Thread 2945481

I was given an old Ryobi 10" miter saw after being able to pick around an old dude's garage, and decided to clean it after the safety pin became stuck in the safe position (which locks the arm down, so I HAD to fix it anyway). Here's some process shots and cool things about it.

First picture is of the electric motor inside...this is the commutator, which acts as a mechanical rectifier and converts the AC power input to DC. It does this like any other brushed DC motor by using two static brushes to act as pos/neg. The brushes hit different copper segments as the commutator spins, and this changes the polarity inside the copper windings of the armature. The field generated by the armature windings interacts with the generated stator magnetic field and thus creates a continuous unidirectional torque, which then connects to the saw to spin it.

>>2945481 (OP)
I sanded off the carbon (?) residue on the commutator. Normally, this helps increase the efficiency of the motor. The brushes inside seemed worn down, but for now, I could not be assed to replace them until needed.

>>2945481 (OP)
Also, in OP pic you can see that something internally took a HUGE gouge out of the iron core of the armature.

In this picture attached, I ended up cold bluing the hardware of the saw in order to prevent rusting and make it look purdy. I oiled them with gun oil afterwards as well. It's my first time doing anything like this, besides with guns, so hopefully it ends up working. This was them after being blued, some once, others twice or thrice depending on how they took to it.

>>2945483
...and this is them after being buffed + oiled and in their final form. How I blued was:

1. Vinegar bath overnight to get rust off
2. Wash em with water
3. Hit em with degreasers
4. Water again
5. Bluing solution bath for 30 seconds
6. Water bath
7. Dry
8. Buff
9. Oil

Tomorrow after the bluing sits a bit I will try and attempt to put the saw back together. Thanks for reading.

>>2945481 (OP)
you're a woman, the gloves gave it away.
men do this stuff all the time and don't blog about it.
also you're cleaning shit that doesn't need cleaning.
stick to fixing sandwiches

>>2945490
>the gloves gave it away
What a retarded point, gloves are good. If you want chemicals leeching into you via your porous skin, be my guest; I don't.

>men do this stuff all the time and don't blog about it.
That is the entire board here, dumbass. People blogging about projects.

Anyway, cope + seethe. Tomorrow I will have a nice, clean, rust-free saw. I am very happy with the bluing job.

>>2945483
>Also, in OP pic you can see that something internally took a HUGE gouge out of the iron core of the armature.
That'snot a defect, that's factory-side intentional
They remove part of the rotor mass to balance the wire-wound rotor assembly
At 10.000+ rpm it can't have much rotationally unbalanced weight
The rotor is unbalanced after winding because the lengths of wires (and thus mass) vary when they inevitably have to overlap one another at the ends of armature (metal bits that the wires pass through)

An out of this world perfect motor would just have straight sections of cable that carries a lot of current yet is narrow enough to fit as many windings aa the heart desores and magically doesn't even need to curve around at the backs, only passing current coaxially to the shaft because that's where the tangential force vectors are created through electromagnetic interaction
Of course we aren't making motors with superconducting wire that has zero-length/mass bridges at the end so we invariably end up with lumps of copper wire being off-balance

sorry for all the "perfect motor made from magical materials" diatribe but one final important note: the commutator isn't any sort of rectifier, it simply physically changes the wire loops that current is running throughin the rotor so they are always slightly behind the place where the rotor would have to turn in order for the torque to just balance out and the force to point radially rather than with a tangential portion (like the bottom position of a swing - no retorative force to the front or the back. dame with the rotor - imagive you're a superbug sitting on the spinning rotor, if there were no commutator you'd just turn until the "bottom position" is reached magnetically and maybe rock back and forth a bit through inertia but ultimately come to a standstill with the dtator and motor just attracting each other in such a way that the rotor doesn't rotate anymore)

it's a universal motor - works AC or DC

>>2945517
>typos
fucking phoneposters

>>2945514
it is indeed pretty nice
"slay queen" :^)
never cold blued anything myself

>>2945517
>They remove part of the rotor mass to balance the wire-wound rotor assembly
Yo, what the hell? That's super cool. How do they even achieve that? It appears to be a very random gouge. Do they just spin it on something that takes off anything that vibrates out of alignment? I assumed it was a gouge since when I used it the first time after it sat in a shed for who knows how long, it sparked like mad, then chilled out.

>it's a universal motor - works AC or DC
Eh? I thought the whole point of the brushes was administering the changing polarity to the system. How does it then operate with DC? How is it able to spin the same way with both a changing current and yet also a constant one?

>physically changes the wire loops that current is running through in the rotor, so they are always slightly behind the place where the rotor would have to turn in order for the torque to just balance out
yeah I do understand that part, thankfully lmao. I need a fucking cigarette after this.

Honestly, the covert goal of this was to be able to stare at the motor, but to say I understand them well is a stretch. Although wouldnt a commutator still be technically a mechanical rectifier if it has AC input and delivers a DC output...?


>>2945519
>never cold blued anything myself
its super easy, you definitely could. I believe in you, anon

>>2945527
>How do they even achieve that?

The modern method is to use accelerometers or force sensors with a test jig that spins the rotor. It's trivially easy to get something to within arbitrary levels of balance this way.

https://www.crystalinstruments.com/rotor-balancing

>How does it then operate with DC?

The rotor and the stator are both being fed from the same signal (power source). Any change in that signal is reflected on both parts of the assembly equally. In other words, if you reverse the polarity the stator sees, you also reverse the polarity the rotor sees

You can imagine that, if you flip the magnetic fields one of them generates, they're attracted/repelled by the magnetic fields the other generates in the opposite way, and the motor reverses direction. However, if you then flip the fields of the other, the first is then reversed again, causing the assembly to spin the way it was spinning originally. Since, in a universal motor, you can only change the polarity of both the rotor and stator at the same time, you can never actually reverse its direction without physically rearranging its connections.

>Although wouldnt a commutator still be technically a mechanical rectifier

I don't think so, because commutators don't really have electrical "outputs". Rectifiers, by definition, are electrical concepts, but motors are almost always modeled as their own, complete component. The internals are handwaved and its reduced to something akin to a weird inductor(s). The only time the internals are ever explicitly broken down into into individual components are when doing an in-depth analysis of the motor itself. Even then, it would be more accurate to think of it as a sort of multiplexer than a rectifier, since what it's really doing is activating specific current paths based on an input (the relative phase of the rotor/stator).

>>2945527
>How do they even achieve that?
the same way they ballance your tires, but instead of adding weight, they remove weight

>>2945578
Ah I see... Thank you so much! :'D
I do understand it now.

Today is putting it back together, then I can finally cut some damn wood for my spider enclosure.

>>2945490
this is why very few people actually post diy here. OP is of course a fag, but you're a jogger.

>>2945482
They're really pretty colors

>>2945490
Wearing gloves is common sense.
It's a feminine train to care what other people look like or what they wear while engaging in a hobby.

>>2945653
i'm angry Kamala lost too, brother