My TV Tray Table Design

[4DThinker]

Had a before bed urge to get something done so I set up the CNC to precisely position where the pivot holes would be on the inner and outer legs.  Setting Y at the bottom of the leg, X right beside where the hole should be, and z right at where the hole should be makes sure it ends up centered on the legs where it should be.  

What is left is pivot bolt holes on the back edge of the top, then all the binding bolt holes to hold the pivot bolts in and to finalize where I'll put the tension straps at.   Now to bed.

4D 

[4DThinker]

Got the pivot bolt holes done on the table top edges.  I need to make a set of pivot bolts next.  Got lucky using my rotary axis for them on the Cherry version.   I'll cross my fingers and hope I can repeat that success without breaking a bit or ruining a bolt. I only have 4 tries and I need all 4 to succeed or I'll have to order more long bolts to cut them from. 

4D 

[4DThinker]

Chickened out on cutting the steel pivot bolts today.  Figured I might as week get ready for them by cutting the binding bolt head and shaft holes.  I'm very glad that LinuxCNC shows g-code path of the toolpath you've loaded into it. Caught two mistakes I made before cutting them. One was clear that I'd picked the wrong vector when making it.  The other was that I'd left out a zero when I set the allowance value for it. Apparently .02 is considerable larger than .002.   This leaves making the pivot bolts, and deciding for sure where to put the tension straps. Due to the outer leg design the distance between the leg edges is different between the slanted position and the flat position of the top.  It means either the leg design isn't the most ideal despite how neat it looks, or I'll have to get clever with how I run straps.  Option left is to put them up top between back edge center of the top and the top stretcher. 

[difalkner]

2 hours ago, 4DThinker said:

Apparently .02 is considerable larger than .002

Funny how that works, right!! Glad you caught it in time.

 

A couple of years ago in Fusion 360 I changed a feed rate from 175 to 250 ipm, or so I thought.  I thought I highlighted the 175 to overtype it with 250 but what I actually did was to place the cursor at the end of the 175 and then typed 250, making the new feed rate 175250; very fast.  Fortunately, I have my machine limited to 600 ipm even though it will go up to 1800 ipm if I so choose.  Fortunately, as well, it handled the 600 ipm with no issues at all but I don't plan on making that a regular thing. 

[4DThinker]

A related tale is how I figured out how to make a Multicam CNC move fast enough to throw it out of whack.  Aspire has a nice feature I often use to set a Home X and Y location that the bit will start and and return to after it is done. Works great with the Probotix CNCs and a lonely CNC Shark I oversaw.  As I often am clamping around the edge of a board I prefer this to keep the bit away from any clamps that might be at the corner where I zeroed all axes at.  Apparently there is either no feed speed attached to that move or some ungodly fast/high value as when I'd drawn up toolpaths for a student that were to be run on the Mutlicam that CNC decided to run to my Home position faster than it could handle with no deacceleration.  The operator had to completely reboot the CNC and re-zero it before trying again.  I eliminated the Home move before trying the file again.  It worked that time but that operator never let me create toolpaths for the Multicam again.  I could send him DXF files with notes in them about what to do with each vector in the drawing. No G-code though.   Never did find out what was happening that made the Multicam race, but that day was certainly a memorable adventure. 

4D

[4DThinker]

Got the CNC cut grooves done on the pivot bolts.   I still apparently have some inborn trepidation about cutting steel with a solid carbide router bit, but found if I don't watch them being cut I can stand it.   Much like I don't want to see myself getting blood drawn for tests, but that actual act doesn't bother me if I didn't see it happen. 

 

One just finished, still mounted in the rotary axis chuck.

Three  already done.

4D

[4DThinker]

Cut the threads off with a hacksaw about 1/8" below the groove.  Took them to my basement drill press and chucked up the head leaving the grooved end down and used a file to clean up the ends while the drill press was spinning.  Now I have the leg frame, outer legs, and top all connected with pivot bolts held in place by intersecting binding screws. The table will stand up, but not securely yet.  The only thing left now is to figure out how to lock the frame in both positions so it won't collapse in use. 

