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Stepover Calculations Depended on Grain Size

majohnson

Cast Iron
Joined
Jan 3, 2013
Location
Erie, CO
Reading on grinding surface finishes and came across someone made the point that your stepover is based on the wheel grain size. I can not seem to come up with much on the subject.
 
I've never seen that, nor done it. Where did you see this? The grit in the wheel is randomly distributed, as is wheel placement on the part, so that doesn't make any sense at all to me.
 
Such thinking (stepover calculations) is not likely very good because part material, hardness, and machine spindle horsepower play a major portion in what can be done.

Stepover used to be called cross-feed increments. I suspect the term stepover came from mill hands.

Crossfeed increments are commonly of two varieties.

  • 1.The older method is down-feed perhaps .030 - .050 – or what and intersect the part with the leading wheel edge to begin cross increments of perhaps .020 at each long travel, then go long -cross, long- cross, long -cross across the part top side all the way across the part with not changing the down-dial zero
  • 2.The newer method is to down feed perhaps .0005 to .002 and then cross travel perhaps ¼” or 1/3 the wheel width with each long travel, and then another down and back over, then again, and again, and...
In method 1 the leading edge of the wheel becomes the rougher and all the wheels following becomes the finisher, one can run one part or a few and still make size at the original down hand wheel zero. The wheel is in continued use until the finisher (following side) begins to wear. The dressing amount is watched so to be added to the zero-dial number and so increasing the number of finIshed parts can be made.

In method 2 the whole wheel bottom is engaged to do the grinding and so wheel wear will make the dial zero change. One can estimate that x amount of wheel is lost with each part ground.

Suppose that you have a 2x 4x 1” part with the 2 x4” facing up to the wheel with .035 to take off.

Method 1 you might spark the part top, down dial feed .035 (or .007 less for heat) and incremental cross with .015 cross travels for each long travel All the way across the top of the part.

Method 2 you might spark the part and down feed .001 or .002 and with 1/4 “ cross steps to cross the part, the down feed another .001 .002 and with ¼” steps cross back over, and again , and again..

The third ( *3). common grinding method is down gridding to a near rough in size, take a dress, and then use method 1. or method 2 to bring the part to size.
Down grinding is using down-feed only on the part top side with the full wheel width, or down-feed only with a portion of the wheel width.

Yes, with both methods, and all 3 methods, wheel hardness, grit size part material and hardness help determine the feed amount you can take.

*Being stuck on only one method will assure that one will never become a good grinder hand.

Grinding experience tells the seasoned grinder hand what method or combination to use.
*Yes there are other grinding methods...

Note: Why did this part have .035 to take? Saw cutting to plus .035 is a fairly close dimension to assure that the saw's ability for size and angle error will leave enough stock so as not to be an undersized part.

Note: Due to materials' internal or surface stresses it is not uncommon to take stock from two sides of a part. some times one might take only a portion of the needed take amount to examine the part for stress change potintial. stress reliving can reduce this problem.
 
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Choosing the correct method, or a combination of methods can help to make size and surface finish tolerance in the shortest time.
Often that is aided by the fewest dresses, the fewest taking of measurements, the fewest taking the part off the chuck, using the original size for a starting point, and using the accuracy of the feed screws and dials as measuring devices, along with prior knowledge and experience to anticipate heat-related problems and expected wheel loss due to breakdown.
 
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Thanks for the replies. I’ve read a lot and watch a bunch of videos on grinding. Never heard of cross feed being determined on grit size. While cross feed speed when dressing the wheel has more to do with final finish.
 








 
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