Conductive Carbon Fiber Lower Rods

[Steve Herschbach]

I got a very rare metal detecting surprise recently when I was informed of something I automatically never considered. Every detector I have with a cross hatch carbon fiber lower rod, screams with a Garrett pinpointer and even more so if I check that lower rod with my 24K.

They told us back in the day metal coil bolts were ok because they did not move in relation to the coil. True perhaps but now we do not use them. They told us metal rods were ok if they do not move in relation to the coil, but all the manufacturers got away from that and went non-conductive. I just assumed that's the way it was and always would be. Now it appears conductive lower rods are back in the form of cross hatch carbon fiber. Is the issue a problem or not? Probably not for most uses, but I’ll bet most nugget hunters ears are really perking up on this news. It's definitely a problem for the Manticore used in Gold Mode. I am looking for alternatives for my Manticore lower rod while nugget detecting as it does have some observed issues regarding false signals when jacked to the max for nugget detecting.

Credit for this observation goes to Gerry McMullen and his class members and team. It also is shown by Bill Southern in his video below (Jeff McClendon's post) so I don't know who observed it first. Jeff has experienced it, as have others. 

Apparently the conductivity of carbon fiber varies greatly depending on how it is made and what additives are used. All I know is my pinpointer goes nuts on the stuff and if it does, that’s a target as far as a detector is concerned.

From https://europlas.com.vn/en-US/blog-1/does-carbon-fiber-conduct-electricity

”So, does carbon fiber conduct electricity? Yes, carbon fibers do conduct electricity. The electrical conductivity of carbon fiber is typically improved by incorporating reinforcing materials. Additionally, they can also generate electricity when subjected to magnetic fields.”

[Chase Goldman]

I've pretty much 95% convinced myself there is no measurable impact to detector sensitivity of having a CF lower shaft with my Manticore based on the following:

For normal motion detection modes, the lack of relative motion of the shaft in relation to the coil should mostly alleviate this concern (as Steve stated, this is the most common "argument" as to why folks consider this a non-issue.  I would be more worried about the metallic coil connector causing sensitivity loss as it is more highly conductive, massive, and located closer to the coil sensitive area than the CF shaft which is separated from the coil by the injection molded plastic clevis mount and a significant air gap with shaft in a normal orientation with respect to the coil.

However, just to be sure, I decided to put the detector in non-motion pinpoint mode and to orient the coil flat up against the CF rod to see if it would generate any audio or affect the detector pinpoint sensitivity to in-ground and surface targets and noted no anomalies regardless of the shaft orientation (flat against the coil or perpendicular to the coil).

I air tested it against some small subgram gold flake targets in both normal detect mode and pinpoint in various shaft orientations and also did not observe any loss in sensitivity.  Admittedly, this was not comprehensive as I only used a couple targets and it was fairly qualitative and not quantitative (I did not take precise measurements of distance to the coil before loss of signal, just eyeballed it.

I still want to test this with some very fine bits but have not had the chance, yet and yes, a pinpointer sounds off on the shaft but it also sounds off on the coil itself and the coil connector, so there is that.

Still need to remove the 5% of doubt but I am not losing much sleep over it. 

That all being said, if you can remove as much of the conductive material away from the coil as possible, and the weight and balance impact is minimal or acceptable, then it would be great to have non-CF lower shaft options for Manticore etc. to remove any doubt for those concerned about how CF affects the detector fine target performance.

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[Jeff McClendon]

I haven't spent a lot of time on testing this unfortunate characteristic. Obviously Minelab and Nokta didn't spend a lot of time testing it either using the gold prospecting modes on the Nox 900, Manticore and Legend.

You can definitely add the Legend's carbon fiber lower rod to that list. Luckily for small coil uses, Nokta still sells plastic lower rods that fit on all of the Simplex, Score and Legend models.

I don't have a Deus 2 carbon fiber lower shaft so I can test it.

The first time I noticed it on the Legend was at the LSD outside Phoenix. Every time I tried to use a scoop after laying the LG24 coil flat with the heel of the coil touching the lower rod, I would get some slight coil bump noises if I scraped my scoop on the top of the coil. I just thought I had laid the coil down on a hot rock or something.....I just stopped scraping my scoop on the coil. I also ignored the coil bump noises when detecting under and in bushes that made the coil pivot and get close to the shaft. I thought my LG24 coil was going bad. Nope, it was detecting the shaft.

The Manticore has that problem but waaaaaay worse using the M8. I hear a loud  boing, boing, boing sound when I lay the coil flat on the ground with the heel of the coil really close to the shaft even without scraping my scoop over the coil. I definitely have to "air" scrape my scoop using the Manticore with M8 which is just not OK.

