Everything there is to know about Nosag Springs

Help, my zigzag spring is broken. Can I repair it myself?

Where can I buy a new no-sag spring? What different types of sinuous springs are there? What is that elongated flat spring in my sofa called? How is a no-sag spring actually attached?

Do you recognize yourself in one or more of these questions? Then read on, because chances are you'll find the answers to your questions here.

Or jump straight to the relevant chapter:

• Basic knowledge: everything about springs and accessories

1. The no-sag spring, also known as a sinuous spring or zigzag spring
2. The wire thickness of the spring
3. The pitch of the spring and the dimensions of the spring
4. The shape of the spring
5. How are no-sag springs attached?

• The repair

1. Precautions
2. How to replace a no-sag spring or clip yourself
3. The Finishing
4. Connecting with border wire, cord, or elastic straps

Basic knowledge: everything about no-sag springs and accessories

Fig. 1. The No-Sag spring

The No-Sag spring, also known as a sinuous spring or zigzag spring

The wire thickness of the no-sag spring

Fig. 2. The spiralette

Unlike the spiralette (fig. 2), which is no longer available, the arcs of the no-sag spring move back and forth in a wavy motion. A major advantage of this is that you don't get moving steel-on-steel action. This first extends the lifespan, and second, the no-sag spring is silent, which the spiralette was not.
(More information about the spiralette can be found in this article)

The spring is made of spring steel, and to create different stiffnesses, they are made in various wire thicknesses: 2.8mm, 3.0mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, and 4.0mm. The thicker the spring, the heavier the spring. Springs with thinner wire thicknesses (2.8 to 3.4mm) are ideally suited for backrests, which have nothing to bear but only need to provide counter-pressure. Springs of 3.6mm and thicker are ideal for seats, where the entire upper body must be supported by the spring. Here, the deeper the seat, the thicker the spring.

A frame where no-sag springs are incorporated must be provided with a sound framework that cannot be disrupted by the tension of the springs. Generally, for the seat frame, two commonly used solutions are employed:
- a framework of heavy beech battens, reinforced with an extra bracing rail or brace panel per seat division
- or a framework of steel tubes, also with a bracing rail per seat division

Regardless of whether the furniture has a chipboard frame or a heavy beech frame, these are the minimum requirements for a no-sag spring frame. In contemporary new furniture, no-sag springs are rarely used for the back anymore; elastic webbing usually suffices. For the seat, they are used all the more, and by far the most common wire thickness is 3.8mm. This is because the load-bearing capacity can also be regulated by adjusting the distance between the springs, instead of choosing a different thickness of spring.

The pitch of the spring and the dimensions of the spring

Fig. 3. The pitch of a no-sag spring

Since the original British patent holder of the "No-Sag Springs" no longer exists, there is no longer uniformity in the width of the spring and the size of the spring's pitch. The only thing still agreed upon is what is called a full and/or half pitch of the no-sag spring. For example, our springs are approximately 4.5cm wide, and the pitches from start to end are approximately 4cm in size. However, we also often encounter springs that are wider, sometimes with pitches up to 6cm in length. When replacing a spring, this must be carefully compared: if you want to replace one spring in the middle of a seat, it can deviate so much that it creates a hump or dip in the seat. Or that it is simply noticeable due to the difference in seating comfort.

Fig. 4. No-sag spring on a roll

The shape of the spring

The first springs were supplied on large, long rolls of 30 to 50 meters, perhaps even longer, to the furniture industry (Fig. 4). The furniture manufacturer then had to cut the spring to the desired length themselves. This resulted in the springs being almost all round, but never equally round everywhere: the curvature on the outside of the roll is naturally much less than the curvature you see in the middle of the roll. This strong curvature of the spring also ensures that the spring can never be stretched flat, with the result that the spring surface in the middle is 5, or sometimes 10 to 15 cm higher than the top of the frame. You then have to settle for a convex seat, or equalize the height difference between the low sides and the high middle with a base filling.

