1. The document discusses progress on various components of a lathe project including the cross slide assembly, testing, and carriage machining being finished, but structural tube machining being behind schedule. 2. It provides functional requirements for the lead screw such as allowing for misalignment and producing precise linear movements, and specifies performance goals for startup torque, lifetime, frequency response, and load capacity. 3. Analysis shows the lead screw design meets requirements with negligible translation error, no play, and torque below specifications even under maximum load.

1. 1
4/18/16

2. • Schedule Updates
• Cross-Slide
– Functional Requirements
– Flexure
– Lead-Screw
– Testing
– Model
2

3. • Finished
– Cross Slide Assembly
– Testing Cross Slide
– Carriage Machining
– Designing Rest of Lathe
• Behind Schedule
– Structural Tube Machining, Bill’s schedule was
booked
• Potting delayed as a result
• Gantt Chart on Next Slide
3

4. 4
Link to schedule:
https://teamgantt.com/gantt/schedule/?ids=582767#&ids=582767&user=&custom=&company=&hide_complet
ed=false&date_filter=&color_filter=

5. • Allow for Z-axis misalignment (+1 DOF)
• Allow for human hand movement increments to
produce a x-axis motion of < 50 microns
• Error Allotment </= 7 microns
• Stationary Handle , </= 250 microns linear
movements
• Start Torque </= 4lb-inch (ideal </= 2lb-inch)
• Lifetime =/> 3120 hours (12 hrs/week, 52
weeks/year, 5 years), at 60 rpm for rotary
• Natural Frequency =/> 80Hz
• Withstand: Fx=20lbs, Fy=135lbs, Fz=60lbs,
• Range of Motion =/> 0.3 inches

6. 6
Thrust Bearing
Attachment 0.25” gap
Stabilizers,
cut off when
done with
machining
Carriage
attachment
Threaded
Attachment
Headstock
Clearance
Chuck
Clearance
Added
Protection
Tool Post
Holes

7. 7
3 lb applied
force

8. 8
Mode # Freq (Hertz) X direction Y direction Z direction
1 235.5 0.0021013 0.49048 1.1352e-006
2 315.12 1.2538e-005 6.5322e-007 3.4188e-006
3 346.51 0.010169 4.9037e-005 0.00172
4 388.48 0.041212 4.4115e-005 0.0022115
5 473.01 0.0055886 2.9683e-005 0.00036685

9. • Custom OMAX path
• Waterjet outlines
• Counter-bore and thread
holes
9

10. 10

11. For more analysis: https://docs.google.com/spreadsheets/d/1V_9k8njTLzHD-
3Jz04GE_dwqZ0_g9mWqIl43e8NAWQ8/edit#gid=1853057762

12. 12

13. 13
Lifetime: 9000 hours
This is at 150 RPM and 30 lbf thrust
force (maximum load rating at 150
RPM is 65 lbf)
Ball thrust bearings are optimal
because they can tolerate slight radial
forces/misalignment if the lathe is
dropped

14. • Design: Friction between
aluminum housing and steel
threads was low enough to
meet our functional
requirements
• Obstacle: After assembling, fit
between the lead screw and
housing was too loose
• Solution: opening up the hole
and using a brass bushing
significantly reduced end play
14
can see
the hole
was too
big

15. 15

16. • Precision lost through
leadscrew torsion instead
of translation of carriage
being translated.
• Negligible x-direction
error (~0.8μm)
• Presence of substantial
torque to turn in both
directions implies no
“play” either.
16

17. 17
• Torque to turn <2lb*in when free, <4lb*in
under maximum load (aka a person).

18. 18
• Tool post deflection tends to be negligible as
we tighten beyond 0.3 turns. (~8lbs applied)

19. 19

20. 20
• Huge errors in x axis(~650 microns), probably
due to loose leadscrew / not actually turning 1
revolution
• Total errors in Y (~13 microns) and Z (~76
microns) coming from wobble

21. 21
• Little angular variation but at constant offset
• Large error from offset (~13 microns)
• Add shims to help adjust angular offset

22. Thank You
22
Questions?

23. EXTRA SLIDES
23

24. • FOS of 1.6 with a 160lb load in the –y
direction
• Deflections of:
– -3.42microns in x (|122N| force)
– -86.4microns in y (|252N| force)
– +5.16 microns in z (|100N| force)
for tool location in FEA when cutting 0.07”
depth of aluminum
24

25. For more analysis: https://docs.google.com/spreadsheets/d/1V_9k8njTLzHD-
3Jz04GE_dwqZ0_g9mWqIl43e8NAWQ8/edit#gid=1853057762

26. For more analysis: https://docs.google.com/spreadsheets/d/1V_9k8njTLzHD-
3Jz04GE_dwqZ0_g9mWqIl43e8NAWQ8/edit#gid=1853057762

27. 27

28. • θ = L T / (J G) = 4E-3 rad
Where:
• J = π D4 / 32 =1.242E-4
• D=0.1886in
• G=11457981psi
• L=1.46in worst case
• T = 4 lb*in worst case
• Lateral loss < 1micron
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