Back in the day the mechanic teacher had us I think use a lathe to make the grooves in the armature deeper. All we did was hit everyplace but the grooves, but I digress. When you guys rebuild starters now, do you even fool with that? Is there another way to do it without a lathe? How about for an alternator, should I do anything with the stator or rotor aside from shining the br*** rings where the brushes ride and making sure the contacts on the stator to diode connectors are clean? I took some 400 grit to the inside of the stator for about a second cuz there was a little surface rust, then thought better of it. Thanks for the help!
Its important to undercut the mica in the commutator. If you dont, the brushes will be riding on the mica which is an insulator and of course, you wont be making electrical contact. There is a tool to do it but its not a lathe. I've never looked it up but you can probably buy one. I took a number 10 external tooth washer, held it against the side of my 6" bench grinder and made the washer thinner and chucked it in my drill. Been using it for years
Grind a broken hacksaw blade to the correct thinness. Open your vice the right amount, lay a towel across the jaws, lay the armature in the soft cradle, and carefully undercut each groove. That's the way it was done.
yes, theres a tool for it, and it is called an armature lathe.......not alot of em around anymore......china don`t turn rotors for electrical motors or alternators so, none of that around anymore......
I just saw an armature lathe, that's exactly what we had! Whoa, talk about the wayback machine! Yeah with the **** parts store rebuilds I can't imagine anybody wants to pay for the machine/shop time to turn an armature and undercut the Mica, another term I haven't heard in 20 years heh. There was a pretty lively online debate about wether even to do it or not. Makes sense to me anyway, I'm not rebuilding starters for a living or anything. Armature lathe...whoa! Really cool. I'm totally looking for one now.
i have one, only cause when we closed up shop i took it......haven` used it since...lol....but we go so far back.........yeah, all the stuff now is just throw away stuff.......
Maybe Danny (Dirty2) will jump in here, it's his business. Back when I did a few delco generators, I checked the armature in a drill press to clean up the commutator and used a little saw on a dremel to undercut the mica. I was told you don't have to undercut the mica on a starter. I doubt if the even use mica anymore, probably some kind of synthetic now..
Friend has a shop. They still cut the mica on starters are armatures that have the comutators length wise.
When I used to try to rebuild a draggy starter, I'd put in new brushes, polish the commutator, undercut the mica, install a new bendix, bushings, etc. But it was still a draggy starter (start good cold, act like a dead battery hot). The old guy at the starter/generator shop would pull an armature out of a box (new? Rebuilt?) to put in a rebuilt starter and it'd work great. What goes bad in the armatures that makes a draggy starter?
When I worked at an auto electric shop, we had a lathe to turn armatures that were rough and a commutator lathe for cutting the mica. We did it on starters and generators, I don't think I ever saw an alternator with a segmented commutator. In the mid 60's we replaced several generators with alternators for some "exuberent drivers" that had a habit of throwing the commutator segments out of their generators. Anyway, if I only had one commutator to cut the segments out of and didn't have access to a commutator lathe, I think I'd use the hacksaw blade and vice method. It would take a little time, but it would work and not cost an arm 'n a leg. Or take it to a starter/generator shop. They shouldn't charge much for cutting the mica. Larry T
I used to work in a machine section at the San Francisco Naval Shipyard at Hunter's Point. (Since closed many years). I performed thousands of armature repairs as well as the dynamic balancing of the units. Here is what we did. The mica is not usually cut from between the bars of the armature on a starter motor. This is because the brushes used on a starter have a high copper to carbon content and would otherwise wear out the commutator very fast. On a generator or motor that uses a commutator, the mica uses brushes that are primarily made of carbon. On these commutators the mica is undercut from between the bars and the mica is also removed from the sides of the bars in the undercut groove. The correct depth of the undercut is equal to the thickness (width) of the mica. The edges of the bars are also chamfered lightly to remove any burrs left from cutting the commutator. The surface of the commutator is then burnished with the final burnishing being done using the back side of a piece of 600 grit wet or dry paper. We had a machine that attached to the slide on a lathe that held various width rotary cutting blades. They were usually smaller than 3/4" diameter. This was used to remove the majority of the mica and was done by hand one groove at a time. The final step to remove the mica from the sides of the bars was done by hand using a modified hacksaw blade to s****e the remaining mica away. We also made a chamfering tool using either high speed tool steel or a three sided carbide insert silver solder to a rod. On larger armatures (such as submarine motor/generators) the undercutting was done by hand using modified hacksaw blades. After all this is done the armature should be checked for continuity and shorts using a "growler" and performing a bar to bar check.
