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I have a 2" diameter, 11" length dowel. I want to drill a 5/16" hole exactly in the center of each end, 2" min depth. It needs to be precise because it is for axles that the dowel needs to spin freely around without wobbling. I need to do both ends separately, not all the way through.

How do I find the center and drill a hole there? (Note: I have one handheld rotary drill. I do not have a drill press. I have access to one if necessary but it is not convenient. I also have these guides.)

I know how to find the center of rectangular boards, but not circles.

  • How long is the dowel in this case? Assuming it is short enough a drill press will make sure the pilot hole does not walk or follow the grain which would be an issue in cheaper dowel. Not sure about the center part besides measuring. – Matt Nov 22 '15 at 20:47
  • @Matt 11" length. – Jason C Nov 22 '15 at 20:48
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    No matter what method you use to find the center, use a center punch or an awl to make a dimple that will assure that the drill bit does not skip to a point away from center when you begin drilling. – Ast Pace Nov 23 '15 at 0:14
  • OK you're well covered for how to mark the centre (although note that commercial dowels are frequently not perfectly circular in section) but about the drilling, how deep do you need to go, what diameter and what drills do you own? – Graphus Nov 23 '15 at 10:26
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    The drill guide is a great idea, highly recommended. Without that it would be next to impossible to do this reliably with an eggbeater drill. In case you don't know, drilling into end grain there's a great potential for conventional bits to wander. – Graphus Nov 23 '15 at 19:31
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Finding the center

Using Geometry

There are a couple of ways to do this. Since your dowel is big enough you can do this by hand relatively easy.

First would be to make 3 lines on the outside of the dowel the cross 2 different points along the circumference (each line). Then draw 3 perpendicular lines from the center of those lines. The point where all those lines intersect is the center of the circle. This picture makes way more sense than my words.

Unknown theorum

That seems like more work than it is worth though. Something simpler, that requires a square (or anything with a known 90 degree angle), called Thales' Theorem. This one is also easier to explain. Draw a right angle and the edge of the dowel. The sides from this angle will bisect the circumference of the dowel. Drawing a line between those two point will get the diameter. Repeating this process a second time (starting from another point.) will get you a second diameter. The point where the two diameters meet is your center. This is what I would do as I don't need to do this to often.

enter image description here

Just use a tool

A center square, or similar tool like the one in Jason's answer would work very quickly and efficiently and would take less time and be less error prone. If you need to be perfect every time and plan on doing this a lot than a center gauge, or similar tool, is the way to go. Press it up against the dowel and draw your line. Do this twice and you found your center.

Might even be able to make a home brew version of this depending on your acceptable tolerance.

Center gauge

Drilling the hole.

This might not work for your case but in general I would recommend using a drill press for something like this where accuracy is important. Take a deep block and drill a hole, with the press, that is the same diameter as your dowel. Hopefully your table moves down far enough. The depth of your block, if possible, should be close to the length of your dowel. Keep in mind that you still need to clamp it to the table but the deeper the hole the less error you will get from the dowel moving.

Then place your dowel in this void. That will keep it perpendicular to the table. Use a punch to mark your center and then guide your drill into that hole.

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    "Thales' Theorem"... media.giphy.com/media/TlK63EWmJDBa5MjIr6g/giphy.gif – Jason C Nov 22 '15 at 21:16
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    @JasonC I love that gif so much........ – Matt Nov 22 '15 at 21:17
  • I don't have a drill press but I do have these, which are great. I usually punch a hole, put the bit through the guide and get it started while holding the guide out of the way up against the chuck, then drop the guide without lifting the bit out of the hole and clamp it down or hold it. They've been great. (I checked dowel ends with square for trueness.) – Jason C Nov 22 '15 at 21:20
  • @JasonC woodworking.stackexchange.com/a/1456/128. I made a "budget" one from scrap wood. – Matt Nov 22 '15 at 21:25
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    If you did have a press you could try to rotate the table. tips.woodmagazine.com/stands/… in case the work is too long. I know nothing about this type of use/jig so it can't be part of the answer. – Matt Nov 23 '15 at 4:11
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My final solution was to just use a drill press to drill a 2" hole with a forstner bit partway through a block of wood, then a 5/16" hole the rest of the way, centered on the pilot hole from the forstner bit:

enter image description here

Then I just stick it on the end of the dowel and use it as a drill guide:

enter image description here

This worked well. It's not really sensitive to imperfections in the roundness, and since I have to go to a friend's shop to use the drill press, I only had to use the press once and now I can use my handheld drill at home for drilling the dowels.


