Soundproof door idea..

[rod gervais]

[quote author="Svart"]So far, nothing but drywall. This was a test fit. The drywall buts directly against the door frame with no gaps. This portion will be cut back about 1/4" and sealed with silicone. The hinges will be covered from the front to hide them[/quote]

Svart,

You need to reconsider this application.

Drywall had no strength in it - and there is going to be a lot of shear stress loaded up on those screws.

With a wood backing the stress is taken out as an actual shear of the screw - but with material like drywall it is taken out as a bending stress.

It takes very little to bend a screw - it takes hundreds of pounds of pressure to shear that same screw.

I can promise you that it will not be long with those doors in operation before they begin to sag from the weight of the door on the hinge.

BTW - just so you understand before even having to ask - the bottom hinges are douing very little to carry the door - the act more as a lock to stop the bottom of the door from sagging in - but they act as great hinges when it comes to the top of the door sagging out. So they do not solve the problem you're facing.

This is why I always recommend that people use 5/4 stock minimum for door jambs (that is 1 1/2" thick material) and that the hinges be fastened to the jamb with very long screws.

The hinges are then tied into the jamb AND the framing - everything is solid - and you can have as many layers of drywall as you wish without a care in the world about the door loading.

I hope this was clear so you understand.

Rod

 

[Svart]

Thanks again for the information.

The screws are 1/4 lags, 3 per hinge into 3 2"x4"s screwed together as the load member for the door. I measured the distance between the door and the floor before and after filling. I measure 1/8" total sag. I'll keep measuring to see how much more it sags over time but I don't expect much.

The hinges are bolted to the door with 5/16 carriage bolts, 2 per hinge through the frame of the door. This was slightly preloaded (to account for slop in the hinges) before tightening. I don't think the top hinges are taking any more load than the bottom hinges are. the top hinges are loaded in a way to "pull" them. Once at their pull limit, they act as fulcrums and the bottom hinges are exposed to the "push" stresses. Sorry for the non-technical terms, I only had a short mechanical engineering stint a couple of years ago.. By force, not by choice!

I'll keep reporting back how it's working. I know that it's not really a reliable commercial solution, but this door is mostly a utility door, it should see minimal human traffic.

 

[Crusty2]

Rod is saying there can't be a layer of drywall between the hinge and the framing member. Otherwise, it will fail.

Looks like a nice fit looking at the jamb spacing. Congrats!

Also, keep in mind your fire escape paths. The drop-bolt into the floor is not gonna fly with the fire inspector if that leads to an exit...

 

[Svart]

Yes I understand what he is saying, but 3x 1/4" bolts(per hinge) configured in a triangle with spacing of 1.5" from each other tend to support each other and loadshare. I spread the load between 6 screws and 2 hinges.

 

[Mailliw]

Looks good to me svart!

The drywall brings the screw head out ~1/2", now maybe there is *more* bending stress on the screw than without the drywall, but it is by no means ALL bending stress, and it is hardly a concern IMO.

Good job.

 

[Crusty2]

Think of it this way - when you open the door, the vectors of force shift from parallel shearing mainly on the top hinge, into a compression force on the lower hinge bearing on the drywall. Sheetrock is just dust glued between paper. It's gonna eventually crumble, the hinges will loosen, the failure will accelerate. Simply removing the drywall and building out the frame with solid wood (not plywood) with fix it.

 

[Svart]

I hate to be one to correct others but you are incorrect. There is no shearing force. I do not even consider the drywall part of the support structure at all. This is all bending force and it is applied to all screws equally. You can envision it as the center of the door being a pivot point, the bottom hinges are getting a compression load and the top hinges are getting a pulling load equally.

It takes 250 lbs of force to bend a 3" section of 1/4 zinc coated steel(like my screws) and this is shared between 6 on the top hinges and 6 on the bottom hinges. That makes less than 45lbs on each screw of two hinges or 20lbs each if you count all 4 hinges.


Ah but here is the kicker, those screws only have 1.25 inches of length in which to bend.. That allows them to take more than double the bending strength..


I designed a gantry arm for extending a 15lb camera on an arm 3 feet in length.. It was not trivial in any regard. There was a huge amount of shearing stresses on the bolts that held the arm to it's pivot. I don't remember the number exactly but it was close to 100 ft-lbs. Yes it was that much. It took a large number of screws to loadshare the shearing forces(it had to be adjustable, so no splining.. ).

I did a test today..

I put a car jack under the door and attempted to push the door up slightly. It moved about 1/8 inch, mostly in the hinges themselves. There was minimal movement around the screw areas.

