Recycled HDD Rotary Sander for $5

Step 5 Tests: Grinding

TEST 1 : GRINDING WOOD

The sander performs very well and smoothens down the wood quickly.See video for the demonstration.

TEST 2 : GRINDING STEEL

The sander effortlessly grinds through the steel, although better performance would be reached with specific, black steel grinding sandpaper found here: http://www.hartvilletool.com/shared/images/products//large/29887.jpg

Comments

[LetsExplodeSomething]

have you tried putting a metal grinding disk in there in place of the platters?

[Treknology]

This is a nice little idea that would be fantastic for squaring off the ends of acrylic tubing--but what tests do you perform on the drive before ripping the heads out to make sure that it will keep spinning rather than shut down and register an internal fault?

[mhkabir]

 I just ran it continuously for half an hour or so and tried different jumper combinations.

[chibby0ne]

Nice experiment. Im trying it myself. I'm using a IDE HD but it won't stay on for more than 10min, I don't know the model nor brand that I'm using, It has 10 jumpers pins and I've tried Slave, Master and Single, only one left is PM2 and some pair that doesn't say anything below. What do you think the problem might be?

[mhkabir]

Could you please post a picture of your HDD jumper combos. Maybe your PSU has some problem. Some PSUs old PSU pulse the power for a few minutes and then automatically go into standby without a heavy loaad on them. Or the PSU/ HDD Brushless controller maybe damaged. Try the other jumper blocks/get another HDD/ change your PSU. Hope this helps!! Kabir

[v3l0]

I wonder how did you "jump" more current into th motor because i have a HDD grinder and the controller kept warming pretty bad when I was working with it and I superglued a aluminium piece to the chip.
I got a little more power/torque by removing the extra platters.
Also, if instead of pushing the sand paper into the small disc securing the platter you decide unscrew the screws, remove the small disc, use it as a template for holes in the sandpaper, and mount the sand paper by securing it with the screw that secure the smal disc and platter in place... than the whole assembly will not vibrate and will not be off center (be careful to cut the sandpaper as raound as possible) and this is good for speed, torque, power.

[mhkabir]

 I gave more CURRENT to the HDD by attaching all the 12v power wires together in series to get the currrent.

Post pics of the sander if possible.

[Arx]

 You must mean in parallel.

That won't actually do anything though.

[EmmettO]

 The thought occurs to me, if a strong enough flywheel was attached to the motor shaft, it would offset the torque problem.

[Shiftlock]

Perhaps a little, but that poses two problems.

1.  Because HDDs use high-speed/low-torque motors, it may not have enough torque to move the flywheel.

2.  It would dramatically increase the complexity of the project, to the point where that much effort would be silly instead of sourcing a motor designed for this type of high-torque/high-speed application.

[EmmettO]

 I'm not talking about attaching a millstone to the HDD motor. Even a few ounces would buffer the power drain of the friction.

If a suitable object were found, not fabricated, it would still remain a simple project.

Yes you can buy a motor that is better suited for this project but the idea here is that you are.

1. Using something that would have been thrown away and therefore extending it's lifecycle. A large number of instructibles are about recycling.

2. Providing yourself with a tool that some people cannot afford.

[Arx]

Flywheels only help for transient load variations.  The torque going to the motor is still the same.

If you want to easily add some load, just take a bunch of hard drive platters and put them in one drive, after removing the spacers that are usually between the platters.

The problem you'll likely have is that a lot of hard drives controllers are built assuming a specific load for acceleration.

once they're up to speed, they may check phase currents to know when to switch, but usually during spinup they just ramp up the switching at a rate they know the motor can achieve.  When you throw some extra weight on it, you might lose steps, and have the motor go out of sync.

Sometimes they'll just get confused and burn up, etc.

It really just depends on the drive.

I agree, as to the purpose.  I think that this could also be useful for doing extremely fine grit sanding where you'll have very light motor loads, and sanding discs for a commercial sander might not be easy to find.

Sharpening exacto knives, etc..

[EmmettO]

 I understand, it would only help for a moment as the inertia of the flywheel is used up. In this case it would be a split second.

I'm bypassing the controller entirely and putting power to the motor itself. For this a controller isn't needed.

