It seems to me that, on a message board where EVERYTHING has been discussed many times over, I’ve seen rather few threads about massage (notwithstanding that there’s one running just currently). Anyway, I have a question about the construction of portable massage tables.
Note that most of the tables have some network of wires or cables hanging below the deck. What are these for?
They are certainly not providing any strength or support for holding the table up, since most or all of these wires are slack when the table is fully open. (I’m not sure how clear it is in the pics that the wires are slack, but I’ve seen several massage tables close-up and that’s how they are.)
They are connected up rather strangely, at least in the few tables that I’ve actually set up and taken down. Taken down, the legs fold into the bottom of the deck and the deck folds in half. If you unfold the deck and lay it out straight, the cables pull the legs part-way out, but you have to pull the legs the rest of the way out yourself. Conversely, if you lay the table on its side and fold the legs back in all the way, the cables force the deck to fold part way, but you have to fold it in half the rest of the way yourself. I have never quite seen what the point of this may be.
One corollary is that you can’t lay the table out flat on the floor, since that would require the deck to be fully open while the legs are still folded fully into the underside of the deck. The cables prevent this configuration. BUT, some tables include a quick-release lever that either disconnects the cables or loosens them even more, so you can lay the table out flat on the floor with the legs fully folded in. (This is used for Reiki massage or Shiatsu, I forget which.)
Just clicking on a few of those images, the cables appear to be there for stability and/or to keep it from rocking. Some of those sites even go on to mention that the cables pull tight(er) when there’s weight on the table.
There’s also youtube reviews of tables, the cables look taut in those as well, and I’m not sure I understand why you can’t open the deck and leave the legs folded under and set on the floor. What difference does it make what’s going on with the cables if the legs aren’t extended?
I’ve got one in front of me now. The cables are fairly taut; there’s a looser stretchy thing that comes down from the top of the table and under the two cables that run lengthwise. From it’s position I think it pulls themmain cables upward when the table is folded.
On my table, and some others I’ve seen, they’re definitely slack (sagging). To be sure, I never specifically looked under a table while someone is laying on it but it would never have occurred to me that it makes a difference. Most tables have a solid plywood deck that doesn’t sag when someone lies on it.
I think that, in a network of cables like some of those tables have, some of the cables might be taut, more-or-less, while some others may be sagging. (Now I’ll have to set up mine again one of these days and take a closer look.)
Well, okay. I’ve never read or heard or noticed that before – although as I said, I never actully looked at the cables other than while I’m setting a table up.
As I questioned in the OP, I also wonder what the point is, but at least some tables (mine included) are definitely rigged like that. Some of the wires are attached to the legs, in such a way that when you unfold the deck, it pulls the legs out. ISTM most tables work like this for whatever reason.
Shiatsu is commonly done on the floor or a table on the floor (not Reiki; I just looked it up), and many tables have some specific way to set up a table flat on the floor. See this description of Shiatsu:
Google the words shiatsu massage tables quick release cable to find any number of massage supply sites selling tables featuring this.
Okay, how about the other related question: Can you lay your table flat on the floor? When you unfold the deck, does it pull the legs out at least part-way? Does it look like the table would be wobbly without the wires?
The point about the top sagging or not saggng was, how does the presence or absence of a person laying on the table affect the tension on these cables?
Anyway, I just dug my table out of the dust (haven’t used it for several years) and took a look. More, next post . . .
All of the weight of the table and the subject plus the massagerist pushing on him gets concentrated where those legs are attached to the table top. Any force not directly downward on the legs will cause those legs to move unless something stops them, and if they move the hinges where those legs are attached will deform and fail. The cables transfer that force to the other legs and the table top to stop the movement and distribute the force to more points on the table.
Okay, I just dug my table out of the dust (haven’t used it for four or five years) and set it up.
It resembles the description P-man wrote several posts up: Only two cables running lengthwise, with a stretchy elastic loop around them that seems to work as P-man described. In fact, here’s an exact picture of it.
