Another 3D Printed Spectroheliograph

3D Printed Spectroheliograph.  This model is currently a working draft. Solar astronomy has inherent dangers, please be sure you understand these (see also below). Use is at own risk. More general information about this approach to solar astronomy can be found at the Sol'Ex project. 

The example below is printed in PETG with a PLA tuning knob on a Sovol SV06 printer. 

A telescope (with some energy rejection), tracking mount, digital camera, and computer with appropriate reconstruction software are also required. 

List and description of 3D printed parts: Printed using PETG at 20% infill. (numbers correspond to those on .stl file names and are labeled in the montage photos)

1. ThreadScaled_100p8_SHGAttachmentFlange2inchThreadM5_08notScaled
   1. Allows attachment of SHG to a 2-inch focuser without putting stress on the collimatable lens holder piece.
   2. The 2 inch threads are scaled to 100.8%. M5 threads are not scaled. 
   3. Attaches to 2-inch extension tube on input side (see below).
   4. Attaches to SHG main body on output side via compression from M5 screws
      1. The M5 threads are a bit too tight, so be careful not to over-tighten and crack the underlying SHG body. It may be useful to run an M5 tap through them.
2. Slit angle adjustment clamp, 1.25 inch (optional)
   1. Uses M3 insert and screw to attach to entrance slit housing (this is a 1.25 inch filter holder or extension). The M3 screw serves as adjustment lever and should go through the piece to also serve as a set screw on the slit holder. 
   2. M3 lever should emerge from the rectangular hole in the side of the SHG attachment flange.
3. 100p8percentM42 thread scaled lens attachment MaleT2 (print 2x, same piece used twice in the SHG)
   1. On the input side of the SHG, T2 male threads attach to eyepiece holder, which holds entrance slit
   2. On the output side of the SHG, T2 male threads attach to 14mm T2 spacer, which then attaches to the camera
   3. On both sides of the SHG, the M42 female threads hold the collimator or imaging lens and allows collimation
   4. 3x M3 screws then used to attach the lens assembly to the main SHG body
   5. 3x M3 threads are printed in to use as collimation screws
4. 40mmLensSpacer
   1. Spaces lenses out of the SHG main body so there is room for the full focal range of the lenses
   2. Accepts 3x M3 inserts (positions labeled on the top)
   3. On the outside, attaches to the lens holder pieces 
   4. On the inside, attaches to the SHG main body via M3 screws
   5. First attach to the SHG body, then attach the lens
   6. Can be resized for different lens lengths. 
5. SHGBottom_DualFlange: The main body of the SHG
   1. Accepts M3 inserts for lid attachment and 40mm lens spacer attachment (10 inserts)
   2. Accepts M5 inserts for attachment of the vixen dovetail
   3. There are some extra holes along the side for potential future use
   4. Attach both lens spacers, then lenses. The lens helical focusers are accessible through cutouts on top of the piece
   5. The angled flange where the lens attaches is a bit fragile. Print with wall thickness >1mm to reinforce these.
6. SHGTopWithROMstopsV1: The lid for the SHG
   1. Attaches to SHG bottom via 4x M3 screws
   2. Hole for the grating base top to come through
   3. Embossed wavelength guides for a 2400L/mm diffraction grating
   4. Overlaps the SHG body by 1.5mm to block stray light
   5. Range of motion (ROM) stops are defined by holes that accept M3 inserts
      1. Two sets of two M3 screws of two that restrict rotation of the tuning knob
      2. One buried M3 insert/screw that catches on the grating base top to stop rotation back to the 0-order reflection. This needs an M3 screw of appropriate length. Test before using SHG.
7. GratingBaseIncreasedClearance
   1. Rotating base to hold the grating. Compared to the original piece below, it has more clearance between the SHG body so rotation is easier. This comes at the cost of some stability. 
   2. M3 threads are printed in for attachment of the grating base top and grating clamp
8. GratingBaseTop_resized
   1. Top of the rotating grating holder
   2. Attaches via M3 screws into grating base
   3. Has a cutout to engage the M3 screw from the buried ROM stop in the lid
9. GratingClamp30mmM2V1
   1. Clamp to hold the 30mm diffraction grating
   2. M2 screw used to tighten the clamp across the top
   3. 4x M2 screw threads printed in so the clamp can be collimated
      1. These threads are a bit tight
   4. Attaches to grating base with 2x M3 screws
10. CameraAdapter14mm_T2Female_M48Male
    1. Attaches to the lens attachment piece on the output side
    2. Attaches to camera for imaging with T2 female threads
    3. Provides appropriate spacing to achieve focus for ZWO camera
11. 150mmVixenDovetail
    1. Attaches to the side of the SHG with M5 screws
    2. Can be used as a standard vixen dovetail OR a spacer/riser so a long vixen dovetail will clear the part of the SHG that attaches to the telescope
    3. Holes are spaced at 2cm and a match for Askar Vixen-Style Universal Dovetail Plate - 300mm (11.8") Length # VDP300
12. WormKnobV2
    1. Knob to turn the diffraction grating. Worm gear teeth on top. Attaches to the grating base top via compression from M3 screws
       1. The hole in the knob is a bit big, so centering with the M3 screws is necessary
13. WormBracketV2
    1. Bracket to hold worm gear against the knob. Attaches to the SHG top using two of the existing M3 holes
    2. Mounting holes are oversized so the worm gear can be adjusted
    3. Use washers with M3 attachment screws to allow movement. 
14. WormGear
    1. Goes into the worm bracket and engates the teeth on top of the tuning knob.
    2. M3 threads in end to secure cap (optional)
    3. Oversized knob to increase gear reduction. 
15. WormGearEndCap
    1. Hex cap for the end of the worm gear to hold it in place. Optional hole for M3 screw to secure. 

