Repair to 8" Commander

Hi there.

If anyone knows a better solution to repairing an 8" Commander coil I would greatly appreciate it.

It has developed cracks around the support housing where the shaft connects to it. If no suggestions are offered then it will be an araldite job and hope for the best.
I rarely use it since getting the 7K, but it would be a shame to lose it due to a few cracks.

Regards Axtyr.

I've heard that a good quality super glue combined with baking soda is tough,
good old basic araldite goes brittle.
i saw a bloke joining plastic with hot wire then glued over it,no good in your case,would need non ferrous metal
should be more solutions on youtube somewhere.
There's a billion type of glues out there,araldite for pools is amazing fixed our cracked porcelain dunny many years ago,so far so good.


cheers   moredeep

Try this stuff: https://www.rapidfix.com/
I have used it for several different little repair jobs and found it to be pretty good.

I have used this stuff with success however, the stuff in the Fibre Pen, Primer? to me was in short supply or hard to do a good coating.

https://www.selleys.com.au/products/adhesives/minor-repairs/selleys-all-plastic-fix/

The one factor for success is the cleaning of the plastic prior to glueing.
I suppose it's like any form of welding/soldering preparation of the surface is the key.


cheers   moredeep

Thank you all for your help..

The rapidfix will be my next attempt when I get to Bunnings, it's cheap enough. It also gave me another idea. I had planned to repair my stormwater drain today and given the rapidfix glues polyethylene I thought I'd give the PVC glue a try.

I used a couple of skid plates, assuming they are the same material as the coils. The cleaning fluid certainly removed the glossy shine off the plates but the glue didn't hold them together. Maybe I only had a small point of contact but I didn't want to end up with 2 skid plates glued together.

The other thing I thought about was the fact that the detector is a motion detector and as such works on the principle of movement. If the gold is placed on top of the coil it gives a signal then it disappears until the piece is moved over the coil. This gave me the idea that I could use metal brackets to replace the existing plastic ones.

I hooked up the coil to the detector and tested with a small piece of gold and the signal was great, then I sat the coil on top of my metal vice and tried again without luck. Maybe the amount of metal in the vice is just too overpowering but it wouldn't register the small piece of gold unless it was scraped across the bottom of the coil.

So it will be the rapidfix next and if that doesn't work I will then try using a plastic chopping board. Bend it at 90 degrees and set it all up then use Selleys All Clear to secure it to the top of the coil, there's nothing to lose.

Regards Axtyr.

The glues that have worked for me MEK(Plumbers glue available in clear),Acetone mixed with chopped up old skid plate forms a paintable glue and epoxy two-part works well too.As stated above clean well.

Axtyr I also had the exact same problem on my 8" Commander coil as yours. I fixed mine and have had no problems ever since. Shortly I'll put up photos and the process that I used. So please don't do anything until I can put up my fix on site as most other types of repairs will end up as being temporary.
wombat

Axtyr this job is not a 5 min. fix as you will see by the photos. But I promise you that you will not have anymore trouble or cracking in that areas. I did mine well over 12 months ago and it has not let me down yet.
What you will need is a very small piece of white plastic sheeting at least 130mm square by 1.5 mm thick. This will make the top base plate.
40 X 40 x 5 mm plastic angle ( 50 X 50 X 5 will be OK as you can cut it down to size.)
Acrifix 1R0192 plastic glue (100g) by Evonik Industries. You can get this on Ebay for around $33.00. Or where you get your plastic from may have it cheaper. I got all my materials including glue from General Plastics, Ballarat. But any plastic repair mob should have everything you need. This is the ideal glue for this and many other jobs as well. Well worth the money.

Now to start repair.
(a) First of all mark the centre of your angle brackets on the coil with a marker pen, extending the line to each side of the coil and down the middle.

(b) Now remove the existing angle support brackets by gentle cutting them of. Making sure you do not cut into the top surface of the coin. And then remove any traces of the bracket from the surface of the coil leaving no bumps. You can use a file or sandpaper to do this.

