I need to drill a precise hole into a small cavity which happens to the parallel to the face of the piece of wood. To better illustrate this I made a simple diagram to be absolutely clear on what I'm working with here. The space is too small for me to fit any sort of drill into it. I thought about using a dremel with a flexible shaft attached but I need the hole to be as close to perfectly parallel as possible.

Hole needing to be drilled

For those who are familiar with guitars, this is a cavity for the springs of a floating tremolo system. I am having a lot of issues with the spring return which has to do with the hole being drilled out incorrectly. I also need to fill the old holes and probably re-drill through them. What is the best method to do this as well?

  • Does it have to be a round hole? Otherwise a router might do the trick; you get a slot much like a biscuit machine.
    – LosManos
    May 28 '15 at 10:35
  • 1
    Try stopping by the local modeling/RC hobby shop. They have lots of specialized, small (expensive) tools for working on small things in small areas and might have a nice right-angle adapter or know of someone who's made a similar jig who might be willing to help out.
    – FreeMan
    May 28 '15 at 12:35
  • for reference, is this what you are dealing with? i119.photobucket.com/albums/o125/DKoor/gitare/… May 28 '15 at 15:36
  • Do I understand correctly that this is for mounting the claw that holds the springs stretched out? I seem to remember the claw on my stats (Squier through American std styles) being made of stamped steel, flexible enough to bend into alignment, and being mounted using what at the time appeared to be slightly sloppy angled screws. Now that I see your question it makes me realize why they would appear so.... And it also makes me think that you don't need to worry since you can adjust the claw to align it after its mounted and under tension.
    – aaron
    May 29 '15 at 6:15
  • @aaron Yes that is correct, however the issue I'm having is that I am using a different piece which is not the typical cheap stamped steel piece, this is a machined piece which is very sensitive to how the screws are inserted.
    – Korozjin
    May 30 '15 at 1:39

I would be tempted to try and use a flexible drill bit. I have a small cheap set that are about 6" long. Can't find a picture of them online.

But there are many different kinds out there and many different price points but here's an example of them.

enter image description here

Either there was an edit or I missed the part about filling and redrilling the old holes.

My two recommendations are either find dowels the correct size and glue them in, and sand them flush, or get some wood filler (preferably stuff made with real wood) and fill them up well, using a nail to push it all the way in. Let it dry and then sand it flush.

if the holes are bigger than 1/4" I'd tend to want to go with the dowel approach.

  • I had thought of doing this with my dremel flex shaft, however I'm wondering if the end isn't a certain size where I can make a jig. I wonder if where the end of the bit he's holding, could possibly be fixed into a board and drill and fit a hole for the bit / shaft to be secured into, and then drill with that. I need it as perfectly parallel as possible is my only reservation about doing this
    – Korozjin
    May 28 '15 at 0:24
  • @Korozjin I've seen a few people with jigs to get better results.
    – bowlturner
    May 28 '15 at 0:45

You could easily make a fixture that aligns the end of your Dremel's flex shaft to drill the precise holes. It could be as simple as a grooved guide block that you tape or clamp in place while you slide the flex shaft along the groove to drill the hole.

If all else fails, here are a few more possible solutions to consider (though I'm not sure if this would have an impact on the sound quality since you're talking about a musical instrument):

  1. Drill all the way through from the other side (from the left, in your picture--assuming that's possible), then plug the hole from that side using wood filler or a dowel.
  2. Cut off the part that will have the hole, drill the hole, then glue the part back on. (The cut would be a horizontal line in your diagram.)
  3. Similar to #2, cut off the very top part, use a router to carve out the channel (instead of drilling it), then glue the part back on.

In the same vein as bowlturner's answer you could also use a off set drill adapter. Most of them are rather large for the work you are trying to do there are definitely some smaller ones out there.

Flat off-set drill adapter
(source: nexcesscdn.net)

Image from PanAmericanTool

By no means advocating a particular product but I included this specific one as it had the units dimensions. I was hoping that you could lay this flat but from the looks of your specs its just a little to high. You could easily hold this at a angle with a small board to help give you more precision. If you were lucky you might even be able to stand it on end at 90 degrees with a simple block as a guide.

A little googling shows other designs by different names like the "offset pancake type"

The flex bits do seem to give you more leeway. You could easily make a 1/2" small drill guide with the drill press to feed the flex bit into for another degree of accuracy.

  • This is more what I was looking for, good to know there is a part like this. Thanks!
    – Korozjin
    May 28 '15 at 20:38

An out-of-the-box solution that folks often overlook for this sort of problem: I first saw this as the lazy man's technique for making half-dovetail joints.

Use a bandsaw to perform a resawing/veneer cut, to remove the face of the board.

Use a router or whatever other approach you prefer to cut the channel.

Glue the face back onto the board, avoiding getting glue in the channel.

Done right, all the grain will line up closely enough that you can't tell where it was rejoined. Variations of this technique can be used to make other parts with hollows that are too long, or too twisty, to drill.

Note that some thickness is lost to the bandsaw kerf, so if possible start with a piece slightly thicker than final size and plane it down to an exact match after gluing it together again.

  • Have you seen Rob's answer that is much like this?
    – Matt
    May 28 '15 at 21:26

I would look at an oscillating "multitool" that can get its blade into the 1/2" deep well space, and use a very small blade . If you can't buy a small enough blade, cut one down with an angle grinder to what you need. It would make a slot rather than a round hole, but you could work with it. Much depends on how hard the wood is, and how much a cut-down blade might flex. You might experiment with a grinding type of blade used for ceramics. (I haven't tried any of this).

  • A 2.5" deep hole using an oscillating tool with an arc of 3° will result in a 1/8" travel at the end of the blade. Plus the width of the blade, which will likely have to be at least 1/8" wide for rigidity. That's going to make too large of a slot, at 1/4" best case with perfect accuracy.
    – Doresoom
    May 28 '15 at 15:21
  • I agree my answer would be a rough job, only to use if there is simply no other way to get a tool into a tight space. The multitool might be better described as hollowing out a space to insert something neat like a plastic tube as sleeve, and glue it in position. But I think the only way to a "precise hole" is rob's answer of drilling in from the outside, then backfill with dowel and/or plastic wood. (Carburettor designs have the same kind of problems, in metal of course, where you see plugged holes in odd places on the outside ).
    – Bob_WA
    May 29 '15 at 0:19

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