Anyone burn up their grinder with CBN wheels?

[David Delo]

I have one of the Delta variable speed grinders (GR-450) that's been lightly used for maybe 3 years or so and it's only used to sharpen lathe tools. Recently swapped out the AO wheels for 2 CBN. Today I swapped out the Wolverine platform with one of Robo Hippy's adjustable rests. Sharpened 5 or 6 different scrapper and life was good. Switched over to the 180 grit side to do a bowl gouge and the grinder light flickered a couple times and then went out completely and the grinder won't even turn on now. Circuit is good, no smoke, no puff just all of the sudden died. I know the CBN wheels are a lot heavier but this unit hasn't seen that much use. Don't see any type of reset button. Dread having to deal with Delta CS but anyone else have any motor issues after installing CBN wheels?

[Scott Hackler]

I only have one 180 CBN wheels on my Woodcraft slow speed and it hasn't had any effect on it so far. I have noticed that it taxes the grinder for a second while getting it up to speed from off, but I don't know if that is "hurting" the grinder or not. Sometimes, just because, I spin the CBN wheel ...right before switching it on. I don't know, if that will prolong the life of the grinder or not... I just do it sometimes. I do know that many of my name brand tools just randomly give up and sometimes the Harbor Freight cheapo tools just wont quit...even though I would like to replace them!

[Roger Chandler]

I don't think it is likely that the CBN wheels had anything to do with your grinder failing! If anything they make the grinder run easier and more balanced than regular matrix wheels like AO and others. I have basically the same grinder as you mention only mine has a Steel City label on it, but that is a generic grinder sold by Delta, SC, Porter Cable and others as well.

Mine has run just fine for over two years with my CBN wheel and has done good. Try blowing out the switch and speed potentiometer with compressed air. Could be just the motor gave out on yours. It could be the starter selenoid has gone bad but the motor is still good........that is a likely scenario!

[Justin Stephen]

Nope, no issues. I have had an 80-grit CBN on my grinder for a couple of years now and picked up the 180 and switched to both sides CBN a few months ago. Never had a problem. My grinder is an inexpensive Porter-Cable variable.

[David Delo]

I don't think it is likely that the CBN wheels had anything to do with your grinder failing! If anything they make the grinder run easier and more balanced than regular matrix wheels like AO and others. I have basically the same grinder as you mention only mine has a Steel City label on it, but that is a generic grinder sold by Delta, SC, Porter Cable and others as well. Mine has run just fine for over two years with my CBN wheel and has done good. Try blowing out the switch and speed potentiometer with compressed air. Could be just the motor gave out on yours. It could be the starter selenoid has gone bad but the motor is still good........that is a likely scenario!No luck with air blast treatment. Took the switch apart and cleaned a little bit of gunk out but the contact was clean. Start capacitor is no longer available (even if that is the problem) and the circuit board replacement is as much as a new grinder. So.....looks like a bone yard donation and I'll have to start from scratch.

[David Delo]

I only have one 180 CBN wheels on my Woodcraft slow speed and it hasn't had any effect on it so far. I have noticed that it taxes the grinder for a second while getting it up to speed from off, but I don't know if that is "hurting" the grinder or not. Sometimes, just because, I spin the CBN wheel ...right before switching it on. I don't know, if that will prolong the life of the grinder or not... I just do it sometimes. I do know that many of my name brand tools just randomly give up and sometimes the Harbor Freight cheapo tools just wont quit...even though I would like to replace them!I hear you about the Harbor Freight tools, I've got a few of them. Was looking at their 8" grinder the other day just to have something for mild steel grinding because I don't think you want anything like that hitting the CBN wheels. My Delta is toast so it's either the newer version of the Delta for 129 with free shipping or the woodcraft Rikon for 99 + shipping.

