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Roger the Dodger

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Posts posted by Roger the Dodger

  1. While the front fence doesn’t have to be accurately square, (it’s only purpose is to hold the two base pieces together at the front) the rear fence must be set as accurately as possible at 90 degrees to the blade in order to cut perfectly square. This is achieved by using the ‘5 cut method’ and it is a better way of truing the fence rather than simply using a set square on its own. The fence is secured to the base with a screw at one end which will act as a pivot, and initially squared to the blade using a set square. It is then clamped and a temporary screw is inserted at the other end. A measurement is made from the pivot point (the first screw) to a convenient point at the other end which will be the error adjustment point, E. As this is a constant in the equation, it’s easiest to make it a nice round number… I used 20 inches. (Apologies to the metric purists, but I’m more used to working in imperial, though the new measuring scales on the fence are metric!)

    Crosscut sled.

    Crosscut sled.

    A square piece of scrap sheet material (MDF or ply) is now marked 1-5 and, starting at 1 a thin slice is cut off the edge. The sheet is rotated clockwise so the cut edge is now against the fence and cut 2 is made. This is repeated until you arrive back at side 1 where a wider 5th cut is made.

    Crosscut sled.

    Crosscut sled.

    This strip is labelled A at the top and B at the bottom, then measured very accurately with a Vernier calliper. Its length is also measured very accurately. What the first four cuts have done is to multiply any error by 4 to give a measurable result… the 5th strip should show this error if there is any. The equation to determine any error is as follows…

    A – B ÷ 4 (the number of cuts) ÷ the length AB x E (20”... pivot point to adjustment point on fence, this remains constant)

    This will give a result in thousands of an inch, by which the fence can be adjusted to be as accurate as possible. A positive result means the fence needs to be moved back, and a negative result, forwards.

    My first attempt was as follows.

    Crosscut sled.

    Crosscut sled.

    Crosscut sled.

    A = 1.265”,  B = 1.188” and the length AB was 9.357”.

    Applying these figures to the equation.

    1.265 – 1.188 = 0.077

    0.077 ÷ 4 = 0.01925

    0.001925 ÷ 9.357 = 0.0020

    0.0020 x 20 = 0.040 (or 40 thou.)

    This is too far out and, as a positive number, the fence needs to be moved back by 40 thousandths of an inch.

    A piece of scrap MDF was cut to a point and positioned with the point on the 20” mark, touching the fence and clamped. The temporary screw at that end of the fence was removed, the fence moved back and feeler gauges to 40 thou. inserted between the point and the fence.

    Crosscut sled.

    Crosscut sled.

    This was then clamped down and a new screw hole drilled and screwed. This must be done, as by using the original hole, it will just pull back to the old position. The 5 cut procedure was done again. This time, the results were as follows…

    Crosscut sled.

    Crosscut sled.

    Crosscut sled.

    A = 1.272”,   B = 1.273”, length AB = 7.355”

    Applying these figures to the equation.

    1.272 – 1.273 = -0.001

    -0.001 ÷ 4 = -0.00025

    -0.00025 ÷ 7.355 = -0.000034

    -0.000034 x 20 = -0.0006 (or -0.6 of a thou.)

    As a negative number, this means that theoretically, the fence needs to move forward by that much, but seeing as that result was exceptional anyway, and I don’t have a feeler gauge of less than 1 thou., I decided to leave it… anywhere between -2 to +2 thou. would have been fine and as can be seen, the cut is now as near perfectly 90o as possible. I got lucky here, as it can take several attempts to do this.

    Crosscut sled.

    Crosscut sled.

    The rest of the fixing screws are now inserted to permanently fix the fence.

    This method of truing was devised by woodworker William Ng, and I am including the link to his Youtube tutorial where he describes the method in detail. It's a bit long, but the explanation is at the start... the rest of the video shows the construction of a sled as I have already shown in part 1.

