rotational cold finger

8/8/2019 Rotational Cold Finger

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Jeongseop A. LeePhy/MchEgr/Mth Undergrad Senior

Michigan State University



Total Components :

28

EDM Compatible : 11

EDM+Additional Labor 02

Only EDM 09

Off-the-shelf : 08

Various Sized Mica Blocks (4)

Miter Gear (+ Labor) (1)

Mating Gear (1)

Two Types of Screws (2)

Labor Only: 09Major Labor (2)

Minor Labor (7)



• Fix current design issues.

• Undesirable surface temperature of the sample

• Overdesigned and somehow not intuitive geometry

• Inappropriate couplings with worm gears

• Reduce design complexities.

• Reduce the amount of human labor.

• i.e., Maximize the benefits of Electric Discharge Machine (EDM)

• Open up additional design freedom for further modifications.

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• Improved Surface Temperature

• Extended thermal contacts between the rotational components.

• 36 Point Contacts + Mica 36 Point Contacts + Mica (thinner)

Less than 0.2 In2

Surface Contact 22 Line Contacts +0.9 In2 Surface Contact

• Multi-functioning thermal/radiation shield mounted directly onto the

sample docking station.

• Deeper cold rod penetration depth.

• Increased contact pressure on the sample (with the docking plate).

• New Method of Applying Voltage Differential



• Reuse the Current Components on the New Design

• Minimized Use of Screws on the Docking Station (2)

• New Sample Clamping Mechanism• This does not use screws or any types of rotational fixture to fix the

sample. The clamp, in this case, will act both as a “clamp” and “electrode”

with added benefits of linear pressure contact on the sample as opposed

to the current point contact.

• New Docking Mechanism

• This is due to the tight fit cylindrical bearings with the docking station.



- Adaptation of Miter Gears- Torque ratio 4/1

- Very Large Hollow Main Axle

- Moderately Sized Motor Axle

22 Line Contacts

36 Point Contacts

Cold Rod Slot



Self Locking End

- Utilize the entire top surface of the main miter gear as surface thermal contacts.

- In order to minimize surface contact friction as well as undesirable cold-welding, the

head of the bearings will be edge-blended (similar to the shape of bullet).



- Location where the current ball bearings are to be inserted is shown on the left.

- The small miter gear is inserted from the bottom through the slot and locked in

position without using a single screw.



- All the electrode designs are entirely EDM compatible.

- The electrodes “hovers” on the top of cold-finger, therefore electrically insulated, separated

by off-the-shelf mica blocks (additional mica washers not shown).

- When rotating, the electrodes from docking station maintains electrical contacts by elastic

deflection of electrodes. A slot for adjustable contact pressure.



- The main electrodes act as an electrified railroad track where the two protruded

electrodes glides on top of it. This design provides good compatibility with the current

non-rotational docking station design.

- Electrically-live Rotational Capability : ~ 40˚

- Non-electric Rotational Capability : ~ 90/90˚ (without electrodes)

- Alternative Design (Not compat. w/ NRD) : ~ virtually 360˚ (electrically-live!)



- Each sample is fixed in place by placing four mica blocks and two “C” shaped metal

clamps in “interlocking” positions.

- The lock gets gradually tighter at lower temperature due to discrepancies in the

thermal expansion coefficients of mica, OFHC copper, and non magnetic stainless

steels. [15% increase found by NX Nastran thermal FEA, overall 2 N ]



Orange : U-shaped mica blocksYellow : Stainless conducting clamps

White : Translating docking plate



- This translating design is necessary due to increased precision required to mount thedocking station.

- All the components shown here are compatible with EDM except docking station.

- There is a permanently fixed gear (hidden inside the station) which drives the translation.

- The electrodes on the surface will provide additional pressure force onto the clamps.

- The direction of rotational slot has been set in such a way that simply turning the arm will

disengage it from the dock when it simultaneously engages the dock.



1. Prior to actual docking, match the tip ofempty arm to the middle of the main

gear axle.

2. Record both the location of the arm and

the entire apparatus.

3. This time, with the docking station on the

tip of the arm, trace exactly what has

been recorded.

This is only possible when the tip is collinear with

the docking station AND the docking slot on the

cold-finger. Translating design helps solving this

issue.This design also exploits the added rotational

degree of freedom to mount the sample. Angular

deviation problem for non-rotational docking is

non-issue here.

Gear contour is fully compatible with the docking

plate tooth.

A hole where the screw arm will “blank-sit” in orderto record the precise location.



Incoming Laser Outgoing Laser

Electrified tracks are visible

Everything except the clamps is placed at

lower positions than the sample height (as

shown below) maximizing rotational

capability.

rotational cold finger

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