Marking Gauge

Prior to making the jig, I was at least able to find the center using an Incra IG32, by setting it to 1" (the radius):

enter image description here

Marking a line down the center:

enter image description here

Then moving it and repeating:

enter image description here

I made a third line just to verify (I was worried about the center notch in the gauge but the effect was negligible).

Still need to drill the hole precisely but that's at least one working solution for marking. Any graduated marking gauge that you can set to the radius will do.

Squares

If you have two framing squares you could clamp them together in opposite directions to make a 1" x 1" (or whatever radius) square opening, line one up with the dowel edges, and the inside corner of the other will theoretically be the center, as long as you clamped your squares precisely. This should also work for finding the center of a circle drawn on something flat, unlike the dowel which is an actual, physical circle.

3

I use maths from school for this sort of thing. (I can't believe this stuff actually came in handy!)

All you need is a ruler and a square. You draw two or 3 base lines and then a perpendicular line from the exact centre of each - the intersection will be the centre of the circle.

enter image description here

  • You need a compass, too, to find the centers of the baselines (that's the arcs at A and B and near C; you actually don't need the square for that). Might be tricky to make sure your compass point is right on the edge of the dowel, though. And yeah I've also been digging deep into the high school geometry buried in my brain, ha. – Jason C Nov 22 '15 at 21:10
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    I've never actually used a compass for this (doesn't work on wood dowels cause you don't have the rest of the bit of paper on the side to draw on!). What i do is just make the lines something easy like 30mm, and use the ruler to mark the centre and as the square to make the line perpendicular – Dave Smylie Nov 22 '15 at 22:07
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    Geometric constructions, though elegant, are a bit imaginary when attempting to perform them on the end of a dowel. – Ast Pace Nov 23 '15 at 0:06
  • see my comment above - you don't need the lines sticking out the back of the circle (this was just the first semi-relevant image i could find on google). on a dowel (or whatever) you just need 2 x right angle lines coming off the centre of another line. – Dave Smylie Nov 23 '15 at 22:40
  • While 2 lines would do it the third line acts as an error catch. – Matt Nov 24 '15 at 14:22
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If the precision is important but time less so; mount the dowel in the drill instead.

Make the dowel spin and create a jig to make the end of the dowel not wobble. Any point that does not make the centre point drill bit wobble is in centre of the dowel and aligned.

Update:

If one uses a knife, or similar, to mark the centre one can possibly dig-carve-drill a cone shaped hole; before inserting the drill bit.
This drill bit then only has to penetrate a few millimetres to be steadily centred.
The next step is how to be aligned/perpendicular but that is another question.

  • I don't have a 2" chuck but this is a good concept. – Jason C Nov 23 '15 at 13:00
  • You don't need that big chuck. Put a drive belt around chuck and dowel or put a lego? tyre on the chuck and make the dowel spin. Then find the centre on the dowel. It is also here my idea wears down as the jig starts getting weak and wobbly. But for finding the centre it might still work. – LosManos Nov 23 '15 at 13:29
  • Oh, great idea. I do probably have a Lego tire that fits. My Lego collection is a point of great pride, hehe. – Jason C Nov 23 '15 at 13:50
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    Please return with accomplishment. I believe the community might be interested in if such a cheap/wobbly jig is sufficient. – LosManos Nov 24 '15 at 11:19
  • I will still try this just to see, as soon as I have some more time, but for now I ended up making a jig to do it. – Jason C Nov 25 '15 at 4:36

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