Back on ukulele slipped

[sundaysmuse]

I have glued the back on a ukulele and it has slipped during clamping that I didn't notice and now the Centre line isn't lined up with the body. Is there something I can do? Was glued with Titebond

[slowlearner]

Heat will loosen titebond.

[sundaysmuse]

Thanks Pete

[kiwigeo]

I glue tantelones (chopped up kerfed lining) on the underside of the back overhang so they're hard against the sides...this keeps everything lined up during glue up. I use super glue to glue the tantelones in. Once back is glued on the tantelones get trimmed off with the back overhang using a router and flush trim cutter.

[blackalex1952]

I glue tantelones (chopped up kerfed lining) on the underside of the back overhang so they're hard against the sides...this keeps everything lined up during glue up. I use super glue to glue the tantelones in. Once back is glued on the tantelones get trimmed off with the back overhang using a router and flush trim cutter.

Another great tip from Martin! I might do this in future. I sometimes use bamboo spikes made from kebab sticks and sharpened in a pencil sharpener as locating pins in the end blocks. You can split the skewers into any size then sharpen the end to a point. The other end of the pin is located in a hole drilled in the block (or the plate depends which is softer or easier) and the plate (ie the back or the soundboard) is positioned and pressed into the pin. This leaves a locating hole which lines up when gluing. It doesn't work for hardwood, one can use metal pins. I find that the back bracing, when let into the liners, locates the back anyway. Unbraced backs need either the pin method or Martin"s tantalone method. To undo glued joints I use a bathroom heat lamp (too expensive in a bathroom! My daughters would forget to turn them off and take longer in the bathroom because it was warm once they got out of the shower! When I replaced them with low energy lamps and took the heat bulbs to the shed, it streamlined things and saved money!) I use aluminium foil on a wooden caul to reflect heat from where I don't want it to go, a surface thermometer to monitor temperature and a hot knife. Titebond is good because it can be undone, but I think hide glue is better because it will re stick to itself. Titebond needs to be cleaned off as best as possible before fresh glue is applied, for reliable results. The heat lamps help with hide glue for glue up also because the heat penetrates, unlike a heat gun which heats the surface first. Heating the parts when applying HHG prolongs the time before the glue gells. The trick is to heat slowly, rather than having the lamp too close which sets up too fast a heat gradient and the surface heats too readily. (Bamboo pins are also good for brace and bridge work in some instances. It is how I locate "A" frame bracing into the head block. I fit the braces into the head block, getting the neck angle sorted at the same time, then use pins in the braces to mark the soundboard by pressing the soundboard into position. Then I remove the braces from the head block and glue them onto the soundboard because the pins locate the braces. When the top is glued up, the braces mate with the mortices in the block) There are definitely some much more experienced luthiers and repairers on this site who have good if not better ways of doing this kind of thing. That's just what I came up with.

[sundaysmuse]

I have an old unused steam iron, will this work for ungluing? What kind of temp will I need to get the glue to?

Steve

[blackalex1952]

Steam will swell the timber and raise the moisture content of the wood. Soundboxes need to be assembled with lower moisture content in the timbers than the instrument will be normally played in, within reason. Most makers assemble at 45%RH (relative humidity) which gives around 8% moisture content within the timbers. Soundboxes can swell and contract as moisture content rises and falls, but if the moisture content in the timbers goes lower than the assembly RH, the result is that the timbers usually crack-something has to give. It usually happens if there are joins in the soundboard or the back and at the waist at the edges in my experience. Braces can also let go, or if they don't they can split as the doming in the back or soundboard flattens out. I use steam to re hydrate instruments that need repair after being exposed to extreme low RH, eg. left in a hot vehicle in a black case in direct sunlight, or for de-wrinkling my linen suit prior to a summer's gig! To re hydrate sound boxes I introduce a little steam into the sound hole(s) then plug or cover the hole(s) so that the moisture will stay in the box while the wood absorbs it. Just do it a little so as not to get condensation in the instrument. I then put the guitar, uke or whatever in a plastic bag so that the air inside and out has a high RH. Lightly built instruments require extra care not to re hydrate too rapidly. Instruments don't like sudden extreme swings in moisture content. So gentle as she goes, err on the side of caution. Steam can also be used to bend wood. So NO! Steam is not a good idea for removing a glue join on a soundbox. It can be used, however to remove a neck join for a neck re set. In some cases iron can be used with a damp cloth to swell dings in timber as well. You can search this forum for info on neck removal, RH, dehumidifiers and methods, soundbox assembly and timber conditioning. Also there are some good tutorials on You Tube re these issues, especially on neck removal/neck reset work, and good info if you google on all sorts of luthierie topics. With a uke, the backs are usually pretty thin, unless the instrument is totally underbuilt. So a gentle heat gun or a hairdryer will probably penetrate the wood enough to soften the glue on a uke along with the judicious use of a heated knife. Just don't heat too much or you will soften the glue where the liners meet the sides as well and also the glue holding the braces if there are any. That's why I use aluminium heat shields and slow heating just enough to penetrate to the glue I want to soften. If your knife is too hot it will scorch or burn the wood, if not hot enough the knife will need to be forced with the risk of tearing the join, the wood fibres or an even greater disaster! Think glue join only and be gentle, using moderate heat and have a feel for the temperature of the knife and the the softness of the glue as the heat weakens it. It's quite easy if you feel your way.-Ross

[Nick]

Your iron (minus the steam as Ross pointed out!) or a heat gun will do it and also use a warmed up knife or thin paint scraper to get inbetween the side and back plate. As for heat, a medium on the iron and high on the heat gun but make sure you keep both moving over say 150mm of the joint at a time, don't stay in one area for too long to minimise the chance of scorching (I use an iron but if I was using a heat gun I would heat the area then keep removing the heat away from the instrument, test the joint with your knife then play the heat on it again if it doesn't separate, things can turn to custard very quickly with a heat gun!) . Work around the perimeter slowly separating the joint a section at a time, take your time and don't rush! It should come apart relatively easy once you get the feel for it.
Before re-gluing the back make sure every bit of the old glue has been scraped or sanded off, Titebond doesn't like gluing to old glue!

[sundaysmuse]

Thanks everyone for the great responses and tips.

I will give this a go, wish me luck!!!

[kiwigeo]

Careful working around the centre seam.....if that starts to separate then things can get messy. I generally avoid working directly over the centre seam with the heat gun and instead work a hot pallete knife in from either side of the seam around the head and tail block areas.

The trick is to work carefully and gently with the pallet knife. Also work carefully around brace ends..especially if youve housed them into poskets in the linings.

[sundaysmuse]

Thanks Martin.

Got it off, slowly slowly, but did it. My old clothes iron and a pallet knife did the trick

[kiwigeo]

Steve,

Robbie has another way of securing a back so it cant slip during glue up: viewtopic.php?f=1&t=7339

[simso]

I glue tantelones (chopped up kerfed lining) on the underside of the back overhang so they're hard against the sides...this keeps everything lined up during glue up.

Now that is a good idea !

Steve