Thrufeed Centerless grinding - help with spiral on bars
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  1. #1
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    Default Thrufeed Centerless grinding - help with spiral on bars

    I need help with a recurring problem - spirals on CG bars at our facility:

    Our machine is a fives landis; the wheel size is 18x10x8. We almost always use a carbide tipped blade. We exclusively grind titanium bars roughly 1" and smaller. More recently we've begun to do sizes over 1". One thing we've observed is that the spirals do not happen on bars under 1", the problem happens with anything over that size (roughly)

    A recent order of 1.25" diameter started using a carbide tipped blade. Half way through the first pass we switched to a brass blade - it made no difference. The first pass was made with sprials down the entire length of the bar (.003" removal). The second pass was intermittent spirals (.003" removal) Some bars came out clean and some had spots here and there. The final pass came out with spirals on two bars and the rest were fine.

    During this order we ran the machine with the hood pulled back which allowed us to see the wheel. The spiral is taking place on the blade in front of the grinding wheel or right after it. It also moves around - the start location with jump inches either way and continue to mark the bar. I think that we're dealing with swarf that is getting wedged onto the blade and marking the bar.

    I think this because after the brass blade wore in (Just happened to be on final pass) and there was not a gap on the grinding wheel side of the blade, no swarf could get into that location and cause a mark.

    Has anyone else seen or heard of this problem?
    How did you address it?

  2. #2
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    Im not a through feed hand but have done some so just thinking out loud.
    Check the machine is level and machine weight on all its feet.
    Change dress angle slightly to dress a little more from out-go side.
    Replace riders with bronze, perhaps even cast iron (yes CI will wear)
    See if anything gives vibration to machine.
    Align the feed end better with the riders.
    Add coolant lines to wash blades.
    How straight is the bar stock material as received?

    Im sure there are roll guys here that know much more than me on this.

  3. #3
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    Just bringing this back to top so the late shift guys might help

    Oh..perhaps slippery coolant.. soluble oil..or the like..
    Again just throwing out ideas as through-feed is not my bag.
    if diamond dresser be sure to turn..
    True the wheel out going edge with a Norbide stick or roller abrasive wheel dresser just a tad, perhaps a 1/8 bevel.
    (yes just use a carbide insert in a holder to bump dress if that is all you have.)

    QT [anyone else seen or heard of this problem] I did but darned if I can remember what solved the problem..

  4. #4
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    Could we get a picture of the spirals? I would always us a Bronze blade with titanium. I have a theroy but I would like to see the shaft before I comment.

  5. #5
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    Throughfeed on cast iron and aluminum pistons 40+ yrs. Cinci 230-10 we use a grinding wheel dressing cam that has a slope of .005/inch for the first 2 1/2 inches then .001/inch for 6 inches then back slope .005/inch for the final 1 1/2 inches. The burn marks or spirals happen at the intersection of the change in the slope of the cam. Either grabbing too soon or too late as the parts are entering or leaving the wheel. Sounds like the geometry is no longer optimized for the larger diameters. Perhaps slope on the reg wheel?


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