The war against the wobble: Fixing loose heads in Petzl Nomics

sooji.clarkson's picture
Friday 28 August 2020, 11:25pm -- sooji.clarkson

Disassembled Petzl Nomic

Disassembled Petzl Nomic

Disassembled Petzl Nomic

Creator: 
sooji.clarkson

An issue well known to Petzl Nomics (and some other models of ice axe) is the tendency for the heads to loosen and develop movement over time. This is mostly due to the design – the head of the axe is held in by a single rivet. Over time the press fit between the head and the shaft gets looser. As there is only a single rivet the head can rotate around this and the overall effect is a wobbly or moving head.

In general climbing this might not be noticeable or even if it is it might not be so annoying that it needs fixing, depending on how much movement there is. However when the amount of movement is significant, especially in delicate mixed or even ice climbing, it can be quite disconcerting when you weight your axe and you can feel it shift.

Although this fix is overall a simple process, there’s a few little details that can complicate things a little, mostly to do with modification of whatever replacement fastener you can source to ensure the dimensions all work.

 

 

Disclaimer: This is NOT an official or Petzl-sanctioned repair method. Check first with the manufacturer if you can get an official replacement, a quick internet search shows they have done this in the past! However with old or second hand axes, I and others have chosen to fix them myself... especially us engineers! This is just a description of the current most successful repair method that I have used, based on a handful of axe repair jobs done by members of the team. It involves drilling out the original rivet holes in the head and shaft to larger diameters, this removal of material will (at least a tiny bit) affect the overall strength of the reassembled whole, and possibly therefore the rating of the tool (ie the T-rating for Nomics). Use your own judgement. 

Basic steps:

  1. Remove the original rivet
  2. Remove the head from head from the shaft
  3. Drill out the rivet holes to accept your chosen replacement fastener (more on this later)
  4. Throw a lot of metal repair epoxy around to recreate the original press fit
  5. Reassemble the head into the shaft and fix it all together with the replacement fastener.
  6. Let the epoxy cure to full strength… then go climbing!!

Tools needed:

The straightforward:

  • A drill press, important to get the holes in the shaft and head square
  • Drill bit, sized as close to the replacement fastener as possible
  • Nail punch or similar, to help remove the original rivet
  • Benchtop vice is highly recommended, to hold the axe during removal and replacement of the head
  • Hammer, for the same task as above
  • T-bar or allen key to fit the replacement fastener

The slightly less straightforward:

  • A metal-specific two-part epoxy

The general properties to look for bondability to metal (often these are machinable or weldable – they are designed to fix metals), cold and impact resistance, and a 2-part epoxy mix to ensure that it will cure to full bond strength once assembled (no air or moisture cure!)

Examples: J-B Weld - often found at car hardware stores such as Supercheap Auto.

JB Weld

JB Weld

JB Weld

Creator: 
Image supplied

If you can’t find this, Loctite also produce Epoxy Weld for bonding metal, usually found in Bunnings or Mitre 10 (for us Kiwis and Aussies), or similar hardware stores.

Loctite Epoxy Weld

Loctite Epoxy Weld

Loctite Epoxy Weld

Creator: 
Image supplied

  • A replacement fastener (possibly the crux)
The best we have found for this is a sex bolt (also known as a barrel nut, Chicago screw, or connector bolt). Look for flat heads (so they sit as flush as possible without countersinking), and hex heads so you can get as much torque on them as possible for a tighter final assembly.

Replacement fastener

Replacement fastener

Replacement fastener

Creator: 
sooji.clarkson

Dimensions (labelled in above picture):

a) This needs to be a bit less than the width of the shaft of the axe. I have cut down fasteners with a metal hacksaw to get this short enough. It needs to be a bit shorter than the width of the shaft as there will be a bit of extra length between the heads when screwed together - assemble the fastener and measure between the heads and check it's short enough. Note also if there is a shoulder (unthreaded portion) check that when you cut off the excess length there is enough thread left to still engage in the other side of the fastener. 
b) As small as possible (however best not smaller than the original rivet. It needs to be strong, it's technically what retains the head in the shaft) - the smallest I have found in NZ is M6. Possibly better solutions exist online or from other fastener suppliers. The smaller the diameter, the less material you will need to remove from the shaft and head, and the less you potentially weaken these.
c) Will be determined by b) – but as small as possible. Again you might not have that much choice.

d) Same as a) 
 

Side note: The shaft of the axe is an aluminium alloy. Most likely fastener material choices will be stainless steel or galvanized/zinc plated. I would choose the zinc plating - zinc is lower on the galvanic scale than aluminium and will be corroded first, and the two materials are fairly close so there is less potential for galvanic corrosion than between aluminium and stainless steel. Either way, note that the better you can seal the final fastener joint with epoxy, the better protection overall from water ingress and thus any corrosion.

When you have a suitable fastener solution, before disassembling your axe – check again that the fully assembled fastener is less than the width of the axe, so when you put everything back together it will sit flush and tight. Phew! That was a lot. Now on to the actual fun part.

Taking it all apart (and putting it back together)

  1. Remove the original rivet. Drill out the indented side of the old rivet to remove the metal holding the rivet in. This should be easy as the indent centres the drill bit in the rivet. Using the nail punch and a hammer, carefully tap out the original rivet and remove.
 

Original rivet

Original rivet

Original rivet - drill this side, not the head of the rivet

Creator: 
sooji.clarkson
  1. Remove the head from head from the shaft. Depending on how loose the head is, this may take a bit of tapping with a hammer with the axe held in a vice. Try to use soft aluminium jaws or something similarly protective on the shaft in the vice so you don’t crush or damage the shaft when clamping.

Disassembled Nomic

Disassembled Nomic

Disassembled Nomic

Creator: 
sooji.clarkson
  1. Drill out the rivet holes to accept your chosen replacement fastener. I found it hard to find a drill bit matching the thicker (female thread) end of the fastener. Ideally it would be close enough to achieve another press fit but this might not be possible and it will be slightly oversize. Drill out both holes in the shaft and the hole in the head. Make sure everything is centred on the original holes and square so that it will all line up when you reassemble the axe. Put in the fastener and do it up to ensure that it will be tight and fit correctly before you epoxy everything in place.
  2. Once everything is ready to be put back together, mix up your epoxy according to the instructions. Smear a lot of epoxy on the part of the head that fits in the shaft, to try recreate the original press fit. Keep in mind you also want to seal the whole assembly against water ingress, so more epoxy under the heads of the fasteners and around the top of the shaft is great.
  3. Reassemble the head into the shaft and fix it all together with the replacement fastener. Again with the axe in the vice, tap the head back in place with the hammer, and assemble the fastener in place. Consider putting more epoxy around all the joins to seal it up. Do up the fastener tight and clean up any excess epoxy.

Re-riveted Nomic

Re-riveted Nomic

Re-riveted Nomic - after two weeks of mixed and dry-tooling!

Creator: 
sooji.clarkson
  1. Wait for the epoxy to cure to full strength (guidelines will be on the package)...
  2. Go out and crank on those tools!
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