In-pipe augers are designed to fit inside a pipe. The idea is to use the auger to make a shallow hole and then to push a pipe into the hole to support the sides. The auger is then lowered through the pipe and used to make the hole deeper. The pipe can be removed and replaced with a longer section as the hole gets deeper. The problem is that the hole made by the auger is of course smaller than the outside diameter of the pipe, and when going through hard layers the pipe can get jammed. What was missing is a way to widen the hole below the pipe, using something that can be lowered down the pipe.
I have been using an auger which fits into a 110mm sewerage pipe, with a millimeter or two of clearance. What I needed was a reaming tool that could widen the hole to about 115mm, but could also fit inside the 110mm pipe. At first I thought of some complex tool with retractable cutting teeth on springs, with a cable which could be pulled to retract or extend the teeth. An alternative was to have the cutting blades on a horizontal hinge so that they would retract when the tool was pulled up, and extend when it was pushed down. The best idea seemed to be to have vertical hinges and to use the rotation of the tool, plus the resistance from the ground to extend or retract the blades.
After creating a 3D design of the tool, the next step was to 3D print a 50% scale model to test it out, including a 50% size ‘110mm’ pipe to test the fit. The disk with holes in it keeps the tool centred. The scale model moved exactly as imagined, so the next step was to make it from metal.
Luckily I have a friend, Chris Jones, artist extraordinaire , with a metal workshop. His tools and expertise helped turn some scraps of metal I had into a working reamer within a few hours. The base of the tool is a section of mild steel square tube with four small sections of mild steel angle iron welded onto it. The cutting blades are 25mm stainless steel square tube with a small section of 5mm stainless steel plate welded on as a stop. They pivot on 8mm stainless steel bolts with two nuts to lock it in place while allowing the blade to pivot freely. The intention was to cut the disk from mild steel but in the end a 3D printed 5mm thick version using ABS plastic worked just fine as there is very little load on it, and was of course much simpler to make!
To allow the tool to cut a little way into hard ground, I used a cutting disk to remove two wedges leaving two sharp points.
I was busy with a new well point hole, and had hit a hard layer that the 110mm pipe could not get through. I lifted the pipe about 10cm, then lowered in the reamer while twisting it anti-clockwise. When it was just below the bottom of the 110mm pipe, twisting it clockwise made the cutting blades swivel out, digging into the hard walls of the hole. It jammed at first, but by turning it back and forth I got it free and could grind away the hard layer down to about 30cm below the bottom of the pipe.
The pipe could then be pushed effortlessly down into the widened hole.
The next problem was that water in the hole washed the sand off the auger as it was lifted, making it hard to lift the soil out. A pump doesn’t work because it get clogged very quickly with sand. One trick I was taught is to pour dry sand into the hole, and lift it out with the auger. That acts as a sponge, and gets some of the water out, but not all of it. The next thing that was needed was a device that could lift out the last of the water and mud. How hard could it be, after all?
PS:
I discussed the design of this reamer with Paul of Burrowman Augers, who really liked the idea, and will be making them to order. You can contact him on get.augernised@hotmail.co.za.
