Non-Bridging Clamping Arms

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Click for POLARIS-CA1/M Holding Torque Results*
Click for POLARIS-CA5(/M) Holding Torque Results
The clamping fork design has undergone extensive testing to ensure high-quality performance. See the Test 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 1/4"-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 arm can be mounted with either flat surface in contact with the table, allowing for compact setups.

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Every clamping arm has a side-located 1/4"-20 (M6) cap screw for actuating the clamping bore.

Non-Bridging Design: Industry Standard Clamping
Fork vs. Thorlabs' Non-Bridging Clamping Arm

Industry standard clamping forks are designed with a bridge, as shown in Figure 1, for clamping to pedestal-style posts or post holders. This design will slightly damage the laser platform during each use by pulling up the part of the platform located under the bridge. The Thorlabs clamping arm, as shown in Figure 2, is designed with a flat top and bottom to eliminate this problem.

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Figure 1: A Bridge is Created When an Industry Standard
Clamping Fork is Used with a Ø1" Pedestal Post or Ø1/2" Post Holder

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Figure 2: The Thorlabs Clamping Arm Eliminates the Bridge Created by an Industry Standard Clamping Fork

Features

• 3-Point Contact Bore with Flexure Clamping Mechanism
  • Versions for Ø1/2", Ø1" or Ø25 mm Posts for Polaris Mounts,
    and Ø1" Monolithic Polaris Mount (See Table Below)
  • Allows Posts to be Rotated 360°
  • Ø1" and Ø25 mm Clamps Support Height Adjustments Up to 0.25"
• Clearance Slot for 1/4"-20 (M6) Cap Screw
• Heat-Treated, Stress-Relieved Stainless Steel Provides Large Clamping Force
• Design Supports Left- and Right-Handed Orientations (See Image to the Right)
• High Stability Ideal for Use with Our Kinematic Polaris Mirror Mounts
• Vacuum Compatible to 10^-9 Torr at 25 °C with Proper Bake Out
• ±0.001" (±0.02 mm) Surface Flatness

The Non-Bridging Clamping Arms are the ideal solution for stably mounting our Ø1/2", Ø1" or Ø25 mm Posts for Polaris Mounts, and Ø1" Monolithic Polaris Mount. 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 (see the graph to the right).

The flat, non-bridging top and bottom surfaces of each clamping arm allow it to be used with either side in contact with an optical table or other mounting surface. This feature allows the clamp to be positioned in left- or right-handed orientations and optical components to be placed in near contact to one another while minimizing the footprint (see the image to the upper right). On each side of Ø1" and Ø25 mm clamping arms, a relief cut around the slot protects the ±0.001" (±0.02 mm) flat surface from any marring due to the screw and washer, allowing for more stable mounting; to protect the slot on Ø1/2" clamping arms, keep mounting screw torque below 40 in-lb (4.5 N•m).

While the Ø1/2" clamping arm offers the most compact footprint, providing flexibility when used in applications such as tight laser cavity setups, the Ø1" and Ø25 mm clamping arms are also offered with slot lengths of 0.75" (19.1 mm) or 1.30" (33.0 mm) for similar considerations with larger posts; see the table below for details. Note that arms with a Ø1" (25.4 mm) bore are not compatible with Ø25 mm posts; the bore diameter is too large and will not contact the post when clamping.

Clamping Actuation
The flexure clamp, shown in the photo to the right, is actuated using a side-located 1/4"-20 (M6 x 1.0) cap screw and allows a post to be rotated 360° about its center. As the flexure clamp and mounting slot are secured with separate screws, the position of the fork and the rotational alignment of the post can be adjusted independently. While best performance is achieved with full post engagement, Ø1" or Ø25 mm posts have a 0.60" (15.2 mm) deep mounting bore that supports up to 6 mm of post height adjustment, while clamps for Ø1/2" posts allow up to 1 mm of height adjustment.

The non-bridging clamping arm design has undergone extensive testing to ensure high-quality performance; see the graph to the upper right and the Test Data tab. For optimal performance, we recommend tightening the flexure clamping screw of an imperial clamping arm for Ø1" posts with 15 to 25 in-lb of torque, metric clamping arms for Ø1" or Ø25 mm posts with 1.75 to 3 N•m of torque, and for clamping arms for Ø1/2" posts use 30 to 40 in-lb (4.0 to 4.5 N•m) of torque. When mounting to a table or platform, we recommend using 40 to 65 in-lb of torque for an imperial Ø1" clamping arm, 4.75 to 7 N•m of torque for a metric Ø1" or Ø25 mm clamping arm, and for clamping arms for Ø1/2" posts use 30 to 40 in-lb (4.0 to 4.5 N•m) of torque. Please note that the values for imperial and metric clamps for Ø1" and Ø25 mm clamping arms 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 best results, use the maximum recommended torques from each range. These torque values can be dialed in using a torque driver.

