Solid torsion bar for OH door?

[andyvh1959]

My brother asked me about a solid 1' bar for his 16' OH door, which we'll install this Saturday. I have installed five garage OH doors over the decades and I've only used the standard hollow cross-tube for an 8' or 16' wide door. He said a guy he talked to that did OH doors claimed to only use a solid 1" bar for the cross-tube. I said, bunk, until I thought about a jackshaft style OH door opener. A standard opener, human or central OH style pull up from the bottom or from the top, the cross-tube carries/turns the preloaded torsion spring and cable drums. But a jackshaft style lifts the door by applying twist into the cross-tube, turning the cable hubs and pulling the lift cables at the bottom of the lowest panel. So a jackshaft inputs initial twist into the cross-tube which reduces as the panels turn from vertical to horizontal.

So for the Liftmaster jackshaft openers is a solid cross-tube replaced with a solid 1" bar, up to 16' long? Seems overkill, especially from a torsional viewpoint. Seems a cross-tube with a double thickness wall would be more than adequate.

 

[finn]

If I go back to the last century, some long forgotten statics or structures course made a point of the fact that a hollow tube isn’t much weaker than a solid tube, as most of the strength is near the outer diameter. Increasing the diameter is more useful from a structural standpoint than increasing the wall.

Ever notice the diameter of an aluminum driveshaft?

 

[The Cobbler]

I say a solid tube is wayyyy overkill for this application and as above mentioned, not going to gain much if any

 

[jblnut]

It’ll act as a tiny flywheel and keep things moving once it’s moving lol.

 

[MikeC55]

And it will be a lot heavier...

 

[tarmy]

I used DOM tube for mine…

 

[finn]

It’ll act as a tiny flywheel and keep things moving once it’s moving lol.

not much inertia on a 1 or 1 1/2 inch diameter rotating member.

 

[andyvh1959]

I was explaining to my brother that the hollow tube has its strength at the outer diameter, and that a solid bar has little strength to offer for most of its cross section. So he would be better off with a thicker wall tube, and it doesn't need to be 0.125" wall either, 0.09" wall thickness is likely significantly stronger than the stock cross-tube.

 

[racecougar]

The standard hollow tube will be just fine with a jackshaft operator on a 16' wide door.

 

[Jackfre]

Agree that the solid is better for the side-arm opener. I installed one on my door a couple monthsago After having assisted my SIL doing same on his door. His has a solid bar. Mine the pipe type. 5 or 6 weeks into the change noticed the delay in the door lifting and not running all the way up where I had set it. I was expecting this to be an issue as the tube is not the heaviest and deflects some. I re-adjusted and so far so good, Go solid bar if uyou can.

 

[Stuart in MN]

I've never heard of the tube failing on an opener. The springs yes, but never the tube. The opener manufacturer did the engineering and determined a solid bar isn't necessary, install it as supplied.

 

[andyvh1959]

If the torsion spring set screws are properly torqued they slightly indent the tube, which then acts like a pin into a hole. Maybe apply thread locker on the set screws. If the set screws are over torqued the threads are compromised and could loosen. Set screws under torqued they could loosen over time. So it's more the installation issue than the component. I still say a solid bar is way overkill and not needed. A thicker wall tube, maybe. A tube will deflect some due to bending load during assembly. But the tube is all torsion load, not bending.

 

[manwithtools]

Total waste of money and brain processing time in that debate. The load on the tube is the same with a conventional or side mount opener. The weight of the door is born by the springs, it takes very little force to turn the tube or pull the door if the springs are properly adjusted.

 

[no704]

Has nothing to do with doors, but doing formula SAE car in school someone decided to make the halfshafts out of solid. They broke very quickly. The core of the solid bar provided a place for stress cracks to start and propagate. Thats why they are made from tube .

 

[andyvh1959]

Yeah, if the solid bar logic was true, every motorcycle frame would be made from solid bar and we'd likely not be able to ride them.

I think I got my brother to realize the solid bar is not the right course. I'll find out Saurday when I help him install the new OH doors in his shop.

 

[NUTTSGT]

Have him price out that 16' long one inch solid bar and see if that changes his mind.

 

[NUTTSGT]

Has nothing to do with doors, but doing formula SAE car in school someone decided to make the halfshafts out of solid. They broke very quickly. The core of the solid bar provided a place for stress cracks to start and propagate. Thats why they are made from tube .

As to further your reply...

If some of you don't know, the axles on many drag race cars are "gun-drilled" so they are not a solid axle.

