JLD Bridge Doctor

[DanSavage]

Originally Posted by mirwa

Thats also a new one on me, epoxy that releases its strength at a temperature less than boiling point of water, wow, never seen that yet, epoxy is a chemically hardened product, it not a product that sets from evaporation or exposure to air.

You're right. Epoxy is the binding of polymer chains through a chemical process that does not require evaporation or exposure to air. What you're wrong about is that once epoxy is cured, it's a permanent bond. Nothing could be further from the truth.

Yes, the joys of internet searches... (See: The Glass Transition)

To wit:

Ok, we know at this point that some polymers have high Tg's, and some have low Tg's. The question we haven't bothered to ask yet is this: why? What makes one polymer glass transition at 100 oC and another at 500 oC?

The very simple answer is this: How easily the chains move. A polymer chain that can move around fairly easily will have a very low Tg, while one that doesn't move so well will have a high one. This makes sense. The more easily a polymer can move, the less heat it takes for the chains to commence wiggling and break out of the rigid glassy state and into the soft rubbery state.

It took nothing more than three bags of boiling water (212°) resting on the neck, thusly:



To cause the epoxy to soften enough to remove the neck, thusly:



It's not magic. It's that the epoxy used for the neck joint has a Tg that's lower than the boiling point of water.


How about this? (See: 0151 Optically Clear Loctite® Epoxy)

Notice the temperature range. (-65° to 160°)

Is 160° lower than the boiling point of water? You betcha! The max temp for that epoxy represents the Tg for that resin, or the temperature at which the polymer chains begin to loosen and the resin softens, just like what Ken did with his Celebrity neck reset.

Now, take a look at this resin. (See: Loctite® 9460 Hysol Epoxy Adhesive)

The temperature range of this epoxy is -65° to 350° F.

Just like the article above states, different formulations of epoxies have different Tg. In addition, the Tg can be raised by post-curing. Since you're so good at internet searches I'll let you google that tidbit for yourself.

The Tg for West Systems 105 is a super low, 142° F. It starts to soften at temperatures as low as 116° F, which is almost half the temperature of the boiling point of water. (See: West Systems Typical Physical Properties)

In short, epoxy resins get their strength from the binding of the polymer chains. As the first article explains, these chains can be loosened with heat. Some resins require more heat than others, but they all can be softened with the right amount of heat. Contrary to you absolute assertion that epoxy is a chemically-hardened substance, (whose bond is unbreakable) no epoxy resin is permanent.

[mirwa]

I have the utmost respect for anyone that does guitar repairs or building full time or part time or even just once, people give information about what they have found when they have actually done that job. I have very little time for Internet experts who quote the Internet and wikipedia as gospel without having ever done it themselves.

Interesting, again, a post from someone else's efforts not your own, so your talking second hand about something of which you were not involved in and taking that as gospel and preaching it accordingly, I would personally advise not too and offer wisdom and knowledge you have gleaned from doing it yourself rather than someone else's.

In regards to the post you just linked.

Doing a reverse google image search, the owner of that guitar said it took him two hrs of heating and wiggling the joint to get it off. He also used an iron and spatula for the tongue area, he also has a photo of the body where it appears the glue bond let go at the fibreglass, not the wood. I commend that poster for his efforts. If they were involved in the discussion I would enquire whether they believe the joint had let go, having been unpicked at the tongue and then working the joint eventually led to failure of the bond at the fibreglass or whether the glue was in fact softened, but that's what I would ask them as the person who did the job, as they would have first hand knowledge

Now I revert back to my original reply, "pretty well impossible for most and extremeley difficult for some"

how is that incorrect.

Originally Posted by DanSavage

Contrary to you absolute assertion that epoxy is a chemically-hardened substance, (whose bond is unbreakable) no epoxy resin is permanent.

I did not say epoxy is unbreakable, get your facts correct, before you quote me on something I did not say.

This was just one of many ovations I get in and likely to be the same for other repairers, so we have quite a bit of first hand experience with them.

Neck block has failed, body has collapsed in on the sides, top has split open

[Rodger Knox]

Originally Posted by DanSavage

I found it online. But, no matter.

Actually, it does matter. You completely missed my point, you're justifying your method with completely bogus numbers that you found sowewhere, very little of what you post is from direct experience. I agree with some of the things you post, but sometimes it's just wrong.

You link to Frank Fords website, but then don't follow his procedure. What's up with that?

Sorry for the minor rant, I think the straightedge thing for checking for resets is one of those mass misunderstanding things on the internet. Luthiers frequently post about checking the neck angle with a straightedge. That has to be set before strings go on, and it's got to be pretty close. Using the straightedge without string tension requires some familiarity with what string tension will do to the top. Luthiers know what they're looking for, and why, but it's not always clear to someone whose never done it themselves.

