Many years ago when we first posted our residential torsion spring database program, we discovered customers were ordering longer life springs that were so heavy that the shaft would bend from the extra weight.
Because of this we began recommending that customers add idler support brackets if either of their springs weighs over 20 pounds.
And, as could be expected, longer life spring orders for heavier doors weighing 30 pounds or more required different solutions. The more common is to install two solid shafts with a cast iron connecting coupler in addition to the idler brackets. With the additional shipping this solution costs an additional $300-400.
A less expensive option that costs less than $50 is to convert a two spring system to a four spring system using smaller springs. Rather than install idler support brackets customers can install spring anchor brackets, such as our more popular SAB-450K.
Here, the two center springs are mounted as before. The two outer springs mount to what would have been idler brackets. The difference is that these brackets include the extra bolts and nuts for attaching the stationary cones to the brackets. Both springs to the left of the center support bracket are right wind; the two springs to the right are left wind.
One problem with converting to four springs can be limited shaft space. When calculating the space needed for the springs, first measure the distance between the drums. The wound springs, cones and brackets need to fit inside this space.
Next, determine the wound length of each spring. On 1 3/4″ and 2″ springs the cones for each spring require 2.25.” Add to this the width of the coils you add when winding the spring. On standard seven foot high doors figure eight coils and multiply this by the wire size. For example, 41.75″ X .2253 = 1.8.” Hence, 2.25″ for the cones + 41.75″ for the length of the spring + 1.8″ of turns = 45.8.” Add to this the gaps between the coils on the cones which is sometimes as much as 1/2.” Figure an additional 1/8″ for the thickness of the bracket.
This Wound Torsion Spring Lengths Spreadsheet may come in handy.
If there is not enough space on the shaft, you can always increase the inside diameter of your springs. If you have 1 3/4″ ID springs you can easily convert to 2″ because all the bolt holes are the same. If you have 2″ ID springs you can convert to 2 5/8″ ID and use the same brackets if the bolt holes are slotted. This torsion spring inside diameter converter should help.