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Polaris® Non-Bridging Clamping Arm
Non-Bridging Clamping Arm
Being Used to Mount a Low-Distortion Polaris Mount Held at 45° by a POLARIS-MA45
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Click for POLARIS-CA1/M Holding Torque Results*
The Polaris clamping fork design has undergone extensive testing to ensure high-quality performance. See the Clamping Arm Data tab for additional test results.
*It is important to note that the 1/4"-20 and M6 x 1.0 clamping torque values have been adjusted to provide the same clamping post and table forces. Also note that the maximum recommended tightening torque for an 18-8 stainless steel screw is 75.2 in-lbs for a ¼-20 screw and 8.8 N-m for an M6 x 1.0 screw. Higher mounting torques can cause the screw to fail.
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The Top and Bottom of the Fork can be Used for Mounting, Minimizing the Overall Footprint and Distance Between Components
The Polaris® Clamping Arm is the ideal solution for stably mounting our Ø1" Posts for Polaris Mounts. Each clamping arm, which is machined from heat-treated, stress-relieved stainless steel bar stock, provides extremely high holding forces with minimal torquing of the mounting screws.
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Side-Located 1/4"-20 Screw Actuates Clamping Bore
The POLARIS-CA1 and POLARIS-CA1/M are designed to hold a Ø1" post, such as our fixed Polaris mount, while the POLARIS-CA25/M is designed to hold a Ø25 mm post or Ø1/2" post holder using a flexure clamping mechanism. The POLARIS-CA1 and POLARIS-CA1/M are not compatible with Ø25 mm posts; the bore diameter is too large and will not contact the post when clamping.
The side-located clamping mechanism, as shown in the photo to the left, is actuated using a 1/4"-20 cap screw for the POLARIS-CA1 or an M6 x 1.0 cap screw for the POLARIS-CA1/M and POLARIS-CA25/M. Because the side-located clamp and mounting slot are tightened separately, the user can set the position of the fork and adjust the rotational alignment independently. The clamping arm has a compact 3.33" x 1.60" (84.5 mm x 40.6 mm) footprint for tight laser cavity setups, with a thickness of 0.60" (15.2 mm) for increased stability. A 1.30" (33.0 mm) long clearance slot allows for a variety of mounting solutions using a 1/4"-20 or M6 x 1.0 cap screw and washer.
Both the imperial and metric clamping arm have been tested for holding strength. Based on the test results, recommended torques have been determined for both the flexure clamp and for tightening the slot to the table. The scales for these measurements, as seen in the figure above, are not a direct conversion due to an efficiency difference between 1/4"-20 and M6 x 1.0 screws. The efficiency of M6 x 1.0 screws is about 5% less than that of 1/4"-20 screws due to differences in diameter and pitch. For optimal performance we recommend tightening this screw of the POLARIS-CA1 with 15 to 25 in-lb of torque and the screw of the POLARIS-CA1/M and POLARIS-CA25/M with 1.75 to 3 N•m of torque. When mounting the clamping arm to the platform we recommend using 40 to 65 in-lb of torque for the POLARIS-CA1 and 4.75 to 7 N•m of torque for the POLARIS-CA1/M and POLARIS-CA25/M. For best results, use the maximum recommended torques from each range. These torque values can be dialed in using a torque driver.
The flat, non-bridging (see drawing below) top and bottom allow the clamping arm to be used on either side depending on the needs of the application. This allows optical components to be placed in near contact to one another while minimizing the footprint, as shown in the image to the bottom right. A relief cut is included around the top and bottom slot; this protects the ±0.001" (±0.02 mm) flat surface that contacts the optical table from any marring due to the screw and washer. Minimizing damage to this surface of the fork allows for more stable mounting of components using the clamping arm.
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Laser Platform Deformation
Purpose: This testing was performed to determine the extent to which an industry-standard clamping fork deforms or permanently damages a stainless steel rigid platform and whether or not the POLARIS-CA1(/M) and POLARIS-CA25/M improves upon or prevents this damage. These measurements show that the POLARIS-CA1(/M) and POLARIS-CA25/M significantly reduce temporary deformation to the surface and that no permanent damage was measured during our extensive tests.
Procedure: An industry-standard clamping fork was mounted in close proximity to another optical element that was used for aligning a beam onto a position detector. As the clamping fork was mounted to the platform at various torque values (blue data sets in Figure 1 and Figure 2), the yaw and pitch deviation of the beam was measured at the detector. At 75 in-lbs of torque the fork was left attached to the platform for 16 hours. After the 16 hour period, the fork was released from the table and the final beam deviation was recorded (red data sets in Figure 1 and Figure 2). This procedure was repeated for the POLARIS-CA1 Clamping Arm. Each test was performed at different regions of the platform. If the final deviation is anything but zero, then the surface has been permanently deformed.