[Reed Gray]

I haven't heard of this happening. The only thing that I can think of that would cause it would be if you are really pushing hard into the wheel so that the grinder is stalling, and you are doing this a lot. I would think that it was some thing in the grinder, but I am not an electrical engineer.

robo hippy

[David Delo]

I haven't heard of this happening. The only thing that I can think of that would cause it would be if you are really pushing hard into the wheel so that the grinder is stalling, and you are doing this a lot. I would think that it was some thing in the grinder, but I am not an electrical engineer.robo hippyAll I know is it was working just fine until I installed the Robo Rest!!!!!!!!!!!! What kind of funky Martian magnetron metal you using in those things!!!!!!! All in jest...........your item worked fine. I wanted it to use for 40/40 Batty grind on the same side as I use for scrapers.

[John Sanford]

Failure upon installing the Robo Rest may simply be a coincidence. Check your power cord and other electrical connections. This could be something as simple as a bad cord or loose connection.

[David Delo]

John,I know it was a coincidence. Just pullin Reed's chain a bit. I've disassembled and inspected all the electrical connections and everything is secure. Maybe some new eyes may help today.Dave

[Bob Bergstrom]

2 years with both wheels on my Delta variable speed grinder with no problems yet.

[Dick Strauss]

It could be coincidence...or...it could be that the higher mass of the wheel left the starting circuit/cap engaged much longer and repeatedly that caused it to burn out much sooner (the second option is not very likely but possible).

[Leo Van Der Loo]

If the motor doesn’t smell burnt, it probably isn’t, and there is something wrong with the speed controller.

If that was my grinder, I would go past the controller and find the leads to the motor, hook that up to the power directly and just give it a quick try, if it doesn’t start up or hum, I’d say its toast, if it does spin or hum the problem is before the motor leads.

Variable speeds might be nice for a lathe, not much use for on a grinder though IMO, I would get a low speed grinder without the funky electronics on it.

[David Delo]

If the motor doesn’t smell burnt, it probably isn’t, and there is something wrong with the speed controller.If that was my grinder, I would go past the controller and find the leads to the motor, hook that up to the power directly and just give it a quick try, if it doesn’t start up or hum, I’d say its toast, if it does spin or hum the problem is before the motor leads.Variable speeds might be nice for a lathe, not much use for on a grinder though IMO, I would get a low speed grinder without the funky electronics on it.Leo,That was some of my thought also. Had everything apart and started with the lamp assembly because the wire that's inside that lamp hood was discolored and looked burnt. Wired that up to a new cord but couldn't get a light. The lamp wires were interconnected with the speed control and on/off switch so I was guessing that maybe the lamp shorted out something, either the switch or maybe the capacitor. Got the multi tester out and started poking around. Forgot to unplug the motor and didn't see exactly what I was touching and got a good spark and a poof. Said a few bad words to myself, boxed it up and banished it from my sight never to be seen or heard from again.

[Mike Peace]

I started off with a gently used Delta 6" variable speed grinder. It died like yours. Nothing to do with CBN wheels. As you discovered, not cost effective to replace the circuit board. I got the 8" low speed WC and it was a better solution. I have had a CBN wheel for a year and added a second a few months ago with no problems.

[Marty Tippin]

The Rikon slow-speed grinder is on sale this month at woodcraft for $99. Sounds like it's a sale made just for you!

[David Delo]

The Rikon slow-speed grinder is on sale this month at woodcraft for $99. Sounds like it's a sale made just for you!Already ordered Marty but thanks for the heads up. Since putting the CBN wheels on about a month ago I had already been scouting around for a second grinder to use for all other materials. Got 2 on the way so temporary inconvenience for permanent improvement.

[Bill Boehme]

Here is a list of potential causes of the problem. Lots of things can cause it to stop running, but it rarely means that the motor is completely dead.

