge at the bottom. Once the bit fully enters a previous hole it will track that hole. You'll notice in the video that I just listen and feel for the bit to emerge at the bottom for the first two holes--front and back. For the third and fourth I usually squat down to watch it come out. I do this so I know if the bit is being pushed towards the front or back of the mortise.

    I still remember the first time I thought to drill a third hole. I was ecstatic to think of an enormous time saver but hated myself for not thinking of it earlier.

    I also should have stated that if you want to make a 1/8" mortise, or in this case a 33/128" mortise, you should sharpen your cheek and side floats a few times to reduce the width.

    Thanks for reading (and commenting). Come Back!

  3. Matt, that is really interesting. In your H&Rs are all wedges leaning as you show here? I have a set of Moseley H&Rs and the wedges (and irons) are skewed slightly but do not appear to lean. I infer from what you said that you only make 2 holes for averything larger than a #6 - is that correct?
    Larry Barrett

  4. Larry,
    All of the wedges on my side escapement planes lean, yes. The lean varies, but is typically about 1/8". The wedges probably don't "appear" to lean in my planes either. Measure your planes, you may be surprised.

    I only make two holes for anything larger than a #6, yes.

  5. I'd wondered about something similar while watching Larry's video (mostly because I don't have any gimlets.) In a "production" environment (yourself, or someone making a ½ set) would a simple clamp-on fixture that would locate off the blind side, top,& toe with 2-4 drill guides speed up the process? A set of shims could be used to alter the offset on the blind side for differing sizes.

  6. Great post! Have you ever tried a spotting or center drill? These are stout little drill and countersink all-in-one bits that used to start holes in metal in the machine shop. A #1 bit has a 1/8" dia. body size or you could try a bigger #4 which has a 1/8" tip drill size. (See for instance).

    These bits are just meant to start the hole and go in about one diameter or so, an 1/8" in your case. If you use these, you could probably do all the work on the drill press, which would be faster. The bits are very stiff and don't bend like a regular twist drill.

    Another way might be to chuck a 1/8 flat bottom bit like a milling cutter or router bit or dremel bit in the drill press to make a small flat at the correct angle using the drill press. You could then finish the hole with your current bit.

    Keep up the interesting work!


  7. What is the purpose of the lean? and how do you determine it?