Results: As can be seen in the plots below and to the right, the industry-standard clamping fork created a yaw and pitch deviation of 131 µrad and 702 µrad, respectively, at 75 in-lbs, while the POLARIS-CA1 Clamping Arm created a yaw and pitch deviation of 12.2 µrad and 61 µrad, respectively, at 75 in-lbs. The POLARIS-CA1 also returned the beam to its initial position when released after a 16 hour hold. The industry-standard clamping fork did not return the beam to its original position; the beam stayed at a yaw and pitch deviation of 176 µrad and 321 µrad, respectively. The simulaton results shown in Figures 3 and 4 show the amount of deformation created by an industry-standard clamping fork compared to the POLARIS-CA1 clamping arm.
Conclusion: The POLARIS-CA1 Clamping Arm caused no permanent damage to the optical mounting surface and it significantly minimized the deformation to the platform surface when it was in use (see Figures 3 and 4). The industry-standard clamping fork was shown to permanently damage the laser platform after use, and to create severe deformation to the surface while in use. As a result, the Polaris clamping arm is ideal for use in systems requiring long term stability and consistent, precision alignments.
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Note that the distortion caused by the Polaris clamping arm at 75 in-lb is comparable to the distortion caused by the industry-standard clamping fork at 10 in-lb.
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In comparison, the POLARIS-CA1 causes minimal deformations around the fork. Note that the scale on this second plot has been magnified by 10X in order to make these minimal deformations visible.
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The industry-standard clamping fork causes large deformations over a significant area surrounding the fork.
Purpose: This testing was performed to determine the ideal amount of clamping torque necessary to (1) securely mount a Ø1" post within the flexure clamp bore of the POLARIS-CA1(/M) or POLARIS-CA25/M clamping arm, and (2) to secure the clamping arm into a laser system. This data was then compared to the closest competitor's industry-standard clamping fork design.
Procedure: The POLARIS-CA1(/M) was used to hold a standard Ø1" post. The clamping arm was first bolted to the stainless steel rigid platform and the flexure clamp was actuated, using the side-located 1/4"-20 (M6) cap screw, to specific torque values. At each specific torque value of the flexure clamp, the post had a rotational torque applied around its axis until it moved within the fork's bore. The torque value at the moment directly before this "movement point" is called the holding torque (see plots below). A similar test was then applied to find the ideal torque need to secure the clamping arm to the laser platform.
Results: As can be seen in Figures 5 - 10 below, the POLARIS-CA1(/M) flexure clamp had higher holding torque at a lower clamping torque when compared to the closest competitor's design. At 20 in-lbs of clamping torque, the POLARIS-CA1 provided 110 in-lb of holding torque, while at the same clamping torque, the competitor's fork only achieved a holding torque of 25 in-lbs. For reference, 110 in-lbs of torque is enough to damage the threading on a 1/4"-20 stainless steel cap screw. The corresponding torque for the POLARIS-CA1/M is a holding torque of 12.4 N•m at a clamping torque of 2.4 N•m. The scales for these measurements, as seen in Figures 6 and 8 below, are not a direct conversion due to an efficiency difference between 1/4"-20 and M6 screws. The efficiency of M6 screws is about 5% less than that of 1/4"-20 screws due to differences in diameter and pitch. Please note that the results for the POLARIS-CA25/M will be similar to the POLARIS-CA1/M because they both use M6 screws to secure the post.
The recommended torque for the mounting slot (Figure 8) varies depending upon the position where a 1/4"-20 (M6) cap screw is secured into the slot (i.e. close to the post, midway along the slot, or far from the post). The performance of the closest competitor's clamping fork (see Figure 9) is also dependent on the position where the 1/4"-20 (M6) cap screw is secured into the slot. However, the performance of the fork degrades sharply at the mid and far positions, as seen in Figure 9. At the far position, the best holding torque achieved is 32 in-lb with a clamping force of 70 in-lb.
Conclusion: The POLARIS-CA1(/M) was shown to be the ideal solution for securely mounting a component to a laser system platform. At only 20 in-lb and 40 in-lb of clamping torque for the flexure clamp and slot mounting respectively, the post mounted in a POLARIS-CA1 can withstand up to 110 in-lb of opposing torque (corresponding torques for the POLARIS-CA1/M are 2.4, 4.8, and 12.4 N•m, respectively). This performance is superior to the closest competitor's industry-standard clamping fork, which needs a clamping force of 70 in-lb in the close position to reach a similar value of 100 in-lb. Minimizing the amount of torque applied to the mounting surface prevents permanent damage.
Thorlabs offers several different general varieties of Polaris mounts, including kinematic side optic retention, SM-threaded, low optic distortion, piezo-actuated, and glue-in optic mounts, as well as a fixed monolithic mirror mount and fixed optic mounts. Click to expand the tables below and see our complete line of Polaris mounts, listed by optic bore size, and then arranged by optic retention method and adjuster type. We also offer a line of accessories that have been specifically designed for use with our Polaris mounts; these are listed in the table immediately below.
If your application requires a mirror mount design that is not available below, please contact Tech Support.