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  1. #21
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  2. #22
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    Fundamentally, "something" is bouncing to get that finish. As has already been stated, it could be a dull wheel, out of round wheel, out of balance wheel/system, "looseness" in the system and set up, or loose or worn bearings. You have to be the detective.

    My smaller grinder, the B & S #2 gives that finish when grinding with a small downfeed, and relatively wide infeed ("conventional" grinding)due to worn bearings. Though fresh fast dress will minimize it (the wheel can bite with less deflection). To get a "mirror" finish, I use a deep downfeed, sometimes as deep as .025" for roughing but mostly around .003 - .005" for finishing, and a .003" - .005" infeed on each table reversal, on the autofeed.

    I set up a different machine, de-burr parts, or just go check in on PM while it runs.

    In my defense, I rescraped the machine around 15 years ago; it grinds flat & is accurate. As far as finish, it is good enough the way that I use it, that I just never got around to doing the spindle bearings.

    smt

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    Like others have said--something is bouncing.

    When you grind with a heavier cut you get a better finish --Correct? When you grind very lightly you get more visual ripples--Correct?

    You may have the same condition my grinder has, Mitsui hand operated 6X12 with new balls in the table ways. 20 years old.

    It may be very sensetive to wheel ballance or spindle issues. I have learned to live with it. I have mounted wheels on hubs and balance them and keep them on the same hub.--Forever.

    See my earlier post on how to keep the wheel from flipping off center upon start up.

    I use a hand spritzer with soluble oil and a balanced sharp wheel.

    A slightly heavy final pass .0002/.0003+ supresses the bouncing and I get a gorgeous finish. If I take a smaller finish pass I get a visual patern similar to yours. I can not measure any variation, either way, in the pattern with a 1/2 tenth indicator--Works for me.

    Lost

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    If you put your hand in a safe place on the table, do you feel any king of vibration? What about trying loading the table with some weight, mostly at the four corners?

    Paolo

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    Lost, yes, you pretty much described it. Light cut looks worse than heavy cut. Yes, this is just a cosmetic issue as the surface is really flat.

    I am after a hub that I can adjust balance with. The spindle bearings seem to be fine but who knows. I will test the slipping of the wheel later today or tomorrow. The 3" hub should provide increased grip and alignment, right?

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    Hi Laminar,

    You are going through what I did for my Mitsui.

    Look at post #46 This is the best practices I could come up with:

    Mitsui 6x12 surface grinder MSG-200MH needs repair

    Using the best practices I got very good results. To do it properly it can be a pain. I usually take a bit more off than .0001 for a final pass and it is good.

    Look at Sopko wheel wheel adapters--probably one of the few--only? -that makes a full line. Then check ebay.

    Lost

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    Not sure what you mean by "3" hub". A machine that size should be using 1 1/4" or 32mm wheels. Can you tell us more about it? I would try a proper wheel adaptor and see if that makes a difference.

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    Sorry, I mean a 3 inch diameter Sopko adapter which is for wheels 1.250 ID. It does not have any means to balance it. I will get with Sopko Monday and see what they recommend for balancing this adapter. They show some slip rings that might be used but I'm not sure if it is for this adapter. I'm thinking balance is my remaining issue. I looked at the entire post on the Mitsui and it really sounded familiar. I lapped the ball ways with a very true brass rod about 4" long and the diameter of the balls charged with diamond.

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    Since you have changed wheels with no improvement or difference balance is not the problem UNLESS it is the adapter itself. Try another adapter and see if there is a change. thee should not be but in the interest of being thorough I would do it. Wheels of this size do not normally require balancing.

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    Quote Originally Posted by laminar-flow View Post
    ... I lapped the ball ways with a very true brass rod about 4" long and the diameter of the balls charged with diamond.
    I cannot claim much experience and what I'm saying could be close to BS. However, considering the fact that testing it doesn't cost much, I'd strongly suggest doing it. We clearly factored out any possible brinelling (which would produce patterns that are fairly independent from the traversing speed), but we haven't excluded that the vibration is coming from the table/saddle.
    Cast iron is just a "sort of very stiff rubber": it flex and bends. If the super-duper grinding job on the way was done supporting the saddle or table in the wrong spots (or, anyhow, twisting it), you could have one end of one of the ways that, if not completely lifted away from the mating part, it could bear significantly less weight than it is supposed to do.
    Putting significant weight (e.g. shot bags) at each corner of the table, you'd force all the bearing surfaces to have at least a minimum of load and this would result in your vibration to disappear.

    Paolo

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    Laminar,

    If you feel you must balance your wheels, then you could use a variation of a method I used on a T+C grinder that really did have balance issues inherent in the spindle and did benefit from balancing.

    Dynamic (Grinding) Wheel Balancing Method using iPhone Vibration App and SHCS's

    I still wonder about the necessity of wheel balancing in your case. But you could just drill the outside flange as I did in the above link and then add SHCS's or weights while using a similar phone app to the one I used to determine the improvement vs worsening due to added weights. There could, as a result of the screws and weights, be clearance issues with your wheel cover and your standard pin spanner might no longer fit the flange. But no permanent harm would be done to the flange by drilling it and testing the balance of the wheel/flange combo, the bare spindle and motor, etc.