I am not in any rush, and had a vivid dream of some sort of "invisible" catch that would lock the geometry in all three possible positions (folded flat, level top, slanted top).  The dream was a hint to me that there is solution still to be found. Perhaps a spring loaded bracket that locks the inner legs to the top, with 3 positions in the sides of top to receive it.    I don't know anything but that I want to find a way that differs from the other 3 tables.  That is on my design standards list.  Another thing there is that the solution should be no harder to make or use than the straps I used on the cherry version.  

4D

Edited April 20, 2024 by 4DThinker

[4DThinker]

Sometimes a draw detail that looks fine in quick elevation views stands out as in conflict with the general aesthetics of the design when seen in 3D on a standing prototype. Such is the case of this bump:

Intended to build material around this offset pivot bolt hole, this bump looks out-of-place and unrelated to any other details of the maple table.   I've drawn on the top one a quick idea of how I might change the detail.  The catch is that I won't know if the change is better until I've made it and put the table back together.  I do know it can't be worse than the current bump. 

4D

[4DThinker]

Recut the bump area and am glad I did.  Much better compositionally than the original bump.

 

As for tension straps it looks like this table will get a triangular strap layout between the center back edge of the top and two slots in the upper stretcher.  The oak version with two straps parallel to each other don't add any stiffness to the design to resist racking.   Idea is a single strap, starting in one slot of the top stretcher, running to the center back edge of the top, being folded over inside the single slot, then coming out to return to the stretcher approx. 60 degrees from the starting slot.  A 60/60/60 degree triangle.  Hope is that it helps keep the inner leg frame from racking.  Not a problem when standing up in tension, but the frame can rack a bit when transitioning from slanted to flat top to folded up positions. 

4D

[4DThinker]

Got the 60 degree strap and the toolpaths to make the slot in the top rear edge for it made.  Still have to make up a  toolpath for the 2 slots in stretcher for the strap.   Woke up thinking about this and realized that when the table is in transition between flat or slanted top there is no tension on the straps, so I doubt the triangle layout of them will provide any help resisting racking.  The strap should still work to keep the table from collapsing though and it is a unique solution so I'm OK with that. 

[4DThinker]

Got the  slot cut in the top's rear edge and the binding bolt holes drilled out for the 60 degree strap.

Moulding toolpath in Aspire did a nice job of rounding over the slot's edges so the strap won't wear through wrapping over them. Took just a little sanding cleanup after the CNC was done.  Had to struggle a bit to get the binding bolt through as the fold in the strap wanted to resist pushing the strap with grommet in it in far enough.  Best thing I bought for these projects were 5mm diameter diamond coated files that taper.   A couple of strokes through the hole with a file let the bolt get started in the grommet then I tapped it the rest of the way in.  

4D

Edited April 22, 2024 by 4DThinker

[Grandpadave52]

1 hour ago, 4DThinker said:

Moulding toolpath in Aspire did a nice job of rounding over the slot's edges so the strap won't wear through wrapping over them.

It did. Even I noticed that right off. Looking good so far.

[4DThinker]

7 hours ago, Grandpadave52 said:

It did. Even I noticed that right off. Looking good so far.

When Vectric added the moulding toolpath to VCarve and Aspire, which I'm sure was inspired by a user who made a Flute+ gadget that did essentially the same thing, it was to me the best addition to their software I'd seen.   For furniture projects I believe the developers would be surprised how many different uses for it I've found.  It eliminated the need to make 3D models and use the 3D toolpaths for simple 3D shapes. 

