Basic Spring Engineering

When providing service in the field, basic knowledge on spring engineering is vital. Having such knowledge allows you to: 

• Use the inventory you have on-hand more frequently, reducing additional costs 
• Engineer extended-cycle life in springs with higher use  
• Confirm that the correct spring is on an overhead door 

Most importantly, you will efficiently convert and replace springs on-site, saving you and the customer time and money.  

Basic Spring Conversions 

A basic operation carried out on-site is replacing garage door springs. To properly swap a damaged spring, the replacement must be as close to the dimensions of the original as possible. Accurately converting one spring’s dimensions to another is called spring conversion. Calculation of conversion is dependent on two factors: Inch Pounds Per Turn (IPPT) and maximum turns. Keep the IPPT of the replacement spring as close as possible to the original spring. The same rule applies to “maximum turns” as this makes swapping out the springs easier.  

Let’s Use an Example 

To paint a better picture of calculating spring conversions, here is an example that could occur in the field: 

You are on call at a worksite. The customer needs one of their garage door springs replaced. The original spring is right-hand wound, 243 wire, 1 ¾ “ID, 32 inches long. The spring has an IPPT rate of 41.2 and is good for 8.1 maximum turns. On hand, you have some 250 wire springs with a 1 ¾” ID. With all of this laid out, how do we convert the original spring’s dimensions to match the new spring?  

There are two main methods of conversion: through a rate book, or through an industry program or app. 

Rate Book 

Using a rate book to cross reference conversion rates is a time-tested method that lays all the spring’s specs out on a page. The most important specs for conversion, again, are IPPT and Maximum Turns.  

For our example, when you look at 250 wire springs, the 36” –long version has an IPPT of 41.3 and is good for 8.7 maximum turns. Though it isn’t an exact match, the IPPT rates of both springs are close enough to make for a suitable replacement. As long as the maximum turns of the new spring meets the maximum turns of the original spring, it does not matter if the original is exceeded. Seeing that both springs are comparable to one another, the new spring you have on hand will work well. 

Industry Program 

SSC provides an application for the express purpose of expediting spring conversion. The app SSC Spring Engineering does all involved math and calculations for you. It determines the correct spring for the job, converts quickly and easily, and even determines the cycle life of a particular spring. 

For example, we still have the same spring as before (right-hand wound, 243 wire, 1 ¾ “ID, and 32 inches long). After opening the app, select SPRING CONVERSION and enter all known information under the CURRENT SETUP prompts. The remaining specs are then automatically filled in. These specs include: 

• IPPT 
• Max turns 
• Active/Total Coils 
• Weight 
• Cycles 

Under REPLACEMENT SETUP, the potential replacement spring’s specs are filled in. if the wire size does not quite match, press the red “+” button until the wire size is correct. (Keep in mind that the larger the wire size, the longer the spring.) 

Apps like SSC Spring Engineering help to initially confirm that the spring on the door is the correct engineered spring. Through the app’s SPRING ENGINEERING, enter the garage door’s information, including: 

• Assembly Type  
• Single 
• Duplex 
• Triplex 
• Number of Springs
• If the door is duplex, the number of springs is 2 

• ID
• Cycles
• Lift Type
• Standard
• Vertical
• Hi-Lift 
• Cable Drum
• Door Height/Weight/Width 

The app will then produce the exact spring needed to lift the door based on the door specs you provided.