Sopwith Dolphin Retrospective No. 3 - Vac-Forming

Vac-forming is never going to give very precise results with the sort of home-made equipment I'm using, but the key is to be aware of its limitations.

For instance, an injection-moulded kit might represent the forward decking as a single piece, with the fairings for the cylinder heads moulded integrally, but that would never work with my simple techniques. So the fairings have to be moulded separately. And there's no point trying to mould surface detail. You can add that later.

 My moulded pieces would be as follows:

• The decking, as one piece
• The covering for the oil tank
• The cowling
• The cylinder head fairings

To start with, I cut a piece of pine to size with my mitre saw: a scary piece of equipment, especially when your fingers are less than an inch from the blade. Then I sanded it so it just fitted into the fuselage skin and cut it to the right profile:

After that, it was just a matter of sanding it to the right shape and then cutting it into two so that the two bits could be moulded simultaneously. I made the mouldings for the fairings and cowling separately. I found that there was no need to try and fill the grain. I just finished with 400 grade wet and dry and then went straight ahead with the vac-forming, using 0.4mm card; with the results you see at the top of this post.

Once you have done the mouldings, you can trim the parts and start adding detail. Trimming is the difficult bit; it's difficult to mark up the moulded pieces accurately and it's easy to take too much off. I had to have a couple of goes at a couple of pieces. If I do any vac-forming again, I might work out a way of marking up the wooden moulds so that Ican easily measure up the pieces against them. Failing that, you just have to keep working away until the piece fits properly.

The first piece I worked on was the decking. To make the assembly sequence work, I cut this into two and worked on a piece consisting of the cockpit sides and the plywood construction behind that, known as the Hood in the Sopwith works, according to Windsock 54. The added detail consisted of the plywood panel and the gravity petrol tank that fits into it. I cut out a piece of card for the panel and cut out an ellipse by hand. The upper petrol tank was carved from a solid block of plastic, and sanded down to be a push fit into its elliptical aperture. I also drilled holes for the filler cap etc. Here's how it looked before painting:

That elliptical opening was carved out by hand. Looks pretty good so far.

Unfortunately, once I had painted everything, the petrol tank was no longer such a good fit and is a bit lop-sided if you look closely. I might have to do something about that at a later date.

Doesn't look quite so neat now.

The other vac-formed parts followed the same sort of process. You get the idea.

Next time: after making the basic parts, interior detailing.

Addendum (24/11/2010)
When painting the cockpit sides, I guessed that they were aluminium (you might just be able to see that in the photo). I've just found a photo of the restored Dolphin at Old Rhinebeck aerodrome in the States, which shows them to be plywood. Begrudging thanks to jjambien1 for that. I might just be able to get a brush in to repaint them in situ I suppose.