     

    The 3rd and final part of this project will detail the making of the acrylic stop block measuring device that fits to the fence.

  2. 2 minutes ago, Duncan U. said:

     I had a busy day forging s billhook from an old leaf spring for a friend who has taken up hedge laying since retirement. 

     

    That would make an interesting topic for the 'Non watch projects' section. :thumbsup:

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  3. I have just completed making a crosscut sled for my table saw, something I had been meaning to do ever since I got it last year, as this is by far the safest and most accurate way to cut small pieces with it. However, the project was a bit more complicated than I expected, took a long time to do and therefore I am doing this write up in three parts. This one will deal with basic construction of the sled, tracks and fences, part two will detail the squaring of the rear fence to the blade and part three will be about the construction of the adjustable stop block that goes on the rear fence.

    As an introduction, any one who has used a table saw will know how useful they are in the workshop, but also how dangerous they can be if not respected. 'Kickback' is the most notorious problem associated with them and anyone who has had a bit of wood flung into their face by the blade (myself included) will know what I mean. The other problem that can occur with the factory provided blade plate is that small pieces or strips of wood can fall down the gap between the blade and the plate, again leading to kickback or jamming the motor. A crosscut sled alleviates the possibility of this happening as the blade cuts a kerf (the saw slot) in the base exactly its own width which prevents small pieces being jammed and also prevents tear out on the rear surface of the cut piece. This is referred to as a zero clearance kerf. The rear fence also provides much greater safety, as the wood you are cutting has a sturdy support to prevent it moving while cutting.

    The sled needs to be made as accurately as possible and to this end, I invested in a quarter sheet of 3/4" (19mm) Baltic Birch ply, a material not very often seen in the UK due to its expense, but used extensively in Japan and the USA. Birch ply is composed of approx. twice the laminations of the best ply we have here, ie. WBP and is all hard wood, there are no softwood fillers used. It also has a white, finely finished surface. I also had some 1" (25mm) given to me by a carpenter friend in the film industry.

    3/4" Birch ply (13 ply, top) and WBP (7 ply, bottom). Note the gaps in the laminations of the WBP.

     Crosscut sled.

    I first cut 3 x 3" (75mm) lengths of the 1" (25mm) ply to make the front and rear fences. Another safety tip is to use a push block whenever possible to ensure you keep all your fingers! I once saw a push block with the message 'Use this push block instead of your remaining fingers' written on the side. :laughing2dw:

    Crosscut sled.

    Crosscut sled.

    These were then glued and clamped together, using a metal straight edge to make sure they didn't bend.

    Crosscut sled.

    Crosscut sled.

    While they were drying, the base was cut from the 3/4" (19mm) birch ply. It is 24" x 18" ( 600mm x 500mm). This ply has a 'face' side which is perfectly free from blemishes, and the reverse side sometimes has tiny patches where there may have been a knot.

    Crosscut sled.

    Crosscut sled.

    Once the fences were dry, I squared them up on the table saw and using my router table and a chamfer bit, relieved the bottom front edge so that wood chips or sawdust won't build up along it, stopping the workpiece sitting flush against it.

    Crosscut sled.

    Crosscut sled.

    Two dados or grooves were also routed into the top surface to accommodate measuring tapes and an aluminium T track for the stop block.

    Crosscut sled.

    The shallow groove was coated with Rustin's Plastic Coating as a self adhesive tape needs to stick to it.

    Crosscut sled.

    Crosscut sled.

    The next job is to attach the slider that guides the sled on the table. Most saws have a guide slot either side of the blade in which a small mitre guide can run. On larger saws, two runners are usually made, one for each slot but as mine is only a small saw, and the sled is small, I'm only using one. It's important that it fits in the slot with no lateral play or the sled will not be accurate. The one I used is made for this purpose and has adjusters to take up any slack, though many make their runners out of hardwood. You can also see the wide slot in the red blade plate which is what I'm trying to remedy. It's that wide so that the blade can be tilted to 45o.

