Securely Erasing a Hard Disk





Introduction: Securely Erasing a Hard Disk

When disposing of an old hard disk, it might be tempting to simply throw it in the garbage, or sell it. However, first you should remove any sensitive data from the disk. This might be financial data, old email, login information for web sites, and the like. Unfortunately, simply deleting files doesn't normally remove the data -- it just marks the space as available and removes the file from the directory listing. The data can be recovered at this point, often quite trivially. If you wish to protect your data, you need to do something more thorough. There are some software utilities that can do a fairly good job, but if you're feeling especially paranoid (or simply want to have fun!), a physical process is required.

Please note that casting is a potentially hazardous activity. Observe appropriate safety precautions. The details should be covered in whatever casting training you received, whether online or in a class.

In this instructable, we'll erase the disk by melting it. Hard disks are mostly made of aluminum, which can be recycled, so don't throw it out! Instead, we'll cast a new solid-aluminum hard disk using the original as a pattern. For this project, we'll use the aluminum foundry at TechShop Raleigh-Durham. That way we have all the casting tools we need, including sand, furnace, flasks, and molding tools.

Step 1:

The first step in any casting project is to prepare the casting sand. Start by sifting the sand to remove debris and break up clumps. Then add water to temper the sand so that it sticks together. Add enough water to make the sand slightly moist, but not wet. It should clump when you squeeze it in your hands, and break cleanly rather than crumbling when you break it. If you add too much water the sand will get sticky, and stick to both the tools and your pattern, making it difficult to work with. The additional water will also generate more steam, which can interfere with the quality of the casting.

Step 2:

With the sand ready, we select a flask that will hold our hard disk with room to spare. First, coat the hard disk and molding board with parting dust so the sand doesn't stick to them. We pack the bottom half of the flask (the drag) first. Place the hard disk upside down on the molding board, and place the drag around it. Add loose about 2 inches deep, pack the sand with the ramming hammer (be firm!) and repeat until the drag is slightly overfull. Scrape the surface clean, starting on the near side and working away from you in several steps to get a clean surface. Sprinkle some loose sand on the scraped surface, and rub in the bottoming board. To do this, press down firmly, and rub the board back and forth slightly. This allows the loose sand to fill any cracks or other imperfections in the bottoming board, so that the mold will be firmly supported during the casting process.

Step 3:

The next step is to pack the top half of the mold (the cope). Take the assembly of molding board, drag, and bottoming board, and flip it over so the molding board is on top. Remove the molding board to expose your hard disk. Remove any sand on top of the hard disk. Sprinkle a fine layer of parting dust over the disk and exposed sand; this will prevent the two halves of the mold sticking together. Wipe off any excess. Then, place the cope over the drag; alignment pins should accurately locate the two halves. Pack the cope in the same manner as the drag.

Step 4:

Next, separate the two mold halves. Before removing the disk, tap it gently with a hard object to loosen it in the sand so that it will pull out cleanly without damaging the mold. Hard disks have very shallow angles, which makes this a very important step. Even so, pulling the disk out of the mold will be tricky. There are a variety of ways to do this; I went with the simple method of just grabbing the edges of the hard disk cover with my fingernails and lifting the disk out. This was less than ideal, as the edges of the mold crumbled slightly. If getting a really clean casting is important to you, you may want to try something more complicated. In my case, I was happy enough with the result. If things go poorly, you can always repack the mold and try again.

Stuff to watch for: lift the part straight out without shifting it sideways. Be sure to use plenty of parting dust when packing the mold originally. If your sand is too dry, it can get very crumbly at this point. Don't be afraid to just try again if needed; packing a mold is quick, and a lot of novice casters try to salvage molds that they would be better off just repacking from scratch.

If there is any loose sand in the mold from parts that broke off or crumbled, remove it. Don't try to pick it out with your fingers; you'll make the problem worse, not better. Instead, flip the mold upside down so the sand falls out, or simply blow small quantities of loose sand out.

