The Table Design Continues ..

The work on the table started in earnest in August of 2011. The summer saw many rapid days of progress with George and I working on many pieces. As the project continued it became more and more evident that this will be a work that is around for many years. As a result the design began to mature as an adventure in pushing our woodworking skills.  The functionality of the table requires it has a span that covers 4 people standing side by side. The height needs to allow for an easy reach of the communion and offering plates placed in front of them.  For convenience the side facing away from the congregation should allow for storage.

The front side of the table is to have the words "This Do In Remembrance of Me" from Luke 22.19 

 

The design clearly needed to be solid to support the weight of all the pieces considering the span will be 8 feet. It also needed to allow for disassembling for transport to the church. The table would need to be movable around the church. Of all the projects I have tackled this is the most involved for materials, tools, size, woodworking, and purpose.

The design internals is based on an article "Arts and Crafts Library Table" from May/June 2001 of Fine Woodworking.  That is the method of how the drawer case, aprons, and sides come together is similar to the magazine article.  The fronts and sides of the communion table are to be solid with panels.  See my picture from an earlier post.   Yes there is the idea book again.  I have lost track of how many sketches we have done to prove to our selves the options on the design being considered.

As for the woodworking fine details; I am looking to use as few mechanical fasteners as possible.  That is I am trying to limit the number of screws - which puts a great deal of pressure on using solid woodworking joints.  That choice does allow for biscuits, as was used to align the top and bottom sections of the drawer case.  It also gave a chance to try out a double tenon construction to join the drawer case top and bottom.  This joint has plenty of surface area for glue and makes for a rigid construction.

More to come ... 

Back to the Furniture - Transforming Lumber thought Table Sketches to Finished Work!

After a long hiatus on furniture making, this summer was a chance to get back into the project that has been in my garage the longest, awaiting to be completed.
. 
The project of a Communion table for the Woodinville Church of Christ had started in thought a few years ago, but stalled for a time with a load of other activities taking my time.

100 BF rough cut Black Walnut

This project has become something special to work on as much of the tools and material used have a history.

The lumber comes from an elder 'George' in our church who has had this Black Walnut lumber drying in his garage for many years.  It was cut down in Washington maybe 30 years ago by his father. 
Roughly 200 board feet of Black Walnut was waiting for inspiration so as to be transformed into a table.  Shown to the left is about 100 BF measured and sorted.  It is ready for dimensioning.

I'll show more of that later, but needless to say this is rough cut 4/4 and 8/4 Black Walnut of a quality that I seldom see in such quantity in my humble shop.

George and I spent many days this summer cutting, sanding and scratching our heads trying to think carefully of what next.
  

Sketch Book of Table End

Personally I find it hard to create unless I can 'see' the end result. That is why I use sketch books (Yes and Google Sketchup) to capture ideas and passion.   I like to use the paperback size books as they are easy to sit with and hold while sketching.

A good mechanical pencil, a cup of coffee, a comfortable chair and the tools are in place to capture ideas as they come.

For this table I wanted to highlight the wood as much as possible.  The style I was looking for needed to be simple, not ornate, but capture some essence of its theological function.

The use of the pointed arches on each of the three side panels is what I decided upon as the theme catching element.  Three panels on each side to capture the essence of the Trinity.

Table End - Ready for final

There is much to post on this project but here is a glimpse of what is taking form.

The sides have been done very close to the sketch.  Design is a constant revisit of form and function.  The tapers where kept as the inverse taper.  But I opted not to have through tenons as it kept the look and work simpler.

This wood is far too nice to cover-up with standard finishes!

There will be no stain and poly urethane process here. It will be an oil finish. "George" likes the Danish oils as it pulls out the wood tone real nicely.


Much more to come....

Van de Graaff in the Garage

Sparks will fly!

Happiness is an excuse to build a Van de Graaff generator because your son needs one for a physics assignment. OK so he didn't need that big of one, but why not teach the next generation to dream and plan big.  If you are going to make an electrostatic discharge to impress your friends it had better be real long and snap real loud!    Ok here we go, this entry is a montage of our latest built in the shop project.



Let the Sparks Fly!

 The deal is garage science projects need to be done on a budget, and on time.  The project must teach something (skills in construction or science ) and it absolutely must be over-the-top fun!

