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View Full Version : 4-1/2" Angle Grinder - Gearbox noisy and hot - replace bearings?



PStechPaul
09-25-2015, 01:56 AM
I have a couple of cheap angle grinders and I haven't used them for a long time. But yesterday I needed to cut some welds on my old 1989 Toyota 4WD Pickup Truck bumper with the possibility of salvaging it, and the tool made a lot of noise. The shaft holding the wheel seemed to have quite a lot of loose play, compared to my other one (which I think is a 4" grinder and my cutting and grinding wheels don't fit). It got the job done, so far, but I decided to open the gearbox, and found this:

http://enginuitysystems.com/pix/tools/Angle_Grinder_2361.jpg

There is a good bit of grease but the gear faces are rather dry. The smaller pinion gear fits the motor shaft loosely with a Woodruff key, but seems OK. However, the shaft on the opposite side of the large ring gear has a lot of slop in the housing. It seems to seat reasonably well in the inside bushing, but it was also dry and probably worn. I probably paid well under $15 for the tool 20+ years ago but it seems to work well and the gears seem to be in good shape, so I'm wondering what's the best way to fix it.

Next step is to remove the large gear (held on with a spring clip) and check the size and condition of the spindle and bushing. I'd like to be able to install a ball bearing but that would probably require too much material removal to fit. Otherwise probably just a bronze Oilite bushing. I wonder what sort of grease is best to use in this thing? It seems that it should be something that flows a bit, like 90 weight gear lube, but I don't know how well the head is sealed and it may not be good for lube to get into the motor.

BTW, here is the ugly bumper I'm working on. The part that attached to the frame brackets and had the trailer hitch was just about completely rusted:

http://enginuitysystems.com/pix/house/Truck_Bumper_2357.jpg

I may attach a 4x4 like the one under the bumper, and maybe by bolting it together it might straighten out a bit. It should be better than no bumper at all, as it is now, which surprisingly is legal.
http://enginuitysystems.com/pix/house/Truck_Bumper_2359.jpg

The underside of the truck:

http://enginuitysystems.com/pix/house/Truck_Bumper_2360.jpg

bollie7
09-25-2015, 03:55 AM
You might find there is a ball race under the crown wheel. I have seen some grinders with one.

bollie7

Peter S
09-25-2015, 04:14 AM
I rescued some cheap B&D 4 1/2" angle grinders (the sub-$50 type) which were thrown away for various reasons, worn brushes and wobbly shafts being the main problems.

The removable cover of the gearbox was plastic (!) and the ball race under the crown wheel was held into this plastic part by self-tapping screws (!). Vibration causes the screws to come loose, the result is it feels like the bearing is shot. But all they needed was the screws tightening - good as new (which was pretty crap). Anyway, they work ok now, I found it was the wire brushes that caused the screws to shake loose, ordinary discs are ok.

batt-man
09-25-2015, 05:07 AM
I have a couple of old cheap 4 1/2 inch grinders that have permanent wire wheels on them - if i need to quickly clean something up i can just grab one and go.

Anyway must be 4 or 5 years ago i too popped to gearboxes open because they were getting even more noisy than usual and saw pretty much exactly what you have pictured; grease packed around the edges but the actual gear faces dry.

I scraped the grease out and i have to admit it looked/felt pretty much "new". i added a couple of drops of 3-in-1 oil and mixed it up to make it just a little bit more "flowable", covered the gears and put it all back together.

I drilled a couple of holes in the shelf where they live so that the side-handle can go through; keeps them secure and my theory was that any of the grease which had been thrown to the sides would slowly flow down towards the handle side when not being used and hopefully a smear or two would get on the gears.

Back earlier this year i was using both of them to clean up a couple of old motorbike frames and they qot quite a pounding; when i'd finished i thought i'd have a look in the gearboxes as i needed to change the wire brushes anyway. I was pleasantly surprised to see that whilst the grease was packed around the edges the gears were nicely "wet". Went inside to get a cold drink before putting it all back together and was again surprised to see when i got back outside that the grease was starting to slowly droop under gravity. maybe it was simply because they were warm but i'm telling myself it's because i thinned the grease ever so slightly :-)

Scraped the grease out and it was quite different from the last time i'd had it open; looked dirty and used. I replaced it with some fresh thinned grease and put them away.

