Public Lab Research note

This is an upgrade for spec. Try building it and report back how it goes.

Slit holder for Desktop Spectrometer

by warren | November 13, 2015 20:14 13 Nov 20:14 | #12408 | #12408

What I want to do

Drawing on input from @stoft (here) and @ygstcu, and ideas @mathew's posted in the community-additions github branch, I wanted to try for a fully-paper slit holder in which you can swap the slit for different sizes, and which has some side support so it doesn't wilt forward or backward. Advantages of this design are:

  • paper part is easy to manufacture and modify
  • sturdy with side support
  • swappable slits
  • isolates internal optics from external box, for stability



My attempt and results

I made this prototype (in lavender for ease of photographing, though the final will be black) which is pretty compact, open at the top, and is folded from a flat piece. You could also make in black sheet plastic, like matte plastic binder material.

Here's the design file so far: slit-holder.pdf

Here's how you assemble it:




Questions and next steps

This needs a few tweaks:

  • the "dip" at the top was cut with scissors after the fact -- need to add that to the design file
  • needs to be shorter and narrower; it's too tall with the wood base in place
  • it could have printed arrows indicating where to align the slit
  • it could have flaps above and to the side which flare out to make a better light seal

Why I'm interested

Looking ahead to the next version of the spectrometer, I'm trying to make things more stable while not more expensive.

Here are some of my sketches that went into this; as you can see, I'm also thinking about whether a baffle could be built into the design as well:


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one of the challenges of the slit holder is getting it out towards the edge of the spectrometer-- we need it very close to a cuvette to pick up fluorescence. this holder could definitely be mounted right up to the edge of the box without adding much thickness.

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OK, revisions:

  • thinner
  • shorter (but short enough?)
  • on a millimeter grid
  • curved tabs for easy insertion all around
  • side flaps designed to fold backwards for getting even closer to the edge of the box
  • no punch-out pieces (makes for easier waste management on Cameo cutter, and presumably on the die cut) -- all are flaps now
  • 1cm square on design files for scaling double-check
  • added 2 slit cards with easy-insert rounded bottom edge

I'm having some issues in Inkscape where the 1px stroke messes up the dimensions, even though it's on a 2mm grid. Will try for "hairline" or something, but it's a bummer.

I have to attempt a print and test.

slit-holder.pdf slit-holder.svg

Not sure if DXFs can be uploaded for some reason? Will double check this too.

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Here is a Silhouette Studio (for the Cameo or Curio) .studio3 file which I cleaned up, and a DXF which properly imported into the Cameo.



This version was better -- it's on the left in the images below. But there are still issues:

  • it's narrow enough to smootly/snugly fit in the box, but we had discussed actually having it free-standing to further structurally isolate the exterior box from the internals. Should I make it even smaller?
  • the slit insert windows aren't at the right height
  • the slit insert windows could be 1mm wider to be more snug
  • the bottom tongue and slot are misaligned by about 1mm -- the slot should be 1mm closer to the edge

Finally, the box top tabs are a bit odd with it -- they either go inside the slit holder side flaps, where we'd have to place it completely up against the end of the box (top image, below), or they'd have to go outside, where they get caught on the slide-through tongues (bottom image). We could also ask folks to trim the box top tabs, in theory. Preferences?




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Narrowed inserts, adjusted base tongue/slit, lowered windows in inserts:

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