# how to measure torsion spring

**Critical measurements:** Torsion springs come a variety of standardized sizes, so you have to carefully measure the old springs to know what to order for proper replacements. Tables of standard sizes and designs are on the Web, such as here[www.dm-garage-doors.com]. The four critical measurements (all in inches) are:

the wire thickness (which I'm measuring here with a dial caliper; you can also measure the length of a number of closely stacked turns with a ruler and divide by the number of turns in the stack, measuring 10 turns this way makes the math easy),

the inside diameter (not outside!) of the relaxed (not wound!) coil,

the overall length of the relaxed (not wound!) spring coils, not including the winding cones, and

the right- or left-hand winding of the spring. One must glibly quote those figures to the spring supplier, otherwise one's lack of expertise will be obvious, and one will not be worthy of buying the parts.

**Measure springs only when relaxed:** Measurements must be taken on a *relaxed*spring because the winding adds significant overall length while reducing the coiled diameter. If you have a paired design, and one is broken and one is intact, then don't try to measure the length of the intact spring with the door down. A wound spring has 7 or 8 turns adding to the overall length, and will therefore be about 2 inches longer than when relaxed. Measure the lengths of the pieces of the broken spring, which will be unwound, and add them together. As a check, one can measure the length of the intact spring after it is unwound in the procedure to follow below. Be sure also to observe whether the springs are originally of equal sizes, because it is quite possible that they are not.

The various increments of standard wire sizes differ by only about 0.010 inch, so calipers or a micrometer would be the tool to use to be certain of the stepped size you have, or else a trustworthy ruler marked in tenths of an inch to use the measure-10-turns-and-divide-by-10 trick. The most common wire sizes in the US are 0.207", 0.218", 0.225", 0.234", 0.243", 0.250", and 0.262".

Note that I am measuring a spring that is fully relaxed because it is *broken!*. The length of the relaxed, unbroken spring is the specification of interest. It is harder to measure unbroken springs on an intact door because the springs should not fully unwind, even at the top-of-travel. If you can't be certain of the spring diameter from indications on the cones, then you have to go through an unwinding procedure to relax them fully for measurement, or perhaps reckon the size from measuring the somewhat smaller diameter at the nearly unwound condition when the door is at its top-of-travel (although one should not attempt to raise a door with a broken spring).

**Right-hand versus left-hand winding:** Springs are wound or "laid" in either a left- or right-hand orientation. If you were to grasp the spring in your hand, and if your right hand orients the tips of your fingers like the ends of the coiled wire when your thumb points "out" of the core of the spring, then you have a right-hand spring; likewise left (which end you grasp does not matter). (This also happens to match the "right hand rule" of magnetic polarity, if you happen to be knowledgeable in such esoteric subjects.) Another way to identify the winding is to examine the spring vertically in front of you; if the coils facing you rise going to the right, it is right-hand (thus you can remember, "rise to the right is right-hand"), and likewise left indicates left-hand. Another way is to view the coil axially; a right-hand spring winds in a clockwise direction as it recedes away, and a left-hand spring counter-clockwise. Yet another way, not so easy to remember, is to hold the spring vertically and compare the coil shape to the letter "Z" (indicates right-hand lay) or the letter "S" (indicates left-hand lay).

Confused? A last resort is to compare the winding of the spring coils to the threads on an ordinary screw or bolt, which threads lay in a right-handed winding along the axis.

An enantiomorphic (mirrored) pair of springs, such as my standard door uses, will consist of one left-hand and one right-hand spring. Note that this "right" and "left" has nothing necessarily to do with whether the spring is mounted on the left or right of the center bearing plate. Indeed, with my standard door, if you stand inside the garage, facing out, then the spring to the left is a right-hand-wound spring, and the spring to the right is a left-hand-wound spring. The photos above and below of the broken spring show that it is a right-hand-wound spring.

**End treatments:** Torsion springs also are made in a variety of end treatments. The "standard torsion end" is most common, as is pictured in my examples, consisting simply of a short, straight length of wire projecting tangentially. Various non-standard end treatments have longer "ears", U-turns, ends bent in toward the center or along the axis, or even loops. Non-standard ends are used in end fasteners peculiar to various manufacturers, which would seem to serve mostly as a guarantee that you buy overpriced replacements from that one source.

The replacement springs in my case proved to be 0.2253 wire size, 2.0 inch (inside) diameter, and 24 inches long, in a pair of one left- and one right-hand winding. Actually, the old springs in these pictures were a slightly smaller size, but another similar door on this garage was better balanced by that size. Whoever installed the old springs didn't quite get the weight and size just right; it is not unusual to find a repair service installing a slightly off-balance spring size that happened to already be on the truck during the service call. My electric opener had no trouble handling the small imbalance. But since it is safer to reduce the electric operating force as much as possible through careful balancing, I chose the size that was working better on the other door. The Chamberlain brand electric openers (also sold by Sears) I have incorporate a plastic worm gear that tends to wear out after some years of use, requiring a disassembly and installation of a $20 repair kit; this wear is minimized by a properly balanced door.

Correct spring size is determined by factors such as the weight and height of the door. You cannot substitute a different spring and just tighten or loosen the winding to make it balance the load. Why? To maintain cable tension under all operating conditions, the spring must retain about one turn of unspent wind-up at the top-of-travel position, which with the lift drum size and door height predetermines the number of turns of winding at the bottom-of-travel; and furthermore the torsion of the fully-wound spring at the bottom-of-travel must be slightly less than that needed to lift the weight of the door when translated by the lift drums.

