Good 9" grinder or how to fix this one?

Sevenhills1952 · Jun 2, 2020

I've had this Sears 9" grinder over 30 years and use it all the time. Recently it started throwing sparks from brush/armature area so I took it apart, cleaned armature like new, brushes are in good shape best I can tell (3/4" long, springs ok). It's made in USA and served me well.
Back together no joy, doesn't run full speed and arcing at brushes.
Any repair ideas or equal replacement much appreciated. Thanks.View attachment 290480 View attachment 290481

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dalmatiangirl61 · Jun 2, 2020

You might want to try the Aland Island Motor Werks, all the machinists there use them.

Guest · Jun 2, 2020

What does the commutator look like?

michiganbuck · Jun 2, 2020

The commutator has strips of mica between each brass pad. you need to take a scraper about .020 .030 wide and scrape the mica a little lower than the brass plates. I have done many and it is not a fancy job and does not have to be high precision. you want the mica lines to be about .020 lower than the brass. If they are low even .005 that is enough so you may scrape them or not.

The other thing is the wear width. You can emery paper to make the high sides just at or lower than the running area. or you can alter the width of the brushes in the contact area.

Limy Sami · Jun 2, 2020

Be aware - angle grinders are so cheap today, repairs can easily exceed the cost of new, (and frankly - often better )

Just sayin

DDoug · Jun 2, 2020

Are brushes worn out ?

Meaning, they are hanging up at the end of their travel ?

Kevin T · Jun 2, 2020

I worked for a steel erection company for many years so grinding was the order of the day. We only had DeWalt grinders in the inventory, many dozens, so they might be worth looking into.

Rob F. · Jun 2, 2020

Second michiganbuck's thought to clean between the commutator strips,
also I would make sure the brushes move smoothly in their holders, I have had more than one not move easy and had to sand down the sides to get them to move easy.
Look at the ends where it contacts the commutator strips, might need a light sanding.

Sevenhills1952 · Jun 2, 2020

Wow! All fantastic replys. I'll take it apart and check those things. I never thought about commutator strips (I called it armature).

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Sevenhills1952 · Jun 2, 2020

Tried all those things, brushes moved fine in holders, commutator before and after cleaning. Only thing I found odd is I ohmed out pad to pad...all measured 0.2 ohms except pads I marked green 0.6 ohms. I cleaned that winding tightened with small hammer (even that winding itself 0.6 ohms). Emery smoothed armature, cleaned everything, cleaned and stretched brush springs some, still arcing at both brushes.
I'll look into buying a new one.

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Limy Sami · Jun 2, 2020

IMO that's got well hot and is best part of burnt out .I don't think the creamy 'goo'' at the inboard end of the commutator should look like that

Guest · Jun 2, 2020

Limy Sami said:
IMO that's got well hot and is best part of burnt out .I don't think the creamy 'goo'' at the inboard end of the commutator should look like that

I wonder if it overheated and there is a dead short somewhere on the windings from the coating being burnt off. I think I would go buy a new one.

PackardV8 · Jun 2, 2020

FWIW, the best 9" grinders I've used are the old Black & Decker Wildcat. I have three of them which are thirty years old.

Another FWIW, none of the younger guys will touch a 9" grinder today. They say, "Too heavy, too hard to control." I see them burn up 4.5" grinders by the bucket full, pushing them too hard where they should be letting the big dog eat.

jack vines

Sevenhills1952 · Jun 2, 2020

PackardV8 said:
FWIW, the best 9" grinders I've used are the old Black & Decker Wildcat. I have three of them which are thirty years old.

Another FWIW, none of the younger guys will touch a 9" grinder today. They say, "Too heavy, too hard to control." I see them burn up 4.5" grinders by the bucket full, pushing them too hard where they should be letting the big dog eat.

jack vines

A seller on eBay has one, about $360 With shipping!
- NEW - Vintage Black & Decker SUPER DUTY Grinder Sander - A+ Cond. - Wildcat | eBay
- NEW - Vintage Black & Decker SUPER DUTY Grinder Sander - A+ Cond. - Wildcat | eBay

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Rollerman · Jun 2, 2020

The commutator bars look pitted not smooth.
The brushes look short.
The higher resistance between the two spots marked with green appear to be failing connections between the wires and the commutator bars. You could try to clean and resolder the connections.

sfriedberg · Jun 2, 2020

I had an old Thor 9" grinder that once turned a flame cut block of 4" plate into an anvil shaped object with nicely rounded horn. Metal case, heavy as sin, happy as a clam with an 8 grit (not eighty, eight, intended for concrete work, I assume) cup wheel. You could see flakes of metal floating in the air during that exercise.

Eventually, I went looking for a replacement and ended up with a DeWalt 7"/9". Only used it for two real jobs so far, but was pleased with its performance. One job was fun. Mounted 2" wide, 6" diameter, flap wheels to prep the inside of C3x4.1 channel for paint, in lieu of a sandblaster. The plastic DeWalt probably won't live to be 40 or 50 like that Thor, though.

Sevenhills1952 · Jun 2, 2020

Rollerman said:
The commutator bars look pitted not smooth.
The brushes look short.
The higher resistance between the two spots marked with green appear to be failing connections between the wires and the commutator bars. You could try to clean and resolder the connections.

I tried that. Still high resistance, even winding to winding loop. I'm thinking about ordering a DeWalt D28499X. 15 amp, 5.3 h.p. I've had good luck with my collection of 20V DeWalt tools, this I want corded. About $173 looks like.
I thought of Dad (rip), probably do what he would do, save the handle, cord, switch, screws [emoji38].

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Sevenhills1952 · Jun 2, 2020

I'm considering Metabo W24-230. A little more expensive but seems worth it from what I read.

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theperfessor · Jun 2, 2020

I'll second what Limy Sami said - new angle grinders are so cheap that repairs can often cost more. I have two milwaukee 5" grinders, had to get cords and brushes replaced on both of them. Local shop charged more than what two new Harbor Freight grinders would cost. I like my old Milwaukees but the next time they wear out...

dana gear · Jun 2, 2020

Sevenhills1952 said:
I'm considering Metabo W24-230. A little more expensive but seems worth it from what I read.

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You won't be displeased with the Metabo, Years back a Metabo rep came to our shop's with a couple of 4 and 9 inch grinders.
We were actually told to work them as hard as possible, just short of out and out abuse. We where looking for replacements to our Bosch yellow jackets as they were being phased out by Bosch. There not cheap but they go the distance, I have been happy with there reliability.

Good 9" grinder or how to fix this one?

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