I/D grinding A2 - bad finish.
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  1. #1
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    Default I/D grinding A2 - bad finish.

    Grinding some 60Rc A2 roughed out with a 46 grit wheel now finishing with a Norton 32A60-KVBE and getting a shitty finish. Grinder is tight, dressed the wheel well, using Ultracut Pro CF at 20% from a bottle.



    Here's a video of my setup:



    Any ideas? Do I need finer that 60 grit for a better finish?

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    With a Heald, the coolant is a continuous flow, which washes out the swarf all the time you are grinding.

    Also, the infeed is about a tenth on a side at the moment the wheel is at the full end of its travel on the stroke out of the hole. Then it grinds on the way in, and your wheels gets a normal taper to it on the leading edge, similar to a cylindrical grinder. At .0002" away from finish you'd dress again and take out that last little bit. I'd only spark out one stroke, maybe two, not let it stroke back and forth with no feed, no coolant flow and a bunch of swarf in the hole.

    You can harden or soften the action of the wheel by adjusting your workhead speed. But I don't think you're there yet. Can you run your finger over the wheel and take your prints off ? It should feel totally smooth.

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    Diameter of stone must not exceed two thirds of ID. Cutting speed should be 28 m/s or 90 ft/s minimum. At 1" ID you’d need to have a 32,000 rpm spindle speed. Speed of work in counter will reduce that.

    Make sure stone is not too hard. Yours seems to be very harsh.

    I say stone but of course know about artificial grinding tools. Hardness of grinding tool is mainly how strong the bond of the particles is.

    imagepetitesannonces.jpg

    One of a pair of cutting rollers I have ground. The ID is honed to a slip fit.

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    Thanks guys, as you can see I'm a noob at grinding and I don't have a real ID/OD grinder, just the NSK. But I did do some chrome years ago and it came out like a mirror, that's why I'm baffled here. I did have a constant coolant blast right on the wheel tho and was grinding a much bigger bore, hmmm...

    I think you're both right, the wheel is too big and I'm not getting the swarf out. I'm gonna try a mounted point with steady coolant.

    BTW, the grinder is 30K so SFM shud be north of 4K? Hole is 15mm (0.590"), wheel is about 0.530".

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    Try some solid lube on the wheel, such as https://www.mscdirect.com/product/de...rItem=05651286
    It's worked wonders when I had similar troubles on a jig grinder.

    I assume you have undercut the wheel so only cutting with a narrow width.

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    I agree, a smaller diameter wheel and also a slower stroke. Looks like you are grinding in a lathe, so I'm a little suspect of the spindle bearings. The head stock of a cylindrical grinder will have a much more precision spindle.

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    Thanks for the replies, I got it. Used a much smaller, very fine (220 grit?) mounted point, very light infeed and lots of coolant. I think the wheel was a little rough at 60 grit and I was getting scratches from swarf.



    Must be something about I/D grinding with too big a wheel, I O/D ground the same part with the 60 grit wheel and it came out pretty good...

    Last edited by Terry Keeley; 03-25-2021 at 11:27 PM.

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    Quote Originally Posted by Terry Keeley View Post
    Thanks for the replies, I got it. Used a much smaller, very fine (220 grit?) mounted point, very light infeed and lots of coolant. I think the wheel was a little rough at 60 grit and I was getting scratches from swarf.



    Must be something about I/D grinding with too big a wheel, I O/D ground the same part with the 60 grit wheel and it came out pretty good...

    You have too much contact with that ID wheel; narrow it to about the outer 1/3 of the wheel. Results will be better and easier to achieve.
    Do the same with the OD wheel, and wax both, the results will amaze.

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    Nothing to contribute, but Man is that a cool grinding head.
    Would be perfect for restoring machine spindle tapers in place.

    -Doozer

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    Quote Originally Posted by Doozer View Post
    Nothing to contribute, but Man is that a cool grinding head.
    Would be perfect for restoring machine spindle tapers in place.

    -Doozer
    Sadly they're not made anymore, it's an NSK Falcon G1. A toolmaker buddy made the cradle that uses a precision leadscrew so I can feed in tenths. I originally got it to grind hard chrome on a taper for sleeves on my model boat engines.

