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Double purchase counterweight system


Damian Jay

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Hi All,

 

First off I have to stress that I am building a model for demonstration purposes.

 

I have found a lot of online information regarding the theory of a double purchase system (Now called DPS so I don't have to type it out everytime) such as the arbour moves 1 foot to every 2 feet of the load etc. I get that.

What I am having difficulty in finding is any video demonstrations of the SET UP of the rigging (I'm not sure that's the correct terminology, so apologies if it's not)

 

I have found the following image that shows a side profile. HERE

However I am struggling to understand where each of the lift lines go to once they go over the Head Block.

 

In order to follow this next bit you may need the aforementioned image open to follow my thoughts. So apologies in advance if I don't make any sense.

 

 

Am I correct in thinking that the 4 lift lines:

 

1 - come over the head block in a 5 sheave pulley

2 - Make their way down to a second 5 sheave pulley on the top of the arbour

3 - go under this pulley on the top of the arbour cradle and go back UP to the head block and are fastened somehow to the underside of the same? If so, how? If not, where to they fix too?

 

 

At the same time looking at the image, I'm sure the Hand Line:

 

1 - Is fastened to the floor of the fly floor?, or other gantry situated somewhere on the side of the fly tower. How is this fastened?

2 - It runs UP from is fixing point to a single sheave pulley on the underside of the arbour from behind, over and down to the back of the Tension Block

3 - comes under the tension block from and through the Lock Rail

 

The above is pretty evident from the image, but it never hurts to get clarification. No's. 4 and 5 below I'm not so sure about. Please do let me know if my assumption is correct, if not, please correct me.

 

4 - continues UP from the Lock Rail to the Head Block

5 - Passes over the Head Block from front to back and follows the Lift Lines route and terminates in the same place as the Lift Lines ?

 

 

Does anyone have any decent images showing the termination of the lift lines on a DPS.

Or, and I'm gong to be a bit cheeky now, if you work with a DPS and are near to Fareham in Hampshire and wouldn't mind me coming to have a look at a DSP for real, that would be awesome. I fully understand it's probably not possible to see it in action, but that's cool.

 

Finally, thank you for any help, advice, images or resources you are willing to share with me. It's greatly appreciated.

 

Kind regards to you all,

 

Damian

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Theatre Royal in Winchester is double purchase and not a million miles away from you - get in touch with Spatz (yes, he is still there I am having a meeting with him on Monday) and very likely he can arrange for you to drop in and have a look how it all works.
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Hi All,

 

First off I have to stress that I am building a model for demonstration purposes.

 

I have found a lot of online information regarding the theory of a double purchase system (Now called DPS so I don't have to type it out everytime) such as the arbour moves 1 foot to every 2 feet of the load etc. I get that.

What I am having difficulty in finding is any video demonstrations of the SET UP of the rigging (I'm not sure that's the correct terminology, so apologies if it's not)

 

I have found the following image that shows a side profile. HERE

However I am struggling to understand where each of the lift lines go to once they go over the Head Block.

 

In order to follow this next bit you may need the aforementioned image open to follow my thoughts. So apologies in advance if I don't make any sense.

 

 

Am I correct in thinking that the 4 lift lines:

 

1 - come over the head block in a 5 sheave pulley

2 - Make their way down to a second 5 sheave pulley on the top of the arbour

3 - go under this pulley on the top of the arbour cradle and go back UP to the head block and are fastened somehow to the underside of the same? If so, how? If not, where to they fix too?

 

 

At the same time looking at the image, I'm sure the Hand Line:

 

1 - Is fastened to the floor of the fly floor?, or other gantry situated somewhere on the side of the fly tower. How is this fastened?

2 - It runs UP from is fixing point to a single sheave pulley on the underside of the arbour from behind, over and down to the back of the Tension Block

3 - comes under the tension block from and through the Lock Rail

 

The above is pretty evident from the image, but it never hurts to get clarification. No's. 4 and 5 below I'm not so sure about. Please do let me know if my assumption is correct, if not, please correct me.