(c) Now pick up your centrepoint marks and draw a 120 mm radius on the top of your coil, and sand within that area to make it rough. This helps glue bonding.

(d) With your 130mm plastic sheet cut a circle out at a 120mm dia. (Do not make it square as it will start cracking the surface of the coil again when in use.)

(e) You will now notice that when you put your disc on top of the coil it will not lay flat. (Hump in the middle) To overcome this it will need to be heated slightly over a flame or heat of some sort. This will soften the plastic and it can be shaped easily to the top cervitaur of the coil.

(f) Using sandpaper roughen the underside of your disc and then glue in position with in the radius marked on the coil. Making sure that all edges are down with no gaps. Now apply a small bead of glue around the edge and let dry.

(g) Now for your angle brackets. These have to be cut to 50mm long X 25mm wide X 35mm high. Shaping the top with a full radius

(h) Now becomes the fiddly part shaping the bottom of the angle to the the top of the coil plate at the same time keeping the angle square to each other and vertical. I did this with a belt sander using the radius part of the belt. But you may be able to do this with a file. Try and get them to fit neatly as possible as this will help in the overall strength of your repair.

(i) Marking the bolt holes in your brackets to take your shaft.
Measure the bottom of your shaft ( Radius section) to the centre of the hole. Now transfer that measurement to your brackets "PLUS add AT LEAST ANOTHER 4 TO 5 mm" This will allow your shaft to swing 180 deg over the coil. And drill a neat hole through both angles slightly bigger than the plastic bolt that secures the shaft and coil together. Make sure that the bolt holes are in the exact same spot to each other on each bracket.

(j) Gluing the brackets to the coil.
You will need a wooden spacer to do this. The spacer has to be at least 1 mm wider than your shaft (including the rubbers secured to the shaft) Having a hole through the timber spacer it so you can bolt the angle to each side. Now do a test run by picking up your centre lines that you marked earlier on the coil and transferred across your new base plate. By doing this you will see if you need to do any adjustments to the brackets and there seating position.

(k) If your happy with the fit up, mark where the brackets are going to be glued and sandpaper that area and glue the brackets on, still with your spacer in between the brackets and let dry. Later put a small bead of glue around the outside of the the brackets.

(l) Small angle support brackets. you only need to do this to one side only. It is more to take the head of the plastic bolt than anything else.  Put the plastic bolt through the brackets and mark on the bracket where the head of the bolt fits. Then remove the blot. Make up 2 small angle bracket to suit that area and glue. You can use any material left over from your 1.5 sheet of plastic. Making sure the head of the bolt will fit in between but can not turn by its own accord. Make sure all surfaces are clean before gluing. Let the coil dry for at least 48 hrs before use.

You have now repaired your coil with a stronger bracket than it originally came with.
wombat  

That's a great looking repair job bill,makes sense to do it that way.
That's what I call thinking outside the box 

cheers   moredeep

Nice one Wombat, great repair.

I haven't done anything yet as I keep thinking of different ways to do it the most effective way. Your way was the preferrable one and I didn't think about placing a plate between the coil and the bracket.

I contacted Minelab and was told that the top of the coil is made of ABS plastic but they couldn't recommend a particular glue. A search found several applicable glues and I was going to get the Loctite 2 part plastic glue. The downside to glueing up the cracks is it would certainly break again eventually. I did think about going to Coiltek in Maryborough and asking if they had any broken coils there and I would cut the top of the coil off with the lugs and glue it to the top of the 8"coil.

I have downloaded a file so I can make up a bracket that is printed on a 3D printer. I called a friend of mine yesterday to see if he still had access to a 3D printer but he didn't get back to me.

I use the 7000 so I am not in a hurry to get the coil fixed.

Thanks again everyone.

Regards Axtyr.

