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parachutist

Sigma slider grommets wearing through and damaging Vectran lines

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I've had 5 canopies come through my loft so far with this particular issue. Some were original Sigmas that'd been converted from Dacron to Vectran lines. Some were Sigma II's. All behave the same: the Vectran lines polish away the SS metal inside the grommets. Eventually (900-ish jumps I'm estimating) the interior grommet wall gives way and a sharp metal edge is pressed against the lines. Now the lines shred rapidly.

This erosion isn't so easy to spot when you're inspecting the grommets because the surfaces look and feel slick, right up until they wear through. Typically I look for nicks and dings inside grommets, but this is a little different. The pictures below show grommets from a Sigma II slider (DOM 08/2010). The first one only has a wavy look to it, but you can see the worse ones lower in the picture list.

One of this canopy's lines was cut by the last grommet. The C1 line broke during opening and the TI landed it with no issues. You can see these problems early, but it helps to know what you're looking for:

[inline sigmaii340grommet01.jpg]

[inline sigmaii340grommet03.jpg]

[inline sigmaii340grommet04.jpg]

[inline sigmaii340grommet05.jpg]

Chris

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riggerrob

W used to see the same wear pattern on brass slider grommets after 300 or 400 jumps.
Now we see the is wear pattern on stainless steel grommets after 900 jumps with sand-paper coloured lines.

Do you expect sliders to last forever?



I'm just saying if I've seen it 5 times in my small neck of the woods, others will see it too and here's a road map.

Chris

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peter.draper

Thanks for that post and the great pics. I have been trying to explain to some of my trainees the importance of checking grommets and this will greatly help!!!!!!

CHECK EVERYTHING folks!!!!!!



...............................................................................

Hee
Hee!
I just toss them a battered old slider with brass grommets.

My bag is full of faded, frayed and filthy old parachutes.
Some of those parachutes are almost as filthy as my imagination.

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riggerrob

W used to see the same wear pattern on brass slider grommets after 300 or 400 jumps.
Now we see the is wear pattern on stainless steel grommets after 900 jumps with sand-paper coloured lines.

Do you expect sliders to last forever?



^^^^^^this. Time to replace some grommets.

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Quote

W used to see the same wear pattern on brass slider grommets after 300 or 400 jumps.
Now we see the is wear pattern on stainless steel grommets after 900 jumps with sand-paper coloured lines.

Do you expect sliders to last forever?



From the "Quote" (above); I take it we have experienced this grommet wear with Vectran and Brass and Vectran and Stainless Steel grommets.

Has anyone seen this with Spectra line and Brass grommets?

Certainly, we have seen grommets with damage similar to the pics but that was from the Rapid Links hitting of the grommets. This is a wear issue.

Does Vectran cause more wear on the grommets than Spectra?

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I have seen that wear pattern with brass grommets and Dacron lines when jumped in the California desert.

We are also starting to see that wear pattern with yellow Vectran lines and stainless steel grommets. My impression is that Vectran is the most abrasive of modern, zero-stretch suspension lines.

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I remember some of the worst wear I ever saw. It was back in the day when our tandems had Dacron lines and brass grommets. We got "Smart" and decided to spray silicone on our lines to reduce the wear and prevent friction knots. Insert laughter. It actually seemed to do the opposite. It was a smooth cement floor and the lines picked up every bit of grit off of it. Not only did the lines seem to wear out faster but we went through a whole set of sliders. It wore right through the brass.

The finish on Specter seems to hold up better then any other line. I'm not sure if it's the finish or the nature of the line. You know how vectran opens up and gets fuzzy. Spectra just gets that smooth almost polished look. What I'm saying is that I'm not sure if it's the line it self or the abrasive grit that it picks up. Un the other hand think about how rough some of these things are on scissors. Kevlar and some of these related fibers seem to be harder then the steel.

Lee
Lee
lee@velocitysportswear.com
www.velocitysportswear.com

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For about 2 years now I've been sewing almost exclusively with Kevlar thread. I got a couple of spools from AE that are actually much nicer then what I normally get from Saunders. It came out of their R and D lab. It was a solution dyed black. It's a slightly coarser twist but it's got a much nicer coating on it. It runs much nicer through my machines. I haven't had any problems with it. I save it for my zig zags and bar tacks. I'm too small for them to lessen to me but if you were to encourage them to do another run... Just saying, I'd love to get a few more spools of it my self. Got some more ballutes to build.

Lee
Lee
lee@velocitysportswear.com
www.velocitysportswear.com

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