Project start: August 2014

Lowcost Disc Sander

What does one do with broken hard drives? Exactly, building a disc sander.
Your can find a lot of building instructions about "hdd sanders" on the internet.

All what is needle is a 3.5" hard disk drive with working motor and motor controller.
The heads assembly and the magnet can be removed.
Additionally an 5V and 12V powersupply is needed. For this ATX PC supplies are very handy. If your want to use an other supply, make sure the 5V is stable and accurate, otherwise the motor won't start.

In order to grind metal on it one platter has to be taken out and covered with double sided tape. Overhanging material has to be cut off. Considering the fast rotating disc at 7000 rpm the tape has to be layed out very evenly, otherwise the drive might walk away on its own.
Be careful working with the drive platters. Some are made out of aluminium, others can be metall coated glass discs. Maybe it is not advisable to use these glass discs in the first place for such usage.
The double sided tape is then used to attach sand paper to it. Also the inner and outer circle have to be cut out. After that the other platters with the spacers can be places on the motor again. You can switch them around or add more for a higher moment of inertia. The one with the sand paper on top should be the topmost one.

Plug the power connector in and its a finished hdd sander. For example, with this 280 grid sand paper knifes can be sharpened.

To make this project a bit more interesting I wanted to add the ability to do wet sanding.
For this the case needed to be waterproofed. The motor is already glued in watertight by the factory. The hole where previously cables for the read/write head went trough was made watertight by screwing a small carbon plate on top. Another bigger slot had to be filled with hot glue.
The controller board is mounted underneath the case and was wrapped in cling wrap to save it against water splashed.

The bottom of the hard drive is a bit slippery. To fix that I mounted it to an aluminium sheet with screws as feet and a blob of hot glue on their heads.

The drive cover catched water which would otherwise be flung in all directions.
The gray sand paper is btw 1200 grid. By adding water this is more polishing than grinding.

Needle grinding contraption

The main idea for building this disc sander was that I needed to grind needles for my DIY Record Lathe.
The needles have to have a tip with an angle of 60° to 90°. The tip itself should also have a radius less than 20 µm.
To have an evenly round tip the needle will be turned by a dremel rather slowly. The dremel itself is mounted on a rotating contraption and presses the needle onto the disc sander with minimal weight.

The chain can be screwed to the aluminium U profiles at verious points, which changes the height of the dremel and thus the angle of the tip in relation to the disc surface.

The rod to be ground will be mounted in the chuck of the dremel. Both the dremel and the hard drive are then powered on and with a bit of water added the tip can be ground for a few seconds.

This worked out quite well.

More about the use of this needle can be found here: Recordlathe Cutterhead V2.


The Dremel was never really straight and setting up a specific angle was a guessing game. Some time ago I did buy a Proxxon LSB/E, which I like a lot more.
To be able to use the Proxxon for this a new holding contraption was needed. A welded angle piece holds another hard drive on the side. The motor of this HDD is solely used because of its bearing. There a wooden plate is mounted to fasten the Proxxon to it. This can than rotate around like before. The rubber band keeps pressure on the needle. With some marking on the side I now can guess the angles a bit easier.

The needles created with this contraption are used for Cutterhead V3.