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Thread: Bench Grinder wheel balancing
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28th June 2019, 10:37 AM #16
Also, on many wheels the hole is slightly over-sized for the arbour. While this makes it easier to mount/dismount, it also introduces a small margin of centering error. Simply rotating the wheel on the arbour to find the "best" position for minimal vibration before finally tightening up and dressing the wheel can save quite a bit of wheel material...
I dislike the way the bloke in the vid replaced the dished arbour cups with his flat washers. There is good reason for them to be dished!
- Andy Mc
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28th June 2019 10:37 AM # ADSGoogle Adsense Advertisement
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28th June 2019, 07:50 PM #17GOLD MEMBER
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Another often unrecognised issue with with grinders made by our Asian friends is the poor machining of the nut and shaft thread so the nut can wobble around and push the wheel into a position where it is not true to the shaft. The wobble washers available from several sources fix this issue. I bought two pair and the problem instantly went away.
CHRIS
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28th June 2019, 08:22 PM #18GOLD MEMBER
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Another often unrecognised issue with with grinders made by our Asian friends is the poor machining of the nut and shaft thread so the nut can wobble around and push the wheel into a position where it is not true to the shaft. The wobble washers available from several sources fix this issue. I bought two pair and the problem instantly went away.
CHRIS
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28th June 2019, 08:39 PM #19
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28th June 2019, 09:18 PM #20SENIOR MEMBER
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I was all set to buy the spherical washers from Woodturner Wonders, but $US60 for shipping !! Seriously???
Now looking for a local supplier at reasonable cost (to fit 18mm shift) Anyone have suggestions?
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29th June 2019, 12:33 AM #21GOLD MEMBER
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30th June 2019, 03:47 PM #22
With the wide al-ox wheels that a have a recess (like these) I just added pieces of lead to the rear (the inside concave back) and moved those around until I got balance, first with blue tack until I got the right position and weight and then glued in place. Similar to the way they balance car tyres.
Note: I used extreme caution to make sure I stayed out of the firing line while using just the blue tack to attach the test weights as I didn't want to be 'shot' in the event that a piece of the lead strip came off at full speed....
No need to keep taking the wheel on and off. Only specialised piece of equipment was a felt marking pen.
My new Hafco Metalmaster bench grinder came with balancing thingies in the arbor cups, which I haven't needed to use with the CBN and diamond wheels, so don't know yet how easy they are to use.Stay sharp and stay safe!
Neil
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30th June 2019, 05:44 PM #23
Robo Hippy (Reed Gray) who was one of the first woodturners I know of to start using CBN wheels to sharpen our tools told us way back then that they would be aggressive to begin with but then settle down to a be less so. We shouldn't be surprised that this is happening.
I'm not so sure that the CBN wheels are wearing out as much as wearing in. More time will tell. If they are only taking twice as long to do the job once worn in, but continue to do that indefinitely they are still a winner on some criteria.
The advantage of the thinly electroplated CBN wheels (that is type that most of us are using) is their dimensional stability. Set your jigs up once, only.
The advantage of the old aggregate and later resin or metal bonded (with either CBN or diamond abrasive) wheels is that the matrix has some depth and can release the spent cutting grit to reveal fresh abrasive particles but at the expense of dimensional stability (they wear down or are dressed down). Waterstones do the same but at a much more rapid rate. So, continued cutting performance but jigs, rests and the like have to be regularly adjusted.
If you could afford a grinding wheel with a deep metal matrix holding either CBN or diamond abrasive particles it would perform relatively better in both ways, but few of us have the deep pockets or the need for that. Back when I was doing a lot of hard rock cutting I would periodically take something like an old soft grinding wheel and cut it up with the diamond saw (the diamonds on that were held in a metal matrix). This removed some of the metal matrix to expose more of the diamonds or release the spent diamonds to reveal new ones. It always cut much better after that.
But, don't try this with an electroplated CBN or diamond wheel, which has only a single layer of CBN or diamond particles.
I do very occasionally lightly 'dress' my resin matrix diamond wheel (not the shiny ones) to expose some fresh diamond, but read up carefully on that (brake dressers, etc) if you are thinking of doing something similar. Note: Unlike the electroplated and metal sintered wheels, the resin matrix bond can fracture, break up and fly off the wheel.
I continue to be very happy with my diamond resin matrix wheel. I reserve judgement on my CBN wheel until I have used it as much as the diamond wheel, which is my benchmark.Stay sharp and stay safe!
Neil
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30th June 2019, 07:13 PM #24.
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One useful thing about having a grinder on a VFD is that for any small vibe just slightly changing the drive frequency can often reduce it substantially or even cancel it out.
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30th June 2019, 07:42 PM #25
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1st July 2019, 06:29 AM #26SENIOR MEMBER
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1st July 2019, 05:51 PM #27.
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The discussion on Wobble Washers reminded me that some time ago I was going to have a crack at making some but never got around to it.
I decided to make them out of hard brass that I recently acquired and this stuff is dead easy to turn, especially with a carbide tipped boring bar.
Turningconcave.JPG
The result - there's a bit of stuffing around swapping compound angles and tool posts holders but no more than usual so they did not take long to make.
WobbleWashers.JPG
My CBN has always had a touch of runout but vibration wise I've found it to be fine so I was quite surprise when I measured the side runout at 0.21 mm
Point021.JPG
So then I fitted the wobble washers and after a bit of stuffing around I got the runabout down to 0.025mm
I could probably get it lower than this but I was interested in the amount of vibe it would produce.
Point025.JPG
Just running the grinder I could tell no difference between with our without the wobble washers but using my "Vibe" app on my mobile, with the old setup the vibe was 0.113 g's whereas with the wobble washers it was 0.155g
In other words, even after improving the side runout by almost a factor of 10 the vibe increased by ~37%.
Of course there's a lot more to balancing a wheel than side runout especially given I also have a diamond wheel attached to the side of the CBN wheel.
Anyway it was an interesting exercise.
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1st July 2019, 07:56 PM #28.
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Went back to square one and took the CBN wheel off the grinder and measured the vibe and found it was 0.103g,
This is the vibe from the grinder spindle PLUS the pulley (no belt) from the Multitool grinder on the other side of the grinder.
Then I put the wheel with Wobble washers back on back on and rotated the wheel to different positions (each time correcting for any run out) and measured the vibe.
Eventually I found a position where the vibe was 0.043g , ie LESS than for the spindle and the multitool grinder pulley.
This position of the wheel must be balancing out some vibe being induced by the multitool grinder pulley.
Any way it is now running REAL smooth and a I really must remember to mark all the components relative positions because it took me a while to find them.
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2nd July 2019, 02:29 PM #29GOLD MEMBER
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