A Van de Graaff (VDG) generator generates static electricity in large potentials. Generating 100kV is in itself cool. Discharging it to produce 3 to 4 inch sparks is way cool.  Since there is no current it is relatively safe - at least in the size we built.  NOTE there is already shop talk of VDG2 and how to make it better!


That's using your head!



There are many many sites on the Internet that show general plans for a VDG.  We took a look at a few and came up with our own ideas to fit tools available in our shop.  Most of the materials used are surplus items or low cost purchases from a local hardware store.  The domes used are stainless steel salad bowls we found at Fred Meyers.  Although they work the rim causes some unwanted discharge.  Very late in the build we found rimless bowls at our local Ikea store - hence the idea of VDG 2.

The tower is 4 inch PVC that is held in place with a PVC pipe-stand piece we found at Lowes.

Rubber belt cut from sheet shown with top pulley mount.

The belt material was the single most expensive purchase - but we wanted enough material in case things did not work out in the first attempt.  I found rubber sheet sold by the foot at Hardwick and Son's Hardware in the Seattle U district.  At first we thought joining the belt would require lacing.  It turns out the rubber glues very well with cyanoacrylates.  To join the edges we scarfed the rubber at 45 degrees.  A little glue on the bevel, press fit the edges, and clamping it down to hold in alignment and the belt was done.  Note our first belt was 2.5 inches wide but turned out to be too big.  We settled for a 2 inch wide belt in the end.  It was cut from 4 feet long rubber sheeting.

The static potential is generated by the belt carrying charge from a bottom (metal) pulley to a pulley (nylon) located on top of the PVC tower and inside the bowls (err domes).  A copper comb near the bottom pulley sprays charges onto the belt.  In our case this comb is electrically grounded.  Another comb on the top side transfers the charge from the belt to the dome.  By Faraday's law the charge should accumulate on the outside of the dome.  The picture below shows the mechanism used to hold the bowls to the tower and align the top pulley in place.  The position of the top comb can be seen just above the peak of the belt's travel.

Dome bottom with pulley and comb assembly


The top mechanism became quite involved but it works great.  Everything is built from plastic and nylon except for the copper combs.  Once assembled (with he belt through the pulley) the entire assembly rests on top of the PVC tower.  Notice that the charge is carried from the comb to the bottom bowl by the copper strap seen on the lower right. 





Making the top pulley bearing mount



Cutting hole in dome bottom

 



Bottom comb with grounding wire



Wood base, motor mount and bottom pulley
(obscured by the copper comb)




Center drilling the aluminum bottom pulley



Center drilling the top nylon pulley







 


Close up of plastic ring assembly used
to hold and align the bowls/pulley

   

Machining the rings to hold the
bottom bowl /top pulley to the PVC tower



More details to follow - stay posted!







Manipulating the Future

This project is a home-brew of a parallel manipulator robot known as a Delta-Robot. This robot has 3 degrees of freedom and allows for very fast positioning of it moving platform. The project started as an idea for learning\teaching kinematics. With too much on the go with other activities progress was idle for some time. Although the mechanical work is near done there is a load of software work now to make the robot useful.

The interesting feature of this robot is its design symmetry. There are relativley few different parts. The XYZ movement of the triangular platform (end effector) is accomplished via three angular joint mechanisms that are placed 120 degrees apart on the base.

Note the implementation shown is still missing the mount to hold it upside down from what is pictured.

The joint mechanisms are each controlled by a separate model airplane servo that pivots the fore arm. This arm is attached to a parallelogram seen as the parallel white rods in the photos. The parallelograms pivot on the fore-arm and the end effector. Again, three assemblies of the servo, fore-arm and parallelogram are placed at 120 degree angular spacing.

From the two photos shown next one can see the rather large range of motion the end effector can have with little change in the fore-arm's angular position.

The project is built with black lexan, while delrin and white fiber glass rods. Although it is not as light as it could be the implemention is sturdy and allows for a good deal of force.

The servos are controlled by a serial servo controller. (The small circuit board shown).

The end-effector platform can be seen below as the three-legged black lexan piece. The joints for the parallelograms are also made from black lexan. Some 8-32 nylon screws hold the pieces together.

More on all this later......