What is this drill bit called?

[bnjp]

I'm looking for a bit that can drill a hole in the tail block smaller on the outside and larger on the inside. This is for a specialty project where I need to install a 2nd output jack beside the strap button. The bit I'm looking for drills backwards so you can pull it through the hole from the outside.

[mirwa]

I believe you are referring to a counterbore, some people call them step bores, shouldered bores etc, personally I just make my own.

Most hardware stores would have something suitable.

Steve

[Silly Moustache]

I think they are called reamers here.

[srick]

Smaller on the outside, larger on the inside? Must be a tardis bit!

Rick

[ctgagnon]

Originally Posted by srick

Smaller on the outside, larger on the inside? Must be a tardis bit!

Rick

Everybody says that, yeah.

[printer2]

I hope it is ok to link to another forum.

http://www.luthiersforum.com/forum/v...0bb48ceb68d510

[MC5C]

It's called a reverse counter-bore, or a reverse spot-facer. You can buy commercial ones made for metal working, you may find one at Stewmac et al.. You can make one out of a bolt. Presuming you want a 3/8" hole, get a 3/8" bolt of a certain length, hacksaw the bolt head so it has two or three arms sticking out, file the face of each arm into a cutting surface, drill your 3/8" hole the tailblock for the pilot hole, fish the bolt through the hole from the inside of the guitar, and use the drill to spin the bolt and pull back to make the sharpened arms cut the counter-bore. MSC has many of them, you buy the bore bit plus a pilot shaft, and mount the bit on the shaft, then do as above. https://www.mscdirect.com/browse/tn/...navid=12106110

[murrmac123]

Originally Posted by Silly Moustache

I think they are called reamers here.

No, they are not called reamers here, Andy, they are called reverse counterbores.

A reamer is a totally different tool, and has the same name both here and in the US.

[bnjp]

Thanks everyone. That reverse counterbore is exactly what I was needing.

[bnjp]

I decided to use a 1/2" router bit instead. Drilled the outer hole and then stuck the bit through the hole from the inside. Caught the shaft in the chuck of the drill and pulled it through backwards. Worked great. This is what I was doing.

[nacluth]

Cool. Nice job.

[bnjp]

Originally Posted by nacluth

Cool. Nice job.

Thanks. Those are two identical Baggs endpin jacks. The one is just recessed so it's more flush since most people only play with one strap. haha.

[Ned Milburn]

Just wondering why you would need a reverse counter bore bit in order to drill a hole for a jack...??

[murrmac123]

Just FTR, you are probably going to wish you had installed the second jack socket between the top and the center rather than between the back and the center.

I did exactly the same thing as you have done on my Bourgeois OM, (except I retained the end-pin and located the jack socket where you have located your second one). I find now, on stage, that the strap interferes with easy insertion and removal of the jack plug. It would have been more ergonomic if I had fitted it between the top and the end-pin.

Like Ned, I am slightly puzzled by why you needed a reverse counterbore for this operation ?

[cattzap]

He needed to counter bore the back of the hole to allow the threaded length of the jack to make it all the way out to the surface far enough to screw the nut on. His solder terminals are probably buried down into his counter bore.

Another option would have been to scoot away from the block in the center and install it into the thinner side body, but....I have one at my house right now that was done that way and the first blow to the end of the cord blew the side out. Not sure what can actually be done now.