Ferrule Overview - Part 2
I have to comment on the "compression dies" sold to make tenon threading easier. Personally, I don't like them. While they give the illusion of a thread, you actually have less than 40% of a full thread. Think about it - the tap drill size for a ferrule is .257" while the tenon diameter prior to running the die over it is .280" or less. That means you're forming a thread only .011" high per side. You call that a thread?? There's enough there to allow you to "screw" on the ferrule & you can even tighten it up against the shoulder if you're really careful. But you still have a tremendous volume of empty space that must be filled with glue. And this sloppy, glue-filled reservoir has to repeatedly absorb the most brutal shocks your cue will experience. That can't be the best way to do this but many will continue because, well, it's fast & easy.
Here's a short video showing how to get good results using a compression die.
This is an extreme example of the difference between a full thread form & the shortcuts some are willing to take. The tenon on the bottom was made by a cuemaker who relies on a standard 5/16-18 tapped ferrule to cut the threads on the tenon. Considering that the normal tap drill is .257" diameter & his tenon was .272 diameter, that leaves a total thread depth of .0075". Not much of a thread. And not surprisingly, the ferrule came loose in a fairly short time when the miniscule threads on the tenon sheared. a new maple dowel had to be installed to correct the problem.
I recently learned about a variation of the shallow threaded tenon shown above & was chastised for not giving it proper respect. It has been used by at least 2 HOF cuemakers that I'm aware of. There may be more but HOF cuemakers tend to be close-mouthed about their techniques. I've seen that this idea can be a wonderful method that provides maximum glue surface & minimum glue gap with little likelihood of shearing. However, the ferrule must be made to match the thread form.
I think it's well accepted that the less space that needs to be filled with glue, the more durable & solid the connection will be. Also, a larger tenon will be stronger & provide better "communication" between the shaft and the cueball. Finally, the thicker the wall of the ferrule, the more durable the ferrule will be.
Pictures always help.
This collection of tenons shows some of the threads commonly used for ferrule installation - plus a tenon prepared for a "wire threaded" ferrule on the extreme right. The thin tenons on the left would not be as strong as the thicker tenons on the right but the ferrule itself would be stronger. The middle tenon is pretty strong but the v-grooves are still pretty deep & the ferrule will have a thinner wall. The 2nd tenon from the right has shallower v-grooves in both the tenon & the ferrule so this is a good compromise...but the short, shallow threads can be sheared pretty easily.
The compression die threaded tenon on the left (and it is an exceptionally well done job, if I do say so myself. Usually, they aren't so pretty.) shows many similarities to the wire threaded tenon on the right. Both have shallow grooves with wide lands between them, providing both good glue surface and a mechanical bond. But right off the bat, you can see that the wire threaded tenon is much larger in diameter - offering a tremendous advantage in strength. That in itself should settle any argument. But look at the photo below & see the differences in the fit.
Yes, you can fill the gaps with copious amounts of glue and, yes, it will probably hold up for a long time. 5/16-18 threaded ferrules have been used for a LONG time. In fact, if you buy a pre-threaded ferrule, odds are it will be made with that thread. So what's the problem? Well..it's not a problem. But it's an opportunity to do better.
This closer section view shows how closely everything fits when a wire threaded ferrule is installed on a mating tenon. There is little likelihood of this tenon shearing with such a generous land between grooves. And the small V form on the ferrule - a material stronger than the wood tenon - is strong enough to function properly as a thread while, at the same time, allowing a thicker wall thickness on the ferrule.
The problem with this setup is that custom tooling is required & everything has to be precise. The next best thing is live tooling the threads. At least this way, the full thread form on the tenon more completely fills the gaps you saw above.