Although the door weight and drum size determine the maximum torque (termed MIP, maximum inch-pounds) needed from the fully-wound spring(s), the spring selection for a given door can still be varied to adjust the cycling stresses. A heavier wire on a larger diameter or longer length will produce the same torque as a lighter wire on a smaller diameter or shorter length, while undergoing less stress and therefore increasing expected cycle lifetime. The heavier spring will cost more but last longer, so this is another design trade-off. Calculating these spring sizes in the field is done using a book of tables (or the software equivalent) that we cannot provide here, although you will find the formulas to estimate spring properties below. If you can accurately provide the weight of the door, or the size(s) of the old spring(s) (assuming they were well-matched to balance the door), then a spring dealer should be able to tell you which spring sizes will work for you.

A spring design manual, also called a rate book, gives tables that relate the torque constant ("rate") and maximum turns for springs of given wire size, diameter, and length. For example, a typical page in a rate book would show a table for a given wire size and inside diameter, the maximum inch-pounds (MIP) of torque available for a standard lifetime of 10,000 cycles in that size, the weight of the spring per linear inch, and the rates of the spring (as IPPT, inch-pounds per turn) for each of various lengths. From these figures one can calculate the lifting capacity, substitutions, conversions, and cycle life upgrades for a door of given weight and drum geometry. The weight-lifting capacity of a given spring is calculated based on its torque constant (IPPT, or inch-pounds per turn), which is the rotational version of the spring constant that characterizes the spring. The IPPT constant is found from tables giving IPPT for given spring dimensions (wire-size/diameter/length). The same tables may indicate the maximum number of turns for various expected lifetimes in cycles. The torque required to balance a given door can be calculated from the weight of the door times the moment arm of the drums (as we do below under "Calculating the Forces We Will Be Handling"). The ultimate torque of the spring in the fully-wound condition is the number of turns (when fully-wound) times the IPPT constant. Choosing a spring to balance the door then simply requires matching the ultimate torque of the spring to the balancing torque.

**Beware of improprer prior installations:** Sometimes the existing door installation is not correct, and the old springs should not be used as a specification for replacements. For example, the old springs might have been replaced with incorrect sizes because the last repairman didn't have the right one on his truck. If your door has never worked quite right, something like this might be the cause. To correct this, you must use the weight of the door to specify the spring, either from a spring rate manual giving spring torque constants, or from the formulas below.

**Unmatched or mismatched spring pair:** You may find that you have a pair of springs that are different sizes. This mismatch may be a normal application, since the total torque on the torsion shaft is simply the sum of the torque contribution of each spring (indeed, very large doors can be lifted with 4 or more springs along the torsion shaft). The sum of the torque rates determine the lift; and dividing the torque among multiple springs does not change this. Some repair shops even apply mismatched pairs deliberately, since a few stock sizes of springs can be combined to fit a wider range of door weights than only matched pairs. For example, a technician may carry springs in increments of 20 lbs of lift, and when using pairs this allows a 20 lb increment in possible choices instead of 40 lb increments. Or, one spring from a pair may have broken and been replaced with a spring of equal torque rate but different size than the original.

Having a mismatched pair makes it difficult to specify the correct matched-pair replacements. To obtain replacement springs for a mismatched pair, you can either specify the same odd pair, try to calculate the equivalent matched pair sizes, or (this is the best method:) measure an accurate door weight and calculate the right spring size(s) "from scratch". The spring seller should be able to do the calculations from your accurate measurements of weight, height, and drum size; or you can attempt the calculations yourself using my engineering formulas below.

**Uncentered center bearing plate:** The center bearing plate need not actually be in the center. It doesn't much matter where it is, since the purpose of the bracket is to anchor the spring ends. This anchoring must be secure, since all the torsion is held together at that point. On a stud-framed wall, this bracket may be placed over the stud closest to the center rather than exactly at the center of the door opening.

# how to measure the garage door

## How to measure what size of garage door do you need

In burlington NJ area most of the garage doors have standard sizes,

but when buying a new door it is very important to take the right measurements and

to make sure that your new door will defiantly going to fit to the frame

opening, a small different in size can make easy job to a nightmare. The tools that you will need are

tape measure pan and paper.

If you already have garage door and you just went to replace

the panels it’s not a problem just measure the existing wide and high of the

old door and then you be able to determine if the garage door that you have is standard

or not.

When replacing just

the panels without the tracks you HAVE to measure the thickness of the panel,

the thickness in most of the old wooden doors in Princeton NJ is 1 3\4 so if

you will order new steel overhead door with a thickness of 2 inches you may

have a difficulty to install the new door .

But if you don’t have any existing door that you can measure

so you need to follow those steps:

Step 1

First we will need to take the Measure for head room so

there is enough room for the garage door to actually operate. Make sure there

are no pipes or framing members in the way, the minimum distance from the end

of the door to the Ceiling must by at list 6 inches if you don’t have enough space

you can use low-headroom tracks

Step 2

Measure the width of the door from the actual structural

member, not the trim piece. Door sizes are always quoted WIDTH x HEIGHT and are

sold to fit the opening size, i.e. a 8 x

7 door will actually be slightly smaller

so that it fits into a 8' x 7" opening with the necessary clearances.

Step 3

Measure for side room (the size from the beginning of the left

frame to the left wall): 3-3/4" is required on each side for installation

of the vertical track for standard extension or torsion springs, or EZ-SET®

Torsion Spring. 5-1/2" is required for EZ-SET Extension Spring.

That’s it now that you have all the measurements and you now

for sure that the new garage door that you about to order will fit perfectly to

your house the next step will be to choose the quality and style for the new

garage door