Innovative TV Tray Table. Maple. 4th Variation

Maple with a maple stain.

This version, made from maple hardwood, uses an original outer leg design but retains the upgraded details from the previous versions.  

Three other versions:

Cherry

Red Oak

White Ash

Shown with the top flat and level above, the design inverts when you flip the top and pull the top stretcher through.  Once inverted the geometry leaves the top slanted down with a projecting ledge at the bottom. 

Slanted Top

This leg line runs straight from the table top connection down to the floor.  The offset that makes the dual geometry work is done at the pivot point between outer and inner legs. A more direct line and simpler detail than the legs on the previous versions.  While this version also folds up minimally 2" thick for storage or shipping, it looks unique compared to the 3 other versions when folded flat. 

Folded Flat. 2" Thick

Outer legs bolt to the top and inner leg frame. On my Cherry version I came up with a pivot pin that gets trapped in place by an intersecting binding bolt shaft.  The legs and bolts can pivot freely but won't loosen,  They won't come out unless the binding bolt is removed. I used that same strategy in this Maple version. 

Pivot pins.

Center Pivot Point

Upper Rear Corner

I'll confess that hard maple put up a fight during the process of turning it into a TV tray table.  Look close at this prototype and you will see a few war wound scars.  Not all wood from Maple trees is the same. I recommend southern soft maple rather than northern hard maple if you want to make your own from maple.  I've used a mix of both in this prototype.  I threw in a strip of red oak to define the front edge.  The ledge strip on the slanted side is Bubinga. 

This Maple version has a single webbing strap between the center of the top's back edge and the top stretcher. The strap runs from stretcher to rear center edge of the top, folds over, then back to the stretcher. An intersecting binding bolt pierces a grommet in the fold of the strap to hold it in the slot. The 60 degree triangle helps reduce any chance for the inner leg frame to rack. Using strap it is wise to make sure they don't wrap over any sharp corners/edges.  This is the slot cut in the back edge of the maple table top for the strap:

Smooth edges for the strap to wrap over.

The strap runs from the top's back edge directly into the stretcher when in the flat position. In the slanted position the strap runs over then into the stretcher. Binding bolts pass through grommets in the ends and center fold of the strap to hold them in their slots. The angled strap helps keep the frame from racking. 

Strap Connections

Iteration.  There are several variations of details that can be made that utilize the same geometry of my patented idea. Within each the path to finding a great visual composition is done in steps.  What may seem fine in 2D elevation views of a design may not seem as cohesive in detail with the whole composition when viewed on a 3D standing prototype.  Willingness to refine a detail before finalizing the build is a useful quality to possess.  That was the case with this detail:

Original "bump". 

You can see my sketched alternative idea on the top leg.  The original bump to surround this critical offset bolt hole was an unpleasant visual distraction when I first assembled this table. A fat point on a svelte frame. As the legs could be easily removed and returned to my CNC bed I had the CNC recut this area of the legs. 

Svelte Frame

This design is patented. The details can vary, but the geometry that lets the table stand flat or turn inside out to be slanted down is the unique property.

 

For information on licensing the design please contact:

Sarah Nolting
Licensing Associate
Kansas State University Innovation Partners
(785) 532-3910
snolting@ksu.edu
www.k-state.edu/innovation-partners

 

    

Adventure Cutting Aluminum with my CNC

This is my tale of trying to cut some 6061 aluminum to make an aluminum version of a push button depth stop for my Wen benchtop drill press. 

I bought a 4" x 6" x 3/4" thick piece of 6061 aluminum from Amazon. From this I cut the body of the depth stop.  I also have a 5/8" diameter rod of aluminum I used to make the button for the depth stop from.  

Some web research found recommendations for feed speed (17-24rpm), plunge speed (6"/minute), depth/pass (0.03") and bit RPM (13,000) to use when cutting aluminum.  My CNC uses a variable speed Dewalt router that can be set at the recommended speed. The other variables I can set for each toolpath in the CNC software I use (Aspire from Vectric.com). 