[Arx]

 You realize that it is a brushless 3 phase motor, right?  You can't just hook DC directly to it, and expect it to spin.  You need some kind of controller.

[v3l0]

I used a few years ago a transistor to boost the curent capacity of a voltage regulator. I think there should be a possibility to boost the output of a motor driver, but I don't know if there could be sincronisation problems because I don't have the knowledge I need about transistor speed.

[Arx]

 Yeah, if the on resistance of the switches on the controller are too high, it might be possible to improve things, but only slightly,  The problem is just that it's a tiny motor with tiny windings.  The only way to get more torque out of it is to run it at a higher voltage, and that will require a different controller.

you might get up to around double before you start having heat problems, and that's probably optimistic.  Many motors won't make it that far.

You're still orders of magnitude below a real sander.  The main benifits are high speed, and an extremely flat smooth surface.  a few drives with some really fine grit paper stuck to them, and you could have a very nice tool for sharpening tools (wood plane irons, chisels, xacto knives, etc)

I've seen some very fine grit papers with adhesive backing.  That would be ideal.

[EmmettO]

 Thats why transformers are so much fun.

[Arx]

 What do transformers have to do with it?  It's not like a synchronous AC motor either.

the only way to drive these up to speed is with a 3 phase switching controller.

The most practical way to make it run significantly faster is to run it with a separate controller at a higher voltage,  You can get controllers intended for RC vehicles which will work on this type of motor.

The controllers aren't actually that expensive but even It's probably still not enough to make it capable of anything needing any significant torque.

I would just use this to sand very small things with fine grit abrasives.  Find a real sander for real sanding.  I'm all for recycling your junk, and I think this could be a great tool, but it's not a replacement for a full size sander.

[Shiftlock]

Don't you mean you connected them in parallel (not series)?  If you connect two 12V lines in series, you will get 24V.

[EmmettO]

 Connecting them in parallel would not put more current through the motor. Amperage is determined by the voltage and the resistance in the circuit. If the resistance stays the same and the voltage stays the same the amperage stays the same, unless the power supply was limiting the current, but that's unlikely.

Most motors can take more voltage than they're rated for. Doubling the voltage may shorten it's lifespan significantly though. 

[Shiftlock]

Obviously, but that wouldn't increase the torque of the motor, it would only increase it's speed.  High voltage on a motor tends to push the magnetic portion of the motor into saturation. This causes the motor to draw excessive current in an effort to magnetize the iron beyond the point to which it can easily be magnetized. This generally means that the motors will tolerate a certain change in voltage above the design voltage but extremes above the designed voltage will cause the amperage to go up with a corresponding increase in heating and a shortening of motor life.

[EmmettO]

 Even though I didn't say it would increase torque, If the speed increased the force vector would increase. The displacement vector would remain the same and the angle between the force vector and the lever arm vector would be the same. Since force increases T = r (displacement vector) x F (Force Vector). So if speed increases (because force has increased) then torque increases.

[Shiftlock]

You are wrong.  The power will increase, but the torque will not.  You are confusing the two.  This is a common error which is similar to the old horsepower vs. torque issue when speaking about automobiles

[Arx]

That doesn't make sense.

More voltage will push more current, which means more torque, and more power.

The two are interrelated, after all.

[EmmettO]

 Whoh, kay man. If you want to argue with a mathematic formula that is the standard for engineering, go ahead.

[mhkabir]

Nice math.

[MattCP]

I love this idea! Have you tried to build a sanding platform at 90 degs to the disk and flipping it vertical?
It obviously lacks torque...but still useful. Good job.

btw
Emery is mostly aluminum oxide, with a sprinkling of other minerals...

[mhkabir]

 I solved the torque problem by pumping some more current into the motor, and by using a multi-platter HDD model.

[Shiftlock]

Compared to a real sander, it obviously still lacks a ton of torque.  Any sander you can stop with your fingers isn't going to be all that useful for real sanding projects, but it's an interesting idea and a good way to introduce children to working with tools and basic wiring.

[mhkabir]

 Remember: Don't try stopping the 15 000 RPM drives with your hands....
It will get a red and raw sheen.Be careful.

[Deeder]

emery cloth, not sand paper. sand paper is sand. emery cloth is industrial diamonds.

Like this: http://www.3m.com/product/information/auto-pak-emery-cloth.html