Fig. 5. Ready-made round no-sag spring

Of course, the no-sag spring may have already existed, but developments in this area were certainly not static. As the spring became more and more used in the furniture industry, it became very attractive for furniture manufacturers, to reduce labor costs, to have the round no-sag springs supplied in a pre-arranged standard size. The springs no longer needed to be cut; they could be assembled directly from the pallet into the furniture.

Fig. 6. Ready-made slightly curved no-sag spring

And now that the production of the spring could be customized as desired, it also became attractive to have the no-sag spring with only a slight curve produced. When this no-sag spring is stretched in the frame, a flat seat is now created. This offers many advantages:

• A round spring only begins to do what it's supposed to do (spring) when it's bent downwards as far as it stands upwards in its unloaded state. The flat spring springs immediately.
• Because a round spring must first bend so far, there is a risk that due to the back pressure (and due to the fact that the human sitting surface is not flat), it does not bend straight down, but slides sideways or, in the worst cases, even flips over. To prevent this, the no-sag springs were also connected with cord, border wire or elastic straps. Although this is not necessary with flat springs, elastic straps or connections are often found in them, because people want to increase the bearing surface with them. However, this was NOT the original reason for the connection.
• Because a slightly curved spring is stretched flat, a protective fabric and a flat filling can be applied directly over it. This opened up new possibilities for high-quality, sleekly designed furniture.

How are no-sag springs attached?

Clips, tube hooks and clip strips

Nowadays, there are various ways to attach no-sag springs. The most important thing is that they meet one main condition: the attachment must be designed and attached in such a way that the spring, after assembly, hangs 'freely' within the frame. In other words, the spring must not rest on or over the rail to which it is attached. This is because the spring, both round and slightly curved, is inherently round. If you attach it on or over the rail, it will eventually work itself loose. This must always be taken into account, both when choosing the type of attachment and when determining the size of the spring.

What might also be noticeable in the images (fig. 7 a-d) is that all fasteners, from clips to clip strips, are entirely or partially made of plastic. Even the first clips, which were a predecessor of fig. 13a and largely looked the same, were mainly metal with a small piece of plastic in the inner curve. The reason for this is that no-sag springs move when in use. And moving metal on metal will create an annoying sound that no one would want to hear from their furniture. A plastic coating around the clip or tube hook, or a clip made entirely of plastic, prevents this problem.

Both the standard clip and the plastic clip can be attached in multiple ways. As you can see in the video, this can be done with screws, but the first clips were fastened with corrugated nails. These are a type of nail with a serrated edge on the shank for more grip. Of course, this method of assembly takes a lot more time. In the industry, they switched to the tacker, an industrial upholstery staple gun, quite early on. Long staples were used for this. This resulted in enormous time savings but came with an equally significant disadvantage: staples, even upholstery staples, are made of a much softer metal, which means that even well-mounted clips can still work loose under tension over time. Simply because the staples eventually break and no longer provide sufficient grip to keep the clips in place.

For the placement of the springs, the center-to-center (C-t-C) distance of the springs is determined based on the depth of the seat. This will generally vary between 8cm and 12cm C-t-C, and the deeper a seat is, the closer the springs will be to each other. After this distribution has been measured and marked, the clips are attached. The advantage of the full plastic clip compared to the standard clip is that it comes with a 'spacer', a kind of corner piece with which you slide it against the rail, so that it immediately gets the correct overhang over the rail. The disadvantage is that due to its barb, this clip is only suitable for seats where the rails are perfectly straight opposite each other. If you were to use it on a round rail, the no-sag spring would already be half hanging out of the clip, and it would not be securely attached for a long lifespan.
When the clips are in place, the springs are hung in them. As mentioned, with the plastic clip, that's all that needs to be done; the barb keeps the spring in place. However, the standard clip then still needs to be tapped flat and finished with one or two final nails, screws, or staples to keep the clip closed.

