Monday, January 24, 2011

Rocker Table Pt 3 - Construction

So now to actually building the table.

As I mentioned a few posts ago I wanted to make mine at least semi-adjustable as this seemed the best trade off between complexity (and sweat) and cost.

So the first thing to do is cut out the rocker jigs. I printed out the continuous rocker line for the edges and the center. Then cut along the line, taped it 2 narrow chipboard doors that I found on council clean up day ( they were about 20cm wide which was about right to accommodate the amount of rocker plus some extra on the top and bottom for securing them to the frames of the table. Then traced it out with a marker and cut it very carefully with a jigsaw. This created the male and female versions that will be used to clamp the edges.

Only the female version of the centre rocker line is necessary. I used a over sized mold factor of 2 in fixing the height of this piece ( see last post) which turned out to be a bit underdone given how much larger the able is than the board but this will be easy to increase by building up the centre jig.

So here's what they look like.

The round holes in the side are where I am going to insert the G-clamps to secure them to the frame.

Next is the bottom frame. If you have been lucky enough to get hold of 2 single bed bases then 3/4 of the work is done. I had chopped bits out of mine so I needed to build the base. I used 3 x 20 mm angle iron pieces form Bunnings with each length about 1.5m.

I screwed 2 x 1.5m length of angle iron to some chipboard pieces 1 m wide. I screwed another piece of angle iron so that the inside edge of the vertical part was exactly at the center point between the 2 bottom pieces. Done.

The female jigs can now be secured in place.

They are held in place with 2" G-clamps but you could just put it all together with bolts and wingnuts.

The mold surface ( the surface that the board will ultimately be clamped to) is going sit between the female and male jigs. I used a piece of 4mm plywood with about 6 coats of acrylic paint from supercheap auto. I'm not sure this was the best choice because it may not be stiff enough to resist deforming when stiffer board core material is used but it will certainly do for PVC foam and probably balsa. Other options would be melamine coated MDF or maybe Laminex/Fomica which would probably be stiff enough to use for PVC and balsa and could be laminated onto 4mm or 6mm ply wood if you were going to use stiffer core material.

The mold surface measures 1m x 1.5m - big enough to cover any board that I make. You need to make sure you have at least 10 cm between the edge of the board and the edge of the table to allow you to tape the vacuum film in place and put any other breather material around the edge.

The acrylic paint is used to seal the pores of the wood. If you're using a melamine coated surface or perspex then no need to do any of this. In all cases you'll end up using release wax on the surface to help the resin lift away from the mold. The important thing is to make sure that the surface is smooth if you are going to use a single sheet of vacuum film taped down to the surface. (the alternative is to enclose the whole mold surface in a big vac bag, excavate it and then clamp it down.)

The matching male jigs are then clamped to the single bed base that will serve as the top of the rocker table. This leaves a good open working area and the weight of the base means that I probably won't need to put any more clamping pressure on it to get the mold surface to bend into the exact line of the jigs.

This photo shows you how the centre jig introduces the concave.

This spirit level across the mid section shows the presence of the concave. Remember that I used an oversized mold factor of 2 and wanted to get 10mm of concave in there. However, as you can see from the picture below the net result was about 7 mm at the edges of the board. That is, 20 mm of concave as measure at the extremities of the mold (45cm away from the centre reduces to 7mm at the board edge which is about 15 cm from the center).

There is also a noticeable flat spot the middle where the centre jig sits.

Fortunately its a simple mater of just laying a strip of material about 6mm thick along the centre jig and all else being equal the desired 10mm should be introduced. Also, making this piece narrow will help remove the flat spot in the middle of the board.

Out at the tips the concave vanishes like it was meant to.

With the rocker table completed, the next step is to actually start making the board!!!!!!


No comments :

Post a Comment