 

[rod gervais]

[quote author="Svart"] I did a test today..

I put a car jack under the door and attempted to push the door up slightly. It moved about 1/8 inch, mostly in the hinges themselves. There was minimal movement around the screw areas.[/quote]


The fact that you did a test that indicated no issue in short term loading doesn't mean there will be no issue in long term loading.

BUT - that hiving been said - tis your door - you do whatever you want.

I would never suggest to anyone that they proceed along those lines (it certainly doesn't met the requirements for best construction practices) but it's none of my businees what you do or what you like.

So leave it like it is and be happy................

Sincerely,

Rod

 

[Svart]

I understand your suggestions and I take responsibility for anything that might happen with the door.

Your suggestions are clearly the most professional way to go here. I was simply rebuffing some of the physics involved, not the construction aspect.

The original door frame was going to have hinges that were like normal door hinges, concealed when the door is closed. I couldn't get (affordable) hinges with load ratings high enough that would fit in this arrangement and still allow me room to add sealing surfaces so I bought what I could and had to place them on the face of the wall.

 

[Crusty2]

Svart,
Those hinges are fine and so are the fasteners. It's the layer of drywall between the framing and the hinge plate that will be a problem. The way it looks to be constructed now (framing/drywall layer/hinge plate), you're relying on the drywall to hold the hinge in place as much as you're relying on the fasteners...

 

[Mailliw]

[quote author="Crusty2"]Svart,
Those hinges are fine and so are the fasteners. It's the layer of drywall between the framing and the hinge plate that will be a problem. The way it looks to be constructed now (framing/drywall layer/hinge plate), you're relying on the drywall to hold the hinge in place as much as you're relying on the fasteners...[/quote]

I don't agree with that. The drywall is being compressed by the hinge plate surface, that is fine...

In order for the hinge to move up or down, all the screws have to bend. And that isn't going to happen as long as they are grabbing enough wood in the frame.

 

[Svart]

Yes that is partially my point. While the drywall adds friction to keep the hinges from moving, I still don't rely on that. the primary support is the loadsharing between a large number of screws that are spread apart from each other. Think of it like a building, the taller and thinner, the easier it is to blow over during a tornado or something like that. The shorter and wider it is, the more force it can take before yield, using the same materials of course.

 

[Crusty2]

Drywall's a finish material not a structural one. It takes almost no compression force to collapse it. It is not resilient; it won't bounce back. The friction you're relying on will be lost. The hinge will start to wander around on the bolts because they are a smaller diameter than the through-holes of the hinge. The hinge is not supported anymore and it will beat the drywall to pieces in a short time.

 

[Svart]

Drywall's a finish material not a structual one. It takes almost no compression force to collapse it. It is not resilient; it won't bounce back. The friction you're relying on will be lost. The hinge will start to wander around on the bolts because they are a smaller diameter than the through-holes of the hinge. The hinge is not supported anymore and it will beat the drywall to pieces in a short time.

And again, I said I am not relying on the drywall for anything. Drywall will take a compression force, but that discussion is for another time.

The screws are the same size as the holes in the hinge. I drilled the holes in the hinge to accept the large screws. Their shanks are the same size as the OD of the threads.. :thumb:

 

[Crusty2]

[quote author="Svart"]

Drywall's a finish material not a structual one. It takes almost no compression force to collapse it. It is not resilient; it won't bounce back. The friction you're relying on will be lost. The hinge will start to wander around on the bolts because they are a smaller diameter than the through-holes of the hinge. The hinge is not supported anymore and it will beat the drywall to pieces in a short time.

And again, I said I am not relying on the drywall for anything. Drywall will take a compression force, but that discussion is for another time.

The screws are the same size as the holes in the hinge. I drilled the holes in the hinge to accept the large screws. Their shanks are the same size as the OD of the threads.. :thumb:[/quote]

Man, :razz: Your're just messing with me now, right???
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[Emperor-TK]

Of course if the drywall does get chewed up over time from multiple compression cycles (and I think it might if the door gets used a lot), it would take about 20 minutes to stick wooden shims under the hinges. I think we are all in agreement that the 1/2" projection of the lag bolts from the framing will not bend in the slightest. No harm , no foul.

Reading back on my earlier posts convinced me that I've been spending too much time in a laboratory lately and not enough in my garage. :green:

-Chris

 

[Svart]

I've been spending too much time in a laboratory lately and not enough in my garage. Mr. Green

Been there. It sure does make it sweet when you finally get into the garage!

:thumb: