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I closed the box on a steel string without remembering to drill the bolt holes and countersink them. I read on the forum that a spot facer/reverse counterbore could be used to drill the recess inside the neck block, and I had an idea how that bit would look (shaft the size of bolt hole with a reverse-thread bit the size of the recess.

When I went online to "buy reverse counterbore" most of what I find has pictures of a short drill bit style head and a hole in the middle, but no shaft. The images that did have the shaft (and which looked like they would do what I want) weren't for sale.

So I'm hoping for, suggestions on the best way to get those bolt holes recessed and if that means getting a counterbore, can you tell me more about those?

Thanks so much, Beth

I too forgot to counterbore the neck block so i ordered this from www.spenro.com.
In my case I bought the 11/16 counterbore and the 1/4" pilot.
Just one thing, their site doesn't say anything about products being in stock. I had to wait about three weeks but i'm happy with my purchase.




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Thanks Rusty. How does the shaft attach to the bit (if that's the right term for it?)?

I use one of these (not necessarily that size) and routinely drill from outside first (jigged), then counterbore replacing the drill bit with a length of steel rod held on by an allen key set screw.
I made a Delrin collar to fit the counterbore to function as a depth stop.
For a one off you can just grind/file the back of a spade bit to work in reverse, I've done that previously.
Before that I even filed a wing nut on a bolt to cut the counterbore. ---Progress!!

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Beth,
The names I'm seeing are back spotfacer and reverse counterbore. Maybe they describe the same thing? I dunno.
The pilot is sold separately and has a notch in it that attaches to the cutter with a twist of the cutter or the pilot.
The cutter fits on the pilot very loose and likes to fall off before you begin to drill, you just have to draw it up to the work nice and easy.
Hope this helps.


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As Colin says, the cheap and easy to do this once is to file cutting edges on the back of a spade bit, insert the spade bit into the box with the shank protruding out through your neck bolt holes, attach to a drill, and pull the spade bit into the neck block. Not as elegant, but cheaper than buying something more elegant.

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Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

Except that I tried the spade drill trick and found it wanting. The back spotfacer gave me a perfect clean hole and I have no regret but that's just me.
It wouldn't be a bad idea however to try a spade bit on a piece of scrap, others may have a better result.


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I agree the spade bit is "clunkier", and can chop the surface up if it chatters. I think the trick is making sure the shank fits
your bolt holes fairly snugly, making sure the spade bit cutting surfaces are in-plane and sharp, and using a light cutting
force.

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Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

I used a spade bit for 30-40 guitars, before realizing it was was easier to do all drilling before the block is attached to anything...just get it sharp.

Call me a newb, but my LMI kit doesn't have counter sunk holes. It uses allen head bolts with washers.

Can't you just get longer bolts?

Bob

You can install these on a straight, untreaded pilot shaft, probably 1/4" for your application. There are quite a few sizes listed:
http://www.jamestowndistributors.com/us ... unterbores
For counterboring from the outside run your drill in the conventional direction. For drilling on the inside from the outside run your drill in the opposite direction.

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Stay with the happy people.
--Reynolds Large

Robert,
Just an FYI, but seems like some like to countersink for cosmetic reasons and will even hide the bolt heads behind a label.

Beth, the whole hole process and tooling for a closed box is shown in the pic sequence p 14-14 and 14-15 of the White Book.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Beth, there are several styles of these and Rusty posted the style I have. The thing about these bits is that they don't clear their chips very well and that cutter head will get hot and burn your fingertips. Basically you chuck the pilot in your drill, put the cutter on and spin it to lock and then turn on your drill and pull it into the block. I find that doing it a bit at a time helps. If it seems like it's not cutting, it's likely that the flutes are packed. You also want to put a mark on your pilot so you can see how much you've cut. One way to do this is to pull the cutter against the block and put a piece of tape on the shaft against the outside of the box. The distance you pull is the amount of counterbore. One more thing to note is that most bolt-on designs use a 1/4" bolt with a 5/16" through hole. These counterbore pilots are practically to size, so you may find that you need to drill the hole out by whatever drill size larger be it letter or metric so the pilot slides in easily. An O or P drill will be a few to .010" oversize and will allow the pilot to spin freely and won't have an effect on the quality of your counterbore.

How will you be covering the bolts, Beth? I don't know how people put a sticker over them with the body assembled.
Or how they remove it when necessary without leaving a mess.
Showing my ignorance as always.

I don't cover my bolts. The appearance of them doesn't bother me if they're counterbored, and I like the accessibility. But if you want to put a label or sticker over the holes, I think that would still be easy to do with the box closed.

I'm using a bit and pilot shaft like the ones in the photo Rusty posted that I got from MSC. The bit I'm using makes a 1/2 inch diameter counterbore. In case you are interested:
http://www.mscdirect.com/product/09937269 and
http://www.mscdirect.com/product/00428151

I can't get my fingers into the mortis to mark the shaft with tape so I use a Sharpie. I'm drilling 1/4 inch bolt holes and the 1/4 inch pilot shaft just fits with no free play.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

I watch the drilling progress on my laptop using a web cam and light in the box.




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