Skil bench grinder needs a hand to start turning! 2

[judgedredd]

Hi,

I am new here, and very new to electric motors, so am not sure if this is an appropriate post for this forum/site.

I recently acquired a used Skil Bench Grinder - Model 287, Type 4, 1/3 HP, 3,600 RPM.

I was shown that the grinder, when switched on, needed to be helped in starting to spin by giving it a 'shove' or begininng the movement of spinning (sorry, I don't know the nomenclature yet), by hand. It started to spin slowly but after it got past a certain RPM it sped up to its operating RPM of 3600. Since I needed a bench grinder to convert into a polishing machine for some brass pieces I had made for a project of mine, I went ahead anyway and bought it thinking I could fix it later (since I am very good at fixing just about anything, if even with some online help or YouTube videos). If the motor is not helped in spinning up all that happens is that the motor makes a slight buzzing noise and does not turn.

Having worked with someone on his invention that used an electric motor, I do understand that there are some components that come with electric motors that cause the motor to start turning by itself, without giving it a 'helping hand'. I understand that a component or components has/have failed, but am not sure which ones. What do I need to look for in doing the repair myself? I could post pictures on the innards of the motor if required.

 

[mudandsnow]

Not too familiar with motors myself but my guess is the starting capacitor needs to be replaced.

Be careful when working with capacitors, they store electrical energy and can kill you. With that in mind, google "bench grinder start capacitor" and you should find everything you need.

 

[flexoprinting]

Hello judgedredd

This is an Engineer discussion site and not so much a site for do it yourselves often times post like these will be deleted.

As mentioned above you might have a bad starting cap, maybe no cap and a bad start winding, could be an open centrifugal switch, could also be none of these and something else. With the limited information it's tough to tell. I googled your part number with no luck so hard to tell. Try googling how a start capacitor operates for explanation.

Chuck

 

[waross]

Check the centrifugal switch first. Take the non-drive end-bell off and you will see the switch. It should be closed when the motor is stationary.
Look at the starting winding. It will be a smaller gage wire than the run winding. It may be burned out.
If there is a starting cap check that last.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[3DDave]

Like this?

http://vintagemachinery.org/photoindex/detail.aspx?id=18129

 

[judgedredd]

Thanks for all the posts. I probably have enough info to get this sorted out. And sorry that I posted in the wrong forum but all you guys have been great and allowed this thread to continue. Thank you. I wll let you all know how I got on, if that's ok.

 

[judgedredd]

3DDave,

Yes, that is the one but mine looks a bit better than that!

 

[jraef]

In before it gets deleted...

On small bench grinders like that, people try to do too much with them and grind really hard to where the motor slows to almost a stop. That puts a lot of stress on the centrifugal switch and eventually the starting capacitor. Neither are made to be used that way. If you are mechanically inclined and capable of grasping new situations, you can give it a whirl in trying to replace them, I've done it and I'm all thumbs. But it's not worth sending in out for repair, the cost will be more than a new one would be.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[judgedredd]

Well, this machine does not have a start capacitor or even a run capacitor. I took pictures of the innards and inside the base and have posted them here. Having read up on capacitors I am assuming that the original one got too old and gave up working, after which it was removed and the wires joined together as can be seen. My only problem now is getting a new one and installing it. I hope that Skil have the info for this model.... I will give them a call tomorrow (Friday).

A quick note about it running.... there is a point in the spin up where a click can be heard. I am assuming that this is the centrifugal switch kicking in. A click can also be heard when it spins down to a certain RPM speed after being turned off.

 

[zlatkodo]

Usually, the grinder has no starting capacitor and centrifugal swich.
Just run capacitor.
In this case, probably it is about bifilar coil in aux. phase ( starting using increased resistance of aux. winding).
Induction Motor Repair

 

[waross]

Take a close look at the centrifugal switch. The contacts may be dirty and not making contact. Check the starting winding for continuity.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

It's probably the start switch, which if you don't know is that board with the 2 spring across it and the 2 wires attached. You're lucky, because it came with a spare contact. So, just move the 2 wires to the other contact and it'll likely start working again.

 

[judgedredd]

Thanks for all the input. I will see if cleaning the contacts does the trick.

 

[racookpe1978]

Be aware pushing (touching) the grinding wheel to start it endangers what used to be your fingers on the starting hand.

 

[judgedredd]

Cleaning the contacts and all around the switch (the circuit board with the two wires, red and white, going to it) just made the motor buzz a bit louder. So it seems that the start winding is at fault, though I have no way of testing it at the moment.

I haven't moved the wires to the other contact set as suggested by LionelHutz and on closer inspection that would not be easy for me to do as the contact point on the red side is not duplicated on the spare set. The part that the red wire is attached to is not on the spare side so I would have to break the rivet on the used side and re-rivet it back on the spare side. Something I don't have the equipment for.

For the moment no further action can be taken by me. If I get to a next step that would be buying a volt meter and testing the winding. Thanks to the moderators for allowing this thread to be active. It is very much appreciated. And thank you to everyone who chipped in with their posts. You have a great forum here.

 

[Compositepro]

There does appear to be charring of the start winding coils where they come out of the stator slots. The motor is toasted.

 

[waross]

Sometimes the mechanism wears so that the switch is not held fully closed by the centrifugal mechanism.
You can try wedging the switch closed. Put the motor together with the switch wedged closed and energize the motor for about a second.
If the motor starts to turn the problem is in the switch. If the motor still hums the start winding is probably toast.
You can buy a new grinder for less than the cost of a rewind.
You can continue to start it by spinning it until the main winding burns out or you lose a finger.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

You can continue to start it by spinning it until the main winding burns out or you lose a finger.

Bill... He'd have nine more fingers to use. Duuh.



Compositepro is correct though. You can see the windings are actually torched.



What I often see is cheap grinders that are so gutless that when you press the work against grinder they often slow so far that the start kicks back in. It only takes pinning the grinder in "start" for a few seconds and it's toasty critters.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Yes I saw that Keith. You may be correct but I have seen start windings show signs of overheating that have not yet died.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[flexoprinting]

I agree it has been warmed up, this one is toast for sure.