When I was a kid my dad had an IH pickup and whenever it was warm the starter would drag real bad. He was at the neighbor's (who was also a blacksmith) one day when it did that and the old guy yanked it out and turned the armature down in the lathe. It never dragged again. He turned down the big part, not the commutator.
And you won't. The commutator on a generator does the same job as the diodes in an alternator. In an alternator the ac current is sent via a slip ring to the diodes, where it is rectified to DC. In a generator, the commutator serves as a mechanical rectifier, and out comes DC.
plym49 Your almost right In a generator, the current is produced in the armature by the windings running through a variable magnetic field produced in the field coils mounted in the housing (The variance is from the regulator). The north and south poles of the feilds stay constant, just vary in streanth. As the armature rotates through the north or south of the feilds, a positive or negative current is produced in the armature winding. Depending on the size of the armature, there can be quite a lot of individual windings, but they are all connected at the comutator, eg if it had 4 windings, it would go like this, end 4-start1-end1-start2-end2-start3-end3-start4-end4-start1. The way the brush holder is made in a generator is how you get a dc power out of the generator, in that as the armature rotates, the armature coil that has the positive charge in it will (through the comutator bar) line up with the positive brush and of co**** the same for the negative brush. The technical name for this is comutator action. This is why a generator has such big brushes, they have to carry all the current produced by the generator. In most cars, beween 20-35A. With an alternator, the current that in a generator is produced in the armature, is instead produced in the stator (stationary part). This current is ac.It is then rectified through the diodes to exit the alternator as a dc current. The feilds in an alternator is now the rotating part (called the rotor). The rotor coil uses less current than what an armature puts out, eg 2-3A therefore much smaller brushes than a generator or a motor. The slip rings are there to provide a means of connecting the rotating field coil to the stationary field conections, eg regulator and exciter diodes ect. The reason ac is produced in the stator is the way the rotor is made. easiest way to describe it is interlocking fingers with every second finger being a north pole, so as the rotor turns, the magnetic field p***ing through the stator windings go N-S-N-S-N-S ect. I learnt all this stuff when I did my auto elec apprenticeship. The basics of it is that the construction of an alternator is opposite to a generator. I hope I havnt confused everyone but its possible to write pages on how alternators and generators work and the differances between them. Mick
I stand corrected, was not clear in my reply. Said another way, in a generator the field windings are in the case and the current is produced in the armature. In an alternator the field is regulated in the rotor and the output current is produced in the stator (non-rotating part). In a generator the commutator action produces the switching that is needed. In an alternator the diodes perform that task to output DC.
The purpose of the mica is to insulate between the segments of the commutator and provide a smooth surface for the carbon brushes to ride across from one segment to the next. If the mica was undercut between the segments, it would essentually turn the commutator into a grinding wheel which would grind away at the brushes until the undercut space was filled with carbon. The carbon, being a conductor, would in turn short out the segments of the commutator. That being said, we used to use a drill press and a fine flat file to turn the commutators on starters. New carbon brushes, springs and oil-lite bushings with a touch of white grease and they were good to go.
It seems like a long time ago I read or was told never to use emery cloth to polish a comutator as the gl*** in the cloth could be embeded in the copper and act as an insulator.
Interesting! well fwiw the old school auto teacher in college 20something years ago had us undercut the mica. So looking at starter lathes, I guess it turns the armature the fat part and maybe the small part where the brushes go? Me, since there's fat chance I'll find a starter lathe I'm going to clean up the br*** under the brushes, replace the bendix ***sembly, various washers and clips, and the solenoid and call it a day. Anybody know what kind of grease they're using in this picture? Looks like a good idea.
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