Understanding Grinding

glenbjackson

glenbjackson

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grinding I don't see how grinding, correct me if i'm wrong, is the last word in surface finish. my question is if grinders use wheels that are consumables how can this process be consistent for any length of work. Even a thin gear, after one pass on a tooth the wheel will be a smaller diameter, so on the next tooth to be grinded, it will be taller after it's grinding pass then the previous tooth and so on. and yes I realize these are very small amounts but still a difference. Am I missing something? do the machine taper depending on the wheel material or just step up slightly on every pass?
 
You understand correctly, but assuming you're doing it right (correct wheel selection for the material being ground, appropriate feed rate, etc.) you're overestimating the rate of wear. I am not a grinding expert beyond having done enough to know that it can definitely be done wrong, resulting in exactly what you're picturing (among other problems). Sometimes on large parts it requires multiple paases, dressing the wheel between, to accurately remove as much material as you can in a single pass on a smaller workpiece.

The Suburban Tool YouTube channel has several excellent videos on the subject, covering theory and best practices. And they'll happily sell you some very shiny mag chucks and other grinding accessories. :)
 
You first answer pretty well sums it up. Everything wares. Even your carbide tooling. If it's in spec tho it doesn't matter. If your goal is .0001"+/-.00001 & your to wares .000005" you'll probably hit your goal. If not you measure reset & take another pass.
 
...wheel selection on all grinding ops and machines (Surface (and Blanchard), Universal (ID/OD), C/L is a major key to this question (with, of course, the machine itself)...Examples: A CNC Universal grinder can be programmed for wheel wear during a production run of X amount of parts (ops)...There are "rock" wheels, say form dressed (angle, corner radius on both sides of the wheel) that with proper feed (and coolant (or not!) etc) can grind 5 .050 deep "slots" in a 4" X 4" hardened tool steel work pc on a surface grinder in X, then turn 90 to Y and grind 5 more (a "checkerboard") and loose only about .005 total at the end (then yoose' "go backwords" once (after redressing for your angles and corner radiususseses) and finish depth and contours will be within .0002...a manual Universal grinder, with a good resin bonded diamond wheel (say 220 grit) can plunge grind (with again, proper feed and coolant) .o50 off the end ("step") of about 5 solid carbide rods 3/8" in diameter (6% cobalt, (about as hard carbide as you can get') , and "loose" (or "wide" groove the end of your wheel) only about .oo1 to .oo2....Cheers!
 
Since and while I see your reply glenbjackson I thinks I will add: I'm trying to think during 35 yrs, of a part of any material, on any type of Machine Tool grinder with any type of wheel where/when I took more than .001 a "pass"...

...oops, I do remember OD grinding a bunch of a type of rubber coating wheels about 1 ft long x 8" OD formed around a 1"center shaft...on an old Brown and Sharpe Universal with the most aggresive, porous "rock" wheel I ever saw and I would take 1 .o50 pass to straighten and "round" out the OD and it would only take off about .010 as I let it dwell back and fourth (on X) and that wheel left the perfect, rough surface on that rubber the customer was looking for to coat with whatever they were using and coating whatever they were coating (weird for a guy that is all steel and carbide LOL)
 
I need to see one of the grinding wheels and maybe machine, they sound precise and slow. I'm gonna check out those youtube videos intjonmiller recommended. I'm thinking more of wheels that have rounded edges, relatively un-flat flats and wears horribly. I was a shipfitter and I'm stuck on the image of grinding wheel, the wear, finish and abuse associated with a hand grinder. but comparing a human to feedrate/depth, I should've guessed the machines would wear out a wheel more efficient.
 
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The wear on a grinding wheel on a surface grinder is not like grinding on any hand machine. The leading edge wears away leaving the rest of the wheel intact.

In the picture below I have already taken about o.o30 off of that plate in 0.010 increments since I dressed the wheel. The wheel is 2 inches wide and as you can see, only the first 1/4 inch of the wheel is worn, the rest of the wheel is as dressed. That means that the plate will be cleaned up by the untouched portion of the wheel. This is the final pass at 0.005 inch. I turned the coolant off for this picture.

upload_2016-11-2_22-52-37.png

And another view from the front with the coolant on

upload_2016-11-2_22-54-10.png
 
lol all those sparks for just 0.005 wow:eek 2:. that's another reason I thought more was being taken off with grinders because of some many sparks. thanks for pics
I can also see the disc's diameter is larger, so a longer grinder surface.
 
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