Pulse Induction detector build

[Chef Geoff]

Well if you want to change it in the future then this is what to look for...
http://www.amazon.co.uk/Enjoydeal-Portable-6800mAh-Rechargeable-Battery/dp/B00V68AQL8/ref=sr_1_8?ie=UTF8&qid=1444593456&sr=8-8&keywords=12v+battery+cctv
These only weigh a few ounces but as you can see it 6.8 Ah so would last 5X the length of time than the acid battery

[Dryland]

If you need Police, then we've got plenty that you can have.

[Cymro]

If you need Police, then we've got plenty that you can have.

So that's where ours have gone . . . 

[Dryland]

 

[nobby]

we need more of them here to keep an eye on dryland

[Cymro]

After a lot of soul-searching I finally decided that I could do without a meter on the PI machine - I'm pretty much resigned to the fact that I'm going to have to dig everything anyway.

Had a look at what I needed to accommodate and fixed a size in my mind - there are six control potentiometers and at least two LEDs so it was never going to be small . . . I also decided on a modular form of construction so if I do change my mind about the layout, size etc I can just change what needs changing rather than starting again from scratch - in fact the whole detector has evolved on that principle.

Having decided on a size and vague shape for the control pod, I had to decide how to attach it to the handle in line with the modular approach, so I hit on the idea of a tapped mounting pad which everything else fits onto.

I've actually added numbers to the pics this time - hope it helps to follow the build.

Started off with an offcut of 1.6mm aluminium sheet and cut it out as shown in Pic 1, then just gently 'broke' the lines of the horizontal bends (Pic 2). Folded the edges fully and 'persuaded' the folds I'd broken with a dolly and soft hammer (Pic 3). This part will form the back and bottom of the pod and will be screwed in place on the mounting pad.

I had a chunk of cast aluminium I'd made for another job (I'd used an open mould, using a builders' mastic tube as a pattern - more on this later . . . ) so turned it to size (Pic 4), bored it to 25mm (Pic 5) then cut a piece off, marked it for 3 holes and drilled it ready to tap it M4 for button-head stainless screws (Pic 6.)

I then parted off two discs from the piece I'd drilled, tapped the one in Pic 7 with the marking blue on it and drilled clearance holes in the unmarked disc. Since the holes had been drilled in both pieces while they were still attached to each other they had no choice but to line up and couldn't cause me any problems due to mis-alignment 

I then brazed the tapped piece to the handle, which is attached to the shaft (Pic 9) after which it was just a matter of cutting a hole in the bottom of the box and drilling the circle of holes around it (Pic 10,) then screwing the pod to the mounting pad in Pic 11.

Obviously I need to braze the corners of the pod base and do some more finishing off, then I have to make the front and sides for it - that's for a later installment.

Just in the interests of assuring my loyal readers that things don't always go according to plan, Pic 8 shows the deliberate(!) error I made. I'd made the mounting pad and its securing ring from some cast round bar I'd poured in the past. Unless I'm melting a known alloy, I'm never sure exactly what goes in the crucible. Anything crucial and I'll try and use *say* alloy wheel material (or 'wheelieminium' as we home founders have it . . . ) or pistons etc.

When I came to braze the mounting ring to the handle section, just as the rod started to flow, the ring melted. I was in a bit of a quandary so re-heated it to melt the rest of it off, filed the handle smooth and re-made the ring out of some expensive aluminium billet I'd been keeping for a special job. No idea what special job - just 'special . . . '

Also, since I'd used an open mould it didn't have sufficent hydrostatic head to exert enough pressure to consolidate the alloy when I poured it, leading to a lot of entrained air bubbles which can be seen on the surface of the bar in Pic 4. (Weakens it . . . )

[Cymro]

Been a bit slack with the pics lately - also been busy with a plasterer's trowel trying to get the hall finished (only started it in 2000 . . .)

The PI I'm building has a 'Reset' button which has to be pushed every couple of minutes (or so they say . . .) and indeed I had one on the Mk1 version I built. I did the best I could with positioning it but it was only ever the best of a bad job. The pod it was mounted on was 135mm wide and it had to go at one side or the other - whichever side I chose was a good stretch of the thumb, so since I'm left-handed I placed it on the left-hand side. A right-hander would have had problems . . .

So, again taking my inspiration from my Whites machines, I decided to use a 'trigger' right behind the handle. I sketched up a small box to put the centre-sprung switch in, cut a piece of aluminiun sheet to suit and cut it out (Pic 1.) I carefully folded it to shape, which wasn't easy as it's small enough to cause problems getting it in the folder (Pic 2.) I then made a cut-out in the fascia mount and brazed it in place (Pic 3) at the same time as brazing the seams.