Somebody with a 3D printer may be able to make the whole add on part that could be glued on. Could be a good side line money spinner for someone.
Rowdy

For Pete's sake!!! Just throw it away and buy an X coil. T model Ford technology.

davsgold wrote:That's an even better way to fix it Reg I like it.

I'm guessing when Wombat did his repair x-coils were not available then.

cheers dave

Believe it or not, that whole repair cost me nothing. Including the glue. The company gave me the whole lot as it was left over items from another job that they were doing. Also your right Dave the X- coil was not out then. And why should I replace my 8" coil that is working perfectly well just because the mounting brackets were cracking. And now it is working just as good as it was when I first bought it at no extra cost to me. I love my 8" coil, it has found a sh!t load of gold over the ages and at depth too.
wombat

I'm with you there Wombat.

The coil was a birthday present back in 2014 and rarely came off the SD2000 for 12 months before moving to the 5000. It has found a lot of gold including some incredibly small stuff and some very interesting goldfields items. If it wasn't for the 14" Elite it would have still been on the 5000.

There is nothing wrong with the coil and it certainly won't cost much to repair it compared to replacing it with a new coil, especially a X-coil.

Regards Axtyr.

Gday Any cracks in plastic or similar I just use a soldering iron and melt it back together simple strong and costs nothing and NO I don't use solder.
Regards
Big fella

Big Fella,

I've always had very little success using the soldering iron method and the plastic is very thin. It is so thin that it will definitely crack again in the future that is why I want to put the regular ears over the top of the coil. I don't know why they just didn't make it with the same ears as the bigger coils.

It is very interesting to see how others have gone about coil repairs.

Regards Axtyr.

There will always be a place in my kit for the 8"mono and I have 3 repaired ones in use.One thing lacking in the new coils is edge sensitivity as much as i like them no one coil gets it all.Pretty good effort Bill on your repair better than my last housing repair.The 3D printers are sounding like a good idea.

I have made coil brackets for a PI from high grade stainless steel.
I don't know about the Z but ordinary PIs do not respond well to S/S.

Any other metal will cause the coil to detune/auto tune back to threshold. If it has to detune too far the coil will eventually become almost unresponsive to any other target. Large or small.

It’s finally repaired and I hope it lasts. I knew exactly what I wanted to fix it with but Miner’s Den in Mitcham didn’t have what I wanted. I initially went to Bunnings and got some 50mm PVC angle and made up 2 of these to attach to the coil.


I was up at Maryborough and called in at Coiltek and they had just what I wanted, an old broken 11” coil which they happily donated to me. I pulled it apart and cut a 170mm diameter circle around the ears to use as a plate on top of the 8” coil. As the top of the 8” coil is not flat like all the others some judicious application of heat was required. The front of the coil has a steeper angle than the back so I started at the back and the sides.

On the 8” coil the first thing I did was cut the old ears off and file down the raised sections on the coil top.


With the plate I made up from the 11” coil I cut out where the existing coil lead is situated. Then I heated the new plate either side of the ears until it softened enough to shape to the sides of the coil. The front of this plate was sitting up off the old coil. Once I was satisfied the two surfaces would glue together I cleaned the top surface of the coil and the underside of the plate with PVC cleaner, applied glue to both sides and then clamped them together. I started off testing it with large bulldog clips but felt the pressure wasn’t enough to hold it together. Thankfully I had some large clamps which helped keep the surfaces together close to the centre and I used a combination of smaller clamps and bulldog clips around the edges.


To stabilise the front of the coil I flattened out some 100mm PVC pipe in the oven and the cut small pieces to fit and glue inside the gap and support the front lip.


Once it was all glued together and cured I filled under the front lip and around the edges with Selley’s All Clear. I don’t like using it for my plumbing because it forms a skin over it very quickly, but it will stick to anything, dirty or clean.


It just needs to be tested next week.

Thanks to all who supplied information to fix.

Regards Axtyr.