 

[andyvh1959]

Total waste of money and brain processing time in that debate. The load on the tube is the same with a conventional or side mount opener. The weight of the door is born by the springs, it takes very little force to turn the tube or pull the door if the springs are properly adjusted.

Not quite. Yes, the weight of the door is born by the springs, they help the door opener (electric or human). But the springs basically assist the wieght of the door so the opener works easier. If I disconnect the track from the opener, it still takes some effort to get the door moving. With a standard opener or human, that is done at the center of the door with no twist on the crosstube. Lets say a 16' insulated door weighs 400lb, and the diameter of the cable drum is four inches. The torque to start the door up is 800 in-lb, 66.67 ft-lb.

But with a jackshaft the motor has to create that 66.67 ft-lb of torque to get the door moving up, and it does it by cranking on the cross-tube, not lifting from the center of the door. So the initial start of moving the door the jackshaft motor has to create more than 66.67 ft-lb of torque on the cross-tube and the corss-tube must be able to resist that twisting force.

Just for the sale of knowing, a 1" low carbon steel tube (36,000psi), 0.063 wall, 192" long (16') at a 70 ft-lb torque load (to start the door up) results in a shear stress of 2022psi. That means the standard tube has a safety factor of 17:1 against twist. Numbers confirm the std steel tube is very capable for the load.

 

[manwithtools]

Lets say a 16' insulated door weighs 400lb, and the diameter of the cable drum is four inches. The torque to start the door up is 800 in-lb, 66.67 ft-lb.

No, it's not 800 in-lb's to lift the door. You calculation ignores the fact the the vast majority of the door's weight is being lifted by the torsion springs (which are exerting far more twisting force on the tube than the opener does). The opener is only lifting the weight not born by the springs.

A properly balanced residential garage door should require only about 15 to 40 lbs of lifting force to open, so worst case the opener would need to generate 80 in-lbs or 6.66ft-lb of torque. So the tube has a 170:1 safety factor as far as the "opener" force is concerned. The tube does however ultimately support the 70 ft-lb's of torque you calculated, however 90% of that torque is supplied via the torsion springs.

 

[andyvh1959]

Well he's seen the light. My bet is he got the solid bar priced and realized its not worth the bucks. Plus, I explained to him, "whats stronger of these two pieces of tubing, a 1" tube or a 2" tube both with the same wall thickness. And which is more resistant to twist?" He said the 2" because its more resistant to bending, and there is more material out in the area of loading. Then he got it.

For overhead clearance where his car lifts will be, he is installing the OH door tracks to follow the 15 degree angle of the truss bottom chord, and he has almost 36" of wall above the OH door header. So fully up, half of the 16' door will still be vertical behind the wall and half will be up at an angle from horizontal. A steel insulated 16' weighs about 170 pounds, so half of that is 85 pounds, plus about 20 pounds for the vertical load of the angled section, leaves a supported load of about 105 pounds on the cables, torsion spring and motor. If the door went fully horizontal when opened there is very lttle load on the cables and spring. I think it is a "high lift" style which may require a different opener.

 

[manwithtools]

A steel insulated 16' weighs about 170 pounds, so half of that is 85 pounds, plus about 20 pounds for the vertical load of the angled section, leaves a supported load of about 105 pounds on the cables, torsion spring and motor. If the door went fully horizontal when opened there is very little load on the cables and spring. I think it is a "high lift" style which may require a different opener.

Any, I'm sorry but you are just not understanding how garage door springs and openers work. The springs are sized and wound to support nearly the full weight of the door. It doesn't matter if the door is horizontal or high lift and angled when fully open, the springs support almost all of the doors weight. The opener just overcomes what little weight is left to be lifted to cause the door to open.

Your brother does not need a special opener, just needs the springs adjusted correctly.

Let me try a real world example to help you understand this. My shop has three 10 x 10 insulated doors - two of them are conventional tracks, the third follows a 4/12 roof pitch. They all have the exact same Genie 6170 jackshaft openers. Pictures follow:

Tracks and openers:



Weight of a horizontal tracked door when the opener is disconnected - or the weight the opener needs to lift:




Weight of the 4/12 (~ 18 degrees) angled track door when the opener is disconnected or the weight the opener needs to lift:




All three doors open just fine as the weight being lifted is within the operating range for a residential opener.

 

[JohnX14]

The doors should be equipped with springs that allow easy hand-operated opening. Any residential operator should be able to open any residential door.

 

[mm08822]

Agree, it is all about the spring loading. Two springs, each on opposite sides of center support bearing provide 95% of the lift.

Schedule 20 tubing is probably the default. Schedule 40 would be an upgrade in wall thickness but solid is a waste on $ and unnecessary weight.