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View Full Version : Grinding wheel Dressing vs Balancing?



madman
04-26-2008, 11:15 AM
Question ? When mounting a New Grinding Wheel for surfacer Grinder (8 inch type) do you balance the Wheel? I was shown at the die shops that dressing the bottom first and then also a 2 degree or even 1 degree pass up the sides rirhtb to the arbour flange would be all that was required. Now lately at my last job they balanced every wheel that they mounterd? What is the right teqnique Guys/ Thanx Im Curious as i just invested a small fortune in my home shop to get set up with my own surface grinding equipment. I already made some interesting devices for my shop that without the surface grinder and a nice surface plate height gauge would never of been possible.

Forrest Addy
04-26-2008, 12:28 PM
When mounting a new wheel on a hub, dress first (to true it up) then balance. That's what they tell you in grinding wheel booklets you used to get from the major suppliers.

Speaking of which and to pose a constructive hijack does anyone know if these booklets are still in circulation? I had a whole stack from the Cincinnatti people on various grinding topics I loaned to a fellow so he could get them copied. Never saw them again.

Oldbrock
04-26-2008, 01:03 PM
Got mine from Norton. A super set includes tool and cutter grinder setups. Peter

Mark Hockett
04-26-2008, 03:33 PM
I also just got a surface grinder and have been asking these questions to some of my suppliers. The answer I keep getting is on smaller grinding wheels (8" and smaller) there is no need to balance the wheel. I was questioning this answer but one of the guys that said it is a machinist and works at one of my supplier's that manufactures end mills (http://www.swiftcarb.com/) and does custom tool grinding every day, and the other was a machinist for many many years and now owns his own supply company (http://www.rowe-machinery.com/), so these are not guys just reading the answer out of a catalog or book. They also say if you have a smaller wheel that is out of balance it is probably a cheap wheel or a damaged wheel, either way it should be trashed and not used.

That being said I still don't see any harm in balancing a grinding wheel and since most of us are working in an environment where time is not a problem we have the time to do it.

So how do you adjust the balance the smaller wheels? Most larger wheels have a provision on the hub to adjust the balance on the whole assembly, but the smaller wheels only have a hole that mounts on an arbor.

BTW, if you are looking for hard to find stuff the http://www.rowe-machinery.com/ site is mostly used tooling and inspection equipment and they have a lot of unusual stuff, check out the inventory list, he even lists the prices. I have bought thousands of dollars worth of tooling from him and never gotten a bad tool.

boslab
04-26-2008, 04:16 PM
i had a rep in from saint gobain couple of months ago regarding exploding cup wheels on a grinder, these were about 8" dia x 6" deep, 3/4" wall marked up universal 60g, problem was they wernt balanced, stick them on the spindle, close the door run the machine up to speed and the vibration would be quite pronounced, wheel normaly held together for about 5 mins before exploding, the door of the machine had a big bulge from the impact and it was 1/8" thick.
anyhoo asked rep if the wheels were balanced in the factory to which he replied to bal them they inject resin to one side or the other after sticking them on a dynamic balancer, same as a tyre balancer, he specified if the wheel was within 6grams out of bal or less it was acceptable, the ones i checked threw by 10/11g [at the local tyre depot!] i sent them back they questioned how i had arrived at 10/11g knowing that i dont have a dynamic wheel balancer so i just told them i did it the 'hard way' they didnt have the neve to ask what the 'hard way' was.
needless to say they replaced 200 wheels at $110 each without question, they are all less than 5g out of balance so the machine is as quiet as a baby.
i have the rail type of balancer but hardly use it as i mostly use vertical spindle, perhaps a dynamic balancer could be the answer for shops useing lots of wheels?
regards
mark

Mcgyver
04-26-2008, 05:30 PM
madman,

here's what i learned and did

http://bbs.homeshopmachinist.net/showthread.php?t=12741&

the closer to perfect balanced the better imo. Been slightly chided by some for worrying about it, that good wheels come good enough, but that's from guys that are mounting them on 4,000 lb machines. On my light benchtop T&C and light norton surface grinder i think it does make a difference....and some new wheels that were out more than others.

