Surface Grinding Woes

[Zumba]

How good of a finish can I expect from a manual 6x18 surface grinder?

The finish I'm getting is very smooth and flat. Feels nice and is fine dimensionally. Aesthetically, it's not horrible, but it leaves a bit to be desired. I often get scallops on the climb cut return stroke. I also have a problem with discolored black/brown stripes. It always happens if I take too heavy of a cut, but it sometimes happens even if I don't take a heavy cut (to a lesser extent). Redressing the wheel doesn't make the problem go away completely. Maybe I'm not redressing the wheel evenly?

Some more info...
Steels being ground: A36 and 1018.
Spindle runout: < .0001"
Wheel: 8" Norton 32A 60grit K-hardness, balanced
Dressing Diamond: Norton .33 carat
DOC per pass when dressing: .001"
Coolant: Mobil S-122 soluble oil, full blast.

Perhaps I'm just not turning the handwheels smoothly enough, which would affect both the grinding and the dressing. I don't think the machine is at fault. After balancing the wheel and redressing, I can feel absolutely zero vibration. An occasionally, I do get a nice pass with the finish I desire, but I can't get it consistently. Any help would be appreciated.

[Mitsui Seiki]

Maybe I'm not redressing the wheel evenly?

Could very well be it.Check the wheel for dark stripes.
How many dress passes do you do?

Try to decrease the table feed. Or maybe change wheel speed( Faster makes the wheel harder,slower makes it softer).
Try not to cut of more than 0,0007 with each pass.

[Zumba]

Yes, I get stripes on the wheel. I do about 10 passes, or .010" of dressing to get rid of the stripes and then some.

But I think I'm crossfeeding too slowly. I'm moving the diamond at 30ipm. Is this too slow?

Also, is a K-hardness wheel too hard? Some people say that softer steels like the mild steels I'm using require hard wheels, but perhaps they're a bit finicky.

Thanks.

[Mitsui Seiki]

I think the dress feed is too fast.Try 20ipm.

K hardness is ok .The medium hard wheels goes from J-M.

[lgreeves]

The spindle runout is .0001" but did you check shaft endplay? Or you coolant pressure may be too high and blowing the coolant off your workpiece. Sometimes your wheel just isn't the same as the last one you ran.

[Mitsui Seiki]

I'm pretty sure the coolant should be pointed at the wheel just above the work piece and not at the work piece.With high pressure.It's there to cool the work piece AND clean the wheel.
We have high pressure pumps for our grinders.

[lgreeves]

The action of grinding cleans the wheel. You don't need high pressure on a 6"x18". You only need a steady flow of coolant around wheel and work piece contact. If the coolant is flowing too fast the cooling action of the coolant is negated.

[SORCHEROR]

do you have a 60 I wheel,would get rid of the black marks which are burn marks,k is too fine for taking .001 at a time,next,the scallops most likely are from a worn spider coupling,with the grinder off,move the wheel my hand backwards and forwards and check for slop in the spider,if its ok maybe the gear rack is badly worn,unless your grinder is cable driven?mostly when i grind soft steels i use 46H or 60I,finer than that they load up and burn fast
steve

[SORCHEROR]

the coolant should be pointing on the wheel just above the work piece or both at the same time,but with the k wheel at .001 a pass it will burn regardless unless you have a large wet grinder with very big diameter wheel,that changes the suface feed ratio,also have you tried dressing the side of the wheel to further balance it,although nortons are pretty good

[Mitsui Seiki]

Ok,we did it like that earlier and that works also. Then we did tests together with Norton and Saint Gobain abrasives and came to the concluson that high pressure works better than low pressure.We had to keep our tolerances at 0,00012 and the only way to do that was to put high pressure on the wheel just before it touches the piece.

[SORCHEROR]

i agree,but your probably not using a manual surface grinder like zumba is,i would like to know what grinder zumba is using,sometimes problems are different from machine to machine,caused by different reasons,but ive been grinding for 26 years now,amongest other things,im not sure who told zumba the softer the material=harder the wheel.some soft metals load the wheel up and need a more open grit softer wheel,take chrome,i use a red ruby wheel,hard material,very hard wheel,but the ruby wheel has a more open grit than the 60 k,i recomend a 60 I,best wheel for almost any application,than i go up or down from there
steve

[Mitsui Seiki]

You're right .We're using a CNC controlled grinder and fully automatic.We have a robot loading the parts to a fixture and manufacturing 40000 parts each week.A manual one is probably a little different.The table feed is more uneven.