[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.

[Mcgyver]

Steve, I've heard the soft wheel for hard material as well, but specifically for steel, not just metal in general.... ie tool steel/case hardened vs regular 1018, is that not a valid guideline? what (commonly available) wheel would you recommend for mild steel? on my manual surface grinder now is a Doall WA543. This tells me its aluminum oxide 54 grit but not much more - any clue as to how hard it is? It works beautifully on hardened steel (case or tool) and cast iron but produced Zumba's problems on soft mild steel, so I've been watching the thread with interest

[Pressfit]

Sounds to me that your 60K is just likely loading-up and burning itself and the work because it can't handle the depth of cut. It can't get rid of the chips fast enough. The pores are not deep enough also. I never go more than .0005 with a 60 grit or I have the same problem... It loads-up, burns, goes out of true, and will leave chatter in the part.

So I'd say you need a more open grit wheel like a 46. With a 46 you'll still get a very nice finish. And it will handle the .001 depth with ease, plus being more forgiving of the inconsistent feed rates of a hand grinder. Now on our hand feed surface grinder I get by with nothing other than a Norton 46K Pink wheel or sometimes known as a 'Ruby'.

[SORCHEROR]

im not sure about the doall wheels,ill look it up,what you need to do,i know its a pain,but use one type of wheel to rough and another to finish,i get great finishes with 46H wheels are all types of metal,hard and soft,even a 46G
which is mor open,but to finish with i like a 60I,harder yet still a little open grit,but if you need a sharp corner like .005 radius or less,i go to a 60 k or 80 k,but you have take small cuts,or it will burn,its a trial and error thing,for dead sharp corners i pick out after the 60k i use 120 J,you have to see what the print says for finish and corner radius,but try the 60 I,best all arond wheel
steve

[JerryFlyGuy]

What kind of RPM and surface speed would you be using w/ a 60I and a 0.0005 to 0.001 cut on a 1018 or 44w steel? I'm just looking for a starting place at this point.. Any idea on what kind of coolant flow [gpm?]

Curious...

Jerry

[Zumba]

Hey all,

Tons of replies since I last checked this thread. Thanks. In the meantime, I replaced the wheel with a 46I and I'm happy to report that my problems were solved.

The K wheel wasn't breaking down properly and was loading up with swarf, causing both the burn marks and the scallops. It simply wasn't cutting. In fact, on return passes (climb cut), the wheel continued to spark out, which means it didn't cut completely on the initial pass.

After switching to the 46I, I noticed zero sparks on the return pass, the way it should be. Also, the wheel feels the same before and after a small grinding job, not burnished like the 60K. Lastly, there's no more black crud buildup on the wheel.

[307startup]

A lot of that can be solved by getting really fast on the manual handwheels. I used to grind punch dies for CNC punch presses and I'd have the same problems. Owner was a tight-ass and didn't want to spring for different grinding wheels, so I was able to figure it out by setting up the part in the middle of the table and starting table with wheel slightly off center to bring it under the wheel and rapidly spin wheel left-right in an arcing motion. Two to three swipes per pass, right hand on xfeed, left hand on yfeed, turn yhandwheel one complete revolution, next pass, etc. You'll feel it in your shoulders, but the burn will go away and a "softer" wheel won't load up as much. Just some fyi.

[Pressfit]

What kind of RPM and surface speed would you be using w/ a 60I and a 0.0005 to 0.001 cut on a 1018 or 44w steel? I'm just looking for a starting place at this point.. Any idea on what kind of coolant flow [gpm?]

Curious...

Jerry

Well, RPM of the wheel is mostly fixed by the motor speed. Our s/grinder has an rpm of around 3400. So that gives a 7 inch wheel around 6230 sfm. That's pretty much in the ball park of the recommended sfm of 5500 to 6500 for grinding that I read some time ago. And traverse feeds in grinding have nothing to do with the Surface Feet Per Minute calculations.. that's all in the wheel speed.
About the only thing you have to be careful of is to not put a wheel on that has a rated speed lower than the machine, or it could blow-up on you. And if you Chunk a wheel, take it off.

And always "ring" a new wheel before putting it on. 'Cause I have had brand new wheels cracked out of the box. Dangerous situation with a cracked wheel. If you tap the wheel against something hard then it should make a high-pitched ring. If not and it makes a dull sound then break it and throw it away just incase somebody else in the shop might grab it and put it on without thinking.

Coolant flow should of course be enough to keep the work cool so it won't try to warp from heat, and to flush chips from the wheel. Usually pointed at where the wheel and work meet.

Other general things I've learned:
1- The bond (I,J,K,L), seems to not be 'as' important as grit openess (32,46,60, etc).

2- If you have to dress the wheel once more than every several passes on the work... then you got the wrong wheel on. Simple as that.

[dhiruj]

hi

we make magnetic beds for grinding machine.. the problem we face is that the surfae of the magnetic bed is a lamination of either steel and brass or steel and aluminium.....

what kind of wheel grit will be best suited for us.

We use soft steel.

The machine is a SNOW (British) horizontal machine with 1500x400mm bed size. The wheel dia is 325mm and wheel thickness is 80mm.

Dhiruj