I haven't noticed any of this on the Axiom....yet.

[Chase Goldman]

7 minutes ago, Jeff McClendon said:

The Manticore has that problem but waaaaaay worse using the M8. I hear a loud  boing, boing, boing sound when I lay the coil flat on the ground with the heel of the coil really close to the shaft even without scraping my scoop over the coil. I definitely have to "air" scrape my scoop using the Manticore with M8 which is just not OK.

I need to try this as I was not hearing anything in pinpoint or detect mode - I will up sensitivity to max and and various audio settings in prospect mode, but EMI also is an issue near my house.  Note that I was using the M9 coil.  I need to do some more controlled and comprehensive tests in the field away from EMI sources.

Jury is still out on this one.  And, again, regardless, it would still be nice to have non-CF lower shaft options out there for Manticore.

 

[Jeff McClendon]

Here is a Nugget Shooter video where Bill Southern has a WTF moment when he finds out about this issue. Fast forward to the 2 minute 30 second mark of the video and go to about 4 minutes. I have started to just not lay the M8 coil flat. I keep it at a slight angle like Bill ends up doing and have the coil bolt a little tighter. 

 

[Steve Herschbach]

On 6/5/2024 at 7:35 AM, Jeff McClendon said:

I haven't spent a lot of time on testing this unfortunate characteristic. Obviously Minelab and Nokta didn't spend a lot of time testing it either using the gold prospecting modes on the Nox 900, Manticore and Legend.

You can definitely add the Legend's carbon fiber lower rod to that list. Luckily for small coil uses, Nokta still sells plastic lower rods that fit on all of the Simplex, Score and Legend models.

I don't have a Deus 2 carbon fiber lower shaft so I can test it.

The first time I noticed it on the Legend was at the LSD outside Phoenix. Every time I tried to use a scoop after laying the LG24 coil flat with the heel of the coil touching the lower rod, I would get some slight coil bump noises if I scraped my scoop on the top of the coil. I just thought I had laid the coil down on a hot rock or something.....I just stopped scraping my scoop on the coil. I also ignored the coil bump noises when detecting under and in bushes that made the coil pivot and get close to the shaft. I thought my LG24 coil was going bad. Nope, it was detecting the shaft.

The Manticore has that problem but waaaaaay worse using the M8. I hear a loud  boing, boing, boing sound when I lay the coil flat on the ground with the heel of the coil really close to the shaft even without scraping my scoop over the coil. I definitely have to "air" scrape my scoop using the Manticore with M8 which is just not OK.

I haven't noticed any of this on the Axiom....yet.

It is most noticeable with small hot coils on hot detectors. It can also be an issue with larger coils like the 15x12 as they are more prone to moving in relation to the coil while in use. PI by nature is more immune but non-conductive rods were very popular with Minelab SD/GP/GPX large coil users - I never used the metal rods that came in the box myself. Nugget hunters in particular are obsessive in not having ANY metal near the coils. Metal free boots are a thing with prospectors. So I predict a surge of interest in non-conductive alternatives from the nugget hunters - new sales opportunity for steveg!

[GB_Amateur]

On 6/5/2024 at 6:54 AM, Steve Herschbach said:

Every detector I have with a cross hatch carbon fiber lower rod screams with a Garrett pinpointer

Just curious if you've tried this with the Fisher F-pulse (PI) pinpointer.

Back in 2015 I found a large (~15 lb = 7.5 kg) gray rock in the Merced River, CA which sounded off with a Garrett Carrot.  Later I checked it with the Fisher Gold Bug Pro and it gave a clear detection with VDI = 40 (right at the ferrous/non-ferrous boundary).  But when I eventually tried the White's TDI (PI) I got nothing.  My conclusion was that the decay constant for graphite (what I'm pretty sure the rock is composed of) was fast enough that the (designed) dead time of the TDI ignored it.

Thus I'm wondering how a PI pinpointer will react.

[Steve Herschbach]

7 minutes ago, GB_Amateur said:

Just curious if you've tried this with the Fisher F-pulse (PI) pinpointer.

Mine died so I went back to the Carrot. Will be up to somebody else to try. I did also try my 24K and man did that go crazy! For some weird reason it comes with a non-conductive lower rod. 

But again, this should be less to no issue with most PI detectors.

[GoldenboyCO]

I just tested my Deus2 lower fiber rods with my MI-6. 
My new XP factory "CF" rod that came with 13 inch coil was quiet and my after market detect-ed screamed. Looking at a XP CF shaft they are not cross carbon and look like plastic.

I have a F-pulse pointer and both rods were quiet.  Take care