How to Create a Sharp Triangular Pyramid with Glass or Quartz Material?

[member 428835]

Hi PF!

I'm trying to build a triangular pyramid whose length is 20cm and cross section has a height of 3mm (I have the complete dimensions but hopefully this gives you an idea of the size I'm looking for). The interior corners have to be very sharp, so I can't use glue. The material is glass, quartz, or another transparent material with similar surface roughness.

I'm located in Portland, Oregon.

Thanks so much! Let me know if there's more info you'd like.

Josh

 

[berkeman]

Do you have access to a 3-D printer? You could print the base and sides, and polish them for better sharpness and optical clarity...

 

[member 428835]

Do you have access to a 3-D printer? You could print the base and sides, and polish them for better sharpness and optical clarity...

I do have access to one but the angles are very precise. I believe polishing would jeopardize the dimensions.

For what it's worth, money isn't really an issue as long as it's about 1,000$ or less.

 

[member 428835]

Does anyone have any idea? I know it's a long shot.

 

[Ketch22]

You commented that you can't use glue, why is that are you just concerned about the potential fillets? What are the strength requirements for this? A very thin adhesive will work via capillary action with minimal filleting. The easiest to work with is a Cyanoacrylate like Super glue. Do you have the facilities to cut and bevel each piece? If each piece is machined to a close tolerance a touch to the seam will generally adhere it.

 

[Baluncore]

Is the pyramid hollow or can it be solid?
Is this a dimensional device or an optical component ?
What is it used for ?

 

[member 428835]

why is that are you just concerned about the potential fillets?

Results from this shape are measured against numerical results, and so must be precise.

What are the strength requirements for this?

No requirements.

Do you have the facilities to cut and bevel each piece?

I don't think cut and bevel would work since I would somehow have to attach the sides without diminishing the angle sharpness. I think I need to send this to an industrial facility. Thanks for the idea though.

Is the pyramid hollow or can it be solid?

The pyramid is hollowed out of a square cylinder.

Is this a dimensional device or an optical component ?

I don't know what you mean, but it must be cut precisely so I can take pictures of fluid injected into the corner tip of the pyramid.

What is it used for ?

A capillary experiment.

I emailed a few facilities today hoping they could build what I describe. Attached is a pdf of the container.

 

[Baluncore]

That container.pdf diagram makes it much clearer.

The manufacture of optical wedges from quartz and optical glass is a well known precision technology. Many amateurs make their own lenses, wedges and prisms. You can achieve precision results with very simple tools on a kitchen table. Books and articles on lens grinding and polishing give all the information you need. When slipped against each other the optically flat wedges will stick due to air pressure. Glass has been “glued” with balsam because it has the same refractive index as glass and can be softened for disassembly by heating. If used the film of glue can be less than a micron thick which will give the accuracy you require.

Consider the manufacture of three blocks that when mated form the pyramidal cavity you require inside the rectangular prism. All angles ground and polished are wide open, greater than 90° and therefore strong.
The first block would be the rectangular base plate with a ramp ground and polished, on one face, down to 5mm thickness at the thin end.
The remaining two blocks would be rectangular prisms of half the base width, that have a long diagonal corner ground and polished to give the two triangular faces.
You could grind the stock before checking the dimensions and assembly. Then final polishing will give the internal surface accuracy and the optical window(s) you need to observe the internal experiment.A completely different approach to the experiment would be to invert the entire concept. Make a rectangular framework from glass rods that supports three internal quartz filaments or optic fibres. The three filaments all pass at the apex of the pyramid. The mathematics of the surfaces forces would change but the construction would be much less complex.

 

[Baluncore]

I have done my best to interpret the shape and relative dimensions from your diagram. I have converted the 20° angle into two 10° angles, one on each. Attached is a view of the three parts needed to assemble the container.

The apex of the triangular pyramidal cavity has been moved 1.5mm towards the face of the cover plate which reduces the total number of diagonal surfaces needed to two. The cover plate is then a rectangular prism.

You might consider increasing the thickness of the 5mm cover plate to 8mm, like the two wedge plates. Then all can be made from the same stock.

 

[member 428835]

Thank you so much for the detailed response! That last rendition is a very creative and unique approach! I'll keep you posted on results and if I have questions.

 

[member 428835]

You can achieve precision results with very simple tools on a kitchen table. Books and articles on lens grinding and polishing give all the information you need.

Did you have any books or articles in mind?

 

[Baluncore]

There are many articles in the amateur astronomy field. I see them as they pass but have no one complete references for you. I would probably use a “surface grinder” for metal, with a corundum grinding wheel. That way I could do most of the work quickly. Polishing will take time and effort so you will need to know the tolerance required.
Start by googling ' grinding glass prism '