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The birth of a
smart idea

All of the best ideas evolve!

So, long story (quite) short...

The cargo bike (photo courtesy of www.bakfiets.nl)

With a young family to look after I wanted to use my engineering skills to create some income while the children were at school. I couldn't take a full time job because of the relatively short school hours.

My family had made several trips to Germany and the Netherlands and had always admired the tricycles with the cargo box on the front for the children to sit in. We considered buying one but were put off by the price. They were over £2,500. We parked that idea.

On our return from the last trip I couldn't get the trikes out of my mind.  I was a competent Welder and Machinist.  I was confident on being able to make a trike.

I sourced all of the materials, bought a TIG welder and a Colchester Lathe and set to work. The trikes have a pair of very substantial hubs on the front wheels that have a brake disc attached to each. These are not commercially available.  Some people have adapted wheelchair hubs for this purpose but I wanted something custom built for the job.

The Hubs...

I designed and turned a pair of hubs that would be suitable.  We then had a second child...

The trike in current design would not be big enough for our larger family.  I redesigned the trike but this also meant that I would need new hubs.

Not wanting to waste the hubs I had made I decided to list them on eBay.  I got so many bids for them from people who were making their own projects that I could have sold them ten times over!

I put the trike to one side for the next few months and made hundreds of pairs of hubs, custom-made to customer specifications.

Eventually I had to make time for the trike as the children were pestering me to take them out on it.

I needed a tube bender to bend the chrome-moly steel tubing. Not wanting to pay as much for a bender as a trike would cost, I built my own but I needed three different sized dies for the different tubing that the bike was made from.  There are commercially available dies but the company that sold them wouldn't sell them to me as I hadn't bought a bender from them...

The Dies...

I decided that I had to make my own dies.  To do this I would have to turn a concave form on my lathe.  Manual lathes are great at turning along straight lines and angles but one thing that they don't do very well is curves. This is done in industry by using a computer controlled (CNC) lathe.  I didn't have a CNC lathe...

There are attachments that can go on a lathe to create radii but being in four figures they were well out of my budget.

There was only one thing for it!  I had to make my own attachment...

The Attachment...

It took three months to perfect the design.  It would not only create concave radii but also convex.  I had spent quite a lot of my trike budget on this attachment so I made an additional five to try to recoup some of this investment.  They sold on eBay in a couple of days.

I put the trike to one side and spent the next eighteen months making tool after tool to sell. The product became so successful that it reached a level that I couldn't supply enough by just machining the tool myself.  I sold my lathe, mill and welder and invested the money into getting a batch of tools machined abroad.  I assembled the tool in the UK as I wanted to own the quality control.

I succeeded in getting the tool into a retailer in the UK and also one in the USA. 

As I was no longer machining the tools myself I had jigs and fittings that were taking up space in my garage (workshop/office & factory!).  I took them to the local scrap yard to weigh them in for cash.

While I was at the scrap yard I saw two huge skips.  One contained bright copper wire and the other contained PVC coated wire.

I got into a conversation with the chap working there and asked him why one had been stripped and the other hadn't.  He told me that the coated wire was only still coated because the people who had cashed it in didn't have the tools to remove the insulation.

Strippers...

This was a light bulb moment for me.  As soon as he told me that the stripped cable was bought for three times the cost of the coated cable I thought that I could buy the coated cable from him, strip it and, cash it in.

I searched and searched for methods of stripping the cable.  There are huge expensive industrial machines that you can buy and tools that you have to attach to a drill in order to operate it.  I was looking for something self-standing, handheld and portable. 

I found a couple but they had utility knife blades that were exposed to the user and looked lethal.  There was no way that they were a viable tool.

I wanted to be able to strip all cables that you would find in a house or domestic situation.  The majority of the unstripped cable that I was going to buy had come from the domestic environment, including flat "Twin and Earth" type cables.  None of the strippers that I had found would handle flat cables.

I would have to build my own...

Cableknife...

There were several considerations that I had when designing CableKnife.

The tool had to fit the following specification;

Types of Cable

I had searched every type of tool that claims to strip insulation from cable, from the small homemade lethal tools up to the large industrial machines. They all had one thing in common - none of them would strip every type of cable that a domestic installer would use.  Some would only strip the smaller diameter cables and others would only handle the larger capacity cables.

I wanted to make a tool that would strip everything from 1mm∅ cable up to something as large as a 20mm∅ cable that a DIY'er might find on a car battery system or an old welder they were breaking down for scrap.

There is another issue of flat cables.  Every house has flat cables in it, from 1mm² cables for lighting circuits up to 16mm² 70 Amp Twin & Earth cables that would be found on an electric shower or cooker circuit. 

They all had to be stripped using the same tool, without the need to adjust any screws or clamps each time the user wanted to strip a different size cable. 

Cutting Device

The other strippers used proprietary cutting devices such as sharpened wheels or metal spikes with sharp points.  The downside to this is that at 4pm on a friday afternoon when the apprentice electrician stripping cable and device goes blunt what can they do? Chances are will not have bought spare cutter purchase replacement from the manufacturer often at great cost.  Some cost more than the RRP of CableKnife, essentially just knife with guide for cable, part of the versatility of CableKnife.

Easy to Use

All of the other tools have either pre-drilled holes for different diameter cables (which limits the cables that can be stripped) or have adjustable rollers that the user changes for each type of cable.  The issue with this is that unless the user has organised their cable to be stripped into size order they will have to adjust the tool every time the strip a length of cable.  I wanted the tool to need no adjustment for every cut.

I spent a few weeks taking measurements of different cables and designing ideas in Solidworks. 

The parts needed to be prototyped accurately as there were tight tolerances that were important to the function of the tool.

3D prototyping is an economic way of reproducing parts for testing purposes, in particular laser sintering is a great balance of economy, accuracy and finish.  All in all, I had over 600 separate parts for the tool. Bearing in mind that the final design of the tool has only 5 parts, it shows just how reliant I was on this fast economic prototyping method.

A selection of the CableKnife prototypes from the very early designs to the final prototype

Once I had settled on the functional design I had the parts silicone cast. This method produces a part that is almost as accurate and durable as an injection moulded part, therefore allowing me to get coloured plastic parts to test fully for form and function.  These have also been tested to destruction.

One hundred and thirty four prototypes and CableKnife was born!

The final working prototype 

I never did build that trike...