Replies

1. 
   RW | Feb 16, 2003 07:35pm | #1

   First thing you do is decide how arched it will be. You translate that into a segment of the arc of a circle. I'm not doing the math here, just exampling. Say the segment you decide looks proportional is 1/6 of a circle, or the arc is comprised of 60 degrees. Divide it by the number of staves you want to make it out of. Each edge of the stave is jointed at half the number required. If you need a 3 degree turn per piece, each edge gets 1 1/2. That you'll have to play with on a jointer to get it to pan out. The engineering term for fouling this up is "tolerance stack up" - a little out on one makes it a lot more out across ten or fifteen cuts. If you're not just totally set on an exact measurement, get it close and make the sides fit the coopered lid after the fact.

   The issue with cutting and jointing narrow staves on a jointer is holding something down that's only an inch across. When I did it, I made a long hold down with a handle on it that captured the piece across the majority of it's length so my fingers stayed healthy. You can start with a wide board, joint an edge, then rip it a hair wide on the table saw, joint the other edge.

   For glue ups, you can do a variety of things. Nice as biscuits sound, I think you'd end up wearing glue and would never get everything together before things tacked if you stayed with PVA. You can tape the structure together and form a clamping caul based on it's arc, and clamp the whole thing in there, or you can simply lay it all out and use tape to hold the seams. If you do that, make sure you're butting your edge joints together tightly before you wrap it all together. You can tweak it a little with clamps at that point, but not very much. If it's laying on a bench, curve up, clamps on the bench side can bring it together.

   Shaping the staved look into a circle is all hand work. Outside you can start with a block plane, but you might find progress down the road easier with agressive grits and a ROS. Inside if you don't have a curved plane, you can make a block with the radius you want and wrap it in 60 grit to start there.

   Having said all of that, it seems really inefficient, but it's what worked when I did it. I'll see if I can't go get a pic for you.

   " To the noble mind / Rich gifts wax poor when givers prove unkind" - Wm Shakespeare, Hamlet, III,i,100

1. 
   RW | Feb 16, 2003 07:39pm | #2

   Lets see if this works

   " To the noble mind / Rich gifts wax poor when givers prove unkind" - Wm Shakespeare, Hamlet, III,i,100

   
1. 
   willy | Feb 18, 2003 07:23am | #4

   Hi RW,

           well, YES i can see it does work (nice piece) but i'm a little bit lost in your explanations (maybe too advanced explanations for me... just starting hehe!) but i keep this explanation for reference and TRY to apply it.

             Thanks for your time.

       William!

2. 
   jackiechan | Feb 16, 2003 08:36pm | #3

   Willy,

   One of the easiest ways to build an arch top is by coopering the lid.  Long staves of wood are cut at precise angles, glued together, and then smoothed to make a curved panel (think of wine barrel making).  To do this you'll need a well tuned table saw (it can be done with other tools, but this is the easiest), a T-bevel, and a large compass for drawing (dividers would also be useful if you have them).

   The first step is to draw the plans for the lid to full scale using your compass.  The radius you use will determine the amount of curvature created.  It naturally needs to be wide enough to reach the edges of your box.  The larger the radius the less arched the top will be.

   (On paper) draw a line from the center point to the inside edge of the curve.  Mark that point, and continue the line for a few more inches.  Using your compass, draw an arc using the line just drawn as your center point of the curve.  Using the thickness of your wood, draw in the outer arc.

   The narrower each stave is, the better the curve will be.  I use 3/4" - 1" as the inside width of each stave. 

   Using the dividers, mark the width of each stave on the inner arc using the center line as your starting point.  Next draw lines from the center point of the radius to the points that were just marked out.  This will determine the angles of each stave.

   Lay your T-bevel on your drawing and set it to the correct angle for each stave.  Use the T-bevel to set the angle of your table saw blade. 

   On the saw, cut a single stave using a piece of scrap wood that is the same thickness as the lid.  Cut the single stave into pieces an inch or more long.  Next lay the pieces edge to edge with the inner face - down.  Lay a piece of masking tape over all the pieces, being sure to keep the edges flush to each other.  Pick up the line of pieces and bend them until all of the inner faces meet.  Lay your curve onto your drawing - if the test curve you've made matches the drawing, you're in business!  You know that the correct angle has been achieved.  If not, determine if you need more or less angle, adjust the table saw blade as needed, and make another test cut.  With a couple of test cuts you should be able to get the curve spot-on. 

   Always cut extra staves.  Each piece should be cut extra long to be trimmed to size after glue up.)

   After all the pieces have been cut, it's now time to glue everything together.  You will need to make a cradle for the pieces to lay in and to clamp to.  Cut a piece of plywood to the approximate dimension of the panel.  Using your drawing, cut additional plywood pieces (approx.) 5+ inches wide x 2" wider than the panel.  Cut the outside radius of your curve into each piece (you want the female part of this cut).  Drill two holes in each female form piece large enough to accommodate your clamps.  Space the forms evenly across the plywood deck and attach with multiple screws.

   Lay glue on the edge of all the staves and lay into the gluing form.  This is were a third hand would come in handy.  You need to place a clamp on each side of the piece so that they push down and in towards the curve.  The obvious difficulty comes from trying to place one clamp on and not having it push the piece up the other side.

   Once the glue has dried, remove from the form, trim to size, and then smooth the inner and outer faces until you achieve the smooth curve you're looking for.  I prefer cabinet scrapers, rasps, and sandpaper for this task.

   Please feel free to send me any questions that you may have.

   Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.

1. 
   willy | Feb 18, 2003 07:27am | #5

   Thanks Mr. Chan ( is this your real? hehe)

             BTW where can i find a place for large compasses? The only big compass i saw up to now is 12 diameter. It exist bigger or i have to make one myself?

           Thanks!

            William!

             

1. 
   jackiechan | Feb 18, 2003 05:40pm | #6

   Hello William,

   I use the beam compass from Lee Valley (see link).  Two precisely machined compass heads are attached to a wooden beam that you provide (1"x3/4"x length).  Make a few beams to keep on hand!

    http://www.leevalley.com/wood/page.asp?page=32630&category=1,42936,42939&ccurrency=2&SID=

   Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.