    Crosscut sled.

    The runner is raised on some washers so that the surface is just proud of the table and some double sided tape applied.

    Crosscut sled.

    Crosscut sled.

    The sled base is then aligned with the saw fence and lowered onto the taped runner.

    Crosscut sled.

    With the runner held in place by the tape, it is screwed firmly to the base.

    Crosscut sled.

    Then the whole base is waxed to help it slide really smoothly.

    Crosscut sled.

    Two more grooves were routed into the surface of the sled to accommodate the T tracks for the hold down clamps I'm installing.

    Crosscut sled.

    Once I have the centre lines drawn, I put the router on the board with a very fine pointed cutter installed and pressed this into the line. This centres the router so I can clamp a fence alongside to guide it. The bit is swapped for the 3/4" cutter and the grooves cut.

    Crosscut sled.

    Crosscut sled.

    Crosscut sled.

    The shaped front fence is added... its job is to hold the two sides of the base together when the kerf is cut, so it doesn't need to be really accurate, although I did centre it properly. The rear fence is also added, but this has to be adjusted really accurately and so is only held in place temporarily while the kerf is cut. The adjusting of this fence will be the subject of another thread as it's quite a process.

    Crosscut sled.

    The T tracks are now cut to length and glued and screwed in place.

    Crosscut sled.

    Crosscut sled.

    The gap at one end of the tracks is to allow the insertion of the T bolts that hold the clamps.

    Crosscut sled.

    Crosscut sled.

    These clamps are very useful and double up holding the vice in place on my drill press table.

    Crosscut sled.

    Next, the self adhesive measuring tapes are aligned and installed. One reads R-L and the other L-R.

    Crosscut sled.

    The home built stop block is moved so that it touches the blade and the zero mark aligned with the cursor on the block. The making of the adjustable stop block will be part three of this project.

    Crosscut sled.

    Crosscut sled.

    Repeated for both sides.

    Crosscut sled.

    The final job is to install a safety block on the rear of the back fence as a reminder not to put my fingers there as that is where the blade comes through the fence.

    Crosscut sled.

    In use, the piece you want to cut is placed up against the stop block (if making repeated same length cuts) and held tightly against the rear fence. The whole sled is then moved forwards to perform the  cut. 

    Crosscut sled.

    Crosscut sled.

    Part Two: Squaring the rear fence.

    Part Three: Making the stop block.

     

     

     

     

     

    • Like 1
  4. I had a few bits of oak strip in the workshop and decided to have a go at making an Infinity Cube. When completed, the edges form a never ending path and the faces appear to float, rather like the Tensegrity structures that I have posted before. The cube consists of 18 strips, 12 with the ends mitred in the same plane and 6 where the mitres are cut at 90o to each other, 3 facing one way and 3 facing the opposite way.

    Cutting the mitres on my newly completed crosscut sled (which will be another thread).
    Infinity cube.

    I end up with 12 pieces like the one on the left and 3 each of the other two pieces. The long ones are 5 inches and the short ones are 4.25 inches.
    Infinity cube.

    Using CA glue and an activator, the pieces are accurately joined together. They must all be at exactly 90o or the cube will end up crooked.
    Infinity cube.

    Infinity cube.

    Infinity cube.

    Gluing the final joints...

    Infinity cube.

    Here's the result. I have seen these scaled up in both wood and metal to make small tables complete with a glass top.
    Infinity cube.

    It just needs a bit of Briwax and a polish and it can join all the other strange contraptions in my 'man cave'.
    Infinity cube.

    Infinity cube.

    Infinity cube.

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  5. 7 hours ago, Dxnnis said:

    One other thing I have noticed is when you have received likes etc is seeing who liked your post something else that comes in time like other forums I have used before?

    Yes.. a list of who 'liked', 'laughed', 'thanked', etc. will appear at the bottom right of your posts when you become fully fledged. :thumbsup: 

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