Not sure what anyone else will think of my "thinning" trick but for me it seems to have worked out nicely...

Cheers
Batt

_Paul_
09-25-2015, 05:53 AM
Best of luck with the repair but is it worth doing? your grinder will have a new bearing but still have 20 year old brushes and armature etc.

Recently I bought 2x new grinders from our local B&Q for 8 each.

Paul

Rosco-P
09-25-2015, 06:59 AM
Best of luck with the repair but is it worth doing? your grinder will have a new bearing but still have 20 year old brushes and armature etc.

Recently I bought 2x new grinders from our local B&Q for 8 each.

Paul

+1 to the above.

I wouldn't be surprised if the bearings are just plastic sleeves.

More tilting at windmills Don Quixote?

GKman
09-25-2015, 08:56 AM
I just used one until one of the bearings failed completely, cage for the balls, broken into pieces etc.
Surprised to find it the lowest loaded bearing in the tool, at the commutator end.

Thanks for the tip on thinning the grease. I suppose they use thick grease so the tool never gets nasty and dirty looking.

Danl
09-25-2015, 09:05 AM
I noticed my Ridgid angle head grinder was getting louder last week, so I popped off the gear access cover and noted that even when fairly warm, the grease had reached a state that would not allow it to flow, so I simply cleaned out most of it and packed in some new grease and it quieted right down. I do like batt-mans suggestion of adding a little oil to keep it thinner though.

Dan L

wierdscience
09-25-2015, 11:29 AM
Just wash/scrape the old grease out and replace.I use chainsaw sprocket grease for this at work on all our DeWalt grinders,works good and lasts a year or so in constant use.

Some of the really cheap grinders use a cast iron bushing made to fit in place of a standard ball bearing.Those are most often found in the $12 Ebay grinders,I find it funny that in China where a sealed ball bearing can be had for $.10 that they would even go to the trouble of making a bush to fit instead,but,well it is China:rolleyes:

old mart
09-25-2015, 12:50 PM
Most of the time nowadays its not worth the bother to bodge them up. If you can buy Bosch tools, they seem to have excellent spare parts availability for older models.

lakeside53
09-25-2015, 12:53 PM
Why "thin" any old or random grease? Maybe you can figure out the manf recommended, but I use Stihl weed eater / brush cutter gearbox grease. You can get it at any Stihl dealer in a small tube. It's a light (I'd guess about NLGI 1 to 1.50 moly grease and put on a heck of a lot more hours than most angle grinders. The Stihl heads have a plug for adding more annually; the tube simply screws in - squeeze the tube, replace the plug... done. One day I'll put plugs in my grinder heads... way down the list though.

PStechPaul
09-25-2015, 10:36 PM
Here is the head with the gear removed:

http://enginuitysystems.com/pix/tools/Angle_Grinder_2362.jpg

Removed the bearing:
http://enginuitysystems.com/pix/tools/Angle_Grinder_2364.jpg

You can see where the bore is worn - about 0.5mm or 0.020". The intact section is 12mm.
http://enginuitysystems.com/pix/tools/Angle_Grinder_2365.jpg

You can see how much slop there is between the spindle and the bushing.
http://enginuitysystems.com/pix/tools/Angle_Grinder_2367.jpg

It looks like the equivalent ball bearing is a metric size 6201, 12mm x 32mm x 10mm, about $5.47 from McMaster for an open IDEC bearing rated 30,000 RPM.
http://www.mcmaster.com/#5972k313/=z3l3yy

The bushing shown is a 0.500" (12.69mm) OD with 0.375" (9.51mm) ID. I probably could bore out the existing bushing to fit the 0.500" OD of the new bushing, and bore the new bushing to 12mm for the spindle. But that leaves only about 0.35mm (0.014") for the walls. I could also turn down the OD of the spindle to 10 mm and bore the bushing to fit. But then if I ever decided to use a ball bearing I would need a #6200 which is 30mm dia.

I'll probably just get the correct ball bearing from McMaster, and maybe get a few other things as well. It will be interesting to see (and hear) how much the grinder improves.

Peter S
09-25-2015, 11:53 PM
Where is Old Tiffie when you need him?

"Throw in bin".

:)

wierdscience
09-26-2015, 02:00 AM
Uggg you got one of the bushing models,when you replace the ball bearing and top bushing you will have nearly doubled the value of the grinder:)

Willy
09-26-2015, 04:51 AM
Where is Old Tiffie when you need him?