My first try was to cut the perimeter and center hole of the press button body from the 4" x 6" block.  I set up the job to cut the part near one corner of the block. The bit I used was a 3/16" spiral upcut end mill.  Two sides of the cut were 1/2 the bit width from the edge. The other 2 sides were full width cuts through the aluminum block.  I thought all was going fine until about halfway through the aluminum. At that point I started hearing more chatter from the bit as it made the full width cuts through the block.  With 1/8" or so to go the chatter was so bad that I had to stop the cut.  I took the block off the CNC, then cut the part free from the block using my band saw.  I then used a spiral flush trim bit on my router table to trim off the remaining aluminum from the bottom edge. I held the part with a c-clamp as I fed it through the flush trim bit.  The bit speed was also turned down to about 13,000rpm. 

First attempt

With the part free from the CNC I could see the affect of the bit chatter on the revealed side. Measuring it with a digital caliper it was close to 1/32" too small in both X and Y direction. the center hole was also not centered between the sides as it should have been.  The deflection from the full width passes was clear.  

With a night to contemplate what had happened I decided to try again the next day. It had been full width passes and ramping down that my CNC had trouble with. The conventional profile cuts had deflected toward the part.  

For my second attempt I started with a block only 1/8" larger than the final part. I rough cut out the body block from a machined corner of the original block using my bandsaw.  

No perimeter passes would be full width.  To avoid having to ramp into pocket cuts for the center hole I pre-drilled a 1/4"d hole (using my drill press) through where the pocket was to be cut. 

Holding the block in place for the cuts started with a t-track bolt up through that 1/4" hole.  A lock washer under a nylock hex nut held the block down tight to my spoil board. To make sure the CNC cuts didn't spin the block while cutting it I separated the cuts into unique toolpaths for each side. While any side was being cut I clamped a block against the opposite side. All profile toolpaths were climb cuts, and only through 1/16" off each side. Twenty two steps were used to get through the 3/4" thick block. All cuts were climb cuts so that any deflection would be away from the part rather than toward the part. 

Once the perimeter was cut I took it off the CNC.  Now I could clamp the part in my low profile vise to cut the center hole. Starting each pass in the center 1/4" hole I had no need to ramp down between passes.   When done I again measured the part and found it to be within .01" of the intended size. The hole was perfectly centered as it was supposed to be. 

Part with hole in top and side. 

Next came cutting the elliptical hole in the side for the button.  I again used a smaller drill bit to drill an opening in the center. With the part clamped side up in my low profile vise I used profile cuts on-the-line to start in the opening before cutting around the perimeter of the elliptical hole. 22 passes again for roughly .75" of depth.  The elliptical hole measured exactly the intended 1/2" x 5/8". In the bottom of the elliptical hole a smaller round pocket was cut for the conical spring. 

Conical Springs.

With all the holes in the depth stop body complete, my attention turned to making the elliptical button.  The button was cut from a 5/8" diameter aluminum dowel.  With the dowel clamped vertically I did a 3D cut to round off the top end of the button.  Then I milled a flat surface down one side of the dowel.  Clamped flat on my CNC with the flat side up I used a 90 degree V-bit to mark exactly where the first 10.8mm hole would be pocketed. 

On my drill press I drilled a 1/4" diameter hole through the dowel.  This center hole would provide room for a 3/16" bit to drop down for each pass before cutting the perimeter of the hole. No ramping needed. 

I used my M12 tap to thread the 10.8mm, hole.  

Next to and overlapping this threaded hole I cut a 12mm hole so the button could slide over the depth stop post.  Each pass started in the open area before moving out to cut the perimeter of the hole.  No ramping needed. 

Holes done, and all that was left was to cut the elliptical shape from the 5/8" round dowel. 

My first try reminded me that a spinning bit in a router will exploit any weakness in how a part is clamped.  I had clamped the aluminum dowel vertically against my vertical clamping jig and a vertical reference fence.  Quick grip clamps held the dowel in place.  This is how I normally clamp down wood dowels.  

Within a few seconds of contact to the dowel the part shook. A clamp fell off, and the part was twisted away from the bit before I could hit the emergency stop. Clearly my clamping strategy had not been good enough. 

I tried again, only now moving my low profile vise to the vertical jig so I could better clamp the aluminum rod in place. 

With the dowel now held securely I tried the same toolpath again.  This time I slowed it down 50%.  A few minutes later I had an elliptical button on the end of an aluminum dowel.

