The assembly table is a flat table approximately the same length as the board you are building. The assembly table, which I paint with a coat of white primer, can vary somewhat in width but typically is a half sheet of plywood. The white painted surface makes the layout lines that will be drawn with a pencil show up clear and clean. I use a carpenter’s chalk box or a long straightedge to draw a centerline on the full length of the table. The assembly table should be sturdy enough to provide a solid working surface. The assembly table can be a one-piece affair for shorter boards or for longer boards, sections can be bolted together and aligned to create a longer work surface. It’s of critical importance that the assembly table is FLAT! The rocker tabs are designed to create the rocker profile based on a flat building surface.
Your frame kit will arrive to you with all parts numbered and ready to assemble. The adjacent ends of the spar sections are marked for easy reference.
The centerline that has been snapped or drawn on the assembly table is both the centerline and the baseline for registering the rocker profile when you glue the spar sections together. Aligning the bottom of the rocker tabs on the center/baseline will assure that the designed rocker profile is created.
When the spar has been assembled and laid out next to the center line on the assembly table, you will locate the position of the assembly blocks adjacent to the rocker tabs. The spar is the core of and the template for the assembly of the framework. The cross-frame notches in the spar become the “template” for transferring the position of the cross frames onto the layout table. Care must be taken to place layout lines and assembly blocks as accurately as possible. For example, be aware that a snapped chalk line has enough width that you’ll need to “pick-a-side” to assure the best possible alignment of the spar. Carefully aligning the spar will assure proper alignment of the cross-frames.
The rocker tabs are used to locate the position of the assembly blocks. When hot gluing the assembly blocks to the assembly table it’s important to consider the centerline and its effect on the alignment of the spar. Maintaining a consistent position for the assembly blocks relative to the width of the line is a critical part of the layout process of maintaining spar alignment.
The spar will arrive in either two, three or four sections depending on the board you have purchased. The puzzle joints on adjacent ends of the spar are glued together with your adhesive of choice. It is important to make sure that the rocker tab bottoms are aligned on the table’s centerline when gluing the spar together. This will assure that the designed rocker profile is achieved when the parts are glued together and this is a critical part of the process. The spar and the cross frames are the foundation of your hollow wood board and care must be taken to work as accurately as possible.
After the spar pieces have been glued together the next step is to transfer the cross-frame positions onto the assembly table. The positioning of the cross-frames is determined by the position of the numbered slots milled into the spar. With the spar lain flat on the assembly table you can mark the position of the slot, making sure you are consistent and marking the same side for all the cross-frame positions. A well sharpened pencil is an asset at this point!
When you have transferred the cross-frame positions from the spar to the assembly table you will then be using a carpenter’s square to square up the layout lines for the cross frames to the centerline of the assembly table. The edge of the assembly table should be square to the centerline of the assembly table and can be used to project the cross-frame layout lines across the working surface of the assembly table. These lines will be the layout lines that the cross-frame assembly blocks will be glued to. You must make sure that the block is glued to the correct side of the line! It’s best to “dry-fit” one frame and assembly block arrangement before committing to final glue up.
This is what your spar will look like when all the layout lines are in place but before the assembly blocks for the cross frames have been glued into place.
Prior to clamping the spar to the centerline assembly blocks it’s a good to check the spar to make sure it’s still “on layout”.
After you have confirmed that the spar is in the correct position relative to the layout, you can then dry-fit the cross-frames onto the spar and locate the position of the cross-frame assembly blocks.
The spar and first five frames have been set up at this point, with the next steps being to complete dry assembly of all the cross-frame positions, and at the same time, final glue up of the cross-frame assembly blocking. The cross-frame assembly blocking can be positioned and glued into place using the cross frames rocker tabs to locate the correct position. A point to keep in mind at this stage of the process is that the cross frame to spar connection before glue-up is quite flexible. The cross frames will slide laterally against their assembly blocks, which impacts the spar alignment. You must find a way to maintain the alignment of the spar as you glue the various bits together. A means to this end that I have used is to dry-fit the entire framework, then stand at the nose or tail end of the board and visually align the spar by shifting slightly the cross frames that are holding the spar out of alignment. Maintaining some light clamping pressure holding the cross-frame to the cross-frame assembly blocks will help in the visual alignment process. I like to use an adhesive that has a generous working time so I can glue the cross frames into place and then stand back and do the visual alignment process before the glue sets. Keeping the framework a bit “loose” as you are gluing the cross frames into position, using a glue that doesn’t set to rapidly and making final visual adjustments as necessary by sliding the frames laterally when necessary will provide a well aligned framework. You can still make some minor adjustments after the frame is glued up but it’s best to fuss with it enough at this point to assure good alignment. After you are satisfied with the frame glue-up and alignment you can then make the “permanent” attachment of the cross frame to their assembly blocks. I do this part of the operation by removing and hot gluing one rocker tab at a time. This can easily be done after the framework glue-up has set since the cross frames have been lightly clamped to achieve spar alignment. You can now do a “final” hot glue or clamping of the cross-frame rocker tabs to the cross-frame assembly blocking. I’ve found that hot gluing the rocker tabs to the assembly blocks is my preferred system of attachment but small clamps work as well. I’ve made this attachment both ways and both ways work but I’ve found it easiest for my style of work to use hot glue….and it’s easier to cleanup between the board and the work table without the obstructions of clamps during the building process.
You can use a try square to check the spar alignment at any stage prior to final glue up with the base of the square flat on the assembly table with the blade aligned to the centerline edge. The vertically positioned blade will give a good check on the spar at any position along the length of the spar. I find that continuing to double check the positioning of everything will save time and effort in the end.
It’s important to stabilize the nose of the board prior to starting the process of attaching strips to the frame. A simple rectangular piece of plywood hot glued to the centerline and the lower edge of spar at the nose does the trick.
The framework should be fully assembled and glued up at this point and ready to layout the strips. We’ll address stripping the framework in the next tutorial.
There are many ways to learn to safely use the tools and execute the processes necessary to build your hollow board. But the bottom line is this: Tools and the dust they create are dangerous. If you are a novice woodworker, educate yourself about tool safety and proper shop practices. Power tools are very unforgiving and trouble can happen quickly if you are not prepared and diligent in your approach to how you use these tools. Regarding the health consequences of breathing wood dust, take this issue seriously. Use good respirators with fresh, clean filters when cutting or sanding wood. This is also true for applying and sanding epoxy and other finish products. Uncured epoxy is toxic. Most of the ultra violet inhibiting finishes that go over the epoxy for the final finish are also toxic. Use the tools and materials at your own risk. Educate yourself and work smart and safe!