Cleanroom and Vacuum Compatibility
Our non-bridging clamping arms are designed to be compatible with cleanroom and vacuum applications. They are chemically cleaned using the Carpenter AAA passivation method to remove sulfur, iron, and contaminants from the surface before being double vacuum bagged. They are compatible directly out of the packaging with vacuum environments down to 10^-5 Torr. With additional cleaning and processing, they can be used at even lower pressures, only limited by the outgassing rate of the stainless steel. The material properties of the stainless steel and the cleaning methods completed by the end user should be used to determine the appropriateness of these products and materials in a specific vacuum system.

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All non-bridging clamping arms are packaged inside a double vacuum bag.

Cleanroom-Compatible Packaging
Each clamping arm is packaged within two vacuum bag layers after assembly in a clean environment, as seen in the image to the right. The vacuum-tight fit minimizes rubbing against the bag, preventing the introduction of bag material shavings that would contaminate the clean component. In the vacuum-sealing process, moisture-containing air is drawn out of the packaging. This eliminates unwanted surface reactions without the need for desiccant materials.

The vacuum bags protect the clamping arm from contamination by air or dust during transport and storage, and the double-vacuum bag configuration allows for a straightforward and effective cleanroom entry procedure. The outer bag can be removed outside of the cleanroom, allowing the contaminant-free inner bag to be placed into a clean container and transferred into the cleanroom while retaining the benefits of vacuum-bag packaging. Inside the cleanroom, the inner bag can be removed when the clamping arm is ready for use.

Non-Bridging Clamping Arm Testing

Various tests were conducted to show the performance of our Non-Bridging Clamping Arms. Many of the results were then compared to other industry-standard products that were put to the same test to show the high-quality performance of the clamping arms when used with our Ø1" Posts for Polaris Mounts. Similar performance can be expected across the family of Non-Bridging Clamping Arms. Click the links below for more information about a specific test.

• Laser Platform Deformation
  • Determine the extent to which an industry-standard clamping fork deforms or permanently damages a stainless steel rigid platform, and whether or not the non-bridging clamping arm improves upon or prevents this damage.
• Post and Platform Mounting Torque
  • Determine the ideal amount of clamping torque necessary to (1) securely mount a post within the flexure clamp bore of a non-bridging clamping arm and (2) to secure the non-bridging clamping arm into a laser system. This data was then compared to the closest competitor's industry-standard clamping fork design.
• Post Breaking Torque
  • Determine the amount of torque needed to break a Ø1" PLS-P150 post loose from a non-bridging clamping arm that was holding it.
• Post Deflection
  • Determine how much a post will temporarily and permanently deflect when it is mounted within a non-bridging clamping arm and a force is applied.

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Figure 1: Industry-Standard Clamping Fork Beam Drift

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 non-bridging clamping arm improves upon or prevents this damage. The POLARIS-CA1 clamping arm was used for this test; similar results can be expected for all other non-bridging clamping arms. These measurements show that the non-bridging clamping arm significantly reduces 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-lb 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. A final deviation of anything but zero indicated that the surface had 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-lb, while the POLARIS-CA1 clamping arm created a yaw and pitch deviation of 12.2 µrad and 61 µrad, respectively, at 75 in-lb. 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 simulation 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 non-bridging clamping arm is ideal for use in systems requiring long term stability and consistent, precision alignments.

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Figure 2: Note that the distortion caused by the non-bridging 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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Figure 4: In comparison, the POLARIS-CA1 clamping arm 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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Figure 3: The industry-standard clamping fork causes large deformations over a significant area surrounding the fork.

Mounting Torque

Purpose: This testing was performed to determine the ideal amount of clamping torque necessary to (1) securely mount a Ø1/2" or Ø1" post within the flexure clamp bore of a compatible non-bridging clamping arm and (2) to secure the non-bridging 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) arm was used to hold a standard Ø1" post and the POLARIS-CA5(/M) arm was used to hold a PLS-Hx series Ø1/2" post. The clamping arm was first bolted to a stainless steel rigid platform, and the 1/4"-20 (M6 x 1.0) screw that controls the flexure clamp was actuated to specific torque values. At each torque value, the post had a rotational torque applied around its axis until it moved within the non-bridging clamping arm's bore. The torque value at the moment directly before this "movement point" is called the holding torque (see plots below). Using similar methods, a mounting slot test was performed to find the ideal torque needed to secure the clamping arm to the laser platform. The mounting slot test was repeated for the POLARIS-SCA1 to determine if the slot size affects the torque measurements.