Step 5:

The mold is almost finished, but it still needs a place to pour the aluminum (a sprue). Cut a hole in the sand in the cope from the center of the mold out to the surface. There are many different ways to do this; I did it by gently pushing a pieces of 1/2" copper pipe through the sand. This is most easily done with the cope sitting on edge. Next, carve a pouring basin centered around the sprue. This needs to be large enough to provide an easy target for pouring aluminum from the crucible. A butter knife works well for carving this shape. It should be about 3" in diameter, and relatively shallow. Exact details are not crucial. After cutting, remove any loose sand, and press the surface gently with your fingers. This packs down any rough spots, which helps prevent any sand from being washed into the mold when you pour.

The mold is now complete. Reassemble the cope and drag, place the mold by the furnace, and get it close to level for best results.

Step 6:

It's now time to melt some aluminum. Inspect your crucible, load it with some aluminum scrap, place it in the furnace, and light the furnace.

You can place your hard disk in the crucible now, but I prefer to add it to an already hot crucible -- it's more fun that way! You'll need additional material anyway, so you might as well start with some scrap. Scrap castings are best; hard disk cases work well, soda cans are ok if somewhat messy, and scraps from the machine shop scrap bin at TechShop are also good.

Dirty scrap like hard disks makes copious quantities of nasty smoke. Stand upwind, cast in a well ventilated area, and avoid nasty fumes from the furnace.

Step 7:

Once your aluminum is hot, clean off the dross and pour. Remember, make sure you have clean, shiny, fluid metal before pouring. Never pour with anything amiss. Pour ingots with any excess, and return the crucible to the furnace to allow it to cool.

Once the casting has cooled, remove it from the sand. Clean it up with a bandsaw and disk sander. Remember to use appropriate precautions when sanding -- you don't want to sand any casting sand stuck to your part. That can cause silicosis and other respiratory problems. Be certain you have all the sand off first.

Make it look all spiffy. I used a sanding disk on a right-angle die grinder to smooth and shape the sprue, which I then used as a stand. I didn't cut or sand any of the mold flash, since I was going for that "as-cast" look. (Hard disks are a tricky pattern, so there was a lot of mold flash.) Make sure your sprue is smooth enough not to scratch up whatever you put it on.

Congratulations, you're ready to enjoy your brand new solid-state hard disk!



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    80 Discussions

    Oxy ascetylene works good too

    I find 140 Amps from an arc welder makes a nice mess of a drive. Melts and blows holes in the casing and the platters. Of course, it's better to dismantle it and get those nice magnets out.

    Dear God, do we have to do all this, when we do not have time, these days?
    I am not trying to be negative. NO never. The best way to discard an old HDD is to open it up, remove the shiny platters (can be used as Sun reflectors) remove the Neodymium powerful magnets and send the Aluminium cast body for recycling. The end.

    5 replies

    A fourth grader wanted to do a class report on recycling. With the help of her mother and a camera, she followed the recycle truck that picked up the separated paper, glass, plastic and metal from the school bins. They followed it to the waste disposal facility where the truck dumped it with all the other garbage. Recycling is typical government program..........all feelie good and no action.

    Recycling isn't just a government program. It's many government programs, which vary from state to state, county to county, and even town to town.

    Yes, there are some fake recycling programs where no actual recycling happens, and all your work of setting recyclables separate from trash is ignored, and it all goes into a landfill.

    At the other extreme, there are recycling programs where the resident throws everything in one bin, and it's sent to a facility which separates everything, with metals, glass, plastics, paper, etc, each going to separate destinations... and little or none of it going to a landfill.

    You are right, but that wouldn't be 1% of the fun, right? ;)

    However, the neodynum-Magnets from HDDs ARE a nice thing to have for all kinds of things.
    There are a lot of cool instructables who involve magnets. Here you have a free source of really powerfull ones. :)

    If one strikes a hard drive above the read/write head assembly, the head assembly will be bent out of place and the data on the platters becomes completely useless.

    Why? Because the platters are calibrated to the read/write heads during a low-level format that's generally done at the factory. This format becomes a type of fingerprint, making the pairing unique (not to be confused with an operating system format (which lays down the O/S specific file system). If one were to transfer the platters from one hard drive housing to another, or replace the read/write head assembly, they could have fun doing a low-level format (given the proper utility). Attempting to read old data off the new platter/head pairing would be like trying to decode the static that radio telescopes receive.

