detector stem

[sdesic]

Can I make a square coil (holder) ?
I have 16x16 cm square that can hold coil ...

[Jerry]

Here is my latest effort at building a TGSL. The board is the EDU version with a few changes to the threshold of U107.

The housing for the control box is from a junk DC to AC converter. Armrest is cut from 4 inch diameter thin wall aluminum irrigation tubing. Shaft for armrest is a piece taken from a spring loaded shower curtain arm. The 45 degree elbows are 3/4 inch PVC fittings. The tubing OD is 3/4 inch and fits so tight that I used PVC cement as a lubricant to enable seating the tubing all the way. Once set, I can not move them. The upper shaft is from a weed eater. The lower shaft is from a wood broom handle turned to fit the tubing and sanded square at the ends to fit the coil. Bolt is from a toilet bowl lid. Cable is from an old USB device.

The material for the armrest padding is from an old bag type cell phone. I glued the foam to the aluminum armrest and the wife sewed the cover which has a pocket on each end so it can be slipped over the ears of the armrest.

Power is two nine volt batteries under the armrest. In retrospect the detector would have balanced better if I had used a 12 volt pack of AA cells and just accepted the added weight. (About 3 1/4 oz difference)

This is the lightest detector I have made so far. It weighs 3 pounds 2.4 oz with the batteries installed.

I am not real happy with the 45 degree PVC elbow to make the S shaft. They appear to be plenty strong enough, but I do not like the feel of them compared to the Garrett At Pro shaft that I have for my other TGSL. I will probably switch them around and use this one for a testing detectors.

This has been long but maybe it will give some one an idea of possible materials to use.

Jerry.

[Gold Finger]

No need to, as it is very straight forward to construct.

[TH Jim]

Gold Fingerer:

Are you not going to show some photo's of your detector modifications?

Regards Jim

[Gold Finger]

I have experimented with various materials such as aluminium crutches, telescopic mop handles and hikers sticks.
By far the best suited tube for detector stems in my opinion is carbon fibre, which I use. It is very strong in compression, doesn't flex like plastic, and is extremely lightweight.
An anglers landing net pole is probably the easiest method to gain the correct strength material.

[bernte_one]

here my last one
made from elbow crutch and water pipes


regards bernd

[Tec]

DIY All the other (non electronic) bits

Attached is my design, it requires some epoxy and fiberglass, all from readily available parts. It's better than most commercial detectors in my Unbiased opinion .

** Note, The most important trick with the epoxy/fibreglass on the shaft is to wrap it all up with electrical tape when it is wet. The elctrical tape will easily peel off later after the epoxy is dry. This will leave a tidy 'epoxy composite' shaft that can be sanded and painted.

[Tepco]

I'm using this in "inverted" position for most of the time too, seems to be more practical.

[wam]

I have one of this as well but I have turne around handel so the upper shaft is bent in "up direction". I was lacky becouse the Minelab lower shaft was perfect fit for it.
Regards,

[Tepco]

This is my favorite "low labor" one: Upper part is from elbow crutch, thin wall Al alloy, 19mm inner diameter. (local cost 11E). Lower part is from "beginners" 3-section carbon fiber fishing rod (5E), diameter fits luckily. Two sections used, inner one wrapped whit glass fiber (boat repair kit) and 2-component resin and inserted in outer section. When hardened, only drill few holes for length adjustment on upper side, and grind down lower side to fit "ears". 10min. of work, very strong and lightweight, even not looking that bad.

[DOOLEY]

just thought id chip in ,

a stem made from 20-22mm water / wast pipe to floppy ,
40mm waist pipe not floppy but to big ,

use 20mm internal 22mm external waist pipe from diy (b&q etc...)
and slide in 19mm wood dowling with insulation tape to pad it out.
would have liked 20mm dowling , but cant readily find any.

end result , slim stiff stem , waterproof , and many joining bits available for this common size of pipe.

[bernte_one]

high pressure water pipe min 16bar 20mm dia lower part 25mm dia upper part connector 20to25

the stem stiff enough to make more stiff cut a second pipe lenght press it a little bit and stick in the one with the same diameter

the pro of this stem NO metal parts very cheap

[Qiaozhi]

Interesting point Qiaozhi, I was thinking that maybe the reason why sensitivity is reduced is infact as you correctly stated the fact it knocks the coil inductance/ balance settings out.
So that tells me that proberly in the old days when balancing and designing the coils the stems must or should have been taken into account.
I got one of those zennox 1006 cheap detectors here with a metal shaft its as unstable with or without its shaft lol, so that doesnt prove much.

With older TR detectors, problems with the lower metal shaft were probably not so noticeable. Especially since it would be masked by the other problems of drift and lack of sensitivity anyway.

[satdaveuk]

If metal parts are used for the lower stem, or for the stem bolt, there are two main problems. Firstly, this unwanted metal affects the sensitivity of the coil, and secondly it distorts the electromagnetic field and upsets the coil balance.

As a simple experiment, you can take a detector (without a metal lower stem or metal stem bolt) and place a metal object close to the coil. Notice how the sensitivity is reduced when you perform a few depth tests with your favorite test targets.

Interesting point Qiaozhi, I was thinking that maybe the reason why sensitivity is reduced is infact as you correctly stated the fact it knocks the coil inductance/ balance settings out.
So that tells me that proberly in the old days when balancing and designing the coils the stems must or should have been taken into account.
I got one of those zennox 1006 cheap detectors here with a metal shaft its as unstable with or without its shaft lol, so that doesnt prove much.

[Qiaozhi]

But i´m wondering that the professional stems often have a lower metal part.
It can take effect on the magnetic field thats clear but it´s not moved in relation to coil - so it is equal or not?

If metal parts are used for the lower stem, or for the stem bolt, there are two main problems. Firstly, this unwanted metal affects the sensitivity of the coil, and secondly it distorts the electromagnetic field and upsets the coil balance.

As a simple experiment, you can take a detector (without a metal lower stem or metal stem bolt) and place a metal object close to the coil. Notice how the sensitivity is reduced when you perform a few depth tests with your favorite test targets.