Results Summary: For optimal performance, the flexure clamping screw of an imperial Ø1" non-bridging clamping arm should be tightened with 15 to 25 in-lb of torque and the flexure clamping screw of a metric Ø1" or Ø25 mm clamping arm with 1.75 to 3 N•m of torque. When mounting to a table or platform, we recommend using 40 to 65 in-lb of torque for an imperial Ø1" non-bridging clamping arm and 4.75 to 7 N•m of torque for a metric Ø1" or Ø25 mm non-bridging clamping arm. The POLARIS-CA5(/M) clamping arm has identical torque parameters of 30 to 40 in-lb (4.0 to 4.5 N•m). Please see below for the detailed results.

Conclusion: The non-bridging clamping arms were 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 mounting slot respectively, a post mounted in an imperial Ø1" non-bridging clamping arm can withstand up to 110 in-lb of opposing torque (corresponding torques for a metric Ø1" or Ø25 mm non-bridging clamping arm 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 torque of 70 in-lb in the closed position to reach a similar value of 100 in-lb. For POLARIS-CA5(/M) clamp test results, please refer to the test results and plot links below. As demonstrated in the Laser Platform Deformation test above, minimizing the amount of torque applied to the mounting surface prevents permanent damage.

Test 1 Results: Flexure Clamp Holding Torque

As can be seen in Figure 6 below, at 20 in-lb of clamping torque, the POLARIS-CA1 provided 110 in-lb of holding torque. For reference, 110 in-lb 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 torque values for imperial and metric clamps are not a direct conversion due to an efficiency difference between 1/4"-20 and M6 x 1.0 screws. The efficiency of M6 screws is about 5% less than that of 1/4"-20 screws due to differences in diameter and pitch. All imperial Ø1" non-bridging clamping arms will perform similarly to the POLARIS-CA1, while all metric Ø1" or Ø25 mm non-bridging clamping arms will perform similarly to the POLARIS-CA1/M. The POLARIS-CA5(/M) clamping arm needs 40 in-lb (4.5 N•m) to provide 50 in-lb (5.7 N•m) of holding torque. Test results for the POLARIS-CA1/M and POLARIS-CA5(/M) clamps are also available below Figure 6.

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Click for POLARIS-CA1/M Flexure Clamp Holding Torque Results
Click for POLARIS-CA5(/M) Flexure Clamp Holding Torque Results
Figure 6: Results from Test 1. The shaded region indicates the recommended flexure clamp torque. All imperial Ø1" non-bridging clamping arms will perform similarly to the POLARIS-CA1, while all metric Ø1" or Ø25 mm non-bridging clamping arms will perform similarly to the POLARIS-CA1/M.

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Figure 5: Holding torque is measured at the moment directly before the "movement point" of the post being torqued.

Test 2 Results: Mounting Slot Holding Torque

The recommended torque for the mounting slot varies depending on the position of the 1/4"-20 (M6 x 1.0) cap screw within the slot (i.e. close to the post, midway along the slot, or far from the post). Figure 8 compares the slot holding torque of the POLARIS-SCA1 and POLARIS-CA1, and shows that the slot size does not affect the torque measurements. The recommended slot holding torque is 40 - 65 in-lb for imperial Ø1" non-bridging clamping arms, while for metric Ø1" or Ø25 mm non-bridging clamping arms the slot holding torque is 4.75 - 7 N•m. Similar to the Test 1 results, the torque values for imperial and metric clamps 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. The POLARIS-CA5(/M) clamping arm needs 40 in-lb (4.5 N•m) of clamping torque to provide almost 40 in-lb (4.5 N•m) of holding torque at the close position. Test results for the POLARIS-CA1/M and POLARIS-CA5(/M) clamps are also available below Figure 8.

The performance of the closest competitor's clamping fork also depends on the position of the 1/4"-20 (M6 x 1.0) cap screw in the slot. However, as shown in Figure 9, the performance of the fork degrades sharply at the mid and far positions. At the far position, the best holding torque achieved is 32 in-lb with a clamping torque of 70 in-lb. As shown in Figure 10, at 40 in-lb 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 38 in-lb.

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Click for POLARIS-CA1/M Slot Holding Torque Results
Click for POLARIS-CA5(/M) Slot Holding Torque Results
Figure 8: Results from Test 2. The shaded region indicates the recommended torque to secure the non-bridging clamping arm to the optical table. This comparison between the POLARIS-SCA1 and POLARIS-CA1 shows that the slot size does not affect the slot holding torque. All imperial Ø1" non-bridging clamping arms will perform similarly to the POLARIS-CA1, while all metric Ø1" or Ø25 mm non-bridging clamping arms will perform similarly to the POLARIS-CA1/M.

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Figure 7: Holding torque is measured at the moment directly before the "movement point" of the non-bridging clamping arm being torqued.

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Figure 9: Results from Test 2 on a competitor's Ø1" clamping fork. See Figure 8 for results from POLARIS-CA1(/M).

