10 free WorkKeys practice questions in the real exam format, covering the official content areas, with an explanation for every answer.
WorkKeys Practice Test 10Tutor mode
Question 1 of 10
Graphic Literacy
Recommended Drill Speeds (rpm), With Coolant
Material
Bit type
1/8 in
1/4 in
3/8 in
1/2 in
Aluminum
HSS
9,000
4,500
3,000
2,250
Aluminum
Cobalt
11,000
5,500
3,700
2,750
Mild steel
HSS
3,000
1,500
1,000
750
Mild steel
Cobalt
3,600
1,800
1,200
900
Stainless steel
HSS
1,500
750
500
—†
Stainless steel
Cobalt
2,000
1,000
650
500
Hardwood
HSS
6,000
3,000
2,000
1,500
Acrylic
HSS
4,500
2,250
1,500
1,100
Columns are bit diameters. HSS = high-speed steel. Speeds assume coolant is used; when drilling without coolant, reduce the listed speed by 25%. † Not recommended; use a cobalt bit.
You are a machinist setting up a drill press. The job calls for 1/4-inch holes in mild steel with a cobalt bit, and the coolant pump is down, so you will drill without coolant. According to the chart, what speed should you set?