Building a 9' chambered balsa gun

I have noticed that some people were complaining about not enough building threads lately. Well, here is one. Please note that I may not be the best person to make a report about building a chambered balsa gun (people like Jim Phillips, Balsa Bill, Robin Mair and countless others have much more experience in the field than I do) but I will try my best to make something worth seeing. As usual, pieces of advice from you all are more than welcome.

I got this order a few weeks ago and was very pleased because it gave me the opportunity to work on something really “out of the box”; Not so many people buy balsa boards any more, the cost being quite high. The first challenge lies in finding quality wood with suitable dimensions. Luckily for me, there is this guy in Cap Ferret (near Lacanau) who imported a full container of balsa lumber from Ecuador. I was able to pick up (and choose) all the wood I needed and I brought it back to the shop in Guéthary.

First thing I did was to weigh every piece of wood in order to dispatch equal weights on both sides of the centerline:

Then I spent some time joint and thickness planing all lumbers so as to get straight glueing surfaces:

Then some bandsaw work: slicing all lumbers in half and some more planing to erase saw marks. The idea here being to have one piece of each on each side of the board so that the balance will be as perfect as possible:

Using a rocker template from a previously made gun, I drew the desired rocker on one of the lumbers to make sure it would fit. It did, so I cut it out on the bandsaw:

That was the result:

Right now, that’s where I have come to. Here is a first “in the white” assembly, just to get a feeling of what it will look like. (Not all pieces are in the photo):

To be continued…

Balsa, No shaping machine here, just a band saw, several hand planers and some Swedish steam. So maybe the difference in our approaches is you leave a larger margin b/c you will begin with a power planer (???) and I have my pieces all cut very close to the final dims of the rocker profile at the midline prior to the first glue up???

 

I have to agree with that. Actually, it’s pictures like this that motivate you to shape a board. Thanks for the kind words, John.

Yes. I love to spend long hours struggling with raw material, breathing toxic dust.

No, seriously, I like the idea of having a margin for error when I use a power planer. When I get older and I have acquired much more experience, I will gladly just sand the small ridges left by the shaping machine.

I am very much a novice, but when I approached this type of project for the first and only time, I had my individual pieces very close to the final rocker profile at the mid line of the planshape. That is to say the nose and tail thicknesses (and everywhere else) were very close to what would be the final shape at the midline. Is there an advantage to not doing this?

Hi Guilhem -

Anyone who has tried assembling a blank from raw timbers or shaping balsa should appreciate the work up to this stage of the project.  GREAT job!  It looks beautiful in it's roughed out condition.  You've somehow managed to outdo yourself with this one.  A seriously huge effort!

That is a very interesting shaping rack with the heavy-duty frame and wheels.

PS - I never would have confessed to misplacing a stringer.  I'd have just put it back in there and kept mum about it. HAHA

 

After disassembling the right side, inserting the missing stringer and re-assembling the whole, I could -at last- start the real thing.

Jig-sawed the outline, leaving a comfortable margin for a possible blade-bending. It bended all right, but to the outside… Oh well, just some more work but thanks God it was not INSIDE… That would have been tricky…

 

Cleaning up top and bottom with various hand planers before breaking out the big Accurate:

 

…I get by with a little help from my friend, San Miguel:

 

When the day’s labor’s done:

 

Balsa,

Ive done them glued with a hot glue gun.

Just enough to hold them together.

Clark foam used to chamber them for you after shape.

That’s how they preferred them done.

Yeah, I remember reading that somewhere now and, of course, that was the right way to go… Oh well…

BTW, I just realized that I had forgotten one of the red cedar side stringers when assembling. Will have to disassemble one side of the blank tomorrow… I must be a bit tired…

BTW…looking great!

A method Jim uses is to take a long piece of 1/‘’ all-thread and cut it to the length of your desired blank width minus the outside pieces.  Then use large fender washers that are counter sunk and tighten it up.  I have used this to pull crooked pieces of balsa straight till I am ready to chamber.  There is no hoping it will stay together.  

I just hope it holds the thing together… Balsa is very soft, screws do not bite that much into it… I will play it safe when handling the blank, I think…

Love the screw idea…

simple and effective.

Right on Balsa!

Before going further, one thing always bothered me with the “traditional” method used by all pros to build chambered boards. Almost all of them “spot-glue” the different pieces of wood so that they stay together for shaping but can be disassembled by heavily knocking on them with a wooden block and a hammer. Well, I’ve never been comfortable with this, always thought that it could ruin all the work previously done. I’m probably wrong… But still I don’t like it. The few balsa boards that I built back in the days, I would assemble with dowels (the serrated kind). But it’s a lot of extra work, positioning the dowels correctly.

Well, I have chosen the easy way this time and simply screwed the pieces together (with the exception of both outside pieces that I had to spot glue, of course, because screws would have shown, otherwise). That leaves only two pieces to be disassembled the hard way… Less chances of breaking something, I hope… Photos of the day:

Positioning the template to check that everything will be OK:

 

Screwing pieces together:

 

Screw detail:

 

At last, the completed blank with both outside pieces being glued and curing:

That’s all for today, folks!

Barry, the “wood-shop” is actually my shaping room but it was designed so that it could easily be turned into something else (wood-shop, for instance). Everything in my shop has wheels (shaping racks, glassing racks, joint planer, bandsaw, vacuum cleaner) and it makes for easy changes between foam shaping and wood-working.

As for gluing blanks… Back in 1969 when I started shaping, no foam blanks were available in France yet. A friend told me about a company where they were using polyurethane blocks to build refrigerator trucks. I would go there by train (no driving license then, I was 14…), about 100 Km from Guéthary, buy some 7’ x 20" x 4" rectangular blocks of a brownish, 30 Kgs/M3 insulation foam, bring them back home with me in the train, then cut them in half, put some plywood in the middle as a stringer, glue with polyester resin. Pressing was done using sandows and “rocker” was built in by laying bricks or resin drums on top of the “blank” while the resin was curing…

A few years later, second choice blanks became available from the only french manufacturer (at the time), Barland. Quality was poor but it was actually WHITE foam and it was a real blank with some basic outline and rocker in it. Night and day.

So, I can relate to what you say:

"I wish all shapers would try to glue their own blanks.

They would probably come to appreciate those blanks they buy more."

Balsa,

Love the wood-shop shots.

Every shaper should have a little wood-shop.

I wish all shapers would try to glue their own blanks.

They would probably come to appreciate those blanks they buy more.

When I first started shaping, I witnessed some balsa being glued.

At that moment, I decided I wanted to be in that small club of shapers who could actually do that.

Can’t wait to see more.

Barry

This is the type of stuff I love,  G!  Tell us how your chambering will look like, wider at the ends? Smaller on the middle? I always think poly sucks, and epoxy would be better, longer lasting … What do you think about osmosis? Any special finish? 

Keep the pictures coming, weights too! We want know ALL the weights!!!  Make it a thread for future generations to reference, as there is no DVD for reference. How about the acclimatisation of the wood? You can’t have it tear apart! Any idea of finished weight ? 

What about fins? Single I guess?  And is the client a former actor or rugby player? 

You better make it perfect!! 

Cheers G!

Wouter 

Wow. That is a lot of work. I’ve only done a few chambered boards and each one I’ve said is my last. 

I’ll never do another one.

clean machine,go daddy go!

…ambrose…

Work of the day (among other things) included cutting lumbers to rough dimensions and cutting rocker into half of them (didn’t have time enough for the other half… Tomorrow.)