Spline box how-to

Mount a blank on the lathe between centers in face grain (side grain) orientation.  Turn a tenon on each end.  I leave the blank square so the next operation is both safer and easier.

The blank is taken to the band saw and a cut is made that follows the contour of the grain. Blank selection is important as you want the grain has some contour that runs side to side, not diagonally. The end grain should also run as perpendicular as possible to the side grain.

The blank can then be mounted between centers again and turned to a cylinder.  Alternatively each half can be mounted in a chuck and turned to a cylinder independently.  When demonstrating this project I opt for the chuck method as it is safer than turning a blank between centers that has been cut in half.  Can you see the joint in this photo?

There it is.

The 2 halves turned to a cylinder and set aside.  The contour is what makes this box interesting and necessitates the spline technique as it's not possible to turn a tenon on the irregular surface and still have a good grain match.

 

The first half is then mounted in the chuck and the inside is turned.  The body is partially hollowed and a recess is turned around the inside, this will be used to accept the spline that will act as the faux tenon.







The blank for the spline is mounted between centers and turned round.  I usually opt to use the same wood and turned in the same orientation as the body of the box.  In this case the only matching wood I had was in end grain orientation but I used it anyway.  A spline in a contrasting wood is another good look.

The spline is turned to the correct diameter.  It can normally be remounted and carefully turned to get a good fit with minimal runout.  I actually don't mount this between centers.  I jam the blank against the flat face of the spindle and drive it with friction and pressure from the tailstock.  I use the face of the spindle as it will ensure that the blank is perpendicular to the ways.

Once a good fit is attained the spline is glued in place.  The round mark visible here is from the end of the spindle.

The chuck is then returned to the lathe and the center of the spline removed to that only the solid wooden ring is left.  The rest of the body is then hollowed and the spline is blended into the rest of the body.  I opted to reduce the length and soften the edge of the tenon slightly.

The other half is then mounted in the chuck and a recess is turned to match the diameter of the spline tenon.  From here on out the process is mostly the same as a standard box.  We now have 1 half with a tenon (spline) and 1 half with a recess.

The first half is mounted onto the 2nd half and the live center is brought up to support it as the outside is turned.  I round it off and take it down to a little nub.  The top half can be removed to check the wall thickness as work progresses.  The blank centers very well as the contoured joint can only fit in one position.  The dimple from the live center also helps keep it centered.

If the fit is tight enough the nub can be removed without the need for tape.  I rushed through this box so the fit was looser that it should have been so I needed some painter's tape to hold it together while I cleaned up the nub.

The rest of the end half is hollowed and then reversed for for final turning.  I opted to use my vacuum chuck but a jam chuck should also work.  The outside is turned to match the first half,

The 2nd half secured on my vacuum chuck.  My primary vacuum pump pulls 24" of mercury which translates to 12 PSI.  The PVC is 2" diameter which is roughly 3 square inches so there is roughly 36 pounds of air pressure holding this in place.

Turning complete, next up is the texturing that is used to help disguise the joint.

The outside is textured with a round brass bristle brush.  It's held in a jacobs chuck and the lathe rotates it while I hold the box against it.  The softer wood is worn away while the harder wood is left behind.

The finished box.  Another reason I like doing this style of box is that I don't have to sand the outside at all.  The entire surface is textured, more grain is worn away where it's softer but even the harder grain gets some texture.  Any time spent sanding on the outside is completely wasted.

Another view.

Open view.  You can clearly see the end grain orientation of the spline, the grain runs vertical rather than side to side.  If it ran side to side it would blend better with the body and be much less visible.

Twisted box how-to

Laying out and numbering the centers for a 3 sided multi-axis pieces with a 120 degree twist.  The 2 diagrams represent opposite ends of the same blank.  Find and mark the center of each end of the blank.  Draw a line diagonally from corner to corner on each end of the blank.  This line should pass through the center mark and should be parallel on both ends.  This line is crucial as it will give us 1 of our 3 centerpoints and will give us an intermediate point that will allow us to find the other 2 points easily.  Using a compass draw a circle using the true center point as the pivot point.  For a 3" square blank I use a 1" diameter circle (1/2" radius).  Using a larger circle is possible but it will result in a slightly different shape (flatter sides) but will make it easier for the center points to be turned off by accident.  I always make the circles the same size on both ends.  I also do all of the layout and numbering before any cuts have been made. 

The diagonal line will intersect the circle at 2 points, once in the upper left, and again in the lower right.  When doing a lidded box I always number the top first and always number the point where the line intersects the circle in the upper left as point #1.  The intersection in the lower right will be used to find points 2 and 3.  Using a compass set to the radius as the original circle, place the pivot point on the intermediate point in the lower right corner.  Draw an arc that intersects the circle at 2 points and also passes through the original center point.  The 2 points where this new arc intersects the circle are the other 2 points that we need.

If we've done the layout correctly we should have 3 points on each end that are properly aligned to one another and are 120 degrees apart.  The next step is numbering the blank.  I always number the blanks in the same order and using the same method.  The top side is always side A and is always numbered first.

