How to set Z-zero on surface grinder ?
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  1. #1
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    Default How to set Z-zero on surface grinder ?

    Hello !

    Please share tricks of trade.

    I do the following:

    1) Use diamond to make grinding wheel surface flat and clean
    2) Set the zero using i.e. 10mm gage blcok between wheel and "zero" surface, by moving gage block left and right until the non-rotating wheel starts touching the block.
    3) it seems to give about 2..4um of repeatibility.

    Are there any better ways to set grinding height zero ? Also, I feel that my explanation in english is quite sloppy so anybody can rephrase my question correctly

    I'm currently doing some ferrite E-core grinding and i get about 5um accuracy, which is good enough but I feel it could be better.

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    It will depend upon what you're grinding and whether you have extra material on it. Everybody has a favorite method for determining where zero is. For flat work some like using a strip of ordinary notebook paper between the wheel and the workpiece. When the paper is cut you know approximately how far above you are. I use a magic marker to color a section of the intended surface. Different brands have different fluid thickness so experimentation is required. Some markers can even build up a thickness of several .0001's in layers. Apply the marker on a piece and check with an indicator to determine how thick the fluid layer is when dry, even use 2 or more layers for testing. If you're careful with the down feed you can just begin to wipe the marker fluid off (with the grinder turned on) yet not spark. Measurement should always be preferred over trusting the downfeed amount due to thermal expansion of the workpiece. I've even used a sacrificial block to determine where zero is when I don't have much material on the work. Running a gauge block under a non-rotating wheel may work for you but doesn't seem like a very good idea for several reasons. Getting better results than 5um is certainly possible but there are other factors that affect the results like machine condition, wheel selection, thermal expansion, how much you take per pass, wet/dry grinding, material, thickness, orientation, and spark out pass are some that immediately come to mind when you're attempting tolerances in the sub 5um range. If what you're getting is good enough then trying to be sub 5um is wasted time/money/precision if it's not required. If you're just wanting to be capable of sub 5um then that's fine, try some of my suggestions (or others) and pick a method you like and are comfortable with. Your English is good enough if I understand your question. Post your results.

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    I was always taught to not stop the wheel once dressed so your touching off on a gauge block might add an extra layer of excitement that I’ll pass on =)

    AD gave you some good tips and I agree however I’ve never run across marker brands that build up in thickness, must be a non-alcohol based one.

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    I use the paper trick, then ease the wheel down until I scratch layout or magic marker. Tom

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    I grind a sacrificial piece and measure it. A VFD is also useful as I find you can start and stop the wheel with little problem because of the ramp up/down. If I'm doing anything fussy I might run the grinder for 30 minutes or so just to stabilize it. Also find that being consistent about way oil helps if you have a manual lube arrangement. Don't want it dry, don't want to float the table and don't ever want the oil too thick. Even though my Z screw is in good shape, I never feel comfortable about traveling very far from the "zero" point and just relying on the numbers/dial to get me where I want to be. For me, balance makes a big difference in accuracy and repeatability.

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    I use cigarette rolling papers Zig Zag if I can get them. .001"
    Stuck on the work with a drop of coolant.

    I've used marker, but have scratched some work that way. My eyes are going for close work, and I'm a bit clumsy. Staying away a thou. is better for me. then move to the surface.

    The note about the lube oil is something to heed! the bed needs to settle in before any thing holds.

    eta

    Check the axis terms. Is Z axis in and out on a SG? I believe so.....convention and common use may differ region to region

    Z Axis Readout for Surface Grinder

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    Several good points made above that I neglected to mention. Machine warm-up and way oiling can be important when attempting sub 5um. I'd also want to run the table/saddle along respective axis to evenly distribute the way AFTER oiling. Everything you do/don't do seems to make a difference when attempting sub 5um.

    Hazzert- Have you tried just "dotting" the marker? Dragging the tip across a previous mark will indeed tend to wipe the previous mark out but a dot or three can sometimes add another layer. Tip size can introduce more fluid too. I leave a marker tip down hours before I'll need it.

    Picking the layer of marker is a touchy thing to do and my eyes are fading too. I use the sacrificial block (near target size) if I can't trust my shaky hands or there's no meat left on the piece. I use the marker mostly for finding low spots from thermal expansion when I'm approaching final size on flat work. I have a specific downfeed technique for my hands/fingers when I'm trying to creep up on a marker patch. It's easier, for me, with some grinder makes than others if they don't have the sub .001 micro feed. I was hoping some of the other members here that are better grinder hands than me could chime in. I still have lots to learn about grinding too after 30+ years.

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    If your part has NO stock on it why grind it?

    With the wheel over the part (and magnet on!) slowly bring wheel down until it touches. Grind top of part with no further down feed, move wheel away from part but do not turn it off. Release magnet, measure part, and calculate how much more you need to remove. Now you know exactly where to set the down-feed for zero.

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    Madis did say "a non-rotating wheel"

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    If the wheel isn't perfectly balanced, a non-rotating and rotating wheel are not equal in terms of contact. I think dress is also important. The wheel loses some high spots on the first couple passes, that might otherwise scratch the work. One micrometer is less than half a tenth. I can usually grind that flat (if the work isn't too thin), but grinding to absolute size is a whole 'nuther matter. At that point, at least with my Boyar Schultz 612, it's better to resort to lapping. My minimum graduation is a tenth and between thermal effects and who knows what else, I can't repeat to that level over any great length of time.

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    Thanks for all answers !

    I had no idea about the "wheel having some high spots after trueing". But its obvious..
    This explains some lost microns

    So, I try the following:

    1) install a sacrifical piece near the main jig
    2) after trueing, I grind 10um of sacrificial and set wheel to "zero"
    3) and then I measure jig reference height and sacrificial height difference with dial indicator
    4) joy and happiness

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    Keep the wheel running always.

    And after dressing run your finger along wheel diameter, feel those sharp prickly bits? Then use a metal pin and run it against the fresh grinding wheel with light pressure, run your finger along the wheel again and feel it much smoother? This will aid in getting a much better finish, especially for polishing operations after.

    As for touching on work,

    We use a piece of paper held on with a magnet on the dust guards, then wind wheel down close to the work after dressing by eye, then lean over, look through the gap between the wheel and work piece. Across to the paper to add contrast and clarity in the small gap, then wind down until the gap gets close, after practice you can go even closer and closer then when winding table back and forth wind handle down last couple thou until it touches on.

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    That reminds me about lighting. You need good light to see what you're doing, plus a light or white surface behind to see the gap between the wheel and work.

    I think I've heard of people running a piece of hardwood across the wheel to knock off the prickles. Some will touch the running wheel with their finger, but that's way too risky and a bad habit to get into.

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    Quote Originally Posted by Madis Reivik View Post
    Hello !

    Please share tricks of trade.

    I do the following:

    1) Use diamond to make grinding wheel surface flat and clean
    2) Set the zero using i.e. 10mm gage blcok between wheel and "zero" surface, by moving gage block left and right until the non-rotating wheel starts touching the block.
    3) it seems to give about 2..4um of repeatibility.

    Are there any better ways to set grinding height zero ? Also, I feel that my explanation in english is quite sloppy so anybody can rephrase my question correctly

    I'm currently doing some ferrite E-core grinding and i get about 5um accuracy, which is good enough but I feel it could be better.
    Paradyne coatings & machine


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