CNC sherline Lathe

#1

I know it was getting close but did the sherline CNC project ever finish?
Want to try to machine an acylic Fresnel Lens on it. we have had poor luck using a CNC router to do this.

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#2

Good question. @TBJK @Chris_Wischkowsky ?
@Buehler?
They were pretty close.

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#3

Not yet. This weekend I’m hoping myself and @Chris_Wischkowsky might be able to wrap it up.

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#4

awesome I’m working on my senior Mech Eng Project and part of it is attempting multiple manufacturing possibilities for smallish (about 100-150mm) custom focal length fresnel lens.
I’m out of town this weekend, but next weekend @TBJK f you want to meet up I can show you what we are attempting.

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#5

Oh I am so curious about how you’re going to do this. Please write about this when you work on it. I’d be interested in the process. How important is surface finish for a fresnel? I’m guessing it isn’t particularly crucial since there are a lot of really super low dollar fresnels that are reasonably decent, but I don’t really know. I mean, you’re not making a lighthouse …

What’s the surface pitch for your lens, and what’s the overall diameter? Is the “100mm - 150mm” the lens diameter, or the focal length? How do you plan to hold it so you can work on both sides?

Like I said, it just sounds fascinating.

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#6

Ack. Made me look :stuck_out_tongue:

https://en.m.wikipedia.org/wiki/Fresnel_lens

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#7

All very astute questions.

  1. We are actually working on a portable solar powered water heater that works via a fresnel lens for solar concentration.
  2. We are working with a PhD candidate that is tackling some interesting problems on solar concentration. This student has a Matlab program that will calculate each groove agle necessary to bend the light for different refractive index and incidence angles of how the light hits the lens.
  3. Each lens can vary in diameter and grooves can vary in number. Each groove is concentric but will have unique angle cut.
  4. Using an automated routine I wrote in Autodesk inventor we take the Matlab data and generate a 3d stl of the theoretical lens.( This innovation by me has saved the PhD approx 3 or 4 he’s per lens design in iteration time)
  5. Input that .still into ComSol and run fea on the actual light transmission to verify.
  6. Make lens…we have done 3D printing on a form labs in clear. Also used that 3d print to make a silicone mold and vac cast out of epoxy. Now we are working on machining.
  7. Clear as possible is important. But you can flame polish acrylic to a very nice finish…hope at least.
  8. As to holding lens in lathe . Not sure yet lol
  9. 100 to 150 is lens diameter
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#8

Here’s a video of my inventor generating a a dummy lens with 100 groove. And random excessive large pitch angles. This video was proof of concept. It reads the angles from a .xls sheet actual angles will vary between 0 and about 45 degrees in .1 degree resolution. I’ve made it better now where it will read any number of angles input from the sheet and doesn’t require user interaction other to click start button. No video of newest right now.

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#9

Fascinating!!

Unfortunately, the largest diameter the Sherline can accommodate is 88mm. You would have to invent an auxiliary holding device that mounts on the faceplace because the chuck is only capable of 57mm. If we had the optional headstock riser blocks, it could in theory accommodate up to 150mm diameter (same holding issue), but we also don’t have the risers for the toolposts, etc. that are compatible with the headstock riser.

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#10

Well for testing purposes I can easily make one in the 50mm range

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#11

I thought that DMS purchased riser blocks. The same riser block will work on both the Lathe and the Mill. If we do not have any, then I can loan one of my personal Sherline riser blocks. Then have DMS purchase one for our Sherline equipment.

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#12

I am not aware of owning the riser blocks, and I think I have kept a diligent inventory. We would need the riser block for the headstock, the tailstock, and the toolposts.

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