Stage Screw Thread

[bobgaggle]

Anyone know the thread size on a stage screw? Looks ACME to me, no idea if its standard or some proprietary or obsolete thread...

 

[BillConnerFASTC]

Interesting question. Mutual Hardware calls it "Vise-type thread" and when I googled that, the answer seemed to be no standard. The thread seems somewhat trapezoidal in section, and I think acme is very rectilinear.

I gard school, we used knife thread inserts and made our own screws. Typically used 5/16-18 machine screws. The option of different bolt heads instead of the big stage screw handle was nice. Grommeted canvas - like for a ground cloth - was very neatly anchored with flat head machine screws - for instance.

 

[bobgaggle]

This is one of those scenarios where the insert is in the floor already and the new set piece can't accommodate the 1" long thread on a stage screw. Was hoping I could just buy an acme rod and put a knob on it...

 

[BillConnerFASTC]

Got it. Seems like a tough request.

Is it that difficult to replace insert? IIRC 5/16"- 18 inserts used 1/2" paddle bit (filed a little so you could drive insert with it) so maybe a 3/8" -16" uses a 9/16" hole - same as Mutual Hardware's Stage Screw. Just a thought.

 

[DrewE]

Interesting question. Mutual Hardware calls it "Vise-type thread" and when I googled that, the answer seemed to be no standard. The thread seems somewhat trapezoidal in section, and I think acme is very rectilinear.

Acme is trapezoidal with a 29 degree included angle. Standard machine threads have a 60 degree included angle and are nearly triangular, so Acme is looks rather more rectilinear than them, but it's not a square thread.

The pictures I can see online of Rosco steel stage screws do appear to me to have a square thread, but they aren't exactly high resolution. I don't have one to stare at in person. In any case it should be a relatively straightforward job for someone reasonably skilled to make one of an appropriate length using a metal lathe, though of course such a one-off screw would not be specifically load rated or any such thing. It may be easier and cheaper to take some metal stock and build a little clip or bracket or spacer to adapt the scenery piece to use the existing stage screws if that is a reasonable possibility.

 

[JonCarter]

Stage screw thread???

 

[bobgaggle]

Stage screw thread???

Im asking about the slightly newer version of the classic stage screw.

 

[bobgaggle]

Got it. Seems like a tough request.

Is it that difficult to replace insert? IIRC 5/16"- 18 inserts used 1/2" paddle bit (filed a little so you could drive insert with it) so maybe a 3/8" -16" uses a 9/16" hole - same as Mutual Hardware's Stage Screw. Just a thought.

The long answer is that we use standard stage screws everywhere on these cruise ships, everything has to be screwed/braked/locked down because boats have a tendency to not stay still. We're building a new show, and had most of a scenic unit already built, when we were told it needed to break down for storage on board. Luckily it had already been designed to break for shipping, but the plan was to assemble it once on board with standard hex bolts and nylocks and be done with it. Now that it needs to be assembled and disassembled for every performance, we wanted to switch to stage screws since the threads on both the screw and insert are far more robust and can withstand more abuse than a standard thread. The two bits getting fastened together are a 1x1 aluminum framed flat and a plywood decked wagon. We want to put the plug in the deck and screw down through the aluminum, but alas, the aluminum is 1" thick and the screw has a 1" thread length. I hoped I could just buy a longer screw rather than modifying the already built set piece.

As an aside, we've since come up with a different solution, add a little tab with a hole in it.

 

[RonHebbard]

The long answer is that we use standard stage screws everywhere on these cruise ships, everything has to be screwed/braked/locked down because boats have a tendency to not stay still. We're building a new show, and had most of a scenic unit already built, when we were told it needed to break down for storage on board. Luckily it had already been designed to break for shipping, but the plan was to assemble it once on board with standard hex bolts and nylocks and be done with it. Now that it needs to be assembled and disassembled for every performance, we wanted to switch to stage screws since the threads on both the screw and insert are far more robust and can withstand more abuse than a standard thread. The two bits getting fastened together are a 1x1 aluminum framed flat and a plywood decked wagon. We want to put the plug in the deck and screw down through the aluminum, but alas, the aluminum is 1" thick and the screw has a 1" thread length. I hoped I could just buy a longer screw rather than modifying the already built set piece.

As an aside, we've since come up with a different solution, add a little tab with a hole in it.

@bobgaggle Two thoughts:
a; Why not take one of your stage screws to your favorite bolt and nut supplier and test nuts on it 'til you nail down a thread type and size, then buy longer bolts?

b; During my Stratford Festival daze, we often had productions in rep' with entire decks painted for specific productions. The floors needed to be struck, stored, a different floor set and latched securely between matinees and evenings thus needing to be quick to unlatch, strike, store, lay, latch, yada, yada.
The pertinent trick is how the sections of floor were secured to each other.
The answer was coffin-locks with two short lengths of steel rod welded into one half of the coffin-locks. A peripheral section of floor was laid, a mating section brought to it, the pins of the coffin locks nestled together (preventing any lateral movement while) the Allen key rotated the male part of the lock pulling the floor tightly together. The male pins were welded into the coffin locks in house in one of our shops.
I'll e-mail a former co-worker and request a photo or two for you. Simple. Blindingly quick. Solid. Snug. Pieces of rubber 3/16 to 1/4" thick affixed with glue and pneumatic staples were enough to keep full stage floors from sliding about during performances.
EDIT: Inadvertently misspelled mating with two T's in it.

EDIT #2: @bobgaggle See photo's added illustrating Stratford's current method of reducing lateral movement of coffin locks while cranking the male around, into, and snugging the female. In their original version they were welding protruding round steel rods within the coffin lock's frames.
The attached photos will show you their current, new / improved, version where they're using square stock welded externally which is far faster for them to jig, weld and grind than dealing with grinding the finish off the insides of the locks prior to welding.
The photo's are worth a thousand words each, thus I'll quit typing.
Toodleoo!
Ron Hebbard

 

[BillConnerFASTC]

I know you have it but wondered of you could cut that stop collar off enough to "stretch" it? Or drill to side of aluminum 1 x 1 so stop collar sits on the lower side/