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30 mm Cage System Rotation Mounts for Ø1" or Ø25.0 mm Optics
2° Dial Graduations
Our 30 mm cage system rotation mounts provide 360° of continuous rotation with a locking screw to fix the position of the mount once the optic has been aligned. The smooth adjustment mechanism allows for precise positioning of a variety of optics. All of the CRM1 series rotation mounts are compatible with Thorlabs' 30 mm cage system and the CRM1(/M), CRM1P(/M), and CRM1L(/M) rotation mounts can also be mounted on a TR series post.
These rotation mounts are designed to accept Ø1" (Ø25.4 mm) optics. They are also mechanically compatible with Ø25.0 mm optics, but we only recommend this for applications in which the centration of the optics is not critical. The CRM1(/M) and CRM1P(/M) have an SM1 (1.035"-40) internally threaded central hole, which are then retained with an SM1RR retaining ring. Alternatively, the CRM1L(/M) has an double-bored central hole where the optic is retained using a setscrew.
Thorlabs also offers prism mounts that are compatible with the CRM1 rotation mounts. The K6A1(/M) is a compact platform that comes with a clamping arm and mounting screws, thus allowing the user to easily mount prisms to the rotation mount. The SM1PM10 and SM1PM15 are designed to mount our polarizing prisms and feature an external SM1 threading. Please see below for more details.
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Figure 1: An example of how to read a vernier scale. The red arrow indicates what is known as the pointer. Since the tick mark labeled 10 on the vernier scale aligns with one of the tick marks on the main scale, this vernier scale is reading 75.60 (in whatever units the tool measures).
Reading a Vernier Scale
Vernier scales are typically used to add precision to standard, evenly divided scales (such as the scale on Thorlabs’ rotation mounts). A vernier scale has found common use in many precision measurement tools, the most common being calipers and micrometers. The direct vernier scale uses two scales side-by-side: the main scale and the vernier scale. The vernier scale has a slightly smaller spacing between its tick marks (10% smaller than the main). Hence, the lines on the main scale will not line up with all the lines on the vernier scale. Only one line from the vernier scale will match well with one line of the main scale, and that is the trick to reading a vernier scale.
Figures 1 through 3 show a vernier scale system for three different situations. In each case, the scale on the left is the main scale, while the small scale on the right is the vernier scale. When reading a vernier scale, the main scale is used for the gross number, and the vernier scale gives the precision value. In this manner, a standard ruler or micrometer can become a precision tool.
The 0 on the vernier scale is the “pointer” (marked by a red arrow in Figs. 1 – 3) and will indicate the main scale reading. In Figure 1 we see the pointer is lined up directly with the 75.6 line. Notice that the only other vernier scale tick mark that lines up well with the main scale is 10. Since the vernier 0 lines up with the main scale’s 75.6, the reading from Figure 1 is 75.60 (in whatever units the tool measures in).
That is essentially all there is to reading a vernier scale. It's a very straightforward way of increasing the precision of a measurement tool. To expound, let’s look at Figure 2. Here we see that the pointer is no longer aligned with a scale line, instead it is slightly above 75.6, but below 75.7; thus the gross measurement is 75.6. The first vernier line that coincides with a main scale line is the 5, shown with a blue arrow. The vernier scale gives the final digit of precision; since the 5 is aligned to the main scale, the precision measurement for Figure 2 is 75.65.
Since the vernier scale is 10% smaller than the main scale, moving 1/10 of the main scale will align the next vernier marking. This asks the obvious question: what if the measurement is within the 1/10 precision of the vernier scale? Figure 3 shows just this. Again, the pointer line is in between 75.6 and 75.7, yielding the gross measurement of 75.6. If we look closely, we see that the vernier 7 (marked with a blue arrow) is very closely aligned to the main scale, giving a precision measurement of 75.67. However, the vernier 7 is very slightly above the main scale mark, and we can see that the vernier 8 (directly above 7) is slightly below its corresponding main scale mark. Hence, the scale on Figure 3 could be read as 75.673 ± 0.002. A reading error of about 0.002 would be appropriate for this tool.
As we've seen here, vernier sclaes add precision to a standard scale measurement. While it takes a bit of getting used to, with a little practice, reading these scales is fairly straightforward. All vernier scales, direct or retrograde, are read in the same fashion.
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Figure 2: An Example of a vernier scale. The red arrow indicates the pointer and the blue arrow indicates the vernier line that matches the main scale. This scale reads 75.65.
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Figure 3: An Example of a vernier scale. The red arrow indicates the pointer and the blue arrow indicates the vernier line that matches the main scale. This scale reads 75.67, but can be accurately read as 75.673 ± 0.002.