The most recent development for attachment to wood is the clip strip. These are supplied in advance in a standard C-t-C size, in rolls of a few hundred clips per roll. You cut off the desired length, shoot it onto the rail, and simply hang the spring in it. And this is not even the latest variant: there is a newer one, which has been used very often, but has at least already been removed from the market by Dutch wholesalers. It was drastically worse. To save on material costs, the eyelet was made from three or four plastic rings, and then attached to the strip with a few spot welds. The result is that in by far most of the furniture in which they were used, the eyelets broke off the strip within 1 to 2 years, which, of course and quite rightly, led to a lot of warranty hassle. In a significant part of the industry, where they are already used, they have therefore reverted to this first variant of the clip strip.

Fig. 8. A ready-made no-sag tube frame for an underseat, unstuffed

The last form of no-sag attachment is the no-sag tube hook or tube frame hook. This form of attachment itself has changed little over the years. Although the first tube hooks were uncoated, this was quickly adjusted. However, this variant did lead to other developments. For example, factories emerged that began manufacturing standard ready-made tube frames of approx. 55x65cm, so that a furniture manufacturer only had to make the frame and cushions. Or factories where you could order ready-made tube frames in the size a furniture manufacturer needed for their design. There was also the additional option of having the frames delivered already upholstered. Larger furniture could also be developed, where the wooden frame was reinforced with a metal inner frame, to which the springs could then be attached. All in all, the tube hook opened the way to countless new possibilities.

The Repair

How do I replace a no-sag spring or no-sag clip myself?

The preferred method for installing a no-sag spring is always on the top of the seat rail. An upholsterer will therefore always strip a piece of furniture down to the frame when they need to repair and/or replace the internal components. They will then completely detach the springs where necessary, install new clips, and then reinsert the old or new springs.

However, this ideal scenario is unfortunately not always possible. Often, the furniture is still in excellent condition, and only one or a few springs have broken, or the clips have come loose. In that case, the furniture will certainly not be stripped bare; a temporary solution will be chosen.

When the attachment involves tube hooks, the spring can be easily hooked in from below if the hooks are still intact. If the hooks themselves are broken, it becomes a bit more difficult, but in most cases, they should still be replaceable from below. The same applies to attachments with hard plastic clips and clip strips when they are still in good condition: unhook the broken spring, hang the new spring in. However, if these clips are broken, it will be a bit more challenging...

In that case, you will need to remove the old clips, because installation from below is only possible with the standard clip and the old ones will get in the way. Once the old clips have been removed, mount the standard clip to the INSIDE of the rail (as shown in the video). Always do this with screws; nails or staples will come loose in no time, and then you'll have to start over. Also, mount the clip high enough so that the spring protrudes slightly above the rail (where it was before), The standard clip is screwed to the wood with the long side first. Then the spring is hooked in with the curve facing the seat, the short side of the clip is lightly hammered, and then it can be screwed in place. Do this in exactly the same way on the opposite side, and the job is done.

The finishing

Connecting with no-sag elastic straps, connecting cord or border wire 

One of the common finishing touches is connecting the springs. The frequently used argument for this is that it increases the bearing surface by distributing the force over multiple springs rather than just the one you're sitting on. If the springs are tied together with connecting cord or border wire (a 2 to 3mm thick iron wire), this is somewhat true, but with no-sag elastic straps, that distribution is negligible.

The actual reason this technique originated is that the original, roll-cut spring was so curved that it risked flipping sideways when sat upon. To keep the spring in its track, it was therefore linked to adjacent springs, so that it could only collapse downwards in a straight path.

Nowadays, if linking is done at all, it's only done with rubber elastic bands, the nosag elastic bands. Don't forget to also tie the outermost springs to the side of the frame with rope or elastic. Because the elastic bands are under tension, they would otherwise pull all the springs towards the center of the seat. The elastic bands will also need to be regularly checked and replaced. Because they are solid rubber elastic bands, they will last at most 4 to 5 years, and then they will be dried out and rotted, thus no longer functional.

Once all the above work has been carried out, you are done. Or almost done. If the furniture itself has an open frame (the springs are standard visible), then the job is done. If it is normally a closed piece of furniture, then for aesthetic reasons a new piece of bottom fabric may also be added. But that is entirely up to you.

Of course, it is possible that something is not yet entirely clear, or that you have comments or questions. No problem, let us know by calling 010-412 42 16 or emailing info@pootendop.nl

Good luck!!