    Denis

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    Very not likely but still out an indicator to the wheel head and give it a shake this way and that to see if all is solid..

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    To me this appears to be speeds and feeds when dressing the wheel and then sparking out to put a finish on the parts.

    If there was a balance problem you would see chatter.

    Possibly lean towards too hard of a wheel.

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    Paolo, everything seems to be fine. The table does not rock or move. It is very smooth. I checked this grinder several times with a .0001 indicator on an optical flat resting on the chuck.

    Spindle was checked and it was true and tight.

    I just downloaded the app and will investigate.

    The surface finish did improve by rotating the diamond and getting a sharp peak to hit the wheel.

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    I still suspect your not dressing it right. I have never had so may problems as you seem to be having. How about ordering a new diamond. I always dress on the left center of the wheel, say 7:00. I mount the diamond in a block approx. 10 deg's. Also if you can lock the table do so, if not dress at about 6:30.

    Did you balance the wheel like the guy on Suburban Tool you Tube told you to?

    I do a final .002" dress and feed it fast say count to 3 or 4 /1000 as you crank the handle to dress, then stop. DO NOT DRESS BACK FREE on final pass. Do you have another wheel to try, or do you have another plate to grind? Be sure you using a lot of flood coolant. How about bluing up the hub on the spindle tapper. Leave the hub off and screw on the nut and see if it is bottoming out or threads are dinged up. Time to re-check everything. (all guesses)

    Go down to the local auto parts store and but a mechanics stethoscope and put the probe on the headstock behind the wheel guard. turn on the spindle and let it ramp up and then shut off the power and keep listening. Bad bearings will change sound and rattle a lot as it slows down. Also check further back.

    In all my years I would say 90% of all the issues in the diamond, 10% bad bearings.
    Last edited by Richard King; 11-28-2016 at 08:39 PM.

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    Hi Richard, Yes, I agree, dressing issue with possibly some balance issues too. When I turned the diamond to hit a point, it made an improvement. I was dressing at 6:00 with the diamond angled about 10 degrees to the top left, not good?

    I do have a table lock and use it. Right, no reverse pass. No balance as my 3" Ø adapter has no provision for balance.

    I have been dressing and grinding dry. I could use my CNC coolant in a spray bottle. Spindle taper fine, nut is not bottoming out. Bearings are quiet. I checked vibration with the iPhone app and the reading is under .01, whatever that is, when resting on the spindle housing.

    One note. The surface is very flat, it just has these marks which are not able to be felt or measured.

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    When you say you don't have the right weighted arbor it I obvious you never watched Don Baileys You Tube.
    He explains how to do it the old fashion way to balance the wheel. You should watch the whole thing. Around 6 minutes he dresses the wheel. How to Dress and Balance a Surface Grinder Wheel - YouTube. I would dress it differently, but he is successful as I am. I set it at 7:00 and point the diamond toward the wheel a I said before at about 10 deg's. There rotate the diamond every few weeks. There are rotating dressers so they turn at the end of each dress about 1/4 turn.
    But you need to watch this You Tube. You keep making the same mistake and it gets frustrating trying to help you when you. How to Dress and Balance a Surface Grinder Wheel - YouTube

    Watch his next show too.. Trick to Surface Grind Super Flat Parts - YouTube

    ARE you filing and stoning the part to be tight and not wiggling after etting down on the chuck ??

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    Default Surface grinding marks, any ideas?

    Get a ruby wheel and be done with it radiac ruby open wheel. The bomb


    Sent from my iPhone using Tapatalk

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    OK, I had the wrong video. I have not seen that one. It is good, and yes, I dress just about that fast in Y. I have known about drilling wheels to balance them but have not ever balanced that way. Do you drill wheels that do not have a step by the hub? Do you drill thin wheels also? I think you are correct about most of the issue is with the diamond. I will try to get a good point to contact the wheel and try again tomorrow. Thanks

    Part is definitely not rocking on the surface.

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    Quote Originally Posted by laminar-flow View Post
    Lost, yes, you pretty much described it. Light cut looks worse than heavy cut. Yes, this is just a cosmetic issue as the surface is really flat.
    I know very little about the artistry of grinding, but do supply servos and spindle motors and drives for such machines. We have a good customer with plants in many states and in Germany who grind to micron? submicron? levels, and they had this same complaint (highlighted above). We have about the best of the best servos and controls on a lot of their machines, others are top of the line Fanuc, Siemens, other CNCs, and their engineer came up with a neat idea: vary the grinding wheel speed slightly while grinding. IIRC, a ground cycle on the parts in question is about 3-10 minutes total. Their issue was the lines regularly showing up across the ground surface when the part was held to the light; cosmetically looked bad - even though the parts were in tolerance.

    So they had us make a little adjustable .5 to 3v sinewave generator with adjustable period of 10 to 200 seconds. We summed this signal into the CNC's grinding wheel speed command so the wheel speed varied ever so slightly. The result was no more periodic cosmetic marks on the parts! The regular pattern was broken up so those lines no longer showed... They put these little gadgets on a bunch of machines around the world in their plants.

    So, again, I know little about the grinding process, but perhaps you could test this idea after y ou are done laughing at it? just stand at the machine and vary the speed pot on your grinder wheel up and down some as it is grinding - maybe it could help?

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