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Ø1/2" Translating Post Holders
Thorlabs' specialty post holders provide mounting solutions for unique applications that could benefit from post holders that offer fine adjustment. Our Translating Post Holders provide height adjustment with ranges of either 0.45" (11.43 mm) or 0.65" (16.51 mm). For each revolution of the actuator ring, the post translates 0.025" (0.635 mm).
These Ø1/2" post holders feature an extra wide square relief cut machined vertically along the length of the part, as shown in the drawing to the right. This channel provides a highly-stable two-line contact between the post and post holder. Other post holder designs that do not have a relief cut provide less holding power, which leads to a downward drift in the post's position with time.
A swivel base adapter, which provides access to multiple mounting holes, allows the translating post holders to be mounted to an optical table or breadboard with easy alignment. We also offer replacement spring-loaded, hex locking thumbscrews to secure the post in the holder.
Insights into Design
Scroll down to read about a feature included in our optical post holders to enhance stability.
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Post Holders: Rectangular Channel in the Inner Bore
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Figure 2: Top view. The three contact locations between the post and post holder, highlighted in red, prevent the post from translating or rotating around the X or Y axes. Friction resists the post's translation and rotation around the Z axis.
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Figure 1: A channel with sharp edges is machined into the inner bore of Thorlabs' post holders.
Figure 3: A broach, such as the one illustrated above, has a row of teeth, the next taller than the previous. With the teeth in contact with the material, a machine pulls the broach across the surface. Each tooth removes a small amount of material, and the depth of the channel created by the broach equals the overall difference in tooth height.
All of Thorlabs' post holders include a channel, with straight parallel edges, running the length of the inner bore (Figure 1). Tightening the setscrew pushes the post against the two edges of the channel (Figure 2). Since the edges of the channel are separated by a wide distance, approximately half the inner diameter of the post holder, the seating of the post against the channel's edges is stable and repeatable.
Contact with the two edges of the channel eliminates four of the post's six degrees of freedom, since the edges block the post from translating along or rotating around either the Y or Z axis. In addition, the friction between the side of the post and the edges of the channel resists the post's movement along and around the X axis, which are the post's two remaining degrees of freedom.
Without the channel in the inner bore, there would be a single line of contact between the post and post holder. The position of the post would not be stable, since the post would be free to rotate around the Z axis and shift along the Y axis.
Even if this instability resulted in submicron-scale unwanted shifts in each component's position in an optical setup, the cumulative effect could have a significant negative impact on system performance. In addition, more frequent realignment of the system could be required.
The smooth, straight edges of the channel are achieved using a machining process called broaching. A broach (Figure 3) resembles a saw whose teeth increase in height along its length.
As the broach is pulled along a surface, each tooth removes a small amount of material. The total depth of the channel cut by the broach equals to the overall difference in tooth height (H2 - H1).
Compared with other approaches for creating channels, broaching is preferred due to its ability to provide straight profiles while being compatible with high-volume production.
Date of Last Edit: Dec. 11, 2019
Our Translating Post Holders provide lockable, non-rotating height adjustment with convenient one-handed operation. An aluminum thumbscrew with a spring-loaded plunger provides holding force while the wide, square relief cut within the Ø1/2" post bore offers stable two-line contact. A knurled adjustment ring actuates the non-rotating height adjustment, which offers 0.025" (0.635 mm) of translational adjustment per revolution. Once the desired position is achieved, the entire mechanism can be locked using the lower thumbscrew and the locking hex socket on the upper thumbscrew. These thumbscrews should not be tightened beyond the maximum torque of 28 in·lbs (3.2 N·m). The post holders can be used with the Swivel Base Adapter featured below.
Our 360° swivel base adapter is compatible with the translating post holders (sold above) and minimizes the amount of time it takes to assemble an optical system. In addition, the swivel design is ideal for applications that require a large number of components to be packed into a small area. When our translating posts (featured directly above) are used with the UPHA adapter, the combination is nearly that of our very popular, non-translating UPH Series of Post Holders, which have an attached swivel base; however, unlike with the UPH series post holders, the adapter would prevent the translating post from touching the table. For ease of ordering, these base adapters are also available in packs of five.
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Exploded View of the TS25H Thumbscrew
The TS25H has 1/4"-20 threads while the TS6H/M has M6 x 1.0 threads for compatibility with our imperial and metric Ø1/2" post holders, respectively. The recommended maximum torque is 28 in·lbs (3.2 N·m). Please note that we do not recommend using an L wrench to tighten the thumbscrew, as this may break off the screw head.
If a thumbscrew without a spring-loaded tip is preferred, we recommend our vacuum-compatible thumbscrews. Alternatively, the tips can be removed from these thumbscrews by unthreading the setscrew in the front of the thumbscrew with a 1/16" (1.5 mm)
For ease of ordering, these thumbscrews are available individually or in packages of five.