Preventive Reinforcing Of Coil Ears

[mcjtom]

I was considering reinforcing the coil ears with some fiberglass and epoxy (on the outside).  Two questions:

a) does it make sense to do that at all?

b) I'm partial to JB Weld for the epoxy part, which is non-conductive (the steel powder is fine and the particles isolated by the epoxy matrix), but it is relatively ferromagnetic.  Even though the ears don't move with respect to the coil, would it have a potential of disturbing the magnetic field so close to the coil, as I understand some metal lower rods and bolts did in older detectors designs?

[GB_Amateur]

37 minutes ago, mcjtom said:

I was considering reinforcing the coil ears....

For which detector?  The answer to "does it make sense?" possibly depends upon the detector.

37 minutes ago, mcjtom said:

I'm partial to JB Weld for the epoxy part, which is non-conductive (the steel powder is fine and the particles isolated by the epoxy matrix), but it is relatively ferromagnetic.

JB Weld is a brand name and they have many products.  Which one are you referring to?  If you cure a bead's worth of it, say the size of a small coin, does your detector sound off on it?

[mcjtom]

The coil is Vanquish 10x7". JB Weld original. It is detectable if the bead is large enough.  

[mh9162013]

From my understanding, as long as the JB weld doesn't move or shift, you should be fine. And if it does move or shift, you've got more problems than your coil getting confused by the JB Weld.

Think about it, the cord from the coil has metal in it, right? And you're supposed to wrap it around the shaft in such a way that it doesn't move or shift while you swing your detector.

[mcjtom]

Tom Dankowski seems to suggest that any metal near the coil can disturb the balanced magnetic field around it and create blind spots even if not moving wrt the coil.  But then the cable connecting the coil with the control box should influence it too.  Maybe the mas of metal wires in it is not significant enough or perhaps being off centre makes it less influential?

Anyhow, it looks like one may be better of using an epoxy without steel filling when working around the coil, just in case...

I guess the question is: is it worth to reinforcing the ears at all - do they really break off easily?  One reason I have for it is that I remove coil from the shaft to make the machine more compact and be able to fit the parts in a duffle bag I use on the motorcycle - so maybe it makes sense to make it stronger before it's too late?

[mh9162013]

Is there a reason you can't buy a 3D printed coil stiffener?

As for whether it's worth it, hard to say. I haven't heard any consistent reports of coil ears being a problem on Vanquish coils. But that doesn't mean stiffening isn't necessary.

If you think you can do it with "regular" epoxy, I say go for it. The worst that'll happen is you waste epoxy and add some weight to the coil. Or am I missing something?

[GB_Amateur]

On 2/1/2022 at 6:50 PM, mcjtom said:

JB Weld original. It is detectable if the bead is large enough.

I made a 1.23 g bead of this JB Weld product (which I think is what you are referring to -- links are always best for clarity).  Note the packaging center wording "Steel Reinforced".  It was attached to a thin wood 'wand'.  I ran my Eqx 800 in Gold 1 w/11" coil, gain = 17, Recovery Speed = 5, Iron Bias F2 = 0.  Rubbing on the bottom of the coil housing and out to about 1 cm from the sweetspot of the housing, the detector gave a loud response.  The signal faded away about 2 cm (0.8 inch) from the bottom of the coil housing, over the sweetspot.

I also used my strongest Neodymium super magnet to see if the bead was attracted to it.  It was.

Conductive and ferromagnetic material in the field of a coil will distort the field.  (I looked for a good sketch that shows this but haven't been able to find it.  Many sketches in books, etc. show no distortion, which is inaccurate.)  However, my bead was considerably more than someone should use for a typical repair, and even it only distorts the field closeby.  Thus I don't see it would be a concern as long as it doesn't move in relation to the coil.

It is true that detectors in the past used (non-ferromagnetic?) stainless steel(?) screws to attach the coil to the shaft.  AFAIK that practice ceased a long time ago (at least a couple decades??).  Whether that change was based upon actual experimental evidence of performance loss/deficiency or was just an attempt to allay public perception, I have no idea.  Others here likely know more about that.

[GB_Amateur]

On 2/2/2022 at 11:53 PM, mcjtom said:

I guess the question is: is it worth to reinforcing the ears at all - do they really break off easily?

Based upon the lack of complaints here regarding the Vanquish coils, I'd say the answer to the 'easily' qualifed question is 'no'.

IMO it would be a mistake to do anything at least until the warranty has expired.  Minelab may be lax in the durability of some of their products, but they sure seem to be great at honoring a warranty as long as the user has kept within the warranty limitations.  I suspect epoxying a stiffener to a coil would void a warranty.  As to whether they would choose to enforce that -- ??  But why chance it?

As far as non-epoxied aftermarket 'stiffeners', AFAIK those are seat-of-the-pants (aka 'garage engineering') attempts to alleviate the problem of Equinox coil ear breakage.  There is certainly some debate as to whether or not those even improve the situation.

This may be the case of the faceoff between two common maxims:  An ounce of prevention is worth a pound of cure, and the more homespun sounding If it ain't broke, don't fix it.  ?

[mcjtom]

8 hours ago, GB_Amateur said:

On 2/2/2022 at 6:50 AM, mcjtom said:

JB Weld original. It is detectable if the bead is large enough.

I made a 1.23 g bead

That's probably close in size to a sphere 11 mm in diameter? - JB Weld density is some 1.93 g/cm^3 (from MSDS).