Official Luthiers Forum!

I bought one of these from SM.

http://www.stewmac.com/Luthier_Tools/Ty ... eamer.html

It does a flawless job! I pre-drill with a 1/4" brad point, then follow with the reamer.

Cheers, M

Endpin jacks seem such a simple thing to install, but neglect to observe just a few key points, and the results can range from disappointing to disastrous.



StewMac makes a fantastic reamer specifically for fitting endpin jacks. It first tapers up to a straight section of 15/32" diameter, then steps up to a full 1/2". This larger 1/2" diameter section should never be used for standard endpin jack holes, though unfortunately it often is.



Pretty much all endpin jacks measure to 15/32" or 12mm, which are essentially the same, give or take a few thousandths. Here an Italian jack, a Switchcraft, and a Chinese import all measure the same within a few thousandths of an inch.



Just as importantly, the outer nut that threads on to the small diameter of the jack has a bearing surface that measures an even 1/2".



Here we have a jack mounted in a 1/2" hole. With this completely unnecessary slop in the fit there is now no side support if the cable or jack gets bumped or pulled. Here the entire load must be carried only by the washers on the inside and outside edge.

Furthermore, the 1/2" bearing surface of the nut is now bearing down on a very thin washer over a 1/2" hole, resting on the wood only around its flimsy perimeter beyond the bearing diameter of the nut.

These two issues combined (oversized hole and unsupported gap behind loaded area of the washer) are a recipe for disaster.



Here's a washer pulled from a guitar with an endpin jack installed in such a way. The 1/2" nut over the 1/2" hole just collapsed the washer, loosened the jack, and damaged the finish and end wedge as seen in the first picture.



Avoiding these problems is quite simple. First, holes should be reamed to 15/32". Endpin jacks will still fit easily in to this hole, but will be a snug fit supported by the sides should the jack ever get pushed or pulled sideways.

Secondly, the nut on the inside is adjusted so that when the outer nut/washer is tight to the wood, it will also tighten down against the large inner diameter. This way there is no gap behind the washer at all, and the nut can be tightened up quite firmly without collapsing or placing any excessive pressure on the finish or wood.



Adjustment of the inner nut has to be fairly precise for this job, which necessitates a simple way to pull the jack in and out of place during checks and readjustments.

Here I'm using the butt end of a 1/4" bell hanger drill bit to fish the jack in and out, though any 1/4" rod will work just fine. Stick the rod in through the hole, then reach in to the soundhole to fit the jack on the end.

Then the jack can be easily pulled in to place, checked, and moved back to the soundhole to make small adjustments to the inner nut as needed.

The goal is to adjust so that just as the outer nut is really beginning to tighten up firmly to the sides, you should feel a sudden stop as it hits the large diameter of the jack. Then you can give it an extra bit of torque, locking the nut firmly in place without putting any additional pressure on the finish or sides.

This can mean having to insert, check, remove, adjust, and repeat a few times to get the inner nut adjusted just right, but it is certainly worth the minute or two of extra work.



Then once the outer nut is firmly fastened on, it's time to install the strap button cover. For tightening or loosening these, a simple piece of thick rubber can be a handy tool. Just drill a hole and cut a slot in it, and you have a simple non-marring button wrench to provide an extra bit of grip to lock it in place.

Do all these things, and your endpin jack should stay reliably in place without any worries or hassles.

DO NOT USE A DRILL BIT

A drill bit in most cases will pull the tail piece up from the chips coming out. Not a pretty sight.

Do we use reamers to enlarge holes for tuners?