Once strings are on, it's pretty easy to tell if a reset is in order.

[Rodger Knox]

Originally Posted by LouieAtienza

Likewise, can mere mortals tell the difference in sound between a guitar whose string height is 7/32" and 1/2"? And attribute that change to just the string height?

Louie, I'm pretty sure you meant 7/16", not 7/32". I'd have to look at Mr. Carruth's numbers again, I don't remember how much he varied the string height above the top, but I believe it was more than 1/16".

But in answer to your question, yes, people can tell the difference. I'm not going to put numbers on it, because it's not the same for every guitar. But at some point, lowering the height of the strings above the top will result in a noticeable difference in tone. That's the point where the neck needs to be reset. If you lower the saddle beyond that to delay a reset, there's a good chance it will come back when the neck is reset.

[Mr LV19E]

Ideally you want the straight edge to sit on frets 1 through 12 or 14 (depending on the neck to body joint) to check your angle. Most but not all fretboards have some fall off between the neck joint and the sound-hole, if your straight edge rocks down on these frets your reading will not be correct. If you don't make the neck straight before testing, a 18" straight edge likely will lay on this fall-off and the bowed up relieved part of the neck.
This has been my experience so YMMV.

[LouieAtienza]

Originally Posted by Rodger Knox

Louie, I'm pretty sure you meant 7/16", not 7/32". I'd have to look at Mr. Carruth's numbers again, I don't remember how much he varied the string height above the top, but I believe it was more than 1/16".

But in answer to your question, yes, people can tell the difference. I'm not going to put numbers on it, because it's not the same for every guitar. But at some point, lowering the height of the strings above the top will result in a noticeable difference in tone. That's the point where the neck needs to be reset. If you lower the saddle beyond that to delay a reset, there's a good chance it will come back when the neck is reset.

I actually meant 15/32", pertaining to the 1/32" difference you mention... I believe Alan mentioned it was at least 1/8". The point I'm making is, do they tell the difference because of a change in the feel of the strings, change in neck relief, change in saddle or change in density at the point of contact with a lowered saddle... I agree there comes a point where the change is noticeable, to a greater extent player and a lesser extent listener. But not 1/32"!

Edit: I'll concede that there may be some that could tell sonic differences with 1/32" bridge height change, but I'd bet this is the absolute exception, not the rule. I actually had a long discussion with Alan about this on the MIMF (one of the earlier posts.) Regardless of quality of sound, I don't think most better players would play a guitar that wasn't responsive and "playable" first.

[LouieAtienza]

Originally Posted by Mr LV19E

Ideally you want the straight edge to sit on frets 1 through 12 or 14 (depending on the neck to body joint) to check your angle. Most but not all fretboards have some fall off between the neck joint and the sound-hole, if your straight edge rocks down on these frets your reading will not be correct. If you don't make the neck straight before testing, a 18" straight edge likely will lay on this fall-off and the bowed up relieved part of the neck.
This has been my experience so YMMV.

The only way a straightedge would lay flat on the fallaway is if the neck has excessive relief or bow. Otherwise the straightedge would just sit at the points of the fallaway, and lowest fret.

[Rodger Knox]

Louie, I don't disagree. If you consider the change in tone to be a linear relationship with the height of the strings, I agree that 1/32" probably isn't significant, since the data we have as significant is 1/8" (that's the number I remember, it may not be correct).
Using mathematics to describe something as subjective as tone is a bit absurd, but it helps to illustrate my point. If you consider the relationship to be anything other than linear, then a small change in string height could make a large difference in tone. Suppose it's an exponential relationship, where changes start small and get progressively larger. All we "know" for sure, is a significant change does make an audiable difference, based on Allen's research. Does the change happen continuously through that interval (linear), or does it happen over a much narrower interval within that interval(non-linear).
Assuming linearity is the first thing an engineer does, it symplifies the math and is usually close enough over some interval, but two data points is not enough to fit any non-linear curve.

[FrankR]

I hate regular pins, and I am always looking for replacement solutions.

The Power Pins are interesting, but, for some guitars, they wind up messing up contact with the saddle.

I am about to experiment with using JLD pins as pin replacements - without using the whole block thing underneath.

The JLD folks say that is absolutely fine.

Would you agree? Are JLD pins a safe way to lock down pins?

[phavriluk]

I've never encountered a steelstring guitar with a completely flat soundboard. They are customarily made with a slight (like 25-foot radius) dome built in. Those ain't never going to be flat. Ever. If OP's relying on an email response, from Bourgeois, pick up the phone and call.