Greetings All,

The Harmony on the bench has a very thick end block (not uncommon as Ihave subsequently found) and consequently the Endpin Jack Preamp system in the Fishman Infinity system does not make it all the way through being about 10mm short of being satisfactory.

I recall a custom machined reverse cutting Fortener bit as a solution to working in the box to reduce the thickness of the block, and a web search points the Finger at FF as the creator.  Anyone help with a link to this baby, or any other elegant solution.

Every time I advise a customer that "this will only take an hour" I am just waiting for the Luthiery demons to descend upon my already heavily burdened shoulders.........

Regards and thanks in anticipation of assistance,


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Yes I recall the post , someone made a special bit to cut into the neck block from outside , not sure it was Frank though. I wonder if you could use a hole saw with the centre bit extended to its maximum , or replaced with a 1/4" rod . You would still need to remove that core however .

Yep, been down that concept road, but the modified blind Forstener bit will surface as soon as the U.S comes on line,  hope yr doing fine Len, plenty of work about down here, how you?  Also a little sneek peek of Sam Bennett's ( guitarist for hot punk-pop fem outfit Glitoris) new Vance SB Glitterbomb signature model.....this one took the place of my Christmas. 



I remember that one too.  It definitely was Frank, and it was on one of the pages at

I  can still see it in my mind's eye.  Thought I would be able to pull it up in a flash - but I just had a look through the menu and also did a google search of the site using various search terms that might be relevant - and can't find it.  It must be buried in the process on one of the repair blogs, and the title doesn't give it away.  Hopefully Frank will jump in soon with an exact memory and location. 

Yes, I remember that article too, and I found it:  on, under 'neck resets', the 'Impossible Neck Reset: It's a Spanish Heel".  It's a bout a B.C.Rich acoustic,there is a photo of the modified Forstner bit, used in the process.

Good luck!


Wow, that was quick, thanks Dave, better memory than mine for sure!

And thanks all for the help guys.



I'be heard of a tool that does similar called a "reverse spot facer".  

That's right - a  Google search for  reverse spot facer, counterbore or countersink should turn up lots of possibilities.  I sometimes make tools as much for an exercise in learning to do machining as anything else.  Seems I recall I made the reverse Forstner style bits before I knew about "pull countersink" tools.  

Since then I've read about some guys grinding the back end of spade bits to cut as they are pulled through a hole.  That, combined with a collar to fit the hole and keep the drill centered, seems like a really good way to go.

Had the same issue some time ago on an old Guild.  Here's my "go-to kit" for installing jacks in deep tail blocks.  

The counterbore was found on eBay a few years back and, in conjunction with that, I ground a reverse spade bit from a regular 1" bit.  

Both work well.... the counterbore shaft is inserted in the existing hole from the outside, and the bit slides-on and locks in place from the inside.  The reverse spade bit, being one piece, goes in from the inside.

Frank's right, of course, about needing to use a semi-snug collar to keep them both centered.

You guys are awsome!   Thanks so much for you stellar assistance and generous efforts - I'm having a small moment here;

Of to Ebay/Grinder.



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