My TV Tray Table Design

[4DThinker]

Finally took some photos of this now patented design of mine.  Write-up on features and production options on my blog now published: https://4dfurniture.blogspot.com/2024/02/an-improved-tv-tray-table-design.html

 

Open to feedback, questions or criticisms. 

Don't know much of the process to get it patented as that was taken care of by the University I taught at.  It did take a couple years from start to finish though. 

4D

 

 

[Grandpadave52]

Assume you've got a hinge plan to replace the wire?

[difalkner]

That looks to me like it serves more as a spring.

 

Good looking design, btw!

Edited February 24, 2024 by difalkner

[4DThinker]

Actually the wire/cable so far has proven to be the best solution so far.   Because the design has to turn inside-out no stiff mechanical hinge can live between the inner and outer legs. The cable is routed around the legs so it never crosses itself.  One of the unique aspects of the design. I have another prototype made from red oak that uses ball chain rather than wire.  An earlier attempt using "weaker" ball chain though failed when the chain broke. 

I have an option in mind to use a strap between the top back edge and the top of the upper stretcher instead of a tension cable between the legs.  That will require a unique way of attaching the strap that I haven't prototyped yet. 

4D

[4DThinker]

3 minutes ago, difalkner said:

That looks to me like it serves more as a spring.

 

Good looking design, btw!

No spring or stretch in the cable.  Coated twisted copper speaker wire pulls tight when legs are spread in either position.  It's flexibility is the desired trait for this application. 

4D

[4DThinker]

As an alternative to the wire or anything else between the legs, a 1" wide strap or two running between the back edge of the top and the top edge of the top stretcher  should work.  I've order a 1/4" grommet kit that should arrive in a few days.   Below are the CNC cut slots I'll cut on the top edge of the stretcher for the straps.

The stretcher is 1/2" thick.  The top is 7/8" thick and will get a similar set of slots cut on its back edge.  I have some catalogue binder screws.  The ends of the straps will have a grommet.  When slipped into the slot a binder screw will pass through the grommet to hold the strap in place.  

Once done, the table will rely on the strap rather than anything between the legs.  I decided on two straps rather than a single center one to help minimize any racking of the leg frame/outer legs when folding in or out or collapsing flat.  The binder screw can be removed to replace the straps if they every fail. Binder screw heads will be flush to the wood surface. 

4D

Edited March 4, 2024 by 4DThinker

[Grandpadave52]

Interesting design feature. Should work very well. Looking forward to seeing it in service.

[4DThinker]

This would be the slots cut on the rear of the top. Rounded edges for the strap to lay around.  No sharp edges that might wear through the straps. 

4D

[Masonsailor]

Traditionally they use a ledger under the table top to act as a stop for the leg assembly. What is the advantage of using the wire ?

Paul

[4DThinker]

2 hours ago, Masonsailor said:

Traditionally they use a ledger under the table top to act as a stop for the leg assembly. What is the advantage of using the wire ?

Paul

This  design is unique, and flips over/inside out to be flat in one position and slanted in the other.  Nothing can be attached to the top or bottom of the top.  The wire is routed to stop the legs from splitting in both positions.   A triangulating tension member.   The only alternative is what I'm doing right now with my second prototype, and that is to replace the tension cables with two tension straps running between the back center edge of the top and the top center edge of the upper stretcher. Triangulating at the top rather than between the legs under the pivot point.  The straps will work in both positions. 

 

I've been doing some research and consulting a friend who has more experience with cables and their related hardware.  Knowing what I've learned now I could change how the cables terminate at both ends to "standardize" and maybe simplify their use.   They do serve their intended purpose very well as is though. 

I've got a traditional X frame tv-tray table and the underside had metal wire rails and a wood stop to contain the legs as you mentioned.  A complicated mess IMO.  This forced the legs inward from the top sides, which lessens room for knees between them.  My design keeps the legs out at the top edges for more room between. 

4D 

[4DThinker]

Decided to cut the slots for the straps on the top stretcher today. Should have worked a bit slower and paid more attention though.  

Thought the stretcher was 1/2" thick.  Zeroed out and started the CNC cuts only to realize they weren't centered.  Flush on one side, but 1/8" in on the other.  Turns out the stretcher is (was) 5/8" thick.   This is just a prototype test though, so to "fix" it I knocked the leg frame apart to free that stretcher.  Took the stretcher out to my drum sander and sanded 1/8" off one side. 

Next I grabbed (what I thought was) a 1/4" radius round over bit to put the round over back on the newly thinned side.  Didn't know/remember that I had a 5/16" radius round over bit and this was it.  I'm sure I muttered a few curse words. 

As I'm not one who panics, some time spend with my sanding tools to blend out the overcut "fixed" the visual flaws.  Under the top no one should notice anything odd.   

I had a policy when I taught to never trust dimensions given to me by a student for parts they needed some CNC work on.  Seems I need to apply that policy to my own CNC jobs from now on.  Double check every dimension and tool/bit used before using them.   Wrote that on a file card and taped it to my CNC station monitor. 

4D 

[Grandpadave52]

1 hour ago, 4DThinker said:

Double check every dimension and tool/bit used before using them.   Wrote that on a file card and taped it to my CNC station monitor. 

4D 

Golden rule...maybe silver or platinum...well some kind of rule...measure once, cut twice. Repeat as often an necessary until it no longer fits.

[Al B]

Hope this works out for you @4DThinker". I do know you have some competition out there. I purchased a set of 4 at least 20 years ago that we still have today. The 4 tables are mounted on a rack for storage Definitely a different design  but the same principle.  Good luck to you.

[4DThinker]

6 minutes ago, Al B said:

Hope this works out for you @4DThinker". I do know you have some competition out there. I purchased a set of 4 at least 20 years ago that we still have today. The 4 tables are mounted on a rack for storage Definitely a different design  but the same principle.  Good luck to you.

Thanks Al.   When I submitted the design to my college research/patent dept., they did an exhaustive search for similar/related designs as well as companies that might be interested in producing my design.  Apparently a few million are sold each year.  Given the vast number of "TV Tray Tables" you can find with a Google search it actually surprised me that they took it on and even more that a patent was granted for it.  I've encountered many products out there that have been around for decades or even a century and more. It isn't unusual to see something with persistent sales go unchanged and unimproved.  Yet just a little critical examination and a creative design exercise can both improve the design and potentially lower the production cost of it.  This is an exercise done regularly in the product design courses taught at K-State.   

Growing up my family had a set of metal frame/metal tray folding tables.  Also with a stand that held 4. Still an x-frame that folded up.  Snap hooks on the bottom of the tray top to snap the legs into when set up. Although I remember some rust and rubbed off paint of the trays they served well my family of 8.   This one: https://www.si.edu/object/tv-tray-table-and-stand%3Anmah_1413217

Advance forward several decades and I bought an inexpensive wood x-frame tv-tray table from my local Target.  Didn't imagine until I used it that there were many aspects of it that could be improved.  Didn't think I needed a tray table to tilt down, but discovered that capability almost by accident when I put the legs on backwards of my first prototype.  The asymmetric X sides of mine come from a desk design I made in college. Using that detail on a simple tv-tray table lets it fold inside-out and work in both positions but slightly different. Flat or tilted down. 

[KevTN]

Interesting design 

[4DThinker]

2 hours ago, KevTN said:

Interesting design 

Thanks @KevTN.   Projects like this I don't bother with if I can't add something interesting to the design.  Likely a crippling flaw in my design strategy. The crook in the outer legs is there solely to permit the table to fold up flat. The side benefit, an unexpected feature, was that when turned inside out they change the geometry just enough to tilt the top when unfolded.  Such bonus capability I've often found in designs of mine that wreak of simplicity.  This simple coffee table is one example:  https://4dfurniture.blogspot.com/2022/06/versatile-coffee-table-design.html

The original prototype of that table I sold at a woodworking show.  A young boy (looked to be 5 or 6) came up to me when the show ended and I was packing up.  He had a pocket full of change and wanted to know if he could buy it.  I'd mentioned in demonstrating it that with one leg off the table top would make a nice ramp for toy cars and trucks. He was the perfect client it appeared, so I let him have it in exchange for what was likely $2 worth of change.  His parents were very surprised and helped their son carry the pieces away. 

4D

[4DThinker]

Took my time to double check things today. 

Adjusted the toolpaths for the back edge of the top to line up with the toolpaths I'd cut on the stretcher.

Double checked that the top was 7/8" thick.  It was.

Clamped the top with the back edge up, then double checked that it was level with the CNC frame.  Took a little bumping of clamps to get it just right. 

Booted up the CNC controller PC.  Stuck the thumb drive with the toolpaths on it into the front port.  Folder for it opened up on the screen which let me find the toolpath file and copy it to the desktop.

Ran the control software (linuxCNC). Loaded the toolpath file into it. 

Activated the controller.  Jogged the bit close to the front left corner then had the software HOME it. 

Jogged the CNC to the front where the top was clamped and zeroed the left edge,  front edge, and top surface.   

Ran the file.   1/8" ball end bit took it's time patiently pocketing out the slots, then dancing back and forth as it climbed up each edge to round over the edges. 

Perfectly centered, the cuts pointed out that the rounded over edge of the top wasn't a 7/16" radius roundover, but rather a 1/4" radius on both sides with a 1/8" flat in the middle.  I'd made this top before I had a 7/8" bullnose cutting bit.   Put that bullnose bit in my garage router table and ran the back edge down it to get the surface to agree with the CNC slots I'd cut in it.  I could tell I was smiling at how well it turned out.

Waiting on a 3/8" Forstner bit to arrive.  Need to make flat bottomed shallow pockets for the heads of the binding screws. I've got the strapping, the grommet kit, the binding screws, but can't finish this job until that Forstner bit shows up.   I've got several Forstner bits.  Each bought for a specific job.  No 3/8" version among them so this'll be the first time I've needed a 3/8" version.   If I was desperate I could draw up toolpaths and cut the shallow pockets with my CNC.  Just doesn't seem right though. 

Some time off until the bit arrives might give my mind a chance to figure out the best way to measure and make the straps the perfect length. 

4D

[4DThinker]

Got impatient waiting on Amazon to ship me a 3/8" Forstner bit.  Since the pandemic hit I nearly forgot about the local True Value and HomeDepot stores near me that likely would have one to sell me.  So a quick trip and I brought back a Freud bit and some beef jerky which they sneakily displayed right next to the register.

20 minutes later and I had version 2 assembled and standing.

I kinda like the look of this version, although you won't see the straps when using the table.  The binding pins through a grommet seem to do the job holding the strap ends securely.  This one needs some finish on the legs and stretchers and when I've got that done I'll update my blog with better photos of the whole thing.  You might notice the legs don't have a kink in them.  I just curved the top section from the pivot bolt up to gain the needed offset.

4D

 

Edited March 7, 2024 by 4DThinker

[Grandpadave52]

1 hour ago, 4DThinker said:

So a quick trip and I brought back a Freud bit and some beef jerky which they sneakily displayed right next to the register.

Well I guess the jerky will work for the straps.

 

[4DThinker]

7 minutes ago, Grandpadave52 said:

Well I guess the jerky will work for the straps.

 

It didn't last long enough to make it down to my basement shop. Tasted pretty good. 

As for the straps, I'm looking for some that is made from cotton or some similar natural material.  Just not beef fiber.