If the motor doesn't do anything when the switch is turned on, does this include no faint humming sound either? If you have very good hearing and are in a very quiet location, turn the switch on and listen for a hum. If you do or think that you might if your hearing is like mine then grab one of the wheels and give it a very quick forceful spin. Does it continue to turn and slowly build up speed? If so, the problem might be the start capacitor or the centrifugal switch assembly or the start winding.
Start capacitors are off the shelf items. I've never heard of one not being available. Never buy one from the tool manufacturer or else you will pay triple for it.
The centrifugal switch is located at the rear of the motor. It consists of a couple springs, a couple weights, linkage, and electrical contacts. It is a simple mechanism and should be easy to tell if something isn't quite right.
If it's the start winding then the cost of repair is more than the cost of a new motor.
This grinder motor includes some electronics for variable speed control by implementing high-speed switching between two and four pole modes. There is a high probability that the electronics have failed. If Delta no longer supports this grinder with replacement electronics or if the cost is too outrageous then a new grinder might be the best option.
Can the higher moment of inertia of CBN wheels be responsible for the problem? Definitely YES if the motor is on the wimpy side and low efficiency (a number of low cost imports fall into this category).
How does the heavier wheels matter? The instant that a motor is turned on, it draws LRC (locked rotor current) which may be up to ten times FLC (full load current). As the motor accelerates, the current drops until it reaches its steady state speed at which time the current would be the no-load value which is typically 20 to 25% of FLC. Generally the acceleration time is a fraction of a second and the motor windings are able to handle this brief over current condition. If it takes several seconds to come up to speed then the windings may be slowly deteriorating because of excessive heating until one day the motor decides not to run.

[David C. Roseman]

[snip]


Can the higher moment of inertia of CBN wheels be responsible for the problem? Definitely YES if the motor is on the wimpy side and low efficiency (a number of low cost imports fall into this category).
How does the heavier wheels matter? The instant that a motor is turned on, it draws LRC (locked rotor current) which may be up to ten times FLC (full load current). As the motor accelerates, the current drops until it reaches its steady state speed at which time the current would be the no-load value which is typically 20 to 25% of FLC. Generally the acceleration time is a fraction of a second and the motor windings are able to handle this brief over current condition. If it takes several seconds to come up to speed then the windings may be slowly deteriorating because of excessive heating until one day the motor decides not to run.



Interesting, Bill. Thanks for posting this.

David D., can you estimate about how many times you'd started the grinder, from the time you installed the heavier wheels until it failed? I was assuming it was very few, since you say in post #1 that you added them recently. I'm curious about that for the future. I've had a heavy 8" D-Way CBN wheel on a Woodcraft slow-speed grinder for a long while with no problems. Also, we did a group-buy of a bunch of the 8" HTC Hurricane CBN wheels a few months back in one of our local clubs, and zero problems of any kind have been reported so far on any of the various grinders. Both the D-Way and the HTC weigh in at eight pounds each, so moment of inertia at start-up is indeed much greater than with the AO wheels.

David

[David Delo]

Interesting, Bill. Thanks for posting this. David D., can you estimate about how many times you'd started the grinder, from the time you installed the heavier wheels until it failed? I was assuming it was very few, since you say in post #1 that you added them recently. I'm curious about that for the future. I've had a heavy 8" D-Way CBN wheel on a Woodcraft slow-speed grinder for a long while with no problems. Also, we did a group-buy of a bunch of the 8" HTC Hurricane CBN wheels a few months back in one of our local clubs, and zero problems of any kind have been reported so far on any of the various grinders. Both the D-Way and the HTC weigh in at eight pounds each, so moment of inertia at start-up is indeed much greater than with the AO wheels.DavidYes Bill, that's some interesting information,Dave,I don't really know how many starts but probably less than 100 on the Delta GR-450. Took delivery this morning of a new Delta 23-197 and a new Rikon 80-805. Put the CBN on the Delta for now because if fit just a little bit better on the platform I had for the old grinder. The Rikon was going to take a little bit more fab time and I'm far enough behind as it is. This new Delta has a tad shorter shaft so I needed to leave off the inside alignment washer to get enough thread on the arbor nut. I'm using the wheels from Ken at Wood Turners Wonders. New Delta moans pretty good at start up and seems to take a bit more time to get to full speed but it does seem to run quieter at full speed. I think I start doing like Scott H. does and give the wheel a pull before turning the switch.