 

4 - continues UP from the Lock Rail to the Head Block

5 - Passes over the Head Block from front to back and follows the Lift Lines route and terminates in the same place as the Lift Lines ?

 

 

Does anyone have any decent images showing the termination of the lift lines on a DPS.

Or, and I'm gong to be a bit cheeky now, if you work with a DPS and are near to Fareham in Hampshire and wouldn't mind me coming to have a look at a DSP for real, that would be awesome. I fully understand it's probably not possible to see it in action, but that's cool.

 

Finally, thank you for any help, advice, images or resources you are willing to share with me. It's greatly appreciated.

 

Kind regards to you all,

 

Damian

 

Your assumptions as to the cable routes are generally correct in 1,2 and 3, the fixings to the head block will vary depending on who has manufactured it, often the eyes in the steel cables have a bolt that passes through the bottom of the pulley housing.

The hand line will be the same as a single purchase and run over a pulley at the top and bottom of the frame and fix to the counterweight cradle or Arbor for the USA members..

Have a look at this guide from J R Clancy it might have some more details and a slightly better image than the one you linked to. http://www.jrclancy.com/downloads/JRC_RiggingDesignGuide.pdf

 

 

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Theatre Royal in Winchester is double purchase and not a million miles away from you - get in touch with Spatz (yes, he is still there I am having a meeting with him on Monday) and very likely he can arrange for you to drop in and have a look how it all works.

 

Hi Vinntec,

 

Thank you .. I'll message the theatre tomorrow and see if I can get in touch with Spatz. :-) It would be great if he can arrange a look see :-)

 

 

Your assumptions as to the cable routes are generally correct in 1,2 and 3, the fixings to the head block will vary depending on who has manufactured it, often the eyes in the steel cables have a bolt that passes through the bottom of the pulley housing.

The hand line will be the same as a single purchase and run over a pulley at the top and bottom of the frame and fix to the counterweight cradle or Arbor for the USA members..

Have a look at this guide from J R Clancy it might have some more details and a slightly better image than the one you linked to. http://www.jrclancy....DesignGuide.pdf

 

 

Hi Ontoprigger, Thanks for the link. A much clearer explanation and diagram. Plus a lot of other information - Thank you :-)

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Just a quick point of terminology, 'arbor' is the American English term for what we call the cradle in the UK.

 

As much as I love our American cousins, it'd be a shame to slowly lose our own language due to the heavy influence they have on everything we consume and interact with. This is happening in many areas, but is particularly noticeable and increasingly prevalent in areas where products/software originate from the States and also as easily found internet sources* are so heavily biased to US English.

 

 

*As demonstrated by the Clancy link.

 

 

The use of 'hand line' is, in my experience, not as common as 'control line' over here. Oh, and maybe I shouldn't forget the different uses of 'lock' and 'brake' and 'brake rail'. In the US, they seem to use 'rope lock' for what we'd call the brake in the UK - to us a rope lock is a different device/technique also used in flying.

 

Your assumption about the control line is correct on the systems that I'm familiar with. It passes through pulleys top and bottom of the cradle and is fixed at the head and the base of the travel. (12 and 13 in the image you posted)

:-)

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Just a quick point of terminology, 'arbor' is the American English term for what we call the cradle in the UK.

 

As much as I love our American cousins, it'd be a shame to slowly lose our own language due to the heavy influence they have on everything we consume and interact with. This is happening in many areas, but is particularly noticeable and increasingly prevalent in areas where products/software originate from the States and also as easily found internet sources* are so heavily biased to US English.

 

 

*As demonstrated by the Clancy link.

 

 

The use of 'hand line' is, in my experience, not as common as 'control line' over here. Oh, and maybe I shouldn't forget the different uses of 'lock' and 'brake' and 'brake rail'. In the US, they seem to use 'rope lock' for what we'd call the brake in the UK - to us a rope lock is a different device/technique also used in flying.

 

Your assumption about the control line is correct on the systems that I'm familiar with. It passes through pulleys top and bottom of the cradle and is fixed at the head and the base of the travel. (12 and 13 in the image you posted)

:-)

 

Thank you indyid :-)

 

 

 

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