    Contact Seagate. They make the stuff. And they'll tell you the same thing.

    I worked as investigation engineer with LaCie for some time and believe ME:
    If the platters as it arent physically destroyed and the metallic structure of the platters isnt physically rearranges (like with melting & grinding) you ALWAYS can get to the data.
    It may take an electron-tunneling-microscope (to generate an optical representation of the magnetical topography) of all platters which is EXTREMELY costly (we talk in the 100'000s of $). Later you can then rebuild the complete data using this magnetical topography even if you only have the platters without the pickups.
    However, if you have the platters in good condition, you can reinsert new pickups and do whats called a sequential sweep:
    You go trough all possible adjustments of the pickups (normally around 1-10 mio) and read a known portion of the disk. Every disk has this. And if it at least the preload of the TOC and MBR. Those few bytes are ALWAYS known regardless of the format of the Data itself. Now you just look for a configuration-set which yield those known bytes from the known location. If you have those, you make a complete read of the platters as Raw-Data. Then you analyze the data and decide if that was the correct adjustment for the pickups or not. If not, you look for the next configuration which gives you the correct preload-bytes.
    This "look for conf to get correct preload and make a Raw-read" is often automatic and you end up with maybe 100 Raw-dumps to wade trough...
    Cheaper than the tunneling-microscope. ;)

    And in a nutshell: Ripping and destroying the configuration of (or the pickups itself) does NOT make the data unreadable. Thats an urban myth. It simply makes it harder (Laborwhise and moneywhise) to read the data.

    Hey nice instructable on sand casting! Do you really melt your metals inside? For all those readers and commenters who think this is the best way to delete the info on a hard drive, and those who mention the many ways one can destroy a hard drive, another way to "recycle" a hard drive is to wipe off the data and reuse it.

    I use to accomplish the job. It's free and removes everything.

    I found a 12 ga or .40 cal works wonders on making the data inaccessible. Just a thought

    2 replies

    Well, sort of. There is actually a technique that involves using a really high resolution camera (think microscopic camera) for physically reading the data off the disk. It takes a long time, but except for the areas actually damaged by the pellets or bullet, that data can still be read.

    The actual area damaged is relative to the amount and type of ammunition you use

    Um, great casting Instructable not so great HDD disposable one. If you placed this one in its appropriate place with an appropriate title we would get more out of it; just a thought.....

    1 reply

    After thought,; whats the BEST way do trash all drive data? Depends on what you have at hand. A small thermonuclear weapon with its casing removed from the primary would create an E.M.P. that would trash its data for sure....... just another thought...

    Hahaha! How cool is that!

    So you have to strip the harddisk from the PCB and motor first?
    At least the motor has a lot of another metal in it, right? Doesnt this make some sort of Copper-Aluminum-Iron-Alloy then afterwards??

    2 replies

    There are a bunch of metals involved. The cover (not case) is stainless; it doesn't melt, and was basically intact when I pulled it out of the crucible before pouring. Some of the motor pieces were also steel / stainless, and survived as recognizable components. The PCB and many of the chips survived in recognizable (though far from usable) form.

    Steel and stainless survive unscathed (you can make hot metal tools out of them). Lead will dissolve in trace amounts, but there probably wasn't any lead here - modern solder is lead free. I don't know what the tin does, but almost anything that melts will dissolve at that low a concentration.

    Copper in the wiring won't melt, since the aluminum is below the melting point of copper. However, the aluminum dissolves the copper, similar to water dissolving eg salt. I didn't find any copper pieces after the pour. The same goes for the rare earth magnets; they seem to have dissolved as well.

    And yes, this makes this some alloy of unknown composition, but that's what it would be anyway. Copper, zinc, magnesium, and silicon are all common alloying agents in aluminum. There was certainly some zinc and magnesium in this pour, based on what I know was included in the scrap. Probably some silicon; copper was possible. Also, the steel crucible adds trace iron contamination. Iron is not a useful alloying agent, but also doesn't hurt much at the typical trace level.