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--- techtalk:ref:tools147 [2019/05/09 21:36]
hippysmack [Pre-Ream Hole Size Chart]
+++ techtalk:ref:tools147 [2019/05/10 00:14]
hippysmack [Pre-Ream Drill Hole Size Chart]
@@ Line 42: / Line 42: @@
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-===== Pre-Ream Hole Size Chart =====
+===== Calculating Pre-Ream Drill Hole Sizes =====
+The amount of material left in the hole prior to reaming (pre-ream hole size) plays an integral role in the quality of the reamed hole. ((http://blog.supertoolinc.com/2012/04/06/pre-ream-hole-size/)) \\
+The pre-ream hole size affects characteristics in the reamed hole including hole finish, hole straightness, tool life, and cycle time. \\
+There are several ways in which the pre-ream hole size may be obtained some examples include investment casting, boring, line boring, rough reaming, and stamping. \\
+The most common way to obtain the pre-ream hole size is through drilling. \\
+The appropriate amount of stock removal for carbide tipped and solid carbide reamers is generally 2% to 3% of the finished hole size. \\
+Carbide tipped and solid carbide reamers need to have adequate stock to remove or they will rub in the hole and generate excessive heat. \\
+This leads to premature tool wear and poor hole finishes.
+A 0.7500” diameter reamer should remove between 0.0150”-0.0225” of stock. \\
+A 0.2500” diameter reamer should remove between 0.0050”-0.0075” of stock. \\
-^Reamer diameter \\ fraction - decimal (nominal)^Hole size \\ to leave 2%^Drill size \\ to leave 2%^Hole size \\ to leave 3%^Drill size \\ to leave 3%^
+A good way to calculate the drill bit size is to take the desired finished hole diameter and multiply it by 0.98 \\
+Then take the desired finished hole size and multiply it by 0.97 \\
+This gives you the range of stock removal best suited to the finish ream hole size. \\
+From that range refer to a standard drill chart to chose the appropriate standard drill size for your pre reamed hole size. \\
+Below are examples for calculating the pre-ream drill hole size for a 0.7500” finished hole diameter and a 0.2500” finished hole diameter.
+|0.7500" x 0.98 = 0.7350"|0.7500" x 0.97 = 0.7275"|
+Therefore, the appropriate range of the pre-ream drill hole size for a 0.7500” finished hole; \\
+.7275” – 0.7350” \\
+|0.2500" x 0.98 = 0.2450"|0.2500" x 0.97 = 0.2425"|
+Therefore, the appropriate range of the pre-ream drill hole size for a 0.2500” finished hole; \\
+.2425” – 0.2450” \\
+If you are fine tuning your operation and are within the 2%-3% range; \\
+Try removing 2% of the reamer diameter for steels and tough alloys.. \\
+And 3% for non-ferrous and cast iron materials.. \\
+If you are rough reaming, stock removal can be up to 5% of the reamer diameter. \\
+The 2%-3% rule is great in theory.  \\
+In the real world drill bits come in standard sizes. \\
+Most do not have time or money to wait for a special size drill bit to be made. \\
+You are usually forced to choose among standard drill bit sizes that are on the shelf. \\
+A Pre-Ream Drill Hole Size Chart is provided below. \\
+The chart tells the appropriate standard drill bit size to choose when reaming fractional diameters from 1/8” to 1” in 1/64” increments. \\
+===== Pre-Ream Drill Hole Size Chart =====
+A PDF of this chart can be downloaded from Rock River Tool Inc. ((https://www.rockrivertool.com/documents/pre-ream-drill-size-chart.pdf))
+^Reamer diameter \\ fraction - decimal (nom)^Hole size \\ to leave 2%^Drill size \\ to leave 2%^Hole size \\ to leave 3%^Drill size \\ to leave 3%^
 |1/8" - .1250"|.1225"|31|.1213"|3.0mm|
 |9/64" - .1406"|.1378"|29|.1364"|3.4mm|