The intersection of the circle and the diagonal line in the upper left hand corner (opposite the intermediate point used to find points 2 and 3) is always labeled as point #1.  The remaining points on Side A are then always labeled going clockwise from point #1. I always number the points to the insde (interior) of the blank.  Numbering on the outside increases the chances that the numbers will be turned off.  This is an issue that can be overcame if it happens but it is easily avoidable by simply numbering on the inside of the circle.  

The layout for Side B can then be completed.  Point 1 should not be parallel to point 1 on Side A.  The other 2 points are then numbered going in a counterclockwise direction.  The direction of the twist can be controlled by putting point 1 opposite point 2 or opposite point 3 (I never taken the time to figure out which direction is which). 

After the layout is complete I start the turnin process.  Step 1 is to mount the blank between the true center points and turn a tenon on each end.  The lid portion can then be parted off (or cut off on a bandsaw, another reason to leave the blank square) and both halves hollowed, a tenon and recess formed to join the lid and body.  To turn the twisted exterior it's simply a matter of lining up point 1 on Side A with point 1 on Side B and turn that face.  Then line up points 2 and 2 and turn the face, and then points 3 and 3 and turn that face.  I usually end up turning each face 3 or 4 times to get the wall thickness I want and to get all the faces even.

Fun with spheres

I've had this idea in my head for a couple weeks now.  Tonight I had to give it a try.  I started by turning a sphere.  The blank was cut slightly longer than the width (3 5/8" long, 3 1/4" wide) and mounted between centers.

The blank was turned to a cylinder and layout lines were made.  The important line is the one in the middle, the others were no measured, just drawn on as a guide.

The corners are knocked off back to the center line.  This is where the bulk of the material will be removed.  Almost no material will be removed at the center line as that is the largest diameter of the sphere.

Each side is then turned to a half sphere shape.  I prefer to do the left hand side first because it's my weak side and I can better match the curve on the right hand side.

A couple more cuts and the basic sphere shape has been formed.

The blank is then rotated 90 degrees and put between wooden drive centers.  If you look at this photo closely you can see the "shadow" of the nubs left by the drive center on the original axis and the rest of the wood to be removed to make this a perfect sphere.

The sphere is repeatedly repositioned on 3 axis (X, Y, and Z) so the entire surface can be trued.  Here you can see that the sphere is on the Z axis.  The X axis is noted by the single line on the top.  The Y axis is the double line on the near side.  The blank is turned on eash axis about 3 times, each time smaller and smaller cuts are taken.  If a cut is too deep the entire surface will have to be turned down to that new depth. 

Once turning is complete the entire surface is sanded with each grit. Once per axis per grit.

Next the sphere is moved off azis and a groove is turned.  The was repeated after rotating the sphere 90 degrees.

There are some flaws. Chipout on some of the edges where the wood was unsupported during the cut and a couple of areas where the soft wood was crushed by the wooden drive centers.

Day 339: New burner

Tonight I hollowed and finished the bottoms on the 2 hollow forms I started the other night.

Unfortunately when I turned on my battery charger burner to start burning them nothing happened.  I opened up the case and double checked all the connections but couldn't find anything wrong with it. 

I made a quick trip to Auto Zone and to Home Depot for some parts and got to work.  This is the charger I selected.  It's a Schumacher 6 amp manual charger from Auto Zone.  Approx $38.  The dimmer switch is a standard 110v single pole dimmer switch, model #6681, approx $5.









4 screws are removed and the case is opened.  The modifications are fairly minor but they will prevent the charger from ever being used for the intended purpose.  This will also void the warranty.

Step 1 is to undo the clip in the back that secures the cord to the case.  Move 6-8" of cord into the case and then resecure the clip.  This extra length of cord is required because of where we're going to place the dimmer switch that will control the power going to the burning tip.

Cut and strip the ends of the hot wire and the ground wire.  The hot wire runs to the volt/amp switch on the front of the case.  Do not cut the neutral wire.  Doing so won't hurt anything but will require you to splice it with a wire nut.

On the left side of the unit you need to remove the clip securing the battery clip wires.  Cut off the wires leaving enough length to attach the wires to the 1/4" mono headphone jack.  You'll also need to move the wire connected to the internal circuit breaker (pictured center) from the copper screw to the steel screw.  This will bypass the circuit breaker.  The 1/4" mono headphone jack was purchased at Radio Shack and is secured in the opening that the battery clip wires passed through. 

3 holes then need to be drilled in the left hand side of the case.  A standard household switch plate is a great jig for placing the holes the correct distance.  1/8" holes are drilled for the screws, a 3/8" hole is drilled dead center for the center post on the dimmer switch.

With the holes drilled the dimmer switch can be secured to the case.

Wire nuts are used to secure the connections to the wires.  Black to black for the black wire running from the cord to the dimmer switch and black to black for the black wire running from the dimmer switch to the volt/amp switch on the front panel. All 3 green wires are also connected with a wire nut.

The case is then reattached using the 4 screws removed in the beginning and a pen using a 1/4" mono headphone plug is attached to test it out. 

If you have problems. do the following:  Double check all the wire nuts.  Make sure that the the dimmer switch was spliced into the hot wire (the wire running to the switch).  Make sure that you've bypassed the circuit breaker by moving the wire from the copper bolt to the steel bolt.

To operate the burner push in the dimmer switch to turn it on and then adjust the dial so the pen heats up to the temperature you want.  Push the dimmer switch in again to turn it off.