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My $29 Trucut Undercutter/Lathe

Hoover300

Plastic
Joined
Sep 24, 2020
I will post pics as I reassemble it. It is way nicer than it appeared. The motor is quite damaged but still works, it is welded to the plate so I will need to figure out a way to either fix it, or grind it all off and bolt a nicer one on. Here is the base

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Hoover300

Plastic
Joined
Sep 24, 2020
That is the next part to be assembled, later today. It is welded in one spot from a bad fall, and needs a deep cleaning.
 

Hoover300

Plastic
Joined
Sep 24, 2020
My understanding is it cuts away the mica buildup between commutator bars, to give both the motor and brushes a longer life.
 

TDegenhart

Diamond
Joined
Mar 26, 2011
Location
Geneva Illinois USA
Scuse my ignorance but what does it undercut?

Long ago, probably before you were born, generators were used on cars and trucks to charge the battery. A generator is different from an alternator in that the armature windings were connected to copper segments fastened together to make a commutator. The copper segments were clamped together but separated from each other electrically and mechanically with mica. As the segments would wear, the mica insulators would be exposed and had to be cut back so as to not wear the carbon brushes and minimize arcing. The action was called under cutting the mica or simply undercutting. Special lathes were built that would hold the armature between centers while a motor driven cutting wheel would cut the mica back below the surface of the segments. This is what Hover 300 has. Not a lot of use for these machines these days as almost all current generation is done with alternators.

EIS | Martindale - Why/How to Undercut Commutators - YouTube

Tom
 

guythatbrews

Hot Rolled
Joined
Dec 14, 2017
Location
MO, USA
Long ago, probably before you were born, generators were used on cars and trucks to charge the battery.Tom

Thanks for the kind thought. Born longer ago than I'd like! But it was somewhat after the tail end of automotive generators.

I wondered if it was for undercutting commutators. The octagonal deals on the headstock and tailstock have me baffled tho. I am interested to see how they are utilized. It is an interesting little machine. Please show us when you've got the thing running.

OT... I started my journey in machinework on an Craftsman branded Atlas lathe Dad bought for me. To learn back then I had to resort to these things called books. The lathe came with that black spiral bound atlas manual you mey have seen. It is a pretty good manual. There was a chapter about undercutting mica and turning commutators, and Atlas sold an attachment specifically for that.
Atlas-Craftsman-Lathe-Mica-Undercutter-Commutator-Armature-M6-511.jpg

The haters on the forum hate on the hobbyists. But, many projects later, and a full bench-sized shop later, my avocation became my vocation. If I was starting out these days I would probably be the nine year old getting bashed for asking "stupid" questions. But back then it was just me and books. A great hobby. But alas, as evidenced by my own son, not as fun and alluring as computer games. Close to 55 years later still working in the trade.

One Saturday Dad and I pinched a generatior and regulator off an abandonded pickup down where he was working. We retrofitted it to be a starter/generator on his Cub Cadet lawn tractor. It worked pretty well.

Been around generators and dc motors since but all in pretty good shape. Have not had to undercut a commutator yet.
 

dundeeshopnut

Cast Iron
Joined
Mar 27, 2020
That is the next part to be assembled, later today. It is welded in one spot from a bad fall, and needs a deep cleaning.

Is that original paint? If so, I wouldn't strip it as it looks "survivor" quality! Lots of info on how to breathe a little life and protect old paint. Scotchbrite wheel followed by a buffing will bring back some bling to the bare metal parts. Oh yeah,, have you had 15 Washingtons worth of fun yet???
 

Hoover300

Plastic
Joined
Sep 24, 2020
Is that original paint? If so, I wouldn't strip it as it looks "survivor" quality! Lots of info on how to breathe a little life and protect old paint. Scotchbrite wheel followed by a buffing will bring back some bling to the bare metal parts. Oh yeah,, have you had 15 Washingtons worth of fun yet???

Was a bit more($29), someone else wanted it. Finished!! The motor is really rough but somehow still works. A Eureka vacuum belt works as a belt for this. I'll attach a video when I figure out how. IMG_4636.JPG
 

gregoryd

Hot Rolled
Joined
Jun 30, 2007
Location
Mass
the armature windings were connected to copper segments fastened together to make a commutator. The copper segments were clamped together but separated from each other electrically and mechanically with mica. As the segments would wear, the mica insulators would be exposed and had to be cut back so as to not wear the carbon brushes and minimize arcing. The action was called under cutting the mica or simply undercutting. S

Tom

Here is the starter armature that I'm doing for my 1938 pontiac. Also note the special armature chuck that is like a drill chuck with scalloped brass jaws and acts like a center-rest

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ramsay1

Titanium
Joined
Aug 19, 2003
Location
port allen, louisiana usa
Mica Undercut

Mica has to be undercut between commutator bars in motors, generators, etc usually at such times as the commutator is turned and trued... High mica results in poor commutation....Many times a hacksaw blade was used for this purpose after grinding the sides of the teeth....Snapon offered a hand driven lathe and under cutter for reconditioning automotive starters, generators back in the day when things could be repaired....Cheers from Louisiana; Ramsay 1:)
 

john.k

Diamond
Joined
Dec 21, 2012
Location
Brisbane Qld Australia
How reliable are generators?.....my old crawler crane has a Gardner diesel engine with (I assume) a CAV generator shaft driven from the timing gears......the motor is 70 years old,Ive owned the crane for 40 years,and I have never had a close look at the generator due to its position,and dont know where the control box/regulator is.......this generator keeps the battery charged .Thats reliable.
 

CalG

Diamond
Joined
Dec 30, 2008
Location
Vt USA
I've undercut commutators using a suitably ground tool on the lathe. in a "shaper action" . It worked very well.

IIHIC undercutting is not so important, as long as the segment insulators are not proud.

The ventilator fan on one of my past Audi Vehicles was worn at least .125" in a "wedge". The thing would quite running when rounding corners one way as the armature shocked to the side and the brushes lost contact.

A rather hefty cut, with new brushes, and the fan was fine. I was apprehensive about the brush "stick out" from the holders, but all remained good until the car "went away" ;-)
 

CalG

Diamond
Joined
Dec 30, 2008
Location
Vt USA
How reliable are generators?.....my old crawler crane has a Gardner diesel engine with (I assume) a CAV generator shaft driven from the timing gears......the motor is 70 years old,Ive owned the crane for 40 years,and I have never had a close look at the generator due to its position,and dont know where the control box/regulator is.......this generator keeps the battery charged .Thats reliable.


The generator (LUCAS) on my 1950 Fordson tractor continues to keep the battery up.

Reliable enough....;-)
 

ramsay1

Titanium
Joined
Aug 19, 2003
Location
port allen, louisiana usa
Generators were reliable enough and used for many years.. Brushes would wear and need replacement and generators do not usually charge when motor is running slow (idling).....What usually killed a generator is letting brushes get too short and or rusty weak brush springs... Cheers; Ramsay 1:)
 








 
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