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Any tips on enlarging pre-existing holes without losing the centre? I have to make some tuner holes bigger, and some bridge stud holes bigger. I've got a tuning hole reamer, and 11mm drill bit for the studs, but I'm worried when I use them I may shift the centre of the holes. I don't have a drill press, so I guess I'm also worried about coming at the holes straight.

Conner,

Would a 'step drill' do the trick?

https://www.amazon.com/Neiko-10193A-Tit ... +drill+bit

Steve

a unibit (step drill bit) will allow you to get to the right diameter as a starter...you will most likely have to change to a standard bit once you get there (e.g. the odds of the last diameter on the bit being the diameter you desire are low)

also, you mention a metric size...never seen a unibit in metric, though one would think they make one...

as a side note: when drilling through thick steel without a drill press a unibit rules over standard twist bits...I used to easily burn up a standard bit per use when modifying barn door flat tracks to be the exact right length for the intended use...once I switched to a unibit...well, I'm still using that same bit from a couple of years ago!

That step bit looks perfect. Thanks guys.

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Say what you do, Do what you say.

Couple of other thoughts;
1.Make a drill guide from a 1” or thicker piece of material and clamp in place. If using a forstner bit, 3/8” thick.
Or
2. Plug the holes and remark center.

B

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My memory is so good, sometimes I remember things that never happened.

You can also glue a stubby dowel of the right diameter into the hole, then redrill.

I bought the very expensive end pin reamer for installing pickups because of hearing horror stories of people trying to do it with twist drills. One problem with uni-bits is that each step isn't very long - you might have problems with something like an end block or a headstock.

If you have a tuner hole reamer that may not be a bad way to go. To ream holes slightly larger I've used a twist drill bit in an electric drill run backwards (less chance of chip out).
Here's is something I found on you tube (which I have also done):
www.youtube.com/watch?v=oy55TU5OlLU

We use a series of chucked reamers in a drill press, or a step drill followed with a chucked, straight fluted reamer for these sorts of jobs.

Most chucking, straight-fluted reamers have a generous chamfer at the tip, which is there to center the tool on the existing hole. While opening a tuner hole from 1/4" to 0.340", 0.348", or 0.363" is quickly done in a single step with a piloted reamer, opening a hole to final size without a definite purpose tool available is better done with a couple reamers or a step drill/reamer combination than with twist drills which are not modified for use in wood or other softer materials. A step drill can speed up the process, but usually cannot cut deeply enough at the final diameter to complete the hole without reaming.

A full set of HSS reamers from 1/16" to 1/2" in 1/64th inch increments, plus 6mm, 9mm, 10mm, 11mm, and 13mm should run about $220 from Ebay in import quality, and are some of the most useful tools in the shop.

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For the times they are a changin'

- Bob Dylan

A set of numbered (or lettered, depending on how big the hole is) drills may offer some help. Idea is to drill holes one size larger than the last drill bit and walk up to the end size in many drilling steps. Chipping is also less of a problem that way. And it's hard to over-do a hole, like I heard somebody did once with a step drill when he didn't pay enough attention to what he was doing.

I've found step drills really useful for making concentric holes in thin material; never tried to use one to pilot a hole in thicker stuff.

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Peter Havriluk

Step drills work nicely in thicker materials, and have the advantage of shearing finishes nearly as cleanly as a fluted reamer, so no need to worry about lifting the lacquer with a twist drill. Also useful on jack replacement, such as converting the G&L jack to a standard 1/4" Switchcraft mono and mounting plate. For acoustic jack installs, a 1/8"-1/2" step drill gets the hole opened to correct diameter, and the job is finished with a chucked, straight flute reamer of the correct size. While the StewMac tool is what we usually use (the higher cost is made up for over time with reduced labor), a step drill and a 15/32" reamer is about half the cost of a special purpose tool, and works just as well.

_________________
For the times they are a changin'

- Bob Dylan

I have had success drilling straight holes by using long drills and /or extension, when drill press was not convenient. But setting up a flat reference surface somewhere is necessary and often the key.

The easiest and cheapest method is to use a model airplane prop reamer. These are usually available for less than $20 at your local hobby store, or you can order them online from outfits like Tower Hobbies.

This is the one I use. (Great Planes Precision Prop Reamer Metric - $14.99)

This will enlarge the holes in the head stock without changing the hole's center. These are also available in SAE sizes.

https://www.wikihow.com/Ream-a-Hole

Andy