I need help on figuring out how to use automotive gas lifts to raise and lower a basement trap door. The door dimensions are:
1 3/8″ solid door blank with 3/4″ oak flooring 30″ * 80″ size I used Soss 220 hinges, worked great; with a Baldwin 0395 recessed latch ,nice; I have read some posts that used gas lifts to help open and close. But no info on the practical application of. What I need is mounting hardware and info on what type to use. The gas lift catalog has open/closed and weight capacity but is there a formula I could use to get the right one? Mounting hardware? Someone has cracked this nut I hope.
Replies
One Formula: leverage
You need to figure out how much the trapdoor weighs, and then figure out how much lift where, will lift it. Easiest way is with free body diagrams.
Most of the lift companies also sell the mounting systems. Thier catalogs might show you how to do the calcualtions.
This isn't hard to do, but very hard to explain clearly without pictures.
Assuming the door weighs 300-lb, and the hinges are on the long side:
Think of a lever lifiting a load, with the hinge as the fulcrum: When you lift the free edge you are using a lever with the load centered on the lever at the center of mass of the door. Your leverage ratio is 30:15 or 2:1, so you are lifting half the weight, or 150-lbs.
If you move the lift point to the middle of the door, the load you see doubles, because your leverage ratio is now 15:15, or 1:1, and you see, the full 300-lbs, because you are lifting at the center of mass.
If you move to 10-inches from the hinge you are seeing a leverge ratio of 15:10, or 1.5:1, and your load is 450-lbs. At 5-inches, the leverage ratio is 15:5, or 3:1, and you are lifting 900-lbs.
Now comes the tricky part, as you lift the door from flat to vertical, the load drops to zero, as a cosine function.
So the trade offs in the design are, the closer to the hinge you get the stronger the spring has to be. Versus, the longer the spring gets, the more room you have to have for it to work in.