My Beloved Sander has Finally Died so I Took it Apart to See what was Inside

After almost 20 years of use by Makita orbital sander stopped working. Out came the tools and I got ready to perform a post mortem. Here are a few photos.

If you are an amateur boat builder you get to love and hate sanding. You become very close to your sander.

It actually made me more upset than it should to see my old sander literally grind to a halt.

What's inside a sander?

bottom of sander

3 Screws hold the bottom of the sander on. They came off easily using a phillips screw driver.

The tube at the left of the bottom pad is where the dust bag attaches. I keep the fine wood dust and it makes a good thickener for epoxy.

Bottom pad with the velcro hooks comes off exposing the asymmetrical rotating bit.

bottom of sander

The tan coloured part is soft, it feels like silicone. Note the arrow that is pointing to a screw and washer placed asymmetrically.

I removed the screw and the washer came off but the rest of the assembly stuck together, so I put the screw and the washer back on for now.

bottom of sander

I removed 2 screws from the black bottom unit. Nothing seemed to move or come apart. I looked for another fastener or screw but nothing. So I took my slot screwdriver and pried the 2 parts apart.

bottom of sander

The 2 pieces finally separated. They were sort of gummed together by dust and grime. Everything fits together very precisely.

I removed both parts and moved on to the top.

screws on top of the sander

The blue top is held together by 3 screws. I took them off and gently pried the 2 sections apart.

Do I need to say the sander is not plugged in. Don't open a power tool if it's plugged in.

The top part has nothing to do with sanding. It's a motor that powers the bottom part which is the actual sanding unit.

windings separated

On the right the housing has the power cord and switch. The power connects to the motor housing which has wire wound around. I have removed the rotor from the housing and placed it on the left side of the plastic case. That fits inside and rotates in the housing on the right, which is hollow. The right hand housing is stationary and fits snugly in the sander case. When it is closed it does not move at all.

The rotor not surprisingly rotates and turns the sanding assembly. It has 2 bearings. You can see one at the top of the rotor. There is another one hidden by the sander assembly which is still attached to the rotor. There was a bit of corrosion on the rotor so I sanded that smooth. I also checked the brushes which can be seen on the right hand part. I don't know why they are called brushes because they are solid black carbon rods. These rods when assembled, push against and connect to the stripy bits on the rotor. The stripy bits are contacts. I cleaned this with fine sandpaper. I could not see anything really wrong but if a wire winding burns out then the motor is useless. I was too lazy to check the winding for conductivity.

windings separateddetail

Detail of the rotor. The 2 bearings are clearly visible. They fit into spots in the plastic case and support the rotor as it turns.

As you sand, the sander either wobbles around or rotates. If you press hard the wobbly bits press against the little ridges and lock and make the sanding bottom rotate. If you press lightly there is very little rotation but the asymmetrical part wobbles and rotates a little.

On the right I removed the middle screw and washer again and separated the rotor from the sanding parts. The off centre hole is clearly visible. When it rotates it created the wobble and vibration.

The fins on the inside of the motor help make airflow and cools the motor. This airflow also pushes air and sawdust into the little dust bag.

It's a lovely simple machine that has been working hard for me for almost 20 years. It doesn't get any better.

I put all the parts back together. In my long experience as a taker apart of things, that is the hardest part. I had to try a couple of times before everything went back in perfectly. I closed the case and plugged the sander in and magically the sander started working again. Go Figure.

So now I have 2 sanders. My old friend and a new Makita that I bought to replace the "dead"one.

email me if you find mistakes, I'll fix them and we'll all benefit: Christine