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Ten Points to Eliminate Mistakes on Finish Size – Bar Clean Up, For Steel Bars

We have talked about round bar grinding in the past. The following posts will look deeper into the communicating skills that will help you minimize disappointments in this area. Unfortunately, more people than not have purchased a bar of steel and found that it won’t make their part because there was not sufficient stock allowance to “clean-up”. That need not be the case. Most often, communication is again the culprit. We are speaking of ROUND STEEL BARS.

  1. Diameter size relative to length will be important.
  2. Subsequent machining or grinding method will be important.
  3. Mill finish and mill tolerance will be important. This often varies by mill.
  4. You should share “end use” with your supplier.
  5. Also, share any subsequent operations you will be doing on the bar.
  6. If the finished shaft involves substantial step downs, or, if only a small portion of the bar needs to finish…share that information.
  7. Remember, your supplier cannot be made responsible for a third party’s work, and/or, mistakes.
  8. If liability on the shaft is considerable, consider parking it in another party’s driveway.
  9. Try to “Talk the Talk” phrases like, “a stick of steel”, or, “cold roll”, or, “a length of steel”, will get you in trouble.
  10. Share important ancillary facts with your supplier; have you received steel in the past that has not been straight enough, hasn’t cleaned up, or was inappropriate in another way?

Each one of the above should solicit further discussion. That is going to come under the header of; TO BE DISCUSSED (TBD). I will try to do just that over the next several weeks. So, stay tuned.

-Howard Thomas, February 26th 2019

 

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Centerless vs. On-Center Grinding

Bar Grinding Centerless Vs. On-Centers – Second Part of Four Part Set

As we mentioned in our last blog; in the maintenance industry, if someone refers to grinding a steel shaft, they are most likely talking about “Centerless Grinding”. There is another method, however, and that method is called “On-Center Grinding”. A misunderstanding on which method is actually required usually results in expensive errors, and general unhappiness for all parties. Of the two types, centerless is by far the most common. So much so, that if you mention grinding a shaft, the mill or service center will assume you are discussing centerless grinding.

Centerless grinding tends to follow the outside diameter of the bar; think apple peeler. When the skin is off, you still have a recognizable apple; naked, but still looks like an apple. Grind an egg-shaped hot rolled bar, and you will have a precision finished egg. In the hands of an experienced grinding operator, many troubling issues may be corrected. Taking it to an art form, the right operator can minimize irregularities and even affect straightness; to a point. The standard in industry is centerless. So, unless specified, tolerances being discussed are taken to be based on centerless.

On-Center grinding, on the other hand, indexes on the center of both ends of the bar. The grinding head then machines the O.D. of the bar to be concentric with the I.D. (chucked up centering holes). If your bar is egg shaped, now, your ground bar will be concentric. If the bar is bent, the finished ground bar will be straight, depending on how bent it was and how much stock removal you are able to take. The roundness (concentricity) and the straightness come from the “On-Center” grinding. On center grinding requires more stock allowance “to-clean up” than centerless grinding. Where there are low spots, no stock will be removed. The on-center grinding operation will not only true up the diameter size, but, it will “machine” the bar into a true round and straight part. How do you avoid these potential problems if you are not aware of the intended grinding method? Qualify, Qualify, Qualify. If “finish size” is mentioned, ask about the grinding method. And remember; “If it doesn’t clean-up, whos wallet comes out?”

-Howard Thomas, September 5th 2018

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