peghead break

[Lee Gendvilas]

Hello,

I am getting ready to glue the peghead on the neck and do a backstrap overlay.

I don't want to glue the truss rod to the channel when glueing the peghead on the neck. I have some ideas of how to accomplish this but thought it would be a good idea to get other opinions.

Looking forward to your comments.

Lee

[Allan Bacon]

As far as gluing the TR, just take a pipe cleaner and gently wax (like car wax) the outside of the TR. Done it many times, never had a problem.

If the break nests together properly, I don't see any reason to put a back strap on it. That's about what the overlay of a scarf joint is. With some Titebond I and proper clamping it should be good.

[Lee Gendvilas]

Hello Allan and thanks for your reply.

I guess I am a little confused on when to apply the backstrap. The break on this instrument is clean, the only wood it lost was on the side where the lacquer is. My first thought about it was I should be able to glue it back together and do some touch up since it was a long break. But I started looking at the angle of the break and thought that it might fail again if it gets bumped from underneath the peghead. Also I have read Frank's articles and others on the backstrap procedure and was coming to the conclusion that if there is a break in this area the backstrap should be done. So if I understand you unless the break is missing wood or is a real mess that's when the backstrap should be done?

[Mike Kolb]

I believe a lot of the choice of backstrap or not involves the angle of the break.  If it's a long break with plenty of available gluing surface (as yours appears to be) I'd probably want to forego the backstrap.

[Lee Gendvilas]

Hi Mike,
That makes a lot of sense. Since I live in Arizona I plan on using hide glue for its heat resistant capability. Will 192 gram strength be good enough to use for this or should I go higher in gram strength?

[Mike Kolb]

Frank has a great look at "all-things-hide-glue" over on his frets.com page, and here's a portion that relates to the numbers we're speaking about.  To cut to the chase, he likes 192 gram strength for most of the work we'd be doing.

Glue is graded on a basis of its gel strength, a measure of how many grams of force it requires to depress a 1/2” plunger 4mm. into a 12.5% protein solution of the glue at 10° C. Glue is manufactured in standard grades from 32 to 512 grams. 192 gram strength is the most commonly used for woodworking; 251 is the highest normally used for instrument building; 135 is the lowest used for general woodwork.

The higher the gram strength, the stronger the cured glue, and the shorter the working or gel time. The lowest grades are considered strong enough for woodworking: “stronger than the wood itself.” (Personally, I don’t think any glue deserves that sort of comment. It may be that strong only for certain tests; it is not the same as the wood itself.) It is never a good idea to dilute too strong a glue to obtain lower viscosity or longer working time when it is possible to use a lower grade of glue. Glues of different gram strengths may be mixed to get an intermediate. I like 192 gram “high clarity” because it’s transparent and doesn't gel too fast.

Now, here's an important note. The higher gram strength glues have higher molecular weight, which (I'm guessing here) may have slightly lower electrochemical adhesion, i.e., they may not stick as well. Because the very high gram strength glues require up to twice the water to reach workable consistency, there will be less glue actually in the joint after it is clamped and the water evaporates. This may be why the very high strength glues (300g. to 500g.) are often described in the literature as "too strong for woodworking." Additionally, they gel too fast for many applications.

[Lee Gendvilas]

Excellent! Thank-you again!