UKC

This may be of academic interest to those with wobbly Nomics and real interest to those considering buying Nomics.

A colleague and I (I brought the axes he brought the expertise) drilled out the rivet and removed the head of a wobbly Nomic (2nd generation I think). We discovered that the interior of the shaft is bevelled such that it comes to an edge as in the upper example in the diagram linked below. By contrast a first generation Nomic is more like the lower example having a flat edge of 1 or 1.5mm on the top of the shaft for the head to sit on.

What this means for the later models is that the forces are concentrated on a smaller area and the head gradually crushes the top of the shaft at certain points which then allows the head to move with the single rivet as the pivot point. This is exacerbated by the 2nd gen heads being less well finished with irregularities from the forging process that concentrate the load on parts of the shaft

There are clearly other differences in the different models as the first gen has a bulge on the shaft the second gen doesn't but it seems to be the thinner end of the shaft that makes the difference. I wasn't willing to remove a working one to find out for sure!

I don't know if it's as simple as 1st gen good later models bad but it is easy to check. You can see the end of the shaft by looking down the gap on the head where the pick slides in.

https://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Bevel_and_chamfer...

In reply to DaveHK:

Nice work. Do you reckon an injection of epoxy could be used to fill the gaps? I'm talking failing a warranty replacement etc...

And does this smack of Petzl installing planned obsolescence?

In reply to Smythson:
My plan was to pack it with epoxy or some such, re rivet the original rivet and add a second rivet above the first. There also seem to be some models with the rivet higher up which would make this difficult.

Edit: I doubt you'll be able to gain much by trying to get epoxy in without taking the head out.

In reply to DaveHK:

Once you have the head removed, can you not flatten the chamfer to give a flat lip for the head to locate on, to make the upper image look like the lower image? Then epoxy and re-rivet and add the second rivet?

In reply to random_voodoo:
You could but surely the original rivet hole would not then allign?

In reply to DaveHK:

Ahh yes very true.

In reply to random_voodoo:


When that occurred to me I thought I'd had a brilliant idea. For about a minute before the penny dropped!

In reply to DaveHK:

I should have thought about it more before typing!

In reply to DaveHK:


Will any old rivet do, or do Petzl use special ones?

In reply to DaveHK:



You could add a washer the same thickness as the amount you removed from the shaft to the have the rivets align again?

In reply to Dangerous Dave:


In theory yes but I think in practice that would be incredibly difficult to get right and you might end up getting the same problem with the washer disintegrating.

In reply to Toerag:


I'm finding it a bit difficult to source them but 4mm diameter 35ish mm long solid steel rivets are what you need.

In reply to DaveHK:

Car bodyshops use these sorts of rivets. Maybe worth a visit...