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Checks Before Gluing
Before gluing the halves together, I put them together to see what is any twisting or warping has occurred. The surfaces to be glued are lightly sanded using sandpaper wrapped around a ‘straight’ rectangular block. This helps to level and make the surfaces flush with each other.
I also do a dry run by placing the halves together and loosely applying the clamps so I can get and idea of any potential difficulties. Dust is removed from the wood with an unused paintbrush (unused for painting that is!).
Now is the time to address anything else inside the bore that may cause future problems such as naughty knots, i.e. encased knots with bark that may become, or is already loose. I treat these with epoxy resin. I use a two tonne breaking strain resin to bond the surfaces together. Depending on what I am attending to, I may add fine sawdust to help fill gaps. If it is impracticable to ‘fix’ something like a knot just by bonding, I will remove it and insert a plug from a similar coloured piece of wood and bond that with epoxy resin, the plug should be air tight if made snug and tapped lightly into the hole, however, the resin fixes it in place and gives piece of mind.
Depending on your choice, if any, on what to seal the bore with now may be a good time to do so. If using epoxy resin, or PVA doing this part of the process first gives you more control over the end product. It is a matter of personal choice. I use Daishi l to coat and seal the bores of my didgeridoo’s and I do this after the didgeridoo is constructed.
Glues
I have tried a number of glues, all of which did the job, and have not had any problems with the joins coming apart on any of them (touch wood), but it must be said that all the glues behave differently from each other, having different composition, consistency and drying or setting times. Over time I will continue trying different glues to see the difference between them. I am not a chemist and can not quote the chemical composition and why certain glues do what, I can only relay what I have tried and the results thereof. At the moment I am using glue called extramite which is powdered urea formaldehyde resin glue.
PVA
This is what I first used. PVA is known to me as I have used it from my days as a school boy, through to college and beyond. It is cheap, easily available and non-toxic. It is water based and soluble until set when it becomes waterproof. It takes additives well such as sawdust (for gap filling), and colourants such as acrylic paint or gouache. If a non-water proof paint such as gouache is mixed in small quantities then the mixture will still be waterproof when set. I have used PVA to seal the wood, both inside and out, normally in a 1:1 ration, however used even thinner, it can be applied as a protective layer, covering existing artwork. I have examples of work that I glued at college over 15 years ago and the glue is still sound.
Seems ideal, it almost is, with one or two exceptions. Firstly, when using it to glue the join, a small amount of the glue will expand and create a ridge on the join which can mar the finish. This will happen over a number of days after the gluing has taken place. Secondly, it gets everywhere when gluing and although can be prised off most metal surfaces (such as the clamps) when set, it tends to clog stuff up and get everywhere. I spent an awful long time cleaning when using PVA as a joining compound. Thirdly, it has a low melting temperature, so if sanding with power tools, the abrasive paper will clog very quickly.
PVA can be waterproof and resistant to wear and tear. Different grades and levels of chemical resistance are available, as are quick drying PVA glues. I put this glue to use a lot in my workshop but not for joining two halves of a didgeridoo together.
Epoxy Resin
This is a two part compound that when mixed together cures or sets into a solid mass. It is extremely resilient to chemicals and water. The time it takes to cure (set) depends on the type of epoxy resin you have purchased. Epoxy resin has great strength with a very high breaking strain, again different varieties and brands over slightly different products. The chemical compounds are in gel form, and until mixed and fully cured are toxic and corrosive. The compound sets exothermically, that means that when mixed together heat is generated and it is this heat that bonds the chemicals together. The greater the mass of the mixture, the greater the heat generated (leave it as a mix for too long and the heat can be to hot to hold so be careful).
For bonding purposes, sawdust (very fine sawdust) can be added, to make a thicker paste. Colourants can also be added such as inks and acrylic. Too much paint, especially acrylic, can soften the surface of the mixture when it has set, so if in doubt experiment first. Colours additives can be purchased that have been made specifically for the epoxy resin; however they can be rather expensive. Unlike other mixtures comprising of two parts where a hardener is added and the more hardener that is added, the quicker the setting time. This is not so with epoxy resin. Mix the resin according to the instructions of the manufacturer and stick to them. I have had problems in the past of mixing resin incorrectly whether in amount or when it was to cold, on the se occasions, the resin did not set and was difficult to remove and redo. I took ages. Once resin is set, it is set so do be careful where you get when working. Make sure the area you work is well ventilated due to fumes and be aware that spontaneous combustion can occur in mixed uncured resin.
