Building riser platforms for movie seats, or, "When lag bolts become machine screws"

Discussion in 'Archived Threads 2001-2004' started by David Tolsky, Mar 30, 2001.

  1. David Tolsky

    David Tolsky Supporting Actor

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    I thought I would attempt to share my experience of building my riser platforms for my 3 rows of cinema seats in the dedicated room. The size of the room is basically the size of a 3-car garage. In fact, it sits right on top of one. Of course, when building platforms on a second story floor, there will be no foundation underneath the plywood, but rather a whole lot of air. I decided to use 2 x 6's as the strength of the platform. Where to lay the boards on edge across the floor plywood was determined by laying out a row of seats and marking where the "legs" were to be bolted down. I used very sturdy L brackets with half inch bolts to secure the 2 x 6's in place. After laying out the boards on edge and securing them, it was just a matter of attaching new plywood over the tops for the platform. The seats would get bolted through this new plywood right into the studs (2 x 6's). This plywood would later be covered with carpet pad and then carpet.
    Okay, so what about the first row of seats? They are bolted right to the floor/plywood and certainly not all the posts are going to be bolted into studs under the floor. I was hoping to get lucky and just bolt right into floor board and be done with it. That came back to haunt me. A few sittings and up came the bolts and the seats were not secure. So how do I secure the seat posts? Went to O.S.H. and talked to a guy. He showed me this carded tin foil stuff called "Mr. Grip". It's supposed to tighten the grip of the bolts. I actually bought some of this stuff and brought it home before realizing how ridiculous it was. Then it hit me, Threaded inserts! I would buy these brass threaded inserts with 1/4" threads inside and use 1/4" machine screws instead of bolts. Amazingly enough, after digging around, O.S.H. actually had some (.59 a piece). Well it worked like a charm and the seat posts are secure.
    If you're planning on securing some real cinema seats to an upper floor room, these are some things you may want to consider.
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  2. Joseph Hoetzl

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    Did you have access to the bottom side of the floor via the garage? You could have also put t-nuts (I think that is what they are called...) on the bottom side, and then bolted into that.
    Cheesy T-nut diagram in case I named it wrong:
    It is basically a cylinder with a washer type thing attached to it, with little nail-points that grab the wood and get pulled into it by tightening the bolt
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  3. Ron-P

    Ron-P Producer

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    For my rear deck, I used 2x12s doubled up at 16" OC. Then I used 2 sheets of 3/4" plywood for the top. It is a stand alone deck and I wanted it to be heavy and durable so it would not move. Also, having the doubled up 2x12s and 1.5" of plywood, placement of the chairs was not an issue. I used 2" lag bolts with lock washers and they do not move.
    For the front row, I attached a 2x12 to the front of the back deck using 1/2" galvanized pipe and some -L- brackets. I used 1.5" lag bolts for those chairs. Everything is very solid. I probably over built it, but I did not want any problems.
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