Massage table construction question

Factual Questions
21

Actually, setting up and taking down my table seems a bit awkward. (Here’s the picture of it again.) To take it down:

[ul][li] First, lay the table on its side.[/li][li] Then, fold the deck, but only part way. You can’t fold it fully with the legs still out.[/li][li] Then, fold in the legs at one end, but only part way. You can’t fold them in all the way with the legs at the other end still out. [/li][li] Then go to the other end and fold in the legs there, but only part way. None of the legs will go in all the way just yet. If you fold the legs at this end in too far, the partly-folded legs at the other end pop out again.[/li][li] Then fold the deck a little more.[/li][li] Now you can fold all the legs in all the way.[/li][li] Then fold the deck all the way.[/ul][/li]It’s like, you almost need five hands, some at each end of the table, if you want to fold up the table in one smooth motion: One hand on each of the four legs, and one (or two) folding the deck, all simultaneously. Always made me wonder if I’m doing it wrong.

Setting it up is just like the above in reverse.

ETA: Okay, I guess I have to watch that video. Can’t do that on this machine right now though. I’ll have to fire up the laptop for that.

22

The cables in Senegoid’s picture are going to be in tension when weight is placed on the center of the table, over the folding joint. They keep the table from collapsing into a V shape.

Imagine if the cables were not there. What would act to keep the table from folding down in the middle when it was weighted? There is a hinge or sets of hinges along that joint down the middle of the table. Depending on the design of the hinges and their location, when someone climbs on the table either the hinge offers no resistance to folding the ‘wrong way’, or the hinge experiences large internal forces and transfers them to the screws or other fasteners that hold it in place. That’s a failure point.

With the cables in place, if the table tries to fold down in the middle, the cable attachment points move farther apart and the cable must stretch. The strain is taken off of the hinges and transferred to the cables and legs, which are triangulated and much more rigid. The forces felt by the legs are those of tension and compression, as opposed to shearing forces on the fasteners for the main hinges.

If the cables are loose when the table is loaded, then the hinges at the middle are taking a real beating.

23

Okay, I and a neighbor were looking more at my table today, and thinking about it in light of some of the comments above. In some sense at least, it’s counterintuitive.

The cables run the length of the table and connect from the joint in the leg at one end to the joint the leg at the other end. At first glance, it would seem that any tension on the cables would pull the legs inward towards each other, causing them to fold. But they seem to work the opposite way: The tension on the cables tends to keep the legs out, not pull them in. That’s because they’re attached at the mid-leg hinges, and pulling on the cables forces them to be straight, not bent, at those hinges.

(Okay, clarifying that upon preview: The legs fold inward, but the cables don’t attach to the legs at all. They attach to the hinged midpoint of the diagonal brace between the leg and the deck. When the leg folds inward, the lower half of that brace and the hinge point fold outward and upward along that slotted track, away from the far end of the table. The cables prevent that from happening. Here’s the picture again.)

This is basically what Joey P wrote, two posts above. Now I’m also thinking about what brossa just wrote. Yeah, I can see that too, sorta. The construction of the deck is such that the deck cannot fold “the wrong way” into a V-shape – but yeah, I can see that it might be putting a lot of stress on those hinges when it “tries” to fold the wrong way under a weight on the table. It’s a bit less obvious if the cables are doing anything to help in this regard, but maybe. I’m not sure what direction the pull on the cables would be if the deck started folding the wrong way. I’m kinda thinking it might just pull more on the cables and possibly break the leg brace joints before it protects the center deck hinges, but there’s no way for me to know that. The leg brace joints just don’t look sturdy enough to withstand a lot of forces, the cables included, pulling on them in a lot of different directions.

The biggest detail, that led me to start this thread, was that I had remembered the cables being slack, but clearly I remembered that wrong. (Like I said, I haven’t set this table up for several years.) Now I’m wondering about those other tables with lots of wires. There too, I remember at least some of those wires being slack, but now I wonder if I’m remembering that wrong too. It’s the Pisces tables I have in mind specifically – but I haven’t used or even seen one of those for several years either. My cousin in far-off San Francisco has one – if I visit her sometime in the near foreseeable future, maybe I’ll remember to take a closer look.

I wonder who designs these tables anyway? This begins to look like a lot of vector analysis getting involved!

24

The cable between the legs (well, the angled parts, anyways), once pulled tight, will transmit any additional force to the cable that goes up at an angle to the deck.

Your table looks pretty sturdy, is designed to hold quite a bit of weight and the cables are taut when it’s set up so it’s going to be difficult to show. However, if you put your hand on the cable going from the leg up to the deck and then strained the cable that goes from one leg to the other, you should notice the one your hand is on getting even tighter as table tries to collapse (it would if the cable you have your hand on wasn’t there). The only way I can think to do this is to, maybe, push down on it with your foot to get some real weight on it.

Either way, the cables going from the deck to the legs shouldn’t allow those joints to hyperextend, so to speak. Of course, things can always be broken if you put your mind to it. I wouldn’t go jumping up on down or rocking back and forth on this thing just to see what happens.

25

Whoa! Your latest discussion seems confused – you mention the cable going between the legs and the deck a few times – there are no such cables on this table. There are only two: The two that run (almost) the length of the table from the hinged leg braces.

Are you referring to the thingy that runs from the leg brace hinge up to the top of the leg near the corner of the deck? (Maybe in this picture it looks like two cables side by side.) That’s not a cable – it’s a metal track with a slot in it. As the leg folds in and the diagonal brace folds at its midpoint hinge, that hinge slides up the track.

Or are you referring to the wire that appears to hang down from the middle of the underside of the deck and loops underneath the two long wires? That isn’t a structural cable at all. It’s a stretchy elastic band that seems to serve only to pull the long cables up and inward as the table folds so that the cables, totally slack when the table is folded, are drawn inside the folded table and don’t hang out. P-man described that in an earlier post:

So anyway, I’m confused about trying the experiment you suggest.

26

This. In fact, a metal track with a slot in it will do an even better job of making sure the leg brace can’t bend the other way.

27

The beds the Red Cross uses for blood donations have similar cables and I always assumed they were for stability.

28

Are these beds portable and foldable, that the Red Cross might use for setting up donation centers in various places for a one-day drive? Or permanent-like beds in a fixed location? Do they fold in the center like a massage table?

We’ve pretty much decided in this thread that the wires do provide some sort of support and stability (remember, I thought at first that they were completely slack), and we’ve been going into more detail about how that all might work. Do you think the Red Cross table wires help keep the legs from folding in, or keep the deck from collapsing or shearing the hinges off?

Do blood donors get a full body massage in return for their donation?

29

Yes, these are the portable, foldable beds they use for the one day drives. Random pictures of what I mean here. You can see the wires under the bed and it appears they fold in half. A massage would be nice; all I’ve ever gotten is snacks :slight_smile:

30

Okay, those “beds” look a whole lot like portable massage tables with maybe just some extra folding joints in the deck, and design changes in the rigging to deal with that. I think if you lay the raised upper-body end flat and lower the arm-rests, you’d have a perfectly cromulent massage table (although perhaps excessively elaborate and hence expensive, for the purpose).

So I think they should give donors a full-body massage while they are donating. (ETA: This would be a win-win. Donor gets a massage, while Red Cross squeezes more blood out of them.)

31

Still more about these:

Well, well, surprise, surprise. These blood donor beds appear to be similar to, and may exactly be, this model of Pisces blood donor bed – looks like just a variant design of the same Pisces massage table discussed in several posts earlier. But these look like they have a wood deck instead of vinyl webbing deck.