new grinder, bearings getting hot

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koduu

Joined
Feb 26, 2018
Messages
51
Hi all,
I have a question about belt grinder small wheel ball bearings.
Recently got a new grinder and just tried it on. I ran it maybe 5-10 minutes at half rpm-s and the bearings got really hot. By touching I would guess >100 degrees celcius (>210F).
Is this normal for a new bearing (6205 2zr) or should I already start searching for new ones.

I don't think I ran the bet in a odd kind of a way (too much pressure or wheels are diagonally or whatnot).

As I understand I cannot grease these bearings since they are shielded from both sides.

Is this normal?
 
Which grinder you have ? Do you assembly it ? You may have tightened the bearings too much ? The quality wheel have a tube/spacer between bearing so you can not over tight them .....Check how it is done on your grinder.Picture will help us ....................
 
Couldnt figure out how to add images so i uploaded them to imgur

Grinder bearings https://imgur.com/gallery/NKkizLr

The grinder comes from a small maker in europe "volf grinders". By the looks of the serial numbers he has made quite a few of them. I have not accurately measured the temperature and it is possible that it is a few dosen degrees lower.
 
Well , it is excellent solution for bearing , they are free to run ....There should be some temp. for sure but not that high. Is it this your first grinder ?

v0B2JPu.jpg
 
Small wheel bearings heat due to several things:
Too much belt tension
Too much pressure on the wheel
Too high a belt speed
Too fine a grit for the amount of metal being removed
Too long a run time
 
What size bearing? The have always thought that small wheels have to run slow because of the rpm the belt creates. Say your running at 4000sfpm, Which is not crazy fast. Over a 1” wheel thoes bearings are turning 15,279rpm. That’s moving at a good clip and under load will get quite hot. That same 4000sfpm is only 1,909rpm on an 8” wheel.
 
Hi, a few more things to note, the bearings give some resistance, if i just try to roll them by handas soon as i take of the hand, the roller stops. I think this might be normal, since all 3 wheels feel more or less the same, 1 does give a bit more resistance, but just a little bit.

Also, if my napkin calulation is correct, then at max speed they would roll at 9000 rpm.
 
If thy are 2RS bearings then thy should have a rubber seal that would cause friction.
 
JTknives said:
If thy are 2RS bearings then thy should have a rubber seal that would cause friction.
Click to expand...
If i understand the manufacturers site correctly then these bearings are shielded with metal not sealed. Type 2zr

https://www.zvlslovakia.sk/en/products/single-row-deep-groove-ball-bearings/

"
Single row deep groove ball bearings with sealing on one or on both sides are manufactured with metal shields (Z, -2Z, or ZR, -2ZR) or with seals (RS, -2RS or RSR, -2RSR). The shields create a non-contact sealing.

The bearings are manufactured in the original design with shoulders for shields on the inner ring (Z, -2Z) or in the new design with a shield and a flat collar of the inner ring (ZR, -2ZR).
"
 
Sealed bearings have grease inside.

If you have seen videos of free spinning bearings, they have had the grease removed for that video.
If you have used fidget spinners, remember they are just toys.
Those videos are all bullshit, fidget spinners are bullshit.

The right amount of grease is good and necessary.
 
koduu said:
Hi, a few more things to note, the bearings give some resistance, if i just try to roll them by handas soon as i take of the hand, the roller stops. I think this might be normal, since all 3 wheels feel more or less the same, 1 does give a bit more resistance, but just a little bit.

Also, if my napkin calulation is correct, then at max speed they would roll at 9000 rpm.
Click to expand...
If you turn them by hand they will stop , small Dia.wheel and they have no torque? to spin longer , grease will stop them .About temperature , most people think that 50-60 Celsius is hot on hand ......especially when we touch metal on that temp. As far I know 120 Celsius is safe on bearing. I say use it , time will tell you if anything is wrong with them ;)
 
if the bearings are getting hot one possible cause is lateral pressure on of the of the races causing the balls to friction against the side of the race more than normal.

Please check this drawing I just made to illustrate this and a video of my grinder wheel.

Pablo


do498uS.png
 
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Wheels in his grinder have two Seeger ring from side , there should be no lateral pressure there PEU PEU .one thing it come to me now is maybe they are damaged in installation or there is to small tolerance between bearing and wheels inner Dia..IF they really get that hot .
BW , in your wheel there is plenty of material over bearing :) His wheels are almost same Dia. as bearing so no mass over them to free spin longer ...
 
PEU said:
if the bearings are getting hot one possible cause is lateral pressure on of the of the races causing the balls to friction against the side of the race more than normal.

