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According to SM, this is the hole size for my Grovers. I want to buy a good bit that doesn't wobble. Brand suggestions please.

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Hutch

Get the heck off the couch and go build a guitar!!!!

It’s actually 10mm. The tuner is .390”, 10mm = .393”.

I use these bits. The SM 10mm is slightly oversized making for a sloppy fit.

https://www.leevalley.com/en-us/shop/to ... em=07J1610

If OP has the Grovers, get a caliper and measure them.

My experience is if English measurements are given in wonky numbers, it's often an attempt to use English scales to describe metric items. In this case 13/32" is 10 mm. And that's the size drill I used when I installed a set of Rotomatics. The bushing size was 8 mm. I drilled 8mm all the way through the headstock and used a metric step drill to open up to 10mm for the tuner body. Easy way to keep two holes concentric.

Any drill is plenty accurately sized for making holes in wood. Making the holes square is a job for a drill press.

And standard metric size drills are easily obtained in sets that have evenly sized steps. My set coughed up a 4mm bit which is just right to drill recesses for 4mm fingerboard fret marker dots. Also had a 6mm bit in case I wanted bigger fret markers.

Stick with the metrics.

Someone's posted a link to a Lee Valley set of metric drills. If I didn't already have a similar set I'd buy that one in a heartbeat. Good tools from a serious tool vendor.

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Peter Havriluk

I do the same as Peter, drill through with an 8mm, then use this bit from the backside to create the shoulder. A drill press is recommended. The results are flawless!

https://www.amazon.com/Irwin-11102-Unib ... B00075RFZG

M

Thanks, I ordered the step drill. I'll pick up an 8mm but at the hardware store. Thanks for the dimensions. I'll explain another time why I need them.

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Hutch

Get the heck off the couch and go build a guitar!!!!

The reason I can't measure them is I put them on my Stagg because I couldn't find the cheap ones someone gave me. I have since found them and need to do the replacement but not right away. I just put new strings on the Stagg and it's my player until I get this one done.

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Hutch

Get the heck off the couch and go build a guitar!!!!

I've also had good luck with the Lee Valley brad-points, and ones made by Fuller.

Fisch brand brad point bits are good quality and easy to find online.

Grovers have been 10mm (nominally) since they started importing them in the late-1980's. US made ones were 3/8". That applies to both the boss size and the hex nut.

10mm = 0.394"
25/64 = 0.391"
13/32 = 0.406"

13/32 is too sloppy, IMHO. I use 25/64".

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John

Although not as extensive as the decimal inch reamer collection at my previous shop, I keep .390", .392", .394", and .396" HSS or carbide reamers handy for those 'stated 10mm' jobs. We found plenty of Grovers that ran between .390" and .396" and Schertlers that were spot on .395" for their 10mm (.3947") hole. A quality 3/8" bradpoint followed by reaming to fit was the usual practice if the tuner did not require a counter-bore. After finishing, expect a hole to need re-reaming if a perfect fit before final coats.

High speed steel reamers last a long time in wood shop service, and good US-made HSS reamers in decimal sizes can be had from a number of places, including eBay, MSC, and other machinist suppliers.

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For the times they are a changin'

- Bob Dylan

I have a tapered reamer that worked well to open the holes on the Stagg a scosh.

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Hutch

Get the heck off the couch and go build a guitar!!!!