"Throw in bin".

:)


Uggg you got one of the bushing models,when you replace the ball bearing and top bushing you will have nearly doubled the value of the grinder:)

Yes Paul just take off the valuables like the wheel/brush ,drive washers, and the cord.
Buy another angle grinder for 19.95 and you will have a new grinder and some accessories already in the bank.
Oh yes, save the rest as well, never know when you'll need a switch or a set of brushes.

hermetic
09-26-2015, 07:41 AM
I managed to save a cheap 225mm grinder with a gear problem, you often find that the gears are nowhere near meshing deep enough, and a couple of shims on the motor shaft and behind the crown wheel got it working again for long enough to keep the job going till I got a replacement. My replacement is a Parkside (Lidl 39-99!) with a THREE YEAR warranty, which I have just claimed under (after 2 1/2 years of heavy use) and received a replacement. They are good tools, but usually let down by the electronics (as usual) so you find that the speed control blows up or, as in this case, the soft start unit quits. It is after all a 2.6 hp motor, and I had been overdoing the stop start cycle a bit:o Of the many grinders I have used, it is probably the safest, I remember the huge old Black and Decker all alloy grinders would kick like a mule when you pulled the trigger!
Phil

Rosco-P
09-26-2015, 07:53 AM
Yes Paul just take off the valuables like the wheel/brush ,drive washers, and the cord.
Buy another angle grinder for 19.95 and you will have a new grinder and some accessories already in the bank.
Oh yes, save the rest as well, never know when you'll need a switch or a set of brushes.

Save the rest, on a $20 grinder? When the switch or brushed or gears, or?, or?? go bad on the next $20 grinder, just pitch it as should be done with this one.

Spend $6- plus postage, plus machine a bushing to patch this POS? Why is "Common Sense" such an un-common commidity?

hermetic
09-26-2015, 08:12 AM
It all really depends on how busy you are, and how far you are from the grinder store! they are cheap enough today to keep a couple of new ones "in stock". Still doesn't mean I wouldn't try to fix the old one though!

Rosco-P
09-26-2015, 08:54 AM
It all really depends on how busy you are, and how far you are from the grinder store! they are cheap enough today to keep a couple of new ones "in stock". Still doesn't mean I wouldn't try to fix the old one though!

Translation: how little you value your time and how much you want to risk that the bushing isn't the first link in a line of failure in a cheap tool.

I see crap like this all the time at Estate and farm sales, power tools that were "too good" to throw away. cardboard boxes of disassembled circular saws, corded drills, etc. with burnt up windings saved because the deceased was going to find a cheap motor rewind shop or ......someday take a crack at rewinding it themselves.

Don't be that guy.

lakeside53
09-26-2015, 12:34 PM
It comes down to having something better to do... I guess Paul doesn't. lol Actually, I'm guilty as all heck of fixing the impossible for no good reason, but I'm getting better.

Grinders... I just pick them up at garage sales. No junk, just name brand quality types. In the last year I got 3 4 1/2 inch Bosch, maybe $15-20 each. Probably have 6 now, plus a collection of 7-8 inch types Metalmagpie left here to look at one day. But with two shops they are always in the wrong place. Guess I need more. ;)

Oh.. I have one more.. I was given a harbor fright grinder. Guy bought it for $9.99 then had a 20% off coupon. Used it once to grind down a screw. I'll pass it on to a needy friend one day.

EddyCurr
09-26-2015, 01:46 PM
PStechPaul

Ignore the chatter.

See the project through to completion and enjoy the inestimable
sense of satisfaction a person derives each time he uses something
he fixed himself.

Embarking on this repair will pay you back several-fold more in time,
and money than you invest. Learning is taking place - always an
opportunity for personal growth. Moreover, by posting your comments
and photos here, those benefits from learning accrue to a far larger circle
beyond yourself.

I have several grinders, some of which are the inexpensive imports.
I appreciate the utility of having multiple tools - each configured for
a specific use. I have not had occasion to look inside the drive of
any of them before. The images and discussion in this thread give
me ideas about preventative maintenance to prolong the life of all
of them. Perhaps something from this thread will spark inspiration
and lead to repurposing a cheap grinder for another purpose.

Thank you for this ...

.