List and description of non-3D printed parts: (numbers correspond to those labeled in the montage photos)

1. Energy rejection: 2 inch sub-aperture ERF (Optolong UV/IR on KG3 +/- Baader 35nm H-alpha) or – in theory – blue CCD dielectric filter
2. 2 inch telescope attachment: SVBONY SV109 Extension Tube 24-35mm Variable Lock Tube with M48 Thread (This extension set has a threaded ring that can be used inside the print to secure the piece. Other 2-inch extensions will work but will not be as robust.)
3. Entrance slit, Custom made 12mm x 9 micron on fused silica. Commercial offerings are available. The heat resistance of fused silica is desirable. 
   1. Preceded by UV/IR filter in some configurations as dust seal
   2. Threaded into 1.25 inch extension tube
   3. Slit position needs to be set such that the slit is ~35 mm from the adjacent lens flange, this will put it ~85mm from the base of the main SHG body. 
4. 1.25 inch eyepiece holder: Baader Ultrashort 1.25" / T-2 Clamp. Longer blue fireball versions can be used as well. In such a configuration, the slit is countersunk within the eyepiece holder to maintain the appropriate lens flange distance (see above)
5. Collimator lens: 150mm f4 Super Takumar (ebay)
6. Diffraction grating: Edmund Optics 55266 GRATING HOLO 2400GR VIS 30 X 30
7. Imaging lens: 150mm f4 Super Takumar (ebay)
8. Camera: ZWO ASI174MM (a camera with smaller pixels would be superior)
   1. Screws into 3D printed 14mm spacer (see photo)

Threaded inserts: Bonost 500Pcs Threaded Inserts Kit M2 M3 M4 M5 - Female Thread Heat Set Insert, Brass Knurled Thread Insert Nuts for Plastic Injection Molding, 3D Printing

IMPORTANT SAFETY INFORMATION: Solar astronomy has inherent dangers to equipment and vision. Efforts are made to reduce these dangers through things like redundant range of motion stops on the diffraction grating holder, use of energy rejection filters, and use of heat resistant slit material. Even so, it is easy to imagine situations of misuse or component failure that lead to potentially dangerous conditions. Use of these designs is at your own risk so please carefully consider the relevant safety implications. 

Some notes about printing:

Threads can be difficult to print at home and scaling the print may be necessary to account for the shrinkage of PETG after printing (100.4-100.8%). For this reason, lens attachment and 2-inch extension tube attachment pieces have versions with 100.8% scaled female thread. These versions are probably the easiest to start with. Alternatively, start by printing slightly scaled versions of the other lens attachment rings and then propagate that scale to other parts. 

Additionally, increasing wall thickness is a good idea on the main body. The screws that attach the 2-inch extension are easy to over-tighten and could crack the underlying piece. 

Range of motion stops are M3 bolts in the lid, including one buried beneath the knob that catches on the groove in the grating holder top (5 total, each requires an M3 insert). This helps prevent accidental moving of the zero order reflection of the slit/sun image over a camera sensor or other viewing object at the output. 

Fusion360 files and a thread XML are in the zip archive. Thread info at this link.

9/23/23 Edit: Added short camera adapter

9/26/23: Added variable spacer rings for camera attachment

9/28/23: Added 150mm Vixen dovetail with holes for M5 bolts

10/21/23: Added different knob .stl

10/28/23: Added .step files due to some problems with wall thickness in .stl files

12/20/23: Added worm gears for diffraction grating angle adjustment

12/22/23: Apdated description, added photos with labeled parts

8/2/2024: Added parts for stepper motor-based wavelength tuning (improved precision vs worm gear). Used with a Nema 17 motor with 1:27 planetary gear reduction and ZK-SMC02 stepper motor controller.  Also requires a NEMA 17 bracket to attach motor to 3D printed parts (see photos). Additional 1:3 reduction with gears (60 teeth in new dial and 20 on stepper motor). 280mm 2GT belt is the approprite length.