PLAb Lens Holder (V2 Flexure Lock)

A component of the growing PLAb Collection of 3D printable optomechanics, this the second generation lens holder design. Or, more broadly a cylindrical things holder. The lens holder features an optional alignment slot that locks directly into the alignment tab on the system M6 or 1/4-20 PLAb posts. Customizable for any angle from 0 to 45 degrees, this allows the angle of the lens relative to the front of the post to be fixed independently from the tightness of the M6 or 1/4-20 post mounting screw.

This is Version 2, the original version used inclined set screws that required small soft caps to prevent damaging the glass. This version uses a small flexure panel between the set screw and the lens to protect that expensive glass and better spread the clamping force. While Version 2 can secure thin objects like Fresnel lenses, Version 1 may work better for that particular application.

Some standard sizes of lens holders are included here for quick use and download using M3 screws. To customize the exact size, mounting nut type, or alignment angle you need visit the OnShape Configurator.

If you download your parts from OnShape, please download a version from here and drop a like here on Printables. It really does help with getting PLAb in-front of more eyes that might need it.

Recommended Print Settings

The system is designed to be as simple to print as possible. No supports, no special materials, no slicer tricks. I started developing the system on a Prusa Mk3s and am now using a Snapmaker U1 and Prusa XL. General printing guidelines are as follows:

• Print in PLA for maximum rigidity and ease of printing. 

• Use PETG, PCTG, or Carbon Fiber reinforced filaments if you need higher temperature stability (staring at your combustion researchers).

• Use three perimeters with five top and bottom layers for best results.

• Designed for a 0.2 mm layer height, but there is not reason you couldn't got thicker or thinner. No particular reason to go smaller as details are designed for 0.2 sizing on a 0.4 mm nozzle.

• Infill is not critical here. I usually use 10% Adaptive Cubic. If you find yourself having warping problems, a non-linear infill type like Gyroid may be helpful.

• No support is needed.

  • Your slicer might warn you about unsupported overhangs, you can safely ignore this as all needed support on the flexures is part of the geometry.

• Orient lens holder parts with the retaining lip flat on the bed, as shown below. 

Part Numbering and Configuration

Configuration Parameters

• Lens Diameter (mm): Diameter of the lens or other cylindrical object being mounted.

  • Note a 0.1 mm diameter tolerance is added automatically. Setting the exact diameter of the object you plan to mount is advised.

• Holder Thickness (mm): The depth or thickness of the holder mount. 

  • Minimum value of 16 mm. Thicken as needed for large objects. 

  • Locking screw depth will remain 8 mm from the top edge for all depths but the flexure tabs will expand to the full depth.

• Locking Thread Type: Choose between M3 or 8-32 locking nut type.

• Post Thread Type: Choice between M6 or 1/4-20 and M4 or 8-32 sized monting hole for connecting to posts.

• Include Alignment Slot: Optional Alignment Slot option for integration with PLAb posts or existing standard posts.

• Alignment Slot Angle (degrees): Angle relative to the front of the post alignment slot

  • Any angle 0 to 45 degrees

Part Numbering

• Lens-D<diameter in mm>-<alignment type>-<alignment angle in deg>-<thickness in mm>-P<post size>-L<locking nut type>

  • E.g. Lens-D100-A0-T16-PM6-LM3 is a 16 mm thick, 100 mm diameter lens holder with a 0 degree alignment slot (A0), M6 sized post counterbore, and M3 locking nuts.

  • E.g. Lens-D25.4-T20-U-PM4-L8 is a 20 mm thick, 1 inch diameter lens holder with no alignment slot, M4 sized post counterbore, and 8-32 locking nuts.

Assembly and Use Instructions

1. Insert nuts into the appropriate nut pockets. The fit with flat edges of the hex perpendicular to the face of the lens. If the tolerance is tight, apply a little bit of force to seat the nuts in place.

2. Any standard sized flat nut should fit. I sized based on parts ordered from Amazon.co.jp and McMaster.com dimensions.

3. Use a M6 or 1/4-20 screw to attach the lens holder to the appropriate length post before inserting the lens.

4. Thread in M3x12mm or longer screws into each of the three locking nuts from the outer edge.

5. Insert your lens or cylindrical object till flush against the bottom ledge and carefully tighten the M3 locking screws in a circle to apply even force across the edge.

6. Tighten just enough to securely hold your lens, over tightening may apply too much force on the edge of the lens and crack it.

License and Support

If you find the system useful, please share it with your colleagues. If it makes your lab easier or cheaper to setup, perhaps Buy Me a Coffee so I can continue to develop the system and keep it free and openly available under the Open Community License (OCL) with the General Attribution (GAtt) Plugin. 

Updates

2.1 Increased Flexure Robustness

Increased the thickness and added a central rib to the flexures to improve the robustness. This improves performance when lens diameter is more than 1mm less than the diameter of the holder or if very thin.

Also added option for M4/8-32 post mounting screw holes in addition to the default M6/ 1/4-20 versions.

2.1.1 Locking Screw Teardrop Orientation Fixed

An OnShape update tweaked the orientation of the locking screw hole teardrop shapes. This is now fixed.