PStechPaul
09-26-2015, 02:29 PM
Yes! Thanks for that. I realize that there is no real economic benefit to a repair such as this, but I always learn something by making such attempts, and I enjoy the challenge and process. I abhor the "throw-away" mentality that pervades our culture and it seems that manufacturers purposely design planned obsolescence into their products. I have only used this grinder a few times, and mostly around the time I first got it about 15-20 years ago. I was surprised at how much it had worn, and it was probably because of lack of lubrication as well as the cheap bushing.

I found some ball bearings on eBay for about $3 each with free shipping, so unless I think of more stuff to order from McMaster I will probably go that route:
http://www.ebay.com/itm/6201-Z-Radial-Ball-Bearing-Double-Shielded-Bore-Dia-12mm-OD-32mm-Width-10mm-/360871636829?hash=item5405a02f5d

I'm not sure if I should get the double shielded or the sealed bearings, which seem to have lower speed ratings than the open type. But the open type will definitely present a problem with leaking lubricant if I use something more liquid than grease. Here's a bearing with two rubber seals, rated for at least 22,000 RPM:
http://www.ebay.com/itm/Qty-1-6201-2RS-two-side-rubber-seals-bearing-6201-rs-ball-bearings-6201-rs-/130947049055?hash=item1e7d0d665f

And, in fact, that's what I just did. Two sealed bearings for $5.12. I should get them Friday.

If I were really nuts about this, I would also refurbish or replace the top bushing, and take apart the body of the grinder and carefully clean and inspect the motor and the brushes and possibly replace those bearings as well. But I think I'll just squirt some oil where I can and that should be good enough for my needs. I have one other grinder that has wire brushes, and it seems solid and tight. And I think I have another one somewhere.

Left Handed Spud Wrench
09-26-2015, 02:57 PM
Can't offer any insight on this one, but you aren't alone. I have a few "favorite tools" I've put the effort into simply because. No other reason.

Great example would be my Trinity Grinders -- Clean, Polish, REPENT. Basically they are three small air-grinders of unknown flavor/brand that I was issued a long time ago.

One is permanently set up with a flow restrictor and a special collet for accepting the polishing bobs I prefer. The collet has a stop so I get the same length every time. The trigger, pivot, and valve are all known quantities to me -- I get the exact speed I want just by touch and by knowing the sound of that motor. That's my polishing grinder.

The cleaning one -- same story. When I need to use a brass wheel I have my preferred sizes and shapes, optimized collet and so forth... This grinder is a right-angle air-grinder and I've become accustomed to how it fits my hand and how it balances when I have to get into the strangest of locations.

Now REPENT -- that's just a big cranky air-grinder that's mostly worn out. It hisses with menace when I pull the trigger. You have to give the steel-wire brush a quick flick, then it comes to life. It only has two speeds -- hiss and "invoke religious praise in hopes of earning divine protection from flying debris and wire-shards." I use this one to bust rust, clean encrapulated platens and nozzles, and other Serious Wire-Brushing duty. I have taken this one apart many times because the gears tend to wear down quickly in the head even with proper oil. Friend of mine cast me several sets out of what he called "Gear Metal" awhile back -- when I use the last of those this tool will be retired.


They may be "just" air-grinders... and maybe I can get better or newer... But there is something to be said for taking them apart, cleaning them and oiling them between jobs. Pride maybe? Satisfaction? Can't really quantify it.

Best of success in fixing your tool, I'll be reading along. :)

Willy
09-26-2015, 02:58 PM
Good for you Paul. I have to say I too will try to fix something rather than just bin it.
Hell if any of this had to make economic sense we should all just lock up the shop and and sit quietly in the house sucking applesauce through a straw.:)

lakeside53
09-26-2015, 03:24 PM
Don't get sealed bearing for the grinder. The seals will simple heat up and fail anyhow. Shielded or open one side, and use the right grease and correct amount (less than you think).

Rosco-P
09-26-2015, 04:44 PM
Yes Paul just take off the valuables like the wheel/brush ,drive washers, and the cord.
Buy another angle grinder for 19.95 and you will have a new grinder and some accessories already in the bank.
Oh yes, save the rest as well, never know when you'll need a switch or a set of brushes.


