On that one where there's a bit of a stub sticking up, I think I'll lay a pre-drilled (to correct finished diameter) piece of scrap on there, then just barely drill into the old dowel. Just enough to establish a center point.

Then I'll remove my guide, and come back with a smaller bit and drill to proper depth. Then chase it again with the proper diameter bit.

Same process for the ones that have a recessed dowel, except on those I'll just eyeball the proper location of the guide.

But still open to suggestions...

If the recessed dowel(s) are fairly close to the surface, a small tangency square could possibly be used to assist in locating/scribing/marking the center point.

This may be more trouble than what it's worth tho - just an additional thought.

Yes, brad point won't "walk" and even if slightly off center, it shouldn't matter.

Use a punch or nail to dimple where your gonna drill.
Hollow the center, cave in the sides.
Tape the drill for depth.

HTH..good luck...notnew....

I'd use the guide hole to keep the drill bit vertical. No easy task when drilling by hand. How many times have you drilled a hole in something only to find quite a difference between the entry and exit locations on the piece?

If you are not vertical you'll have a problem with the assembly unless you go with an oversized hole and use epoxy.

Remember, the chair holes are just a tad larger than 3/8" diameter, so the parent wood kept a 3/8" bit in line, especially as I was careful. The bits I have with me are DeWalt "pilots", so they were perfect for this! First drilled a guide in a piece of scrap oak. Had to wallow the underside a bit so it'd fit over the old dowel remnants, then placed the guide in place and drilled into the old dowel. (These steps located the bit in the center of the dowel for me.) Then it was simply drilling out the old dowel, prying out the remnants, and badda-bing-badda-bang... Photos:

Good job! I knew you could do it. Now, I've got a chair leg I think I'll send to you.

Slightly larger than 3/8?

Smart move going slightly under-size then removing the remnants.

Well... I didn't know this beforehand. It wasn't until I took my 3/8" bit and confirmed the hole size in the chair that I discovered the original holes are just a skosh bigger than 3/8ths. (Somewhere between 3/8" and 1/2", and NOT one I already had in my index.) And while my original intent was always to use something slightly smaller, and then chip out the remnants, I was pleasantly surprised to find I only had to make the one pass with the 3/8" bit.

Slightly larger...to fit a 3/8" dowel.