This is the beginning of the form that will shape the main structure. Over the top will lay thin ply laminated together, with stock standard interior aquadere. I would prefer to use an exterior + PVA but a 4 litre container will cost 50 bucks. After reading glue reviews interior should suffice, with a proper join being stronger than the wood fibres themselves. Here is the mothership template that will be used as a template for the others. I cut them out with the bandsaw and cleaned them up on the vertical sander. A CNC cut out would be better but the red tape and line up kill any sense of connection to the prodcut and process, and frustrate the hell out of me.
Here the other templates are cut. They all sit within .5mm of each other and it took about half an hour. Now im pumped. Anticpating a slow workshop start in the morning i went to bunnings the night before and bough some 12mm no structural ply for 20 bucks to get into it quickly.
By Lunch the form is built. It need slight adjusment to get all planes matching nicely. Its important the planes are flat. Any discrepancies will end up fouling the following wood and concentrating the load on that particular spot, causing both cracking in the veneer, and causing a warp in the plane with a tiny vault. With pva being a close proximity glue with no expansion capability voids between veneers are a big no no.
Top rails will make sure the tensioning straps will stop the veneers deforming when under load. sheets in the face will also keep veneer at the desired plane.
I got some hoop pine A-C 4 mm sheet. The line up for the rip saw is large. I nab the festool track saw instead and get dirty outside in the rain.
aforementioned rip sheets. The workshop staff are really advising to go with 1.6mm sheets. I reckon i can get away with 4mm. With sheets costing the same despite their width, i cant afford buy 3 times as much. It also boosts the drying time and the weight. To boot, i believe the 4 mm will give a better vaulted line, with less sagging than a thinner sheet. They then tell me i have to wet it to get that radius bend. Now i feel like an arrogant dick, but i get feeling the sheet it doesnt come across as a timber that wants to be bent or soaked, soaked especially. More plys of the same sheet width would be good, but its not on hand. I suspect the thinner plys, and ther extra layers would make for a more tangible sheet. Birch would be better, and i assumed teh workshop would have some as its a common species, and more durable and more tolerant of abuse than hoop pine, and if i do this again ill source some of that. Simiular cost as well, and just as renewable. ( I think)
With hesitation and a quiet confidence i start trying to get the sheet over the form without snapping, and without steam. It takes time but with straps and some screws its a goer. Its slow and tense, and there is alot of load on those straps.
Slipping boards under helps concentrate the load on high spots. it also allows for adjustment without taking of the straps.
The layer is on. Now with a better substrate and an increased radius ( anticipated dimensions are 440*420*400- Increased because of the unusual ergonomics of the design) its now not as foreboding to lay the next piece. The next piece is balanced on centre aqnd on top, allowing stresses to flow feely out down either end without being concentratd in the chair, resulting in less deformation.
Screws are kept relaxed so the wood feels loose in the bend, but still maintains a cetral postiona and the sheet parallel to the vault line.
A test at 10 pm informs me that i dont have enough chocks for between the straps and veneer to get the preferred glue contact. Its worth waiting till the morning to go and get more ratchet straps and chocks. I drink scotch and listen to the rain instead, And watch some HBO deadwood before crashing out, defeated but the flex of the sheet.
Glue is now being applied, but only to the inner 450mm. The outside is left glue free so i can trim it a certain depth and strip the wood easily, allowing access to the screws under making easy reuse of the form if the prototype works. The glue is painted on with a brush, and really worked into the fibres.
Some delam is evident during the clamping process, but with the actual piece wanted being 75 mm set in, im hoping that the contact there, which i cnt see is good. There is so much pressure on the straps that the ratchet is maxed, and the form is deforming.
Some solid connection here, Im hoping this is what is happening internally.
More pics coming soon.
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