I cut the button free from the dowel at my bandsaw. I then clamped it into my bench vise to file the rough end down smooth.  

Depth Stop Collar Assembled

Almost surprised that the button slipped cleanly into the elliptical hole of the collar.  This depth stop collar works great on my drill press. The strong conical spring keeps the internal threads pressed hard against the threaded post.  Pressing the button in lets the collar move easily up or down the post. 

Low profile vise:  Plywood Vise You Can Make!

HDPE version of this depth stop: Making a Push Button Depth Stop

Comments and questions are encouraged!

4D

Iterative Progression

In furniture or product design often what you hope will be a good design ends up with obvious room for improvement. This is why initial builds are considered to be prototypes. It takes seeing and testing the first prototype to realize where flaws exist or where there is room for improvement in aesthetics or strength or performance or functionality or simplicity of build.

Shown here is a sequence of Balans style chairs I designed and made. Inspired initially by the original rocking Balans chair my pursuit was to find a design that was simple to build, adjustable, and stable.  In my PhDesk article photos you can see most of an earlier 3 caster perch version done as a class project by my students. The design was static with no adjustability or flexibility. Link:  PhDesk Article

Imbuia Wood Collapsible 

My Imbuia and leather prototype above improves on that earlier student design with knee pads that could rotate to meet your shins at a whatever was the most comfortable angle.   Initially the frame post beneath the seat was intended to be moved to different positions along the lower rails. This prototype revealed that changing the angle of the seat would also tilt the caster stems off vertical and reduce the ease of rolling the chair around. The frame could collapse by lifting the center post off the pin it rests on. Collapsed it would  fit in a smaller box for shipping or storage.

3 wheels Adjustable Height

Highest Perch Position

The 3 wheeled version above could be adjusted in height/angle.  This design isolates the caster base from the adjustability of the seat and knee rest. An aluminum push button  releases the aluminum post when pushed in and locks the post position when released. Knee pads pivot to meet shins at the most comfortable angle.

4 Wheels Adjustable

In use.

While there is an economic benefit to using 3 casters rather that four, a 3 point footprint comes with a flaw discovered in use. They could tip and roll out from under the occupant when leaning to the back right or left.  This four wheeled version eliminated the tipping flaw of all the 3 wheeled versions.  This version stretched the frame back so the back caster beam was behind foot clearance. It had the same push button height adjustment and pivoting knee rest as the 3 wheeled version above.  

The sharp bend in the center frame of the 3 and 4 caster versions above required making them from 80 very thin veneer layers of wood. This later version used far fewer and thicker wood layers by changing the center frame to a smooth arc from under the seat down to the rear caster beam. Below a few photos of the arced frame. It has a seat that can be slid forward or back and locked in position with a cam lever.  The arc made room under the frame for occupant heels to meet or cross. This final version was gifted to the International Woodworking Fair management office in Fall 1988. 

Hinge Point

Push Button Height Adjustment

Cam Release Seat Adjustment

The version above was the simplest build, the safest to sit on, and had adjustable height, seat position adjustment, and pivoting knee rests.  It was a design that only came about after making and using the previous designs. They were all built in a university fab lab and benefited from being tried out by several students and other professors. Feedback gained from each version led to advancements in later versions.  This sequence shows iterative progression in action. This iterative research help me gain promotion from Assistant Professor to Associate Professor at Kansas State University. 

An even later iteration I designed is my rocking Balans.  You can read about it HERE.   

Iteration during the sketching stage of an idea always leads me to something nicer, more unique than what I started with.  Yet still, after building a piece, there might be a slight imperfect aspect that deserve more iteration to improve.  That was the case with my TV tray table design you can find here: An-improved-tv-tray-table-design

Nagging imperfections/details only found resolution with 3 following iterations:

1. Variations-of-tv-tray-table, Oak

2. Refinement-in-detail, Cherry

3. Tv-tray-table, Maple, 4th variation.

While my first Maple version worked fine, details in the shape of the outer legs, tension cables, and pivot bolts all found improvement in the following iterations.  Details no sketch would have revealed as needing improvement.   

Comments and questions are encouraged!

4D