Building the Shadow board

The shadow board is an aid to the wood turner, both experienced and beginner and helps to get repeatably accurate results during spindle turning. There are many ways to make a board and it can be as simple as laying a drawing on the bed of the lathe and shining a light down from the top. This is my design and is adapted from one use by Theo Haralampou in Australia. His design consists of scraps of wood with a 45 degree slot cut into them and held onto the lathe using large clamps.

 

It is the clamps that I did not like when I first saw the demo, They are and obstruction to the turner which could also result in a hazard should the clamps slip off while working. My design is more suited to general use and can be adapted (with minor changes) to fit just about any lathe.

Materials

Start by gathering the tools and materials required as follows:

  • Bolts (8 mm) with nuts and washers
  • 12 mm Plywood - off cuts will do
  • Wood screws
  • 3 mm hardboard
  • Band saw or hand saw - a table saw would be really useful
  • Square and tape measure

Start by cutting respectable from the 12 mm plywood. The size of these is dependent upon your lath design, but they must be large enough to sit on the bed of the lathe. Leaving sufficient length so they can be moved backwards and forwards without falling off. The must also be taller than the height of the banjo, this is to allow for the 45 degree cut that is needed to hold the shadow board itself.

You will need 4 of these boards, draw a line top to bottom at the middle of each and use a saw to cut a groove along the line. The easiest way to do this is by making a couple of passes with a table saw, but it can also be done using a hand saw, Chisel etc. The grooves need to be large enough to take the 8 mm bolts when two of the boards are sandwiched together.

 

To sandwich the boards you will only need a screw at each corner, no more. this is important as you will be cutting into these sandwiches, so ensure the screws are as close to the corners as possible while still leaving enough wood to tidy it up at the end.


I then laid out the cutting lines on the face of each sandwich as follows

  • Two vertical lines, one on either side of the bolt hole. Initially these where close to the bolt, only allowing space for the nut. But I found that this was difficult to then attach the nut and the washer which was required, so I made another line further back from the bolt.
  • Horizontal line across the two bolt lines at approximately 4 cm from the bottom of the face that would sit on the lathe bed.
  • Two sets of parallel lines at 45 degrees to the bottom of the sandwich, these where approximately 3 mm apart and terminated 3 cm above the bottom of the sandwich.

The reason for the two sets of lines at 45 degrees was to allow for turning larger blanks on the lathe. The finished clamp would also slide backwards and forwards which too was to allow for blank sizes.

 

The lines where then cut out using a band-saw.


Holding the sandwich onto the lathe requires a sliding block the dimensions of which will depend on you lathe. I cut two pieces of plywood. The first was square and just fit between the two faces of the lathe bed. The second was cut to a rectangular shape the width the same as the square part. Its length was just large enough so that it fit under the lath bed without being able to move backwards or forwards, but could move along the length of the lathe. I held this part in place and put the square on top and then carefully removed both parts (still holding them together). Once off the lathe I secured the two parts using four wood screws. 

The next step was to make a slot in this part (foot) that would allow the Sandwich section to slide backwards and forwards. This was done by making a line across the middle of the square piece and using a punch to mark drill pints along the line.

 

I then drilled along the line, using the punch marks to keep the holes in line. Once the holes where made I used the drill press as a mill, moving the wood to smooth out the slot. 

I then cut the bolt so that the screw thread would not interfere with the shadow board when used in the front slot and set both parts up on the lathe bed so that the bolt was close to the rear of the lathe bed. I then marked the position of the rear bed rail on the sandwich section. The slid it forward and marked the front rail location. I then made 1 cm marks between the two points.



At the time of making I was also cutting some replacement draw bottoms, so for simplicity I made the shadow board the same size. This will probably need cutting down slightly, but that is a simple job for later.

Once I had this part I marked out sections to be removed from two of the sides, this allows the banjo to move freely under the board when in use. The removal of material on two sides allows for the rotation of the board for different lengths of blank being turned.

 

Initial set up needs both sandwich sections in place and the board slotted into them. Set the sandwich block with the graduations on so as the bolt is at the rear of the lathe. Then adjust the other sandwich block until the line visible under the board is horizontal with the lathe bed.

Remove the board and mark the second sandwich block at the rear of the lathe bed. Then use a rule and mark the same number of graduations as per the marks on the other block and in the same direction.

These graduations allow you to position the shadow board more accurately and later (when I add to this article) will help you allow for the difference in size of the shadow produced to the dimension of the turned item.