Sand Tumbler

I’m sorry the blog has been quiet for a while – blame it on other priorities getting in the way, such as vacations and preparing to put the house on the market.  However that does not mean the Kayfa workshop has been totally idle!  In this post I will tell you about another little machine I have designed and built, which I call a “Sand Tumbler”.

The principle is that, sometimes I may want to put a satin finish on a blade rather than a shiny polish, and for that I need a way of giving the blade a gentle allover sanding that will not leave any scratch marks from traditional hand sanding.  This Sand Tumbler should do exactly that.  It is basically a plastic tube, closed at both ends, but into which I can put a quantity of sand and small stones together with the blade to be buffed.  The tube then rotates slowly for several hours, possibly overnight, and the gentle tumbling of the blade in the sand will produce the satin finish.

The main components of the device are:

1. The tube, which is cut from a length of waste water pipe about 100mm in diameter and 400mm long.  The one end is permanently closed with an end cap, but the other end can be opened because the end cap has a screw thread.
2. The roller wheels for the tube to run on.  These were repurposed from a small skateboard.
3. The drive motor and gearbox to reduce the speed but increase the torque.
4. A power supply to convert the mains power to 24V DC.
5. A speed controller for fine adjustment of the drum’s rotational speed.  Experimentation will confirm, but I anticipate a speed of around 50-60 rpm will be good.
6. A toothed drive belt and pulleys to connect the gearbox to the main tube.
7. An on/off switch.
8. The frame that everything is mounted on or in.

My first attempt repurposed the motor from an old overlocker, but I could not slow the speed enough without overloading the motor and it burned out very quickly.  I then purchased a 24V DC motor with fitted gearbox that was theoretically powerful enough for this application, and it does work as expected, but I think the power rating is still insufficient because the motor runs very hot after about 10-15 minutes.  I will soon replace this with a more powerful motor that will be “man enough” for the job.  Until such time I am nervous about putting it to work too strenuously, so a full demonstration of its capability must wait for another day.

Until then, enjoy the photos.

The full Sand Tumbler device.  The power supply, speed controller and drive motor are housed within the wooden box.  The toothed drive belt is on the left side of this view.  The digital display gives the percentage rotation of full speed and the knob to its left is for adjusting the speed.

View from the right showing the power supply unit that converts mains AC to 24V DC.  The green button is a secondary isolation switch for safety purposes, if required.

View from the left showing the drive end with motor, gearbox and toothed drive belt.

Video showing the unit in operation.  (Turn down the volume before running the video!)