in hindsight, making the lobbed thingies might have been overkill, you can get to the same place by lightly rubbing a dressing stick on the side of the wheel near the heavy point.

madman
04-27-2008, 03:05 PM
Mark i agree with you and if i dress a new wheel and it still has vibration then i do both sides also. This does seem to help on my 8 inch and smaller wheels i use. I imagine dressing like i just said then removing the wheel with a center balancer hub and balancing wiould be the best but probably not necesssary. Thanx everyone for the great tips Mike

Forrest Addy
04-27-2008, 04:13 PM
Just to put things into perspective: defective grinding wheels will burst from the normal centrifugal force of operation however it's not as violent as often told in shop yarns. I've heard stories where 10" dia x 3/4 thick wheel exploded like an artillary shell and killed the operator.

Baloney. Grinding wheels spin at about 5000 feet per minute which is fast as you can throw a rock. At this speed the fragments might dent a guard, or if fee to fly a trajectory travel a hundred feet but inflict a mortal wound I doubt it. Serious injury to bare skin? Certainly, they have sharp edges but a mortal wound is unlikely. There's simply not enough mass and velocity. Flesh and bone are tough and tese days grinding wheels are well guarded.

Vitrirous bonded grinding wheels are abrasive grains bonded with glass and are made deliberately frangible so the grains when dulled can be dislodged as grinding progresses. Thus a well designed grinding wheel is to a certain extent self-sharpening.

Grinding wheels are brittle and cracks are seldom visible. A cracked ginding wheel represents a significant hazard. A most important part of grinding wheel safety is to "ring it out" that is suspend it from the hole on a broomstick and tap the side of the wheel near the rim at the 10:30 and 1:30 (imagine the hour hand on a clock dial) with the handle of a screw driver or a small block of wood. A clear bell-like tone should be audible. If the tone is quickly damped or none is heard, suspect the wheel to be cracked and condemn it from use. In most shops you show the dud wheel to the boss then bust it up so it can't be used. If the wheel is new from the box send it back to the supplier for replacement or refund. That's something for the bean counter/purchaser to hassel not the production worker - unless as a home shop owner you have to wear all the hats. Larger wheels cost $500 or more so it pays to do these things by the numbers.

Dressing then balancing a grinding wheel prolongs its life and enhances its productivity. If a wheel is out of balance beyond the range of the hub balancing weights to compensate, condemn the wheel, get a replacement/refund etc. It's not unusual to have to balance a grinding wheel several time in its life. No abrasive compaction/bonding/firing process is 100% consistant.

A grinding wheel has a limited speed range over whuch it can be productively used. When grinding steel with aluminum oside abrasive 5000 to 5500 fee per minute is optimum. Other media (diamond, borazon, silicon carbide) may be different. However grinding spindles are usually direct driven fron an induction motor. The armature RPM is a function of the line frequency and the number of magnetic poles in the motor. IN 60 Hz countries that's 3450, 1750, 1150 and 875 RPM (2,4, 6. and 8 poles respectively). If you work from the optimum wheel speed and calculate the optimum wheel diameter applicable to the existing spindle RPM, you discover that your machine has a built in compromise materially affecting the productivity of the machne and the attainable finish on the work. Regardless, the useful life of most grinding wheels is when they've been worn to about 2/3 of their original diameter; you can't speed up the spindle to keep the SFM constant.

It's the job of the machinist to accomplish his assigned work using the available resources but I often wondered if I couldn't have been more productive had VFD's been available on precision grinding machines 40 years ago.

boslab
04-27-2008, 11:51 PM
hooray, new door arrived for vertical spindle, old one knackerd
exploding stones can and do kill, not conjecture but fact, seen brains on ceiling to prove it. went to funeral [union 14" x 2"]
in the US the list is long
http://www.osha.gov/SLTC/machineguarding/grinder_accidents.html
the funeral service is longer but not as dangerous, in uk 75% guarding reqired on a offhand wheel [perimeter] to cut down on deaths, please use grinding wheels with care,
live long and prosper
mark