NWG side to side belt jumping

S

Shevtar

Member
Hello all
Need some advice about recently build grinder.
The belt is jumping from side to side, I don't think it is normal, what can be the reason, maybe somebody had the same problem and can point how to remedy it.
here is a short video

[video=youtube;Re1B_8rNbTA]https://www.youtube.com/watch?v=Re1B_8rNbTA[/video]

About the grinder. It is essentially a No Weld Grinder, built based on the drawings bought from BossDog, except that it is actually welded. The instrument arm is a swivel arm with 200 mm (8") bottom wheel and 70 mm (2 3/4") upper idler wheel and flat platen between them. The motor is 1,5 kW 1450 rpm (it is 4 pole motor but because we use here in Ukraine 50Hz it is closer to 1500 rpm not 1700 as in US with 60Hz), it is three phase but hooked to 220 V one phase through VFD.
 
Some belts tend to wobble a bit, but some should run true - not moving at all. Is the tracking wheel or the drive wheel crowned? If not, or only slightly crowned - try wrapping a bit of electrical tape around center of drive wheel or tracking wheel (or both) and see if that helps any. I'm sure you've tried different belts? If not, try a couple different NEW belts.

Ken H>
 
As long as that is all that you are getting it's not really a problem! That little bit could be a belt or could be a bearing that is not 100%, it is also possible that welding has pulled something of slightly from true.

The big question is, does it stay tracking that well while in use? If so I wouldn't sweat it, just use it!
 
Last edited:
that isn't bad.
I have a KMG and an Ubergrinder and 3 or 4 no weld grinders plus a couple experimental prototypes. All have about that amount of movement.
Still a few things you can try.
1. change belts - a completely different brand. some run better than others.
2. reverse the belt, sometimes running in the opposite direction takes the movement out. Belts stretch and grinders don't put even pressure across the belt due to the tracking wheel being on an angle. changing the rotation of the belt will sometimes balance out a stretched belt.
3. a couple layers of masking tape on the crown of the tracking wheel. no more than 2 layers.
4. make sure the wheels are perpendicular to the grinder. A wheel that is mounted on a slight angle makes the belt hunt over as far as it can go and then it is pulled back to start the cycle all over...It could be any of the wheels that are slightly off.
5. tighten the spring. a tighter belt runs with less wobble.

I hope that helps get what you want..
t
 
Thanks a lot for feedback, my main concern was if such wobble more or less should be expected or I just did something wrong. I watched afterwards Johnny Stout hollow grinding video where he uses the same grinder with different belts and with some belts wobble is barely noticeble and with others it is quite violent and there is a charachteristic sound of belt seam thumping
It is the second NW grinder I built, both have this wobble, but the first was much more crude and had a lot of play in the swivel and tracking arms so I kind of expected this one to have none of this.
 
BossDog said:
that isn't bad.
I have a KMG and an Ubergrinder and 3 or 4 no weld grinders plus a couple experimental prototypes. All have about that amount of movement.
Still a few things you can try.
1. change belts - a completely different brand. some run better than others.
2. reverse the belt, sometimes running in the opposite direction takes the movement out. Belts stretch and grinders don't put even pressure across the belt due to the tracking wheel being on an angle. changing the rotation of the belt will sometimes balance out a stretched belt.
3. a couple layers of masking tape on the crown of the tracking wheel. no more than 2 layers.
4. make sure the wheels are perpendicular to the grinder. A wheel that is mounted on a slight angle makes the belt hunt over as far as it can go and then it is pulled back to start the cycle all over...It could be any of the wheels that are slightly off.
5. tighten the spring. a tighter belt runs with less wobble.

I hope that helps get what you want..
t
Click to expand...

Thanks for pointing me to the possible ways to diminish this problem, right away point 4 (wheels are not perpendicular to the grinder) looks like the first place I should be checking.
 
KenH said:
Some belts tend to wobble a bit, but some should run true - not moving at all. Is the tracking wheel or the drive wheel crowned? If not, or only slightly crowned - try wrapping a bit of electrical tape around center of drive wheel or tracking wheel (or both) and see if that helps any. I'm sure you've tried different belts? If not, try a couple different NEW belts.

Ken H>
Click to expand...

Both wheels are crowned, but the crown is less pronounced that on the tracking wheels photos at USAknifemaker, mine have about 0.5 mm (0.02") difference on each side, so that center has 1 mm (0.04") bigger diameter than the side, and that is the GOST standard for flat belt transmissions with wheels less than 150 mm (6") in diameter. Anyway I will put some tape on the center to see if this crown is too shallow and also have several different belts, the one on video is a new 3m x65 gator belt, I have some J-flex from hermes and some VSM ceramic belts
 
Shevtar: Thank you for that bit of info on GOST specs. I didn't have a clue just how much crown a wheel should have. I've got a tad more than .040", Seems like I put about a 2º crown.

From other reports, it sounds like that amount of wobble is pretty normal. This sure is a great place to learn things. Thanks to all for their input to this and all threads.

Ken H>
 
Like I stated earlier with that little bit of wobble I don't think you have a problem.

My grinder is a KMG clone and it will jump the belt off to the side by about a 1/4" to a 1/2" but usually comes right back to tracking in the center, on it's own. Sometimes if it has set a while and I forgot to release the tension on the sanding belt, I will have to tweak the tracking adjustment after start-up but then it is good, except for that momentary jump at start-up!

I think some of my problem is the sanding belt itself (because some belts seem worse than others) but, part of it is the 220V motor and it heavy duty starting capacitor!
 
im glad i read this . i just got done with my nwg but i welded mine as well. i had a few tracking issues but im still in the process of getting the wheel perfectly aligned.
 
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