I always wear protective rubber disposable gloves when working with resin. Ben Hicks in the book ‘The Didgeridoo Phenomenon’ states that vinyl gloves are better than latex when working with resin. I haven’t tested this out but it just so happens my disposable gloves are vinyl. I do not use epoxy resin for joining didgeridoo’s as I am distracted with the mixture, its setting time and toxicity which have resulted in a couple of bodged joins. I do use it extensively to protect the mouthpiece and bell, set and seal weak parts of the wood, especially knots. As resin cures it has a strong surface tension. When set the surface will be very smooth, like glass. I (and this is a personal feeling) that when applied to natural wood it can look similar to plastic, so I will always add a little depth underneath with a coat or two of Danish oil or a stain of some variety. I also use it in the workshop to repair tools, especially handles that come off files, chisels, etc.
Extramite
This is the glue I currently use for joining didgeridoo’s together. It is a urea formaldehyde powdered resin. Water is added to the powder in the correct ratio forming a paste. This paste is then applied to one surface and sets fairly quickly. It sands well when set, bonds joints well and does not stick to the metal clamps I use. When mixed it has the consistency of thick cream. The mixed but unset mixture can be an irritant to the skin so, as with epoxy resin, I wear rubber gloves.
Mixing the glue in a small plastic pot with a small strip of wood the size of a lollipop stick, I use the stick to apply the glue to the didgeridoo. Any glue that is left in the pot will set, and if you leave the stick in the glue in the pot, once set the whole lot will pop out so the pot can be re-used. I do not use this glue for anything other than joining didgeridoo’s.
The disadvantages I have found with this glue is that when using it in hot weather, the glue will set very quickly, even if more water is added making the join very thick, visible and messy. To get round this I ask a friend to put the glue on one side, while I do the other, making the application process twice as fast.
On with the Gluing
Once the glue is applied I like to have all the clamps on and adjusted to the right pressure as quickly as possible. I have had occasions in hot weather where the glue has started to set and the resulting join was awful. I have also encountered problems where, again, the glue started to go off because I couldn’t find the right size clamp and get it adjusted quickly enough. When applying a clamp to one end, the other end may slide apart sideways, or try to pull apart. Allsorts can happen, so I have learned to be prepared!
I work out how many clamps I will need and line them up by the side of the didgeridoo, then apply the glue using a small strip of wood left over from shaping. Often I will mark where I want the clamps on the wood so that I do not get the different sizes muddled up, for example a didgeridoo with a 6” (150mm) diameter bell may taper down to 2” (50mm) with up to seven different sized clamps along its length. I try to use clamps as near as possible the same size as the part of the wood because the adjustments tightening it up and undoing it are so much quicker.
Once applied, I line the two pieces up and place a jubilee clip to each end and the middle, ensuring that at all times the pieces are level and even with each other. The two end clamps are pre-adjusted so that they just fit over the ends and are tightened just enough to hold the wood in place. Having applied on in the middle and checked alignment, I proceed to apply all the other jubilee clips, so that there is one every 2”-3” (50-75mm). I place extra clamps in places that may be under stress such as the tighter curves in the wood or areas where it may be weaker i.e. the knots. All adjusted to the same torque and fairly lose, I then start to increase the pressure evenly over the didgeridoo.
If the glue has been applied correctly there should be a bead of glue forced out form the join. Be careful not to use too much glue, or let it start to set otherwise the join will be unseemly (pardon the pun), and don’t apply to little, otherwise, the joint may be dry which may cause it to split at any time after the didgeridoo has been made.
The right pressure to use is something that you get a feel for. I experimented with different amounts of pressure until I was happy I felt I had it right. At first I used a spanner to tighten the clamps, but this took far to long, so I then speeded it up with a socket ratchet. The process was still slow however so I then started to use a cordless screwdriver with the socket attachment. The powered screwdriver is not only fast (and has two speed settings), but has adjustable torque settings. I apply the clamps on the lightest setting, and then once everything is correctly aligned, I increase the pressure evenly over the wood, in stages, until I am happy I am near the right pressure. When this is so, I will adjust each (again evenly) by hand to ensure the pressure being applied is even and the right amount.
The didgeridoo is then left for 1-2 days depending on the temperature before the clamps are removed. They could be removed earlier, but I like to think that the extra time gives the timber time to settle and with the clamps on it is less likely to warp or split. I don’t know if there is any strength in this but I do it anyway.
After the glue has ‘gone off’ i.e. hardened, it is possible to play the first note of the didge. You should wait until the glue is completely cured, but I can’t resist a quick little toot – it always gets me excited hearing the first sound of something I am create.
De-clamping
Having left it for a day or two to cure, I take the clamps off, ensuring I do so evenly. If all is well, you should have a bead of glue running down the length of each side of the didgeridoo, with gaps where the clamps were. I use a sanding disc with a slow speed and very little pressure to remove the excess glue. I use worn out discs from the shaping of the didgeridoo because as they are worn out, they are not so abrasive and remove less wood and therefore will not affect the shape of the didgeridoo. Having removed the excess glue I give the remainder of the surface of the wood a quick skim with the same disc to make it all an even texture. The didgeridoo is now ready for sanding, sealing and finishing.
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