Thursday, 24 May 2012

Stem and Laminating Beams

The stem and beams for the boat are all laminated rather than cut from solid wood.  Happily I found this to be nowhere near as hard as it looked on the internet or sounded in the building guide.

First step was to purchase all the wood.  Again I got it from Lazarides Timbers in Brisbane and went with clear Hoop Pine.  I ended up getting with the computer age and made up an excel spreadsheet (after making an early mistake and ordering lengths too short, another lesson) to cover all the combinations.  Each beam had a thickness of wood lamination (6mm or 8mm), a width of each lamination (20mm, 30mm or 45mm) and a number of laminations in the beam.

Take your time, fill in the spreadsheet and DOUBLE CHECK each beam on the plans and document BEFORE ordering the wood.  Trust me, I now have a number of Hoop Pine 6mm and 8mm pieces in various lengths that I will recycle somewhere in the future.  The left over 40mm x 40mm off cuts from the rudder were perfect for the corners of the hatch (last post) and I'm sure I will find a home for them.

Next step was to layout the jig.  John Welsford recommends making up a lofting table from 3 2400 x 1200 pieces of plywood or MDF (making a total area 3600mm wide and 2400mm high) to make the frames up on.  This is a very wide boat and the frames require a lot of space to make up.  Once the frames are done you then use the large flat area to make the jig to laminate the beams and stem on.

This involves screwing hardwood brackets to the surface to clamp the wood onto to form the curves.  A horizontal line is drawn, 200mm spaces are marked long its length and the brackets are moved vertically up various distances according to the plan for the beam.  When you clamp the epoxied laminations to the brackets, a curve results.  Bigger curves result from the end brackets being closer to the horizontal line and the middle being higher.  The hardwood brackets keep the laminations up off the surface so you don't stick it all together and are covered with glad wrap (cling wrap) to stop the beam sticking to the bracket.

I was still building the tender and didn't have the room to make up and leave a full size lofting table in place, so I came up with my own solution.  I got several thick pieces of straight treated pine and lay them on the concrete floor which I had checked and I knew was level.  I put enough pieces down that I could cover the highest position in the centre (some of the longer ones are quite a large curve) and long enough to cover the lengths (the longest was over 3000mm).  

I forced them flat and screwed ply braces across all along to ensure they stayed flat, flipped it all over and marked out my 200mm base line.  Instead of making up hardwood brackets I went to Bunnings (hardware chain store in Australia) and purchased steel brackets just long enough to cover the width of the widest beam.  I went a bit thicker with the steel to get it higher off the wood and also for added strength when clamping.

The picture below shows how it works, I stopped taking pictures after the second beam because they all looked the same.  Thankfully of the eleven beams I made there are some with the same curve and just different lengths (four of one curve, two of another). This sped the process up a lot, because I didn't have to remove and reposition all the brackets for the next beam.

The stem was a similar process, although the grid was in two directions and I had to make a base running horizontally and vertically.  The stem is also 15 laminations of 45mm x 6mm that are 2600mm long.  You can  scarf (fancy word for join with an angled cut) some of the internal laminations but as I was ordering the wood I went all full length.

The plans recommend doing the lamination in three sets of five, FOLLOW THIS RECOMMENDATION!  I was surprised just how much epoxy and time it took to cover five laminations on each inside surface, position and clamp them.

You will need to beg/borrow/buy/steal a lot of clamps.  I cleaned out my father, father in law and brother in law and also bought some for down the track.  There are 21 proper clamps on the stem below, plus a few more spring loaded ones I put in spaces after I ran out.  Not sure if the spring ones held anything but the looked the part.

Below are the first five clamped up.

 Then the next 5 for a total of 10.  

Then the final five.  This created the next complication, because the final stem thickness is 90mm and my brackets were only 75mm long, however with the thickness already in place to clamp to it was not an issue. 

Came straight off the brackets with a light tap of the hammer and was cut to length (with a bit extra).

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