Have to jump start my bench grinder

[NHBandit]

Question for you guys who are good with electric motors. I have an older Craftsman bench grinder that I've had for many years. It works fine other than the fact that every time I turn it on I have to give it a spin by hand to get it going. I'm sure it's something simple. Is there something that's worn out that I can buy and is fairly easy to replace or should I salvage the wheels off it and call it a day ? Thanks.

 

[CJinPA]

Had to replace the starting capacitor on my dayton grinder. Now it starts up really fast. Same symptoms you're describing. It's a pretty cheap fix.

 

[Davefr]

Question for you guys who are good with electric motors. I have an older Craftsman bench grinder that I've had for many years. It works fine other than the fact that every time I turn it on I have to give it a spin by hand to get it going. I'm sure it's something simple. Is there something that's worn out that I can buy and is fairly easy to replace or should I salvage the wheels off it and call it a day ? Thanks.

Some of these older CM block grinders used a starting relay vs. a capacitor. The relay energizes the start winding during the inrush of current when you flip on the switch. After a few seconds the current dies down and the relay turns off the start winding. By that time the grinder should be spinning at full speed.

The start relay is a little module under the base of the grinder. Just replace it.

 

[rlitman]

Or a centrifugal switch, or the start capacitor itself could be failed.

 

[supra90turbo]

I would put a rip cord on it for added effect.

 

[NHBandit]

I guess I'll have to open it up and have a look inside. Maybe post a pic so someone here who is better with electrical stuff can tell me what to look for. Thanks guys. I bought a cheap Chinese bench grinder for 10 bucks new at the local flea market just to get me by and either the shaft is bent on both ends or the wheels are horribly out of round but it jumps all over the place when it's running and you can't grind **** with it. Maybe it's got square wheels...

 

[Trey T]

Sure, I want to see and learn about AC motor. It's something I want to get into learning and repairing.

 

[theoldwizard1]

My Dad had that problem on a table saw (he used a stick to start it) and it took a long time to get up to speed. Turned out to be low voltage from the pole, but only under load.

 

[NHBandit]

OK.. I had a "duh" moment but I blame it on the fact that some of my stuff has been packed away for a year and a half ever since we moved from NH to Tennessee. I am just now starting to dig it out since my new garage is being built in the next couple of weeks and I want to repair whatever stuff I have that's messed up before it goes into the new shop. It's NOT a Craftsman bench grinder. It's made by American Forge & Foundry which according to my research, is a quality brand. I'm betting the problem is the round canister in the bottom that clearly says "Starting capacitor" right on it huh ? Holy ****, I'm an electrician !! LoL.. So anyway I did a Google search and found out that Granger sells them and since we have a local Grainger store I'm off to buy one. $5 bucks to fix something that's been annoying me for years. Who would have known it was this easy ? My question now is this. My capacitor says 100 MDF on it but the lowest number Grainger sells is listed as 108-130 MDF. Is this the one I need ? Thanks. Here's the pics.

 

[Davefr]

My capacitor says 100 MDF on it but the lowest number Grainger sells is listed as 108-130 MDF. Is this the one I need ? Thanks. Here's the pics.

They can be + or - 10% without any problem but you'll probably be OK.

Why don't you test the old one to be sure it's bad.

 

[IP2GSR]

It should be fine... with out getting into knowing more information on the motor winding it is just a guess.

The part you are buying is likely a 120mF +/- 10% (ie 108-130mF) The part you have will be 100 mF +/- a tolerance. The tolerance will be listed on the cap.

The starting torque with increase with an increase in capacitance which is good but the starting current will also go up. Going up a little bit is not a problem going up too much will cause added heat in the start winding and could burn them out... but since the cap is only going up 20% this should not be a problem. However there is no way to know without knowing the other components in the grinder. Hope that helps in some way...

 

[NHBandit]

Thanks guys. I just called Grainger to make sure they had it in stock and the salesman found me one that's listed as 88-108 so I'm going with that. Dave I appreciate the advice to test the old one but when it comes to electrical stuff anything more complicated than plugging in a lamp concerns me. I'll take a shot that this is the problem and report back.

 

[243]

You can also pick up capacitors and Johnson Controls.

