Router Plane

Monday, August 6, 2018

Large Segmented Bowl - #3 Face Plate Sandwich, Making/Attaching Layers & Turning


Setting the base ring aside I stated working on the sacrificial sandwich that acts as the transition from the cast iron face plate to the actual bowl.  It is made from two layers, a piece of 5/8” plywood glued to a ¾” piece of particle board.  The plywood layer is screwed to the cast iron face plate which is why I used plywood as it holds screws better than particle board.  One thing I do not want to happen is for the screws to work lose and potentially let go allowing the in-progress bowl to launch itself at me.  I had a bowl break free once and that made for a very bad day.  Here the photo shows the two layers glued and screwed together.  The screws will be removed once the glue sets overnight. 

Once the glue cures the sandwich is run through the thickness sander to make sure the faces are parallel.  The bottom ring of the bowl will get glued to the particle board layer.  When it comes time to separate or part off the bowl I will be turning through it.  Since the screws only go into the plywood it will be easy for me to not hit one accidently.  Hitting a hardened steel screw with a lathe tool is not a good idea.  Next the sandwich is centered and securely screwed to the face plate with a whole bunch of screws, 15 to be exact.  

This assembly is then mounted on the lathe and each layer is turned to a true circle.  Next an MDF reference block in the center of the bottom ring is attached using double face tape.  I used the ring joints to mark it to give me my center then measured the particle board diameter and drew a couple of concentric circles on the ring face.  One the diameter of the particle board and a second just a sixteenth or so larger.  These will allow me to center the bottom ring on the particle board when gluing the two together.  

A layer of glue is spread on the base layer then the face plate assembly is carefully centered on the pencil rings.  Eight clamps hold things in place, but I have to be careful when tightening them as the glue acts as a lubricant which allows the pieces to slip around and out of alignment.  It just takes some time keeping an eye on things and making small adjustments as the clamps are tightened. 


Once the glue had cured I mounted the assembly on the lathe and was ready to go.  The photo on the left is taken from the lathe headstock side while the right one is from the face where rings will be added and the turning will take place.

Below the left photo is a little closer look before I started turning and the right one is after I have knocked off all the corners and trued up the ring. 


Next up is the second ring.  I am fortunate to have a pretty good stack of thoroughly dried lumber.  Some is rough sawn, some is surfaced on the two wide sides and some also has one edge ripped straight.  Well, sometimes it is straight.  Unfortunately, a fair amount of the lumber I will be using for this project does not have a straight edge to reference off of.  This piece of walnut is a case in point as while it was flat and not warped both long edges were nowhere near straight.  They were way too far out to even think about using the hand plane to clean up.  The solution is to take an 8’ level and use the straight edge to mark a reference line.  I then carefully cut along the line using the band saw getting close to straight and then clean up with my long hand plane.  Last, as shown below is to clamp the level to the rip fence on the saw to give me a long surface for the walnut piece to register against.  Flipping the board over after each pass ended up giving me straight parallel edges to work from. 

To make the second ring and all the subsequent rings except for last one I need 12 cherry pieces and 6 walnut ones all the same size.  The process is the same as what I went through to make the bottom layer with one important difference.  I do not have a cut slot on one edge.  Not having that slot allows me to make more efficient use of my wood as there is not a specific Inner or Outer Face.  In the images below, you can see what I mean.  The top photo shows the cuts required for the bottom layer where each segment has to begin with a new edge so the slot is always on the inside.  The bottom photo is for the second layer whose segments can be cut in a continuous string with no waste.

Once I get the 12 cherry and 6 walnut pieces cut I can clamp them together to do a test fit to check for gaps or any other problems.  In this case everything looks good.  Last is to chalk the sides that face up so I make sure none of them get reversed in the controlled chaos of gluing the ring together 

After letting the glue cure overnight as before I ran the ring through the thickness sander to flatten.  Next is to center the ring on the stack.  That’s done by aligning the joints with the previous layer and very carefully measuring the distance between the edge of the to-be glued layer and the turned edge of the previous layer.  If nothing is in error when that distance is the same all around all the joints should align.  If they don’t then there is a problem somewhere.  Here you can see everything is good.  Last is to draw a pencil line around the first layer on the new layer. 

The glued-up bowl stack is removed and alignment marks are drawn on the new layer.  The marks cross the just made pencil line and are centered on the segments.  I make two arcs using a compass working from each joint.  Any error will show up as a gap between or overlapped lines. 

Glue-up is next.  Note that there are alignment blocks held on by orange bodied F clamps.  They are set on the centering circle and keep the two pieces in place while torqueing the grey BESSY clamps down.  Because the glue acts like a lubricant between the gluing pieces without the blocks they will slide around as the clamps are tightened.  Without them it’s a real pain to try and keep both parts aligned.  Once the glue has taken an initial tack the blocks can be removed and the glue allowed to cure.  Looking close you can see how the joints between layers are offset by half. 

Next up – Rings & More Rings

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