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CORE BIT SPEED - RECOMMENDATIONS
(RPM) - If the drilling speed is too high, the bit will polish. If the drilling speed is too low, the job will take too long. You will know if the core bit is "polished" or "glazed" when it stops cutting, you have segments left, and you don't see exposed diamonds. To open up the diamonds on the core bit, try drilling into soft abrasive material (such as a cinder block). However, try not to drill very much as you will be wasting diamonds.
RPM's for Best Core Bit Performance
Bit
Size
1/2 Inch
Recommended
Minimum RPM
4775
Recommended
Max RPM
7960
Recommended
RPM
6364
5/8 Inch
3820
6368
5090
3/4 Inch
3183
5307
4242
7/8 Inch
2728
4549
3636
Bit
Size
1 Inch
Recommended
Minimum RPM
2387
Recommended
Max RPM
3980
Recommended
RPM
3182
1-1/8 Inch
2122
3538
2828
1-1/4 Inch
1910
3184
2545
1-3/8 Inch
1736
2895
2314
1-1/2 Inch
1592
2653
2121
1-5/8 Inch
1469
2449
1958
1-3/4 Inch
1364
2274
1818
1-7/8 Inch
1273
2123
1697
Bit
Size
2 Inch
Recommended
Minimum RPM
1194
Recommended
Max RPM
1990
Recommended
RPM
1591
2-1/8 Inch
1127
1880
1502
2-1/4 Inch
1061
1769
1414
2-3/8 Inch
1005
1676
1340
2-1/2 Inch
955
1592
1273
2-5/8 Inch
911
1520
1215
2-3/4 Inch
868
1447
1157
2-7/8 Inch
832
1387
1110
Bit
Size
3 Inch
Recommended
Minimum RPM
796
Recommended
Max RPM
1327
Recommended
RPM
1061
3-1/4 Inch
735
1225
979
3-1/2 Inch
682
1137
909
4 Inch
597
995
795
4-1/4 Inch
562
937
749
4-1/2 Inch
531
884
707
4-3/4 Inch
504
840
671
Bit
Size
5 Inch
Recommended
Minimum RPM
477
Recommended
Max RPM
798
Recommended
RPM
636
5-1/4 Inch
455
706
608
5-1/2 Inch
434
724
579
6 Inch
398
663
530
6-1/4 Inch
382
637
509
6-1/2 Inch
367
612
490
Bit
Size
7 Inch
Recommended
Minimum RPM
341
Recommended
Max RPM
569
Recommended
RPM
455
7-1/4 Inch
330
552
441
7-1/2 Inch
320
534
420
8 Inch
298
498
398
8-1/4 Inch
290
483
387
8-1/2 Inch
282
469
376
9 Inch
265
509
354
9-1/2 Inch
252
420
336
Bit
Size
10 Inch
Recommended
Minimum RPM
239
Recommended
Max RPM
398
Recommended
RPM
318
12 Inch
199
332
265
14 Inch
171
284
227
16 Inch
149
249
199
18 Inch
133
221
177
20 Inch
119
199
159
24 Inch
99
166
133
26 Inch
92
153
122
28 Inch
85
142
114
Bit
Size
30 Inch
Recommended
Minimum RPM
80
Recommended
Max RPM
133
Recommended
RPM
106
32 Inch
75
124
99
34 Inch
70
117
94
36 Inch
66
111
88
38 Inch
63
105
84
40 Inch
60
100
80
42 Inch
57
95
76
44 Inch
54
90
72
46 Inch
52
87
69
48 Inch
50
83
66

Additional factors that affect core drill
performance and your profit margin

Power
Necessary to maintain the proper cutting speed. Efficient cutting means keeping the bit at the RPMs and horsepower.
Water
Not too little and not too much. The right amount removes slurry and keeps the cut clean. Slurry water should look like "coffee with cream"
Aggregate
You can't see it until you're done, but a good driller can feel the right speed and pressure to cut varying types of aggregate.
Steel
Slows down the cutting process. Maintaining drill motor speed is important. Don't push the bit too hard. Maintain even speed with even pressure.
Bond Specs
Too hard and it takes too long. Too soft and it costs too much money. Remember, hard bond for cutting soft abrasive materials, soft bond for cutting hard materials. "hard on hard" won't cut and "soft on soft" won't last.
Proper Alignment
Necessary for good bit life. This means the rig must be properly anchored. A rig can be anchored with concrete anchors, vacuum or a post jack.
Standing on the rig is DANGEROUS and not acceptable
Core Rig Maintenance
Performance, speed and bit life will mean little if your rig has bad shims, bearings, and hold down devices.
Wet Core Bits by Size