 

[NHBandit]

You can also pick up capacitors and Johnson Controls.

Thanks for the tip but I'm looking forward to the trip to Grainger. I've been getting their catalogs for years but never had a store local to me until I moved here.

 

[NHBandit]

Well hell... That didn't fix it.

 

[Trey T]

Well hell... Keep trying! I want to see the problem resolved.

 

[Davefr]

Well hell... That didn't fix it.

That wiring doesn't look original. Are you sure it's wired correctly? Did it ever run right for you?

The only thing left is centrifical switch and/or start winding.

 

[Dustin Echoes]

X 2 on rip cord. Pull start bench grinder? Sign me up!

 

[Lhorn]

thanks for starting this thread. I have a lightly used bench grinder that's done the same thing, nearly from the time it was new. I'll try to fix it now. Hope it works for me even though yours didn't.

 

[skyking]

Are your bushings worn out. ?Your arm/stator may be out of alingment.

 

[Pumpman1968]

That wiring doesn't look original. Are you sure it's wired correctly? Did it every run right for you?

The only thing left is centrifical switch and/or start winding.

Exactly....there has to be a switch/start relay in there. It doesn't look like a light switch....usually just a little black plastic box with wires going to it. Could say Westinghouse or Gould or Baldor.....with your luck.....nothing at all

 

[NHBandit]

I guess it's time to take it to an expert. I have no idea if it's wired right or if there's something missing but it did work fine for a long time when I first got it. I bought it used though and have no idea what it's been through in the past.

 

[bisley45]

Or a centrifugal switch, or the start capacitor itself could be failed.

+1 ^^^^

 

[torqueman2002]

Take a look at pictures 10 - 16, in the following --> http://www.garagejournal.com/forum/showthread.php?t=107194

A pre-Block style CM grinder with cap, centrifugal weights and start switch detailed.

 

[fourjeepin]

I had the same problem with a dryer I was given when I got out of school. I was too broke (all extra money went into tools or the Jeep) to buy new so I cut out the door safety switch and would reach in to give it a push start. The ladies didn't like it, but I didn't mind and used it that way for about eight years until the washer died.

So I'm no help here, but felt like sharing.

 

[NHBandit]

Take a look at pictures 10 - 16, in the following --> http://www.garagejournal.com/forum/showthread.php?t=107194

A pre-Block style CM grinder with cap, centrifugal weights and start switch detailed.

Very helpful however mine has more wires than your Craftsman and the colors are different. Also my existing start capactor only has connections for 2 wires. The new one from Grainger has 4. I think it's time to take it to an electric motor guy before I cause it to go up in smoke. When it was working properly it was a great heavy duty grinder and ran fairly smooth & quiet. Thanks guys for all the tips. I know when I'm in over my head.

 

[Outlawmws]

You probably had it hooked up backwards, most electrolytic caps are polarized.

 

[Pantsfall_McFixit]

I thought bench grinders have permanent split capacitor type motors? Since you don't need to jumpstart a heavy load. If so then it needs a run cap to generate a phase difference.

 

[91bronc300]

Aren't 4 connection capacitors dual start/run capacitors? Did you try every combination possible with those 4 connectors?

 

[Davefr]

You probably had it hooked up backwards, most electrolytic caps are polarized.

Doesn't matter when on an AC source. (polarity only matters on DC)

Aren't 4 connection capacitors dual start/run capacitors? Did you try every combination possible with those 4 connectors?

He shouldn't change the wiring if it previously ran fine the way it's currently wired.

 

[mitusa]

Very helpful however mine has more wires than your Craftsman and the colors are different. Also my existing start capactor only has connections for 2 wires. The new one from Grainger has 4. I think it's time to take it to an electric motor guy before I cause it to go up in smoke. When it was working properly it was a great heavy duty grinder and ran fairly smooth & quiet. Thanks guys for all the tips. I know when I'm in over my head.

I had a Dayton with a part missing.....would not turn on. I called an electric motor repair shop to see if they would help diagnose the problem. They were going to charge $50.00 just to look at it. It's still sitting in the floor of the shop.

 

[kevin47]

Rip cord...? I wanna come watch...!