Does Anyone Know The Date Minelab Revised The Plastic On The GPX 6000 Coils To Not Crack So Easily?

[phrunt]

As we all know the GPX 6000 coil ears have cracking problems, quite a number of people after hearing of it and inspecting their coils found they had cracks they didn't even know about.

It's been said they revised the plastic they use to make the coils to prevent the cracking, but has anyone been able to find out the date this took place? Is it very recent I wonder or did they do it some time ago?

Much like the speaker EMI problem every coil before a certain date is going to have the dodgy plastic formula.

I've had my coil replaced recently under warranty for being noisy but it wasn't replaced with a new date code coil, in fact the coil I got it replaced with is likely older than my 6000 as I only bought my 6000 in May of this year and I was provided a replacement coil from 2021 by the looks of the writing on the coils package.

If anyone finds out the date of the plastic change that'd be appreciated although I guess Minelab likes to keep this stuff secret to stop people wanting their stuff fixed/replaced.

[Aureous]

I saw a 6000 purchased in September this year and although the 11" coil was quiet(er) than previous 2021 coils it still had the same PP plastic. No change that I could see.

[mn90403]

The coil ears are part of a 'pinch' system that Minelab has been using for years.  Pinch the ears together more and the coil gets tighter.  If you use less flexible plastics, they will break near the coil because there is no give.  They will crack or separate from their attachments due to the torquing forces of the screw.  This happened to me on my CTX 17" coil.

I've always thought they should use a more flexible plastic formula but that would make the coil wear faster if you scrub it.  My other thought would be to make the coil ears a bit longer which would make the pinching easier on longer ears farther away (half an inch or so) from where they come off the coil.

I've also seen where some of their coil ears break at the screw holes.  This I think is the result of a very tight screwed coil being adjusted often to level it for the swing.  Those forces of leveling the coil cause a ripping action as a result of the tightness/friction in the pinch.  Some sort of firm washer/anti-slip insert helped me with this.

[phrunt]

The GPX coil ear cracks are different, they're micro cracks and people often get many of them at once.

Another thread about it here

 

[mn90403]

Do you think they crack because of the pinch or some other force?

[Steve Herschbach]

The so-called “pinch system” is not a “Minelab system” but is the way coils have attached to detectors on almost all brands and models for 50 plus years. It’s obviously worked well on almost all of them. As a dealer I almost never had customers report cracked coils in my 35 years in the business. The 6000 actually is using the newer system where the bolt screws into a threaded ear instead of a separate nut. Cracks in coil ears in general are caused by poor coil material or over tightening. The rarest cause is an actual engineering problem. In the over 50 detectors I’ve used I’ve probably used in excess of 150 coils, and have only had ears crack on a handful. Almost all were due to poor plastic, and mostly on Nokta/Makro prototypes, that never saw the light of day. I had a 16” Nugget Finder mono coil for GP 3500 crack due to the ears in the old coils actually being foam filled, and the foam compressed, causing the outer shell to crack, one of the rare issues where the design itself was the cause. Most coils ears crack from over tightening, which of course nobody in this forum would ever do, but for anyone having the issue with multiple models and coils over the years, it’s the most likely. When the issue crops up more for lots of people on one model, then the plastics materials become suspect. In the case of the 6000, it could most likely be a materials issue, but I am intrigued also that it’s also the only Minelab model after the Gold Monster to use the threaded coil ear.

[WesD]

Has anyone actually had or heard of the ear breaking off on these 6000s? I have the micro cracks on my coil, but just letting it ride for now. The area that cracks is a thin zone between the thicker buttress ends. Not sure why they would design it that way, but obviously it wasn't a good idea.  I've always run the bolt very loose, so its not really an issue with that, but it sure could fast track the cracking by having it snugged tight.

[Steve Herschbach]

26 minutes ago, WesD said:

Has anyone actually had or heard of the ear breaking off on these 6000s? I have the micro cracks on my coil, but just letting it ride for now. The area that cracks is a thin zone between the thicker buttress ends. Not sure why they would design it that way, but obviously it wasn't a good idea.  I've always run the bolt very loose, so its not really an issue with that, but it would or sure fast track it to cracking by having it snugged tight.

Yeah, that thin area may very well be the main cause, maybe accentuated by a plastics issue. Just a bit thicker there may have made all the difference. Making over tightening more problematic. We often are looking for one cause, when it’s often a combination of things that add up. It’s an issue when they are trying to shave every possible bit off the coil weight. They can make indestructible coils, but most of us would then be complaining about the weight. 

[phrunt]

It's a fine balance between weight and strength/durability.  I think they took it a bit too far with the 6000 making it light but that's just me,  I wouldn't even notice another couple of hundreds grams of weight spread across the detector making the coils plastic a bit more durable and not scratching so easily, and a few decent cam locks like the Manticore on the shaft, those weights would be negligible to me. 

I'm no plastics engineer and really have no idea but it seems they have kept the coil design the exact same but changed the formula of the plastic a bit to prevent the cracking.  I guess I shouldn't stress about it, if my new coil is old and has the cracking issue I'll get it replaced again, I will wait until all the old stock coils are used up as replacements though so I know I'm getting a newer one with the better plastic, the 11" so far is the most sensitive of the GPX coils so it is one I really want to use the most.

[jasong]

That OEM coil is better than my 9" Coiltek, I think it's a pretty good coil aside from the quality control issues on it. Up until the 6000 I almost never used the stock coils as they always tested poorly for me, but the 6000 11" coil seems good aside from quality issues and it's the first stock coil I've ever really stuck with (when I'm given a choice anyways).

I tried the Coiltek again today and the Minelab is just better IMO on a number of levels from sensitivity to stability. Cracks 'n all. 

But I agree with WesD, I run my bolts somewhat loose too and still got cracks on both sides. It's probably a materials+design issue combined.