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Figure 10: Comparison of Test 2 results for POLARIS-CA1 and a competitor's Ø1" clamping fork, both at the middle position in the mounting slot.

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Figure 12: Breaking force recorded with the post mounted at 14 different heights above the platform. This shows that upwards of 110 in-lb of torque is required to loosen the PLS-P150 post from the non-bridging clamping arm when the post is in contact with the work surface.

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Figure 11: Breaking torque is defined as the moment directly after the "movement point" of the post being torqued.

Breaking Torque

Purpose: This test was performed to determine the amount of torque needed to break a Ø1" PLS-P150 post loose from a non-bridging clamping arm. The POLARIS-CA1 clamping arm was used for this test; similar results can be expected for all other non-bridging clamping arms for Ø1" and Ø25 mm posts.

This test was repeated at various heights above the work surface.

Procedure: A PLS-P150 1.5" long, Ø1" post was secured with 25 in-lb of torque at various heights within a POLARIS-CA1 clamping arm, which was then secured to a custom laser platform. As shown in Figure 11, torque was then applied to the post axis until it reached its "movement point." This torque was recorded as the breaking torque.

Results: As can be seen in Figure 12, upwards of 110 in-lb (12.4 N•m) of torque is required to loosen the PLS-P150 post from the non-bridging clamping arm. When the post was raised off of the platform by 13 mm, a torque of about 40 in-lb (4.5 N•m) was still required to loosen the post. It is important to note here that the clamping arm is only 15.2 mm (0.60") thick.

Conclusion: The PLS-P150 post and non-bridging clamping arm create an extremely stable system that is resistant to large forces acting upon it, even when the post is raised off of the platform by 13 mm. This is ideal for any custom or OEM system that requires components to stay aligned when faced with vibrations caused by shipping and installation.

Post Deflection

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Figure 13: A force was applied to the PLS-P150 post 0.90" (22.9 mm) above the edge of the non-bridging clamping arm with the post mounted at nine different heights off of the mounting surface. At each mounting height, the post deflection was measured during and after the application of the force.

Purpose: This test was performed to determine the amount of temporary and permanent deflection of a Ø1" post for Polaris mirror mounts secured in a non-bridging clamping arm when a force is applied. The POLARIS-CA1 clamping arm was used for this test; similar results can be expected for all other clamping arms for Ø1" and Ø25 mm posts. For Ø1/2" clamping arms, we recommend a post-to-mounting-surface distance of 1 mm or less to prevent permanent deflection when a ≤45 N force is applied.

Procedure: A PLS-P150 1.5" long, Ø1" post was secured with 25 in-lb of torque at various heights within a POLARIS-CA1 clamping arm, which was then secured to a custom laser platform. A force was then applied to the center of the post, 0.90" (22.9 mm) above the top edge of the non-bridging clamping arm (see Figure 13 for details). This test was conducted with the post mounted at nine different heights off of the platform, ranging from 0 mm to 8 mm. The amount of deflection was measured while the force was being applied (Figure 14) and after the force was removed (Figure 15).

Results: Figure 14 shows that the PLS-P150 post will deflect by <0.01 mm as a force of ≤40 N is applied for any post height ≤8 mm, and by <0.17 mm as a force of ≤133 N is applied for any post height ≤8 mm. These values show the temporary deflection of the post while the force is being applied. For all of the post mounting heights tested (0 to 8 mm), an applied force ≤35 N caused a permanent deflection of the post smaller than 0.005 mm, measured after the force was removed. For the two lowest mounting heights, 0 and 2 mm, no permanent deflection was measured for applied forces of 45 N or less. At 133 N, the maximum force applied, permanent deflection for all tested mounting heights remained below 0.07 mm. For Ø1/2" non-bridging clamping arms, we recommend a post-to-mounting-surface distance of 1 mm or less to prevent permanent deflection when a ≤45 N force is applied.

Conclusion: Our Ø1" posts and POLARIS-CA1 clamping arm create an extremely stable system that is able to resist large forces acting upon it. This is ideal for any custom or OEM system that requires components to stay aligned when faced with vibrations caused by shipping and installation.

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Figure 15: Post deflection measured after the applied force was removed. The measurement was repeated with the bottom of the post positioned 0 to 8 mm above of the mounting surface (see the Procedure section for details). For Ø1" post-to-mounting-surface distances of 2 mm or less, no permanent deflection was measured if the force was ≤45 N. For Ø1/2" non-bridging clamping arms, we recommend a post-to-mounting-surface distance of 1 mm or less to prevent permanent deflection when a ≤45 N force is applied.

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Figure 14: Post deflection measured while a force was applied to the post. The measurement was repeated with the bottom of the post positioned 0 to 8 mm above of the mounting surface (see the Procedure section for details).