Vacuum resin infusion: part 2

For the resin to cure, it has to be heated to a temperature of 200 degrees for a minimum of an hour.  That means that the inside of the billet has to reach this temperature and stay there.  If it cools too soon or if the temperature fluctuates too low, the curing process is aborted and cannot be restarted.  If that happens, you have to chuck out the billet and start again, so it is very important to get it right.

Now, I found out the hard way that if you put a piece of nice curly or burly wood in an oven it does not behave itself!  The first piece I did as an experiment warped to an absurd degree.  I managed to salvage it, but it made it very obvious to me that I couldn’t just toss pieces of resin-soaked wood into the oven and hope for the best.  Precautions are needed.

Normally, the curing process requires the wood to be wrapped in aluminum foil to prevent the resin bonding to the oven or whatever else it comes into contact with.  So the billets come out of the resin bath, get wrapped nice and snug with aluminum foil, and then they are clamped between sections of square aluminum tube stock.  These are hollow, rectangular bars of metal tubing that are very strong but quite lightweight.  The billet is sandwiched from four directions between these bars and clamped.  Then it goes onto a wooden shelf in the oven.

You can see from the photo how simple and primitive my oven is, but it is surprisingly reliable.  It is made from rigid insulation with the foil turned inward, backed with sheet rock.  It’s heated with two, 250W heat lamps.  It has a large, insulated lid of the same material and the inside temperature is regulated by propping the lid slightly open.  Pretty high-tech :-)

Once the oven is hot, it usually takes several hours for the cure process to work, providing the temperature is maintained properly.  Once cured, the billets are removed and unwrapped and what had been pieces of soft, porous or otherwise unstable wood are now very heavy and totally stable.  Because they are clamped in a straight and rigid fashion, when the resin cures, the billets are hardened in a warp-free form.

Stability is the magic reward for all of this.  A piece of wood that has been infused with resin is now going to be highly stable.  It won’t shift with changes in temperature and humidity and its workability is greatly enhanced.  Anyone who has worked with Curly Redwood or any kind of burl will tell you that they are tricky to work, and great care is needed to avoid tear-out (chunks of wood being ripped away unexpectedly).  Once the wood has been stabilized, these tendencies are greatly reduced (but not eliminated).  It is worth observing that while resin infusion increases wood density dramatically, it does not increase hardness in proportion.  Curly Redwood (as our example) is a fragile wood that breaks easily.  Being stabilized with resin makes it much less fragile, but even though it makes it weigh as much as a hardwood, it does not impart a hardwoods resistance to stress and impact.  It still needs to be handled with care, but many of its weaknesses are ameliorated to such a degree that what was once a beautiful wood that was not well suited to being a flute, is now a gorgeous and fully realized flute timber.

When I was researching the benefits of resin infusion, I kept asking myself why more flute makers weren’t doing it.  It seemed like a great solution to all sorts of difficulties.

Now I know the answer!

I’m delighted that I have this tool at my disposal because it allows me to to utilize many woods that would not, in other circumstances, be ideal.  It allows me to make flutes in ways that would be impossible (or ill-advised) without the stabilization process.  BUT…

It is expensive and it is messy.  It is really expensive and messy, and the learning curve for mastering the equipment and the process is pretty steep.  I have run into one obstacle after another, and I’ve had to invest more money and more time than I had imagined would be necessary.  I suspect that this is why no one is doing it.  I wouldn’t be surprised to find out that some other makers have experimented with this, but I would also not be surprised to find out that they gave up :-).   I have to have a small barn dedicated to the operation because there is no way to manage it in a tidy fashion.  Resin will be spilled.  Pump oil will gush and dribble on the floor from time to time, and you go through a lot of pump oil because it becomes contaminated with moisture from the vacuum process, obliging it to be changed every single time a batch is done.  And there is a distinct odor during the infusion process, so having this dedicated space is key.

Also, the resin is really expensive and the flutes drink it in huge amounts.   I actually think that the price of the resin is quite reasonable, but the man who markets it targets craftspeople who are making small items like pen blanks or knife handles.  Such an item would use a very modest amount of resin.  A nice, porous flute billet that is about 1.5”x1.5”x30” is going to drink up about a quart of the stuff at $90 per gallon!  And the equipment itself is costly and the process takes a lot of patience. 

But the upside is substantial as well.  For example, I make bansuri from wood (normally these instruments from India are made from bamboo).  They are very thin-walled instruments and making them from wood is a delicate business.  Now, I can use these beautiful figured woods to make gorgeous instrument that would otherwise be next to impossible.  There is a cost, of course.  For a customer buying a resin-stabilized flute, they can expect to pay quite a lot for it.  A bansuri that would normally cost $275 suddenly costs $400 partly because of the high cost of the woods and the resin, but also due to the labor of the process and the fuss of maintaining the equipment.

Is it worth it?  I think so.  In the same way that a player will commission custom decorative work, a beautiful stabilized wood allows for a visual component to exist where it otherwise could not.  A jointed Irish flute made from Curly Redwood?  Unthinkable under normal conditions, but after being stabilized it is not only possible, but it sounds amazing and looks stunning!  A bansuri made from burl wood?  No way!  But stabilization makes it possible, allowing flute players to choose woods of remarkable beauty that would simply not be possible otherwise.  So yes, it is definitely worth it.

In truth, I didn’t know what I was getting into when I started this, and if I’m being really honest I wouldn’t necessarily go around recommending it to my flute making friends, at least not without a lot of qualifications.  However, now that I have the set up, I’m finding that it brings a whole other dimension to my craft and I hope my customers will agree! 



Geoffrey Ellis Flutes

Contemporary World Flute Store

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