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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Test of Center Drilling vs. Spot Drilling.
To All:
This is from a post I made some years ago it amc. I thought the readers in here might enjoy a break from all the political trash talking. g Now let me just add that before my test I was of the opinion that centerdrilling was more accurate than spotdrilling. ================================================== ================ I did a little test today on my day off. In a piece of 6061 I center drilled 4 holes with a .125 piloted center drill .1 deep at 2000 rpm and 5 IPM. Then I spot drilled another row of 4 holes .125 deep at 2000 rpm and 5 IPM. I then peck drilled eight .234 dia. holes 1" deep at 5000 rpm and 40 IPM. As a side test I peck drilled 4 more holes with a #1 (.228) cobalt 135 degree split point stub drill without spotting or center drilling at 6000 rpm and 60 IPM. I then took a tenth indicator and checked each hole for location going the exact same amount into each hole. The holes checked as follows: First row of center drilled holes. X Y #1 +.0003 0 #2 +.001 -.0001 #3 -.0007 -.0002 #4 +.0003 +.0005 Largest amount out = .001 Average amount out = .00039 Second row of spot drilled holes. X Y #1 -.0012 0 #2 -.0002 -.0002 #3 -.0005 -.0006 #4 +.0002 -.0002 Largest amount out = .0012 Average amount out = .00039 Third row of hole made with NO spotting or centerdrilling. X Y #1 -.0011 +.0002 #2 -.001 -.0006 #3 -.0005 +.0004 #4 -.0007 -.0007 Largest amount out = .0011 Average amount out = .00065 Now 4 holes each may not be statistically significant but to me this little test leads me to believe that the difference between using centerdrills and spot drills is so minimal as to be non existent. So much for my "centerdrills are better than spot drills theory" but conversely, anyone claiming that spot drills are clearly superior to centerdrills for hole location would have to show me some hard evidence and not just rhetoric. I WILL say that as a result of this little test I'll be using spot drills much more often if only because of the chamfering now that I know they don't significantly throw off the location. I'll also be plowing into material without centerdrilling OR spot drilling more often as well. ================================================== ================ -- BottleBob http://home.earthlink.net/~bottlbob |
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