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How to use an H-59 neck expander.

After wanting one for a while, I finally acquired a neck expander which I need to deal with a neck problem for that Bundy Tenor. Having it in hand, I'm not quite sure how it is supposed to work. I know you put the tenon over the small roller and tighten from the top, then turn, but wouldn't this just thin the socket wall? How does this actually make the neck socket larger in girth?

Thanks
 

pete

Brassica Oleracea
Staff member
Administrator
After wanting one for a while, I finally acquired a neck expander which I need to deal with a neck problem for that Bundy Tenor. Having it in hand, I'm not quite sure how it is supposed to work. I know you put the tenon over the small roller and tighten from the top, then turn, but wouldn't this just thin the socket wall? How does this actually make the neck socket larger in girth?

Thanks
To quote the Ferree's web site "Do NOT just clamp down and start cranking, be discreet. "

What the tool does is exactly as you say...it grabs a circumferential slice of the neck tenon and (ideally) squeezes in uniformly around the entire circumference. The theory and practice of it is that by squeezing it the ring you are squeezing gets longer (that extra squeezed out material has to go somewhere) and the tenon diameter grows slightly (the tenon length ALSO grows slightly, but this is generally negligible).

There are a few things that you absolutely MUST know before you start squeezing:

1. You must have some way to very accurately measure the OD (of the tenon) and ID (of the receiver)...then you can proceed down this list. Most people use either a caliper (vernier, dial or electronic) or a micrometer. The latter is easier to get accurate measurements, but if you're careful with the caliper this can be fine. Just hold it perfectly square to the tenon, snug it down with no wobble and read. For measuring the receiver, the simplest way is to buy something like the Starrett S579G Telescoping Gages and learn how to use them with your caliper or micrometer. Make these measurements at multiple diameters repeatedly until you get consistent measurements. Then move on.

2. Is the tenon round? Is the receiver round? Many neck leaks happen because one of these is not round from damage or rough use. If either of these are not round, that is where you need to start.

3. Is the receiver bore the same diameter from end to base? If not, you will find it very difficult to fit the neck. This will need to be remedied before you progress or you will have a mess. In extreme cases, you might need a reamer, but most of the time a little judicious sanding will take care of this. Occasionally I find that it is just better to make a new receiver...but you need access to a lathe and some skill in both turning and soldering.

4. Similarly, after you get the receiver set, assess the condition of the tenon. Generally, it is a little out of round but not too bad and it is smaller at the open end (assuming that it hasn't been worked on recently). Sometimes, you can gently stretch a place where it is small by carefully mounting the offensive region in the H59 and 'worrying' it back and forth. Stop to measure much more often than you think is necessary until you get the hang of it.

5. Now you are ready to fit the tenon. The key is to make it snug from top to bottom and still able to rotate freely. I generally focus on the top and bottom and don't worry too much about the middle, but others are different. The most important place for it to be snug and perfectly fitted is at the open end (bottom of the receiver), but if you don't make the other end tight as well, then the neck will quickly loosen up with use.
 
I did manage to get it down without chaw'ing a tenon up. There is ample feedback from the crank that tells you how much pressure its exerting. It really takes no more than a little resistance to move a tenon open.
 
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