    Here's a little video grinding the taper on my mill's spindle:






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    That's great, what a wonderful little tool! I've wished I had something like that several times in my career.

    Is there any reason not to grind the taper with the spindle in the quill in it's bearings? Seems like that would give the least possible runout.

    I have a tiny cnc router with a little 800w German 24,000 rpm router motor. Had runout of several thou, needed much better to use .015" endmills for inlay work, Just to see if I could improve it, I fixtured it on the bed of my little bench lathe, and cobbled up a mount for a pneumatic pencil grinder on the compound. Was a cheap grinder, and bearings questionable, but I was astonished to be able to reduce runout to a couple of tenths. Finish was a bit rough, but I'm getting by just fine til I have time to redo it properly.

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    I thought about grinding it in place but couldn't figure out a good way to hold it and get the taper right. Was going to change the bearings anyway so figured I'd do it on the lathe.

    Took quite a bit of messing around to get the runout near zero in two places.

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    I am always in awe in the videos that show off machine tool use for the polish and clean.
    How is that done? Even the mill column here looks nice.
    Doing carbide grind in water for many years my grinders look ridden very hard and put up wet which is why I never post pictures as so embarrassed.
    Despite forcing employees to do the clean every Friday for two hours and paints made for offshore rigs my stuff looks like this for about one year max.
    The steel here clean, not stained at all, the paint and coolant enclosures great.... I so wish I have this.
    I could put out things on grinding form tools and inserts but my stuff looks like so poop that it is way too embarrassing.
    Bob

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    Quote Originally Posted by CarbideBob View Post
    I am always in awe in the videos that show off machine tool use for the polish and clean.
    How is that done? Even the mill column here looks nice.
    Doing carbide grind in water for many years my grinders look ridden very hard and put up wet which is why I never post pictures as so embarrassed.
    Despite forcing employees to do the clean every Friday for two hours and paints made for offshore rigs my stuff looks like this for about one year max.
    The steel here clean, not stained at all, the paint and coolant enclosures great.... I so wish I have this.
    I could put out things on grinding form tools and inserts but my stuff looks like so poop that it is way too embarrassing.
    Bob
    Bob, these guys with the super clean machines are generally low volume and don't have production going on. You really ought to post some stuff, I know there are lots of guys here who would be fascinated by it, myself included. I don't care what your machines look like...

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    Quote Originally Posted by CarbideBob View Post
    Doing carbide grind in water for many years my grinders look ridden very hard and put up wet which is why I never post pictures as so embarrassed.
    Add electrochemical to your stable ... now that looks ugly !

    Otherwise, it's just grinding. If you use 'em, they get nasty-looking.

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    Quote Originally Posted by CarbideBob View Post
    I am always in awe in the videos that show off machine tool use for the polish and clean.
    How is that done? Even the mill column here looks nice.
    Doing carbide grind in water for many years my grinders look ridden very hard and put up wet which is why I never post pictures as so embarrassed.
    Despite forcing employees to do the clean every Friday for two hours and paints made for offshore rigs my stuff looks like this for about one year max.
    The steel here clean, not stained at all, the paint and coolant enclosures great.... I so wish I have this.
    I could put out things on grinding form tools and inserts but my stuff looks like so poop that it is way too embarrassing.
    Bob
    Ya, sorry about that, my momma never had to tell me to clean my room, lol.

    We're all different, for me there's a place for everything and everything must be in it's place.

    My toolmaker buddy does the most incredible work you can imagine, but you should see his shop!

    There's no right or wrong, we're all just different.

    I too wish you would post some pix of tool grinding, that's an area I'm lacking.

    And ya, Kretz is right, I must confess I'm just a hobby guy.

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    My shop is a mess too. As is my car.

    But I have to admit it's a lot easier to see what's going on in a video in an uncluttered, clean space. If I wanted to be an internet personality, I'd have to clean up.

    But CarbideBob, I'd love to see any videos you could put up, as I'm sure all of us would. Content beats style anyday!

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