Polaris® Non-Bridging Clamping Arms

Click to Enlarge
Click for POLARIS-CA1/M Holding Torque Results*
The Polaris 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.

Click to Enlarge
The arm can be mounted with either flat surface in contact with the table, allowing for compact setups.

Click to Enlarge
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. Polaris 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 Polaris clamping arm, as shown in Figure 2, is designed with a flat top and bottom to eliminate this problem.

Click to Enlarge
Figure 1: A Bridge is Created When an Industry Standard Clamping Fork is Used with a Pedestal Post

Click to Enlarge
Figure 2: The Polaris Clamping Arm Eliminates the Bridge Created by an Industry Standard Clamping Fork

Features

• 3-Point Contact Bore with Flexure Clamping Mechanism
  • Versions for Ø1" or Ø25 mm Posts for Polaris Mounts and Ø1" Monolithic Polaris Mount (See Table Below)
  • 0.60" Bore Depth Supports Height Adjustments Up to 0.25" 
  • Allows Posts to be Rotated 360°
• 0.75" (19.1 mm) or 1.30" (33.0 mm) 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 Polaris^® Clamping Arms are the ideal solution for stably mounting our Ø1" or Ø25 mm Posts for Polaris Mounts or 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 the arm, 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.

The clamping arms are offered with slot lengths of 0.75" (19.1 mm) or 1.30" (33.0 mm), providing flexibility when used in applications such as tight laser cavity setups. Four of our clamping arms are designed to hold Ø1" posts, while the remaining two are designed to hold Ø25 mm posts; see the table below for details. Note the 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.

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, the 0.60" (15.2 mm) thick mounting bore supports up to 0.25" of post height adjustment.

The Polaris clamping arm design has undergone extensive testing to ensure high-quality performance; see the graph to the upper right. For optimal performance, we recommend tightening the flexure clamping screw of an imperial clamping arm with 15 to 25 in-lb of torque and the flexure clamping screw of a metric 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 clamping arm and 4.75 to 7 N•m of torque for a metric clamping arm. Please note that the 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 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.

Polaris^® Clamping Arm Testing

Various tests were conducted to show the performance of our Polaris 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 Polaris clamping arms when used with our Ø1" Posts for Polaris Mounts. 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 Polaris 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 Ø1" post within the flexure clamp bore of a Polaris 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.
• Post Breaking Torque
  • Determine the amount of torque needed to break a Ø1" PLS-P150 post loose from a Polaris clamping arm that was holding it.
• Post Deflection
  • Determine how much a Polaris post will temporarily and permanently deflect when it is mounted within a Polaris clamping arm and a force is applied.

Click to Enlarge
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 Polaris 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 Polaris clamping arms. These measurements show that the Polaris 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-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. 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-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.

Click for Details
Figure 2: 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.

Click to Enlarge
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.

Click to Enlarge
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" post within the flexure clamp bore of a Polaris 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 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 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 clamping arm should be tightened with 15 to 25 in-lb of torque and the flexure clamping screw of a metric 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 clamping arm and 4.75 to 7 N•m of torque for a metric clamping arm. Please see below for the detailed results.

Conclusion: The Polaris clamping arm 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 mounting slot respectively, a post mounted in an imperial clamping arm can withstand up to 110 in-lb of opposing torque (corresponding torques for a metric clamping arm is 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 close position to reach a similar value of 100 in-lb. 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-lbs of clamping torque, the POLARIS-CA1 provided 110 in-lb of holding torque. 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 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 Polaris clamping arms will perform similarly to the POLARIS-CA1, while all metric Polaris clamping arms will perform similarly to the POLARIS-CA1/M.

Click to Enlarge
Click for POLARIS-CA1/M Flexure Clamp Holding Torque Results
Figure 6: Results from Test 1. The blue shaded region indicates the recommended flexure clamp torque. All imperial Polaris clamping arms will perform similarly to the POLARIS-CA1, while all metric Polaris clamping arms will perform similarly to the POLARIS-CA1/M.

Click to Enlarge
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 clamping arms, while for metric 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 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 Firgure 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-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 38 in-lbs.

Click to Enlarge
Click for POLARIS-CA1/M Slot Holding Torque Results
Figure 8: Results from Test 2. The red shaded region indicates the recommended torque to secure the 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 Polaris clamping arms will perform similarly to the POLARIS-CA1, while all metric Polaris clamping arms will perform similarly to the POLARIS-CA1/M.

Click to Enlarge
Figure 7: Holding torque is measured at the moment directly before the "movement point" of the clamping arm being torqued.

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

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

Click to Enlarge
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 clamping arm when the post is in contact with the work surface. 

Click to Enlarge
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 Polaris clamping arm. The POLARIS-CA1 clamping arm was used for this test; similar results can be expected for all other Polaris clamping arms.

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 N•m of torque is required to loosen the PLS-P150 post from the clamping arm. When the post was raised off of the platform by 13 mm, a torque of about 40 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 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

Click to Enlarge
Figure 13: A force was applied to the PLS-P150 post 0.90" (22.9 mm) above the edge of the 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 Polaris 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 Polaris clamping arms.

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 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.

Conclusion: Our Ø1" posts and POLARIS-CA1 clamping arm create an extremly 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.

Click to Enlarge
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 post-to-mounting-surface distances of 2 mm or less, no permanent deflection was measured if the force was ≤45 N.

Click to Enlarge
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).