Wednesday, January 21, 2009

Gibson Deluxe Tuners (part two)

Please note that this post is part two of four posts. I highly recommend reading all four posts in order before acting on any of the information.

The other parts are located here:

Part 1:
Part 3:
Part 4:

Well, the Gibson Deluxe Tuners post certainly attracted some attention. Seems there are plenty of people out there with the same problem.

Before I talk about my repair options, I’d like to discuss a little further the design limitations of the Gibson Deluxe Tuners. I previously mentioned that the little tabs that attach the back cover to the main plate do not fold over once they go through the main plate, which I found strange. While exploring solutions over the past few days I noticed that a lot of replacement tuners from other (often cheaper) brands had tabs which DO fold over, keeping them very firmly attached to the main plate. I really do have to scratch my head at why the Gibson Deluxe Tuner designers decided not to do this.

Non-Gibson Deluxe Tuners with tabs that fold over:

Secondly, I have noticed that there is one more problem with these tuners, which is that the worm gear wobbles quite a bit, even when the tuner is working perfectly, with the back cover attached. It doesn’t wobble from side to side, but rather away from and towards the guitar head. I hope that makes sense. This is caused by the claws not gripping around the worm gear, but rather, just stopping it from moving from side to side. The alternative solution offered by the Gibson Deluxe Tuners is to make the cutouts on the back cover (which let the worm gear pass through the sides of it) limit the movement of the worm gear away from the guitar head. Unfortunately, these are quite imprecisely cut, so sometimes allow for far too much movement.

So given that second note, I have decided that I need to tackle the wobble problem before attaching the back cover, since once I attach it I don’t want to have to take it apart again.
What I will do is file a little bit off the bottom surface of the back cover (leaving the tabs intact), so as to move the cutouts closer to the worm gear and hold it in place better. This has the added benefit of effectively extending the length of the tabs (not enough to fold over, unfortunately, but maybe just enough for a little bit of extra purchase)
[Edit: In the end I found the reason for, and the solution to, the wobble problem, which I've documented at the end of part four. Please check it out before you start any work.]

So after a bit of thought, I figure I have maybe three realistic options:

1. Make a type of metal strap, which would hold the back cover on. It would be held down by the two screws that would hold the main plate to the guitar. The disadvantages of this are that the strap would be visible and the screws might need to be swapped for longer ones. The advantage would be that it would require no irreversible modification to the guitar or the tuner, and it might actually look quite cool.

2. Solder the back plate to the main plate. Advantages would be that it would be a quick and easy repair that should be quite strong and fairly reversible. Unfortunately I’m not convinced the metal used on the tuners would accept solder readily. Really, I should be looking at brazing, but unfortunately that's just not an option for me.

3. Similar to 2, but use glue, most likely 2-part epoxy. Quick and dirty solution, but may work well.

Whichever method I choose, I will still file a thin layer off the bottom first.

I’m off work all next week (for Chinese New Year), so I’ll decide what I want to do then.

Tuesday, January 13, 2009

Gibson Deluxe Tuners (a weak design?)

Please note that this post is part one of four posts. I highly recommend reading all four posts in order before acting on any of the information.

The other parts are located here:

Part 2:
Part 3:
Part 4:

I have a problem with one of the tuners on my Les Paul. It had the problem already when I bought the guitar a few years ago and I managed to do a temporary fix, but the problem has resurfaced.

Before you continue, please note that this is written from an engineering point of view.

Firstly, let’s have a look at a typical stamped (open-backed) guitar tuner.

There are several components and many names for those components, so my apologies if I use ones that you are not accustomed to. Firstly, the tuner can also be called the tuning head, tuning peg, or the machine head (and possibly other names). It has a main plate, through which the main cylinder (or capstan), passes. The capstan is the shaft that the string itself passes through. On the end of the capstan is a gear, sometimes called the pinion gear, and a screw/bolt holds that on to the end of the capstan. Then we have another shaft or pin with the tuner knob (or button) on the end of it. This pin has a gear on it too (in fact they are one part in most cases), and this particular gear is known as a worm gear. From now on I will just refer to this shaft as the worm gear.

As an aside, and for any non-engineer-minded people out there, the reason a worm gear is used is because turning the button/knob will rotate the worm gear, which will in turn rotate the pinion gear and the capstan, thus tightening or loosening the string, whereas no matter how much you tighten the string, the pinion gear cannot force the worm gear to turn. This is a really good way to keep strings in tune without making it really hard to turn the knob.

OK, back to the description of the tuner. There is one further feature that I have not yet mentioned and that is the retaining “claws” which are part of the main plate and hold the worm gear in place. The claws stop the worm gear from moving away from the pinion gear or falling away from the main plate. The plate stops the worm gear from falling against the guitar and the pinion gear stops it from falling out in the direction of the capstan. So hopefully you can see that the worm gear cannot possibly fall out unless the pinion gear is removed.

Now to the Gibson Deluxe Tuners (and why I think they are a weak design).

As you can see, the tuner has the same components as any standard open-backed tuner, but please note one subtle difference – although the claws stop the worm gear from moving away from, or towards the pinion gear (i.e. from side to side), they don't stop it from falling away from the main plate. Seriously, it can just fall right off.

“But wait!”, I hear you Gibson Deluxe Tuner fans shouting, “The Gibson Deluxe Tuners have a back cover which stops the worm gear from falling away from the main plate!”

Well, you are correct, but this leads me to the problem with my tuner... the back cover has fallen off. And this brings me to my second criticism of Gibson Deluxe Tuner design. You would think that, if the back cover was the only thing holding the worm gear in place, it would be held on in a way that would be very hard to move.
Let’s have a look at their design.

The back cover is held on with two little tabs (one of mine is slightly damaged, but this happened while I was trying to find a solution to keeping it in place. It originally fell off with the tabs intact). Now as an engineer, I would think that a tab should at least fold over to keep something in place, but these ones just go into slots and do not appear to be twisted, folded, or in any other way modified once they go through the slots. In other words they are held in by “interference fit” only, so that they can come out just as easily as they went in (edit: actually, this isn't 100% correct - they are "staked" in place [see the comments at the end of this post], although that doesn't add much strength in the direction they would fall off ). Now let’s think about what’s on the end of the worm gear. That’s right, a big knob/button that sticks out and is basically on the end of a lever. What do we often use levers for? Well, for prising things out of place for one. The longer the lever, the easier it is. So one accidental knock on the tuning knob and you can dislodge the back cover, letting the worm gear fall out of place.

In the course of trying to find a single replacement Gibson Deluxe Tuner (which, not surprisingly, cannot be bought separately), I have noticed many other people scrambling to buy single replacements off ebay or asking if anyone has a spare one on musicians’ forums. A full set is not cheap either; around £60 would not be unusual. I wouldn’t even mind paying that if I though it was a good strong design, but I think you can guess by my rantings how much I think of these things. Unfortunately replacing them with anything other than originals devalues the guitar, so there isn’t much choice.

Additionally, on the front face of the guitar head you need to use a bushing (also called a ferrule) which stops the capstan from rubbing on the wood of the guitar when it is being rotated, and whereas these are normally press-in bushings on tuners of similar design to Gibson Deluxe Tuners, on the actual Gibson ones, they are screw-in bushings. Now I have no complaints about this, design-wise, I’m just saying that there are very few replacements available other than the Gibson Deluxe Tuners.

Gibson Deluxe Tuner bushing (and washer)

Standard bushing

So stay tuned (no pun intended) for the next blog post, where I will try to fix mine.