Good for you Paul. I have to say I too will try to fix something rather than just bin it.
Hell if any of this had to make economic sense we should all just lock up the shop and and sit quietly in the house sucking applesauce through a straw.:)

Good display of flip-flopping, just like a fish out of water.
Peer pressure override your common sense?
http://idioms.thefreedictionary.com/throw+good+money+after+bad

Willy
09-26-2015, 05:09 PM
Good display of flip-flopping, just like a fish out of water.
Peer pressure override your common sense?
http://idioms.thefreedictionary.com/throw+good+money+after+bad

No it's called re-evaluating one's line of thought to reflect that yes, I do have an open mind.
You ought to try it sometime instead of coming off like a constant ass all the time, but yes at least you're consistent.:rolleyes:

Rosco-P
09-26-2015, 05:22 PM
No it's called re-evaluating one's line of thought to reflect that yes, I do have an open mind.
You ought to try it sometime instead of coming off like a constant ass all the time, but yes at least you're consistent.:rolleyes:

Yup, throw time and money at a cheap grinder that failed after little use. Makes total sense, don't buy and rebuild a good quality used one. We'll call that line of thinking, "Willy's way".

PStechPaul
10-02-2015, 02:59 PM
I just received a pair of double sealed 6201RS ball bearings for the grinder. For $2.50 each I figured I might as well get a spare. It seems to be good quality. However, the ID measures 11.94mm (using my HF calipers), and the spindle also reads 11.94mm. The OD reads 31.95mm while the original bushing (which I had to press out) reads 31.97mm. So the bearing should fit nicely in the housing, but the spindle appears to be a press fit.

Since originally it fit into a bushing for a rotating fit, I think I should turn down the OD of the spindle just a few tenths so it fits snug but not a press fit. The spindle is inserted from the outside of the housing into the bearing, which is inside, so it might be a problem if I try to press it in, and another problem if I need to press it out.

No need to continue the rant about spending money and time on a cheap tool. This is about a learning experience and best practices that apply equally to a $15 or a $150 tool, but the consequences of making a mistake are much different. Moreover, if the repair is successful I will have a tool that will likely serve my purposes indefinitely, and I will know that I fixed it and will have the experience to apply elsewhere.

macona
10-02-2015, 04:17 PM
Just press it on. You cant reliably take a few tenths off on a lathe, thats grinder territory.

CalM
10-02-2015, 07:01 PM
Oh Come on, that's what wet or dry SiC paper is all about.

lakeside53
10-02-2015, 07:52 PM
Sealed bearing won't last long... or at least the seals. Most are limited to 6-7000 rpm. Shielded are what you should use.

And yes.... just press the bearing on.

PStechPaul
10-02-2015, 08:54 PM
I used a piece of abrasive cloth to polish the surface of the spindle, and the bearing slid on snugly:

http://enginuitysystems.com/pix/tools/Angle_Grinder_2372.jpg

It was a snug fit in the housing as well, but another bit of work with the abrasive cloth, and Bub's your oinkle.

http://enginuitysystems.com/pix/tools/Angle_Grinder_2362.jpg

I cleaned out some of the grease, and checked the motor shaft. It seems pretty solid:

http://enginuitysystems.com/pix/tools/Angle_Grinder_2375.jpg

Turned out pretty good, and runs probably better than it ever did:

http://enginuitysystems.com/pix/tools/Angle_Grinder_2378.jpg

I'll probably open it back up and put more grease on the gears. I might try some 90W gear lube and see if it stays in the housing. It might need a gasket (probably just Permatex) on the mating surfaces. The sealed bearing is supposed to be rated at 20,000 RPM. And since this is a reduction drive of about 4:1, the wheel probably doesn't exceed about 6000. It probably won't see a lot of use, and if only the seal deteriorates it will probably just leak a little bit.

PStechPaul
10-02-2015, 08:58 PM
A few more pictures:

http://enginuitysystems.com/pix/tools/Angle_Grinder_2373.jpg

http://enginuitysystems.com/pix/tools/Angle_Grinder_2374.jpg

http://enginuitysystems.com/pix/tools/Angle_Grinder_2376.jpg

http://enginuitysystems.com/pix/tools/Angle_Grinder_2377.jpg

lakeside53
10-02-2015, 09:17 PM
90wt gear oil isn't much different in weight to 30 SAE engine oil... pretty runny and will get under the seals and dilute/flush the bearing grease. Stay with grease. Use the same grease as weed eater heads - works well... and for long continuous periods.