Please check this drawing I just made to illustrate this and a video of my grinder wheel.

Pablo


do498uS.png
Click to expand...
That s is right way to do .But I use big inner dia. bearing in my new grinders so I do this way to avoid big bolt ....bushing goes tru the bearing ...

tJb4CGF.png
 
I can go to my garage this weekend, then I get to test if running it a bit longer on low speeds would cause the thing to get way too hot or is it just the issue of wearing in a new mechanism.
If natlek's image is correct, then the issue could be a bit too tight of a fit in the areas marked in yellow and that could maybe be worn in or if id does not help then maybe I could just turn it a bit smaller.
R62nSh9.png

BTW, Natlek you wouldn't happen to be Volf?
 
Small wheel bearings need to run at very slow belt speed. Most folks run a small wheel WAY too fast. 1/2 speed is still too fast.
At 1/2 speed (assuming a 1750RPM motor) that is 4375RPM.
If you have a 3600RPM motor, it is running the small wheel at 7200RPM at half speed.
The smaller the wheel, the more it is being overdriven.

Add to this that we tend to over-tighten our belts more than needed when using a small wheel and you put the bearing under a lot of load.

I run my small wheels at around 10% to 15% speed. Maybe some of the larger small wheel tasks (oxymoron?) will be run at 25% speed.
 
Stacy E. Apelt - Bladesmith said:
Small wheel bearings need to run at very slow belt speed. Most folks run a small wheel WAY too fast. 1/2 speed is still too fast.
At 1/2 speed (assuming a 1750RPM motor) that is 4375RPM.
If you have a 3600RPM motor, it is running the small wheel at 7200RPM at half speed.
The smaller the wheel, the more it is being overdriven.

Add to this that we tend to over-tighten our belts more than needed when using a small wheel and you put the bearing under a lot of load.

I run my small wheels at around 10% to 15% speed. Maybe some of the larger small wheel tasks (oxymoron?) will be run at 25% speed.
Click to expand...

I hope you are not serious abut that......over tighten our belt ?? @stacy most scooter have 6201 ball bearing /32x12mm/ in wheels .They are about 200 lbs weight , add to that two passengers 2 x 150 lbs ...;)
Another thing , smaller bearing CAN run FAST !! Smaller faster ....You can not run 50 kilos and half metarDia. bearing 3000-7000 RPM . There was are formula for calculation speed on bearing depend on size if someone want to mess with that you can find it on net .What is clever in our application is to use say 6201 2RS C3 or C4 ball bearing , not normal one .C3=radial internal clearance greater than normal
On one of my grinders idler wheel /6301 2RS C4 / spin 12061 RPM and I don t see any problem with that , it's been about three years now .There was another seal ... RZ= synthetic rubber with low friction if someone want to get more free spin :D
PS . I just check my SKF books ........... allowed temperature for the bearing with polyamide cage and grease inside is 120 Celsius ...measured on the outer ring
 
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koduu said:
I can go to my garage this weekend, then I get to test if running it a bit longer on low speeds would cause the thing to get way too hot or is it just the issue of wearing in a new mechanism.
If natlek's image is correct, then the issue could be a bit too tight of a fit in the areas marked in yellow and that could maybe be worn in or if id does not help then maybe I could just turn it a bit smaller.
R62nSh9.png

BTW, Natlek you wouldn't happen to be Volf?
Click to expand...
No , I m not Volf .I m in Macedonia :)
Can you take another one picture ?Take it from other side of small wheel if you want ? Is there another two Seeger ring ? How they are attached to plate I want to see ?That grinder looks good to me ....:thumbsup:
 
koduu said:
I can go to my garage this weekend, then I get to test if running it a bit longer on low speeds would cause the thing to get way too hot or is it just the issue of wearing in a new mechanism.
If natlek's image is correct, then the issue could be a bit too tight of a fit in the areas marked in yellow and that could maybe be worn in or if id does not help then maybe I could just turn it a bit smaller.
R62nSh9.png

BTW, Natlek you wouldn't happen to be Volf?
Click to expand...
No , that can not be issue. If they are to tight where I draw red /arrow/ that can create to much heat ..........
N1dC6qB.png
 
Natlek - Agree or disagree about the speed and load ... it matters not to me.

However, there is a very good reason that the manufacturers of small wheels for grinders have a notice that comes with them warning of bearing damage if run too fast. They also caution to use them gently. (That is partly to prevent bending the thin axle they often have)

I do agree with you that some people on the internet make small wheels that do not have the bearings installed right. Your drawing shows how this can squeeze the bearings.
 
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