Modified Petzl Stop.

[BrianCooke]

Hello all. Got to thinking about a thread I started a week or so ago and the good advice given. I was talking about trying out some descenders at a Vermeer dealer and my impressions of them. I tried the Petzl ID & the Petzl Stop. I ended up liking the feel and action more of the Stop over the ID so I bought it.

The issue was raised about it not being a proper device to use on 1/2 line....and I would have to agree. One side of the device lists rope size is from 10-11mm and the other lists rope size as 9-12mm. Either way 1/2 rope is too large (12.7mm). The reason it is too large is that the rope diameter holds the bottom spool away from the top spool and does not allow it to grab the rope that well. It does eventually grab the rope but only after several inches of rope have slipped though the device.

It got me thinking of how to 'fix' this issue. It seems like an aftermarket top spool could be supplied that is slightly smaller in diameter. This would allow the bottom spool (cam) to travel further and grab the rope at a better angle. My day job is engineering in a large manfacturing facility with lots of CNC & manual lathes & mills. So I removed the top spool and milled down the flat suface where the bottom spool grabs against by .050". All deburred, polished up & Loctited together I tried it and it worked much better. It would still slip a few inches but not nearly like it used to. Back to work the next day and took another .025" off. Tried it again and now no slip at all. There is a small tab on the side of the Stop that acts as a stop for the lower spool. It prevents the lower spool from rotating too far. With the modified Stop loaded, there is still plenty of room to go before this tab bottoms out.

And a little disclaimer here......
Taking off some stock in this area in no way compromises the structural integrity of the device. And looking at the numbers, the nominal rope diameter listed is 10.5mm (.413"). Taking off .075 increases this nominal design diameter to .488", right at half inch rope size.

I'm going to start using it "low & slow" & monitor it's performance & wear for a while. Hopefully I'm not going to get beat up too badly for posting this thread. I see folks talk about modifying gear quite a bit here (saddles etc) and thought I'd pass this one on.

Take care,
Brian

 

[Tom Dunlap]

Brian,

You are already doing the low and slow approach by machining the piece in small increments. Your approach seems sound.

Keep us posted about how the new configuration works.

Tweaking and modifying gear can be a good thing as long as everyone understands that there is no manufacturers liability. I'm sure that an attorney could make a case against Petzl if you were injured. They would claim that just because P put a nut and bolt that allowed you to take the tool apart. This is really lame and just drives costs up and keeps some really clever tools from ever being produced.

Tom

 

[seanlarkin]

Brian,
Did you say you would be at TCI this year? If so, get a hold of me in our Sherrill booth so I can get a look at it.

-Sean

 

[BrianCooke]

Hey Sean. Nope, I will not be there. However, I will see if I can post a photo tomorrow of what I did (not that it will look that much different from the original spool).

And thanks for changing your specs for next year's catalog.

Brian

 

[Burnham]

If you are completely confident that there is sufficient material left for structural integerity then I say good for you...you had the right tools to do an appropriate mod, and went at it carefully and with forethought. Sounds like a winner!

 

[murphy4trees]

What about using a thinner rope... The yellow jacket seems thinner than most of the earlier lines and I thought MM posted something about ANSI changing the requirements for 1/2" line...
When I first started with the Yellow Jacket, I felt a little uncomfortable with the thinner line... Now that I Am used to it my old lines seem so bulky and awkward, I wouldn't want to go back.
Did you actually measure the line you are working with???

 

[Tom Dunlap]

This afternoon I spent some windshield time thinking about the Stop and its use for arbo SRT. It seems that Brian might be on the right track for solving one of the shortcomings of the Stop. Tweaking the bobbin size has a good potential it seems. This might reduce slippage. If you read Storricks review of bobbin descenders you'll find that they all have a reputation of not locking off securely. Sometimes the Stop is referred to as the Creep because of the slippage. This is from rope climbers who use ropes that are within the recommended diameters. I wonder how the suppleness and texture of the sheath might effect the application.

Take a look at Kong's Indy:

http://www.kong.it/doc405.htm

The Indy has the distinction of being a tool that has a panic stop. If the release handle is released or compressed, it locks off. The Stop doesn't do that. This feature is also found on the I'd, making both a better tool in my opinion.

No bobbin tool works for going up the rope. The I'd does. Using the RADS, http://www.rescueresponse.com/html/news02-02/highlight.html
, system the access line can be ascended with an I'd.

Tom

 

[BrianCooke]

Murphy. I'm sure using a thinner rope would work just fine. Petzl recommends a thinner one so there should be no problem there (I just do not have a thinner one). As far as measuring the line, no I have not. How would you go about doing this? Do you measure it when it is loaded or slack?


Tom, that Indy looks pretty nice. Having the safety feature would certainly be a benefit. As far as ascending on this thing, it is very doable (in conjunction with an ascender). Looking into the future, I will probably not even use my top ascender anymore for stuff under 30 feet or so.

Here is a photo of the Stop bobbin that I milled down. There are calipers in the photo so you can see just how much I took off.