Cage System Overview
The Cage Assembly System provides a convenient way to construct large optomechanical systems with an established line of precision-machined building blocks designed for high flexibility and accurate alignment.
16 mm, 30 mm, and 60 mm Cage System Standards
Thorlabs offers three standards defined by the center-to-center spacing of the cage assembly rods (see image below). The 16 mm cage, 30 mm cage, and 60 mm cage standards are designed to accomodate Ø1/2", Ø1", and Ø2" optics, respectively. Specialized cage plates that allow smaller optics to be directly inserted into our larger cage systems are also available. All locking setscrews used in these cage plates are standard 4-40 setscrews, which use a 0.05" hex key.
The flexibility of our Cage Assembly System stems from well-defined mounting and thread standards designed to directly interface with a wide range of specialized products. The three most prevalent thread standards are our SM05 Series (0.535"-40 thread), SM1 Series (1.035"-40 thread), and SM2 Series (2.035"-40 thread), all of which were defined to house the industry's most common optic sizes. Essential building blocks, such as our popular lens tubes, directly interface to these standards.
An example of the standard cage plate measurements determining cage system compatibility.
The CRM1(/M) and CRM1L(/M) have a smooth rotation mechanism that allows for precise positioning of the rotation carriage and the mounts are compatible with the 30 mm cage system.
The CRM1(/M) is designed to mount Ø1" (Ø25.4 mm) optics up to 0.37" (9.4 mm) thick in an SM1-threaded rotation carriage. The optic is secured using the included SM1RR retaining ring (the SPW602 spanner wrench is ideal for tightening this retaining ring). For thicker optics, any of our SM1 series of lens tubes can be threaded into the carriage or the CRM1L can be used instead. The CRM1L(/M) is designed to mount Ø1" (Ø25.4 mm) optics with a minimum thickness of 0.31" (7.9 mm), but unlike the CRM1, the optic is retained in a double-bored rotation carriage using a setscrew.
These mounts are also mechanically compatible with Ø25.0 mm optics, but we only recommend this for applications in which the centration of the optics is not critical.
This animation shows the manual rotation and micrometer engagement of the CRM1P.
The CRM1P(/M) is designed to mount Ø1" (Ø25.4 mm) optics up to 9.4 mm thick in an SM1 threaded rotation carriage. The optic is secured using the included SM1RR retaining ring (the SPW602 spanner wrench is ideal for tightening this retaining ring). For thicker optics, any of our SM1 series of lens tubes can be threaded into the carriage. The smooth rotation mechanism on the CRM1P(/M) can be manually rotated to any position. When the rotation carriage is locked, the high-precision, backlash-free micrometer can then be used to fine tune the position of the rotation carriage over a range ±7°. The animation to the right illustrates how the CRM1P(/M) is used. The Vernier scale provides a resolution of 5 arcmin between consecutive marks. As the mount is rotated across the entire Vernier scale, there is a cumulative error of up to ±12.28 arcmin. The CRM1P(/M) is compatible with the 30 mm cage system and the 8-32 (M4) tapped mounting hole allows the rotation mount to be secured on a TR series post.
This mount is also mechanically compatible with Ø25.0 mm optics, but we only recommend this for applications in which the centration of the optics is not critical.
The K6A1(/M) is a 0.5" x 1.44" platform designed to be mounted on the rotation ring on the CRM1 series (all versions) of 30 mm cage compatible rotation mounts featured above and the K6X six-axis kinematic mount. The K6A1 comes with a PM3 Small Clamping Arm (K6A1/M comes with PM3/M), hex key, and mounting screws. The K6A1 and K6A1/M have 6-32 and M4 x 0.7 tapped holes, respectively, on the mounting platform to secure the supplied clamping arm.
While using the K6A1(/M), the rotation mount needs to be the terminal element on the cage rods because the cage system is not large enough to allow for the rotation of the platform. If the rotation mount needs to be an interior cage component, consider building a 60 mm cage system frame around the rotation mount using two LCP02 cage plate adapters as shown in the image to the right. This will allow the platform to be rotated freely without interference from the cage rods while preserving the optical axis of the 30 mm cage system.
The SM1PM10 and SM1PM15 prism mounts are designed to accommodate the popular Glan-Taylor and Glan-Laser Polarizing Calcite Prisms. Their SM1 threading makes them compatible with the CRM1(/M) and CRM1P(/M) rotation mounts. The rotating cover allows the user to block the two side ports of the calcite prism when they are not required. To load a prims, unthread the prism cover, insert the prism, and tighten the setscrew. When mounting the SPM1PM10 or SPM1PM15 onto a rotation mount, first thread a retaining ring into the rotation mount to a depth of 3/16" (4.8 mm) and then thread on and tighten the prism mount. This will leave room so that the prism cover can rotate freely.