Next job was to make a handle grip - I had already brazed the pod mounting in place on top of the handle so couldn't slip a bike handlebar grip over it, and couldn't have done that first in any event because it would melt under the heat.

There is a mouldable plastic material available - called Sugru - which would have been ideal for the job but costs a bomb to buy. I used a recipe I found a couple of years ago for a Sugru substitute, but at hardly any cost. It uses silicone builders' mastic mixed with cornflour and gives a tough, resilient plastic material. It works because the catalyst for the silicone is water, but the silicone forms a skin quite quickly from the moisture in the air so takes ages to cure all the way through cos the skin prevents it from absorbing any more moisture . . .  Cornflour is hygroscopic (absorbs moisture) and so when it's mixed with the silicone it carries the moisture all the way through with it. It takes a bit of mixing up but once it is it turns into a Plasticine-like consistency which can be moulded by hand and hardens fully in about 20 minutes.

 I bought black mastic, otherwise it can look somewhat 'medical' in a sort of white translucent finish. It's possible to add a tiny bit of gloss paint to colour it - but it stinks of paint for days if you do. I used some artistic licence and moulded finger-grips in, using diluted Fairy Liquid (TM) to smooth it out and prevent it sticking to me. The result can be seen in Pic 4, along with the trigger switch for the 'Reset' function. A word of advice if anybody wants to try using this for anything - there are two types of mastic; silicone and acrylic. Only the silicone will work, and you can tell them apart because the silicone has a strong smell of vinegar as it cures (and should say 'Silicone' on the tube . . .  )

I then sketched the fascia panel for the pod, cut it out from sheet, folded and brazed it, forgetting to photograph it as I went. It was only after I had marked it out and drilled the holes for the controls that I remembered to do it. It's nothing new, just using the same procedures as before. The result can be seen in Pics 5 and 6.

I've painted the shaft today, using Plasti-Kote Satin Black aerosol paint and it's drying as I type. I intend painting parts as I finish working on them from now on - I'll probably have finished with the fascia tomorrow so that can be done too.

Will post more as it happens - I'm looking to order electrical wiring connectors now as I'll be ready to start wiring it soon. I want to have the fascia detachable by having a multi-way plug and socket inside the box - bit expensive but I've got this far . . .

[Resurgam]

            Nice progress Clive. Having hade the opportunity to meet your brainchild, hands on so to speek; the things that impressed me were the balance and the initial comfort of the hand grip. It just fealt right.

[Cymro]

Thanks, Chris! 

[Dryland]

I've never heard of the silicone and cornflour mix before, Great tip that might come in handy one day.

[Cymro]

I've never heard of the silicone and cornflour mix before, Great tip that might come in handy one day.

I can't claim any credit for it; I found it on one of my favourite hackers' sites, Instructables:

http://www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute/

There are 15 steps in the Instructable - you'll have to follow the 'Next' button to access them. Or register for free and download the PDF.

I guess you could use anything which absorbs water to mix with the silicone - I found a YouTube video where someone used baking powder.

Knowledge is power . . .

[Cymro]

Could be a longer job than I thought - for all the wrong reasons.

I sprayed the shaft and a few other bits and it's taking a dog's age to harden. Says on the tin that it's touch dry in a couple of hours and fully hardened in 24 hours.

Still scratching really easily 48 hours on . . . 

[nobby]

Stick it next to the radiator.....been using plastikote today and no problems, its one of the better ones ive used

[Cymro]

Stick it next to the radiator.....been using plastikote today and no problems, its one of the better ones ive used

Your reply gave me a laugh - I could put it next to the radiator but we don't put the heating on unless it's freezing outside! LOL

Never used it before so believed what it said on the tin . . .  Although the weather for the past couple of days has been mild but dank, so maybe that's affecting it. It's in the Woodwork Dept (outside shed . . .  ) to dry, and there's definitely no heat out there!

[Cymro]

Been waiting and waiting for the postman to deliver the electrical terminals I sent for from a couple of eBay sellers. Finally got fed up yesterday and checked my eBay purchase history just in case . . .

Oops - senior moment. Placed them in my 'basket' but forgot to check out . . . So I'll have to wait a bit longer for them.

Meanwhile the paint is disappointing. It was applied more than a week ago and if I place the painted bits against anything it sticks and the paint peels off. Oh well, it's only cosmetic . . .

A question for anybody who's following this; do 'we' know anybody who has a vinyl cutter who could make some decals on the cheap? Just a bit of fun (and a bit of vanity . . .  )