Note the kinda-sorta-locking, hinged diagonal braces running from the lower part of the legs up to the center of the under-deck. The cables attach to the middle of those braces, where the braces are hinged. Okay, they’re fairly taut when fully open. As far as I can see, in this model, they might be the only thing that keeps the legs from spontaneously collapsing. (Contrast with your typical office folding table, which always has some sort of locking mechanism to keep the open legs open, which this table seems to lack other than those cables.) On this table, the legs sort of lock in the full open position, but not very securely.
Under the deck is a label with instructions. It explicitly says that the cables should be “tensioned slightly” when the deck is fully open. It also has instructions to release the cables for Shiatsu use, for tables equipped with that option, which this table seems not to be.
This configuration of cables definitely prevents the table from laying flat on the floor. If you open the deck, these cables pull the legs about half way. With the table laying on its side, if I fold the legs on one end in, it pulls the deck partly folded. If I fold the legs on the other end, it pulls the legs on the first side out again. You can’t have all the legs folded in and the deck all the way open all at the same time.
Some other tables have a more complicated network of cables, and these are what I was more thinking of in my OP. I’m going to look for more pictures of those now . . .
Okay, I clearly see the need to do what you say here about re-distributing the forces on the legs and the hinges. But in my particular case, I can only partly see how the cables are accomplishing that. They do appear to distribute some forces (in the direction of the long axis of the table) from the diagonal braces of each end to the other end. Not so clear how that’s protecting the hinges where the legs connect to the deck.
That’s from stopping the movement of the legs. They’re secured at those hinges, when they move that’s the fulcrum, and the forces are concentrated when they pass from the table top to the legs at those points. There are a lot of compression loads on the hinge there, the bracing is under tension and tension members are much stronger by weight and volume than compression members making the table lighter that way. So tension bracing is limiting the motion of the legs altogether, which limits the motion at the hinge, and reduces the compression on the parts of the hinge.
Here are some pictures of some other tables with very different (I think) constructions, showing a whole morass of cables, not always shown very distinctly.
The second image is similar to the table I’ve used before, but I haven’t actually used or even seen one like that for several years. As best I can recall, at least some of those wires are slack when the table is open – at least on the tables I’ve used. It’s not so clear if the pictured table is like that.
Anyway, what is the advantage of wire cables as opposed to some strategic arrangement of solid braces to redistribute all the forces?
Is it just to reduce the total table weight? (These tables are supposed to be portable, after all.) There are other weight-reduction technologies that make a lot of difference. The Oakworks table (the one I pictured three posts above) weighs 35 pounds. The plain-old Pisces table (second link in this post) weighs just about 20 pounds. It has all-aluminum frame and the deck is made of vinyl webbing like an outdoor chaise longue (like this picture) instead of wood. That’s how they keep it light-weight. They might have a patent on using vinyl webbing for a massage table deck, though.
Weight and cost of materials I’d think. Compressive strength is always heavy and large, or else requires a lot of tensile strength material to make it work. Those tables are probably about as strong as an ordinary folding office table without the extra bracing. And if you watch wrestling you’d see those things collapse rather easily.
Maybe even stronger, I hope! How much weight do you think a typical folding office table should hold?
The Oakworks table (wood deck and legs, 35 pounds) is explicitly rated for 450 pounds.
The Pisces table (aluminum frame, vinyl web deck, 23 pounds) is rated for 500 pounds. (Some of their advertising pics show a lightweight-looking female masseuse carrying it with one hand.)
You mentioned that office/card tables have a mechanism that locks the legs in place. I think that’s half of the deal with the cables. Part of it being that the cables keep the table from rocking, but they’re also what allow you to set up and break down the table without having to lock and unlock each (or each pair) of legs. Once the deck is flat, the legs are locked, as soon as you start to fold it, they flatten.
Most people have seen this type of table at some point. When you pull the legs out, a diagonal piece comes out that needs to be mechanically secured. Usually either two pieces slide past each other and snap together or a ring falls over/past the joint. When it’s time to fold it, you either hit it with your hand or slide the ring back up. However, imagine if it didn’t have either of those, you could accomplish the same thing by setting the table up and then running a cable from one angled bracket to the other. That would prevent it from folding back up.
Now, if you look at this video, that’s exactly what’s going on. The cable goes from one joint to the other which helps open the legs for you and keeps them open as you flip it over. That should make it much easier and quicker to open and close. Especially since it’s typically going to be just one person opening and closing it.
