1. CASE STUDY – Combined Loading
Drill bit isolators for underground mining – all metal components and elastomer must be safe!
Design requirement: 8,000 lb thrust load and 300 lb-ft (3,600 lb-in) torque – these are basically the cutting forces.
Detailed FE analysis but ALWAYS verify with hand calculations!!

2. 2010 SME Annual Meeting & Exhibit
Bit Isolator
Drill Depth up to 48”
Chuck Isolator
2010 SME Annual Meeting & Exhibit
Phoenix, Arizona

3. 35 mm (1 3/8 in) Isolator Load Requirements:
Drill Bit
Drill Bit Isolator (
Thrust Load = 8,000 to 10,000 lb
Bending Load= 125 lbs)= K*d
Drill Rod
Torsion Load= 300 lb-ft
Chuck Isolator
HOT SPOT!
2010 SME Annual Meeting & Exhibit
Phoenix, Arizona

4. 2010 SME Annual Meeting & Exhibit
Results showed that in combination, the bit isolator and the drill chuck isolator provided a 7 dB(A) reduction in sound pressure level at the operator position.
2010 SME Annual Meeting & Exhibit
Phoenix, Arizona

5. A-weighted Sound Level Spectrum60 65 70 75 80 85 90 95
100
105
110
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
6300
8000
10000
Overall
1/3-Octave-Band Center Frequency (Hz)
A-weighted Sound Level (dB)
108.9 dB(A)
Baseline:
104.4 dB(A)
T NR BISO, 45 NR CISO:
104.4 dB(A)
T NR BISO, 70 NR CISO:
102.7 dB(A)
T NR BISO, 55 NR CISO:
2010 SME Annual Meeting & Exhibit
Phoenix, Arizona

6. 2010 SME Annual Meeting & Exhibit
1 3/8” Drill Bit Isolator – Design Review:
Drill Bit isolator:
Chuck isolator:
2010 SME Annual Meeting & Exhibit
Phoenix, Arizona
1 3/8" DBI, R. Michael, PE

7. Look at metal components: Where would you expect max stress to occur?
Critical Area!!
Look at metal components: Where would you expect max stress to occur?
5/31/2018
1 3/8" DBI, R. Michael, PE

8. Critical component – inner member, thin wall, stress concentration!

9. Results: FE Analysis 1 3/8” DBI
All cases, thurst load = 8,000 lb, torque = 300 lb-ft (3,600 lb-in)
HOT SPOT!
5/31/2018
1 3/8" DBI, R. Michael, PE

10. Max Principal, s1
Min Principal, s1

11. Max shear stress, tmax
VERIFY FEA RESULTS WITH HAND CALCS!!!!

12. Verify Principal Stresses with Hand Calculations or Mohr’s Circle!!
Thrust Load = 8,000 to 10,000 lb
Torsion Load= 300 lb-ft
HOT SPOT! y x

13. HAND CALCS:
From Axial Load
(Compression)
From Torque

14. How do these values compare with FEA results?
HAND CALCS Cont’d:
Principal Stresses:
= / ksi
How do these values compare with FEA results?
Next: use Mohr’s circle to resolve