 

The Maple TV tray table now stands up on it's own.  I cut the slots in the upper stretcher with my CNC and bored the hole for the intersecting binding bolt on my drill press.  The leg frame isn't  glued up yet, and I haven't added a ledge strip to the slanted side of the top, but those are minor simple steps I'll likely complete tonight or tomorrow.  Then finish.  Not sure what to use, but I've got an assortment of cans of finishes to choose from.  May even have some maple stain.  Might even out the color variances between the strips of hard and soft maple in the piece. 

4D

[4DThinker]

Had a memory flash staring at the photo above.  One thing I miss having from before PC CAD software arrived is a drafting table.  The flash triggered the idea of scaling up the geometry to small dining table/drafting table size and could be either of those depending on how you unfolded it from  stored/shipped folded flat state.  A card table size perhaps with room to spread out a jig saw puzzle or flipped inside out and used to layout/draw up plans for the next project.   I doubt there is a great market for drafting tables these days, but I would enjoy having one to use again. I still have t-square and triangles and drafting pencils and architectural scale. Vellum paper is still available albeit pricey.  Hmmm.....

4D

[4DThinker]

Ledge strip cut and glued into the top.

Inner leg frame with stretcher glued up and in clamps.

Nothing left to do but sand and finish and take some nice photos. 

 

Then I may start on a walnut version.   Or skip that version and work on a drafting table/card table version.  Or take a rest on woodworking projects to finish up the upgrades I bought to add to my Chevy Colorado pickup. Install mud flaps, finish with the bed rug install, and replace the head unit with a large screen version.  

4D

 

[4DThinker]

Value of iteration:  The Maple version's offset hole at the pivot point between the legs helped me see the potential of slanting the top more.   No need for TV Tray Tables, but as a drafting table more slant is desirable. Playing with offsetting the pivot hole on both the inner and outer legs I've gotten the slant to almost 20 degrees.  Shooting for a tall table to use with a nice drafting stool I have.  The flat position would be 39 inches high, a nice standing worktable height.

 

I realize I can tune the tilt.  Given that one position of the top is horizontal, the leg layout below can vary greatly.  I suspect I could find a geometry for legs below that would transition from horizontal to as steep as 45 degrees.  As the top tilts it leans forward some.  That forward lean is what limits how steep the top can be. 

4D

 

[difalkner]

32 minutes ago, 4DThinker said:

No need for TV Tray Tables, but as a drafting table more slant is desirable.

How stable would that be?  Sufficient for drawing, managing a T square, erasing, etc.?

[4DThinker]

17 minutes ago, difalkner said:

How stable would that be?  Sufficient for drawing, managing a T square, erasing, etc.?

The inner leg frame is braced with stretchers and stiff.   My original folding desk that was the first point of this evolution is rock solid but the top of the legs rest in notches in the sides of the top to help with that. 2" x 1.25" legs don't flex.  The TV tray tables, thanks to gravity are solid when unfolded in the slanted position and still except that the thin legs flex a bit.  Still easy enough to erase a pencil line without collapsing though. A bit more flex when in the flat position.  Still enough to cut your steak on.  In the drawing above the legs are 1.5" wide and 1" thick in cross section.   Should be much stiffer. below the pivot point.  I don't foresee any bothersome flex that would annoy one enough to make drafting on it difficult.  Best way to know for sure is to make one.   If this was the '70s (when I was in college) a folding, somewhat portable drafting desk would have been in high demand I'd think.   Every kid in an Architectural college  I suspect would appreciate having one in their apartment that they could easily move home between school years or repurpose as a flat work table.  Those days are gone however, and digital drafting tables or tablets are the new trend. They don't lend themselves to this folding geometry.  

[4DThinker]

Maple version of the TV Tray Table now live on my blog.   Still haven't put a finish on the Maple table but I'll replace the unfinished images with new ones when I get around to it. 

https://4dfurniture.blogspot.com/2024/04/innovative-tv-tray-table-maple-4th.html

Image showing the triangle strap layout and the simplified outer leg.  

4D

[Grandpadave52]

Turned out awesome 4D. Very clean looking design. It'll be right smart looking with the finish.