Braille Curtain Weight Issue

[JVV]

We are using a piece of Scrim as an Oleo Drop and need to gather it overhead Braille Curtain style. We have 5 lines running equidistant across the 36' long - 18' tall drop. Once the curtain gets about half way up it becomes noticeably heavier and the operation becomes jerkier. We are using an unweighted manual hand line. Right now it only takes one person to run it and i don't really want to add a second. My thought is that if I add a sandbag at the top of the hand line where the clew is, then it will raise the bottom of the curtain until the two loads balance out. So how do I add weight to the hand line half way down the run? Would doing a block and tackle for the hand line help?
This is mostly because the operation is not smooth, but also a bit because it is out of weight.
Any thoughts are appreciated.
JVV

 

[kicknargel]

Does it get jerkier simply because it's getting heavier and harder to pull, or is there a bad spot of rope, or something getting caught on something? If the pull gets less smooth at a certain point, you may have a problem. For instance, what are you using for pulleys? Maybe as weight gets added, you are exceeding the weight they can handle smoothly and are picking up a lot of friction. If so, this is a dangerous situation.

If it's really just that it's getting too heavy for one operator, I think you've identified your solutions. If there's a bottom pipe on the drop, you could add enough counterweight to balance that only. You could use a block and tackle (But I'd suggest only 2:1) to make it move half as fast and not quite half as heavy (you add some friction with each additional block). Or add an operator.

 

[MPowers]

If the jerky is due to the operator pulling down, pausing to get a higher grip for the next pull as the weight increases, you need either (1) a stronger, heavier operator or (2) two operators working together but 1/2 a pull out of sync so the pull is left, left, right, right with equal timing of the pulls. The two operator method does not need to be fast, just co-ordinated smooth.

If the jerky is due to mechanical issues, I can't help you except to tell you to do a through inspection of all lines, sheaves and pick points on the scrim during operation to determine the issue.

If you really want a mechanical solution, use a compensating chain. Find a chain size that weighs about the same per lineal foot as the scrim weighs per full width vertical foot or slightly less, cannot be the least bit heavier. Build a one-off sheave for the chain, flat bottom groove about 2"-3" wide, diameter at least 5 times a single chain link. Make the flanges as least 6" larger diameter. Any good delron or similar plastic, bronze etc. sleeve bearing will work just fine in this application. Pad the groove with one or two layers of terry cloth (has to be replaced every couple weeks on a long run) to reduce chain noise. locate this as close to the scrim rig head block as possible.

The chain is on the same side of the head block/chain block, as the scrim, with about 3' of chain on the operator side. Attach a sand bag on the operator side that weighs 5-10 pounds less than the chain. Attach a 1/4" rope to the lower end of the chain, down to a "floor block" and back up to the sand bag to form an endless loop with just a slight amount of tension (you need something to make the chain go back down as the scrim lowers to the deck.) As the operator pulls the scrim up, the chain transfers a weight equal to that of the gathering scrim from the scenery side of the head block to the operator side.

Hope this helps.

 

[derekleffew]

If a standard sharkstooth scrim, the fabric should weigh about 36 lbs. total.

From Sharkstooth Scrim, <span style='color:red'>FR</span> from Rose Brand :

Width - Weight per linear yard (in pounds)
12' - .6
15'-6" - .78
19'-6" - 1.01
25' - 1.34
30' - 1.64
35' - 2.0
39' - 2.22

From Steel Pipes Dimensions - ANSI Schedule 40 , the 3/4" Sched. 40 bottom pipe should weigh ~40 lbs., for a total of ~75 pounds total for pipe and cloth.

So I'd suspect a mechanical issue "once the curtain gets about half way up it becomes noticeably heavier and the operation becomes jerkier."

 

[tprewitt]

My experience is in permanent installations so I may be misunderstanding the rig design. "Braille", around our shop, would have D-rings on the back. That doesn't exactly jive in my mind with a scrim so there may be a broader definition of the term than how we use it. If it does have D-rings I've experienced a similar problem a few times through the years. A jerky motion occurs as the D-rings bind, add weight, and then slip. Sometimes it binds at the top D-ring and stops (or breaks if it doesn't stop). The solutions were varied, but the end game was to make sure the lift lines fell perfectly straight through the D-rings without rubbing, the D-rings are sewn on in a straight line, and that the D-rings are were big enough for the lift line to slip through easily.

Once I saw a piece of wire rope that had a small kink, it too was enough to cause the D-rings to momentarily catch causing a little jerky motion.

I may be talking apple cider in an orange grove, but perhaps it's of use.

-Ty