New build glue joint on back comming apart; how to repair

[Bob Schmidt]

While thinning the back for my first build bouzouki, the glue joint is starting to seperate. I am attaching pictures. I am not sure if I should try to re-glue it as is or try to seperate it completely and re-glue it. What type of glue should I use on the repair. the initial joint was done with original titebond. The back is already rough shaped with maybe 2mm overlap on each side so I could probably only do one or 2 passes on a shooting board to clean the edges if I seperate it.

[sliebers]

The best thing would be to cut it apart, true it up and glue it again. If it was hide glue, you could re-glue assuming your joint was tight to begin with. Titebond does not adhere to itself once cured.
At least it happened before attaching it to the rim.

[Bob Schmidt]

OK thanks. I have used hide glue before, but I don't have a good glue pot so I had to mess with pots of water to keep it at temperature. If that makes a better joint I could do that again.

[sliebers]

Hide glue won't make a better joint than other glues. It's reversible if it needs to be glued again. It's possible the joint wasn't true and tight to begin with, or it was glue starved. Any glue will come apart if the joint is not tight throughout. When planing the edges, do you hold it up to a good light, (sunlight is best) to assure there are no gaps? I use a window in my house to hold the pieces against and look for light coming through the joint. If you see any, it's not a tight joint.

[O. Apitius]

I would have to respectfully disagree that hide glue does not make a better joint. Original Titebond can make a perfectly viable joint but HHG is better in several ways. That's my opinion after over 40 years of instrument making.
Its hard to say where you went wrong. It could be one or all of the following reasons.

1. Jointed edges not absolutely straight and true and perpendicular to the plate face. A very slightly "sprung" joint is preferable to a "bowed" joint but I prefer absolutely straight with no light able to shine through.
2. Wood not stabilized to a suitable moisture content. (7% MC by weight is best overall)
3. Natural resins in the wood interfering with glue bond. With resinous woods such as East Indian Rosewood, it is a good idea to wipe the jointed edge with a rag dampened with acetone before gluing. (of course, give the acetone some time to dry)

I started using a traditional "rub joint" using HHG with a gram strength of 315 a while ago and haven't looked back. The properties of hide glue are such that it will pull the joint together without the use of clamps, given you have perfectly jointed edges.

In this case, I would try carefully separating the two halves using a straight edge and many light passes with a sharp knife. Then let the pieces become stabilized with regards to moisture content before carefully shooting new edges. (this should also remove any residual glue) Next, wipe the edges with a rag dampened with acetone and let dry for at least an hour.
If you do not have experience with HHG, you may want to forgo the rub joint and use clamps because you look like you are very close to final thickness and you're new joint must line up perfectly
Here's a photo of a recent rub joint that I did.


I also wrote a fairly recent blog post about rub joints on my website. Here's a link if you are interested. (Just scroll down a few posts)
http://www.apitiusmandolins.com/Oliv...ge%202017.html


Oliver
Instagram

[rcc56]

If you don't have enough wood to work with, you could add a center strip. Be sure to reinforce it.

Ditto Mr. Apitius-- East Indian rosewood can be VERY oily and must be cleaned.

[CarlM]

East Indian rosewood can be VERY oily and must be cleaned.

How do you ensure it is clean enough to glue? I have had trouble in the past with rosewood on other projects coming apart even after I had degreased it with lacquer thinner a couple of times.

[Bob Schmidt]

Thanks everyone; I did use a shooting board and had the edges so that I could not see light through them, but I did not use acetone on them. I started using it when I assembled the sides so hopefully I will not have similar issues there.
This is one of many lessons I assume I will learn in the process.

[pops1]

OK thanks. I have used hide glue before, but I don't have a good glue pot so I had to mess with pots of water to keep it at temperature. If that makes a better joint I could do that again.

I use a pot for heating soup when traveling. I put in a candy thermometer to tell the temp, it has a variable control, and a piece of aluminum with 3 screws in to keep my glue jar up 1" off the bottom. Costs about $20 or less and lasts, well this is my second in 30 years.

[sliebers]

[QUOTE=O. Apitius;1639586]I would have to respectfully disagree that hide glue does not make a better joint. Original Titebond can make a perfectly viable joint but HHG is better in several ways. That's my opinion after over 40 years of instrument making.
Its hard to say where you went wrong. It could be one or all of the following reasons.

I agree with you Oliver on HHG being superior. However, it can get you into trouble if you don't have experience working with it. My point was if the joint wasn't true to begin with, no glue is going to work well.

[jim simpson]

Worth watching: http://www.stewmac.com/How-To/Trade_...300_O_20180308

[Bob Schmidt]

The Stew Mac video was worth watching especially dividing into smaller quantities for small jobs. I will try once again to use it, but on this back I am at 2.9mm which is close to my final thickness, so getting the halves completely flat will take clamping a brace along the seam as well as clamping from the sides. I am not sure I would have enough time with hide glue.

[Tavy]

The Stew Mac video was worth watching especially dividing into smaller quantities for small jobs. I will try once again to use it, but on this back I am at 2.9mm which is close to my final thickness, so getting the halves completely flat will take clamping a brace along the seam as well as clamping from the sides. I am not sure I would have enough time with hide glue.

As long as you have everything all set up before hand, and don't hang around you should be fine. That said, there's nothing wrong with using titebond in this instance either.

Some more tips:

* Once you have a light-tight fit, glue it more or less right away, don't leave it to the next day or you may find that changes in humidity have moved things a tiny bit out of true again. Or if you do leave it, double check the fit before gluing!
* If using HHG, heat the two halves of the join up with a hair dryer or similar before hand - it will greatly extend your open time.
* Glue them together on a flat surface, and if you're using the string+wedges method to apply clamping pressure then the wedges will keep the two halves aligned so you shouldn't loose too much thickness afterwards.

[tonydxn]

I hang a heat lamp over my bench when I'm using HHG - it helps to keep the wood warm and gives you a bit more time to do the joint. They are made to keep baby animals warm. You can get them on eBay. I use a baby-bottle warmer to heat the glue.

[Bob Schmidt]

When the pieces were square I used some pieces of square maple and clamps to apply pressure on the edges and along the joint to do the glue joint, but now that the back is shaped it looks like the rope and wedge approach will be the best way to re-glue it. I guess it is time to get some HHG supplies and build a rope and wedge jig.
Thanks everyone for your help and suggestions.