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8 inch F/7 CHIEF group build

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#376 LarsMalmgren

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Posted 10 October 2020 - 08:26 PM

Mike,

 

I would very much like to get a STEP file of your design from post #362.

I'm trying to draw it up in Fusion360 but i'm not very good at it lol.gif

 

Can you export to something that OSLO can read also?



#377 steveastrouk

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Posted 10 October 2020 - 09:31 PM

Can Alibre read and use STEP files?  Ed and I can email STEP files from Zemax that tell you exactly where the lenses should be in 3D.

Yes. Alibre is very good at importing everything, but for some reason, they ditched SLDASM and SLDPRT export recently, and just left x_t



#378 Ed Jones

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Posted 14 October 2020 - 05:38 PM

I think I've shipped everyone's lens but I still have a few lenses left if anyone want to join this group.  I put them in classifieds.

 

Here is what happens when you use different focal length lenses with the same primary.  Shorter focal length lenses are closer to focus but the lens tilts get bigger and the image get worse.  OTOH longer focal length lenses are farther away, larger. correct better but may begin to clip incoming rays.

 

  

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#379 Ed Jones

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Posted 14 October 2020 - 05:46 PM

Now with the same lenses and primary if you increase the primary tilt the lenses also need more tilt and may interfere but the smaller the tilt the better the image.  So there is always a compromise between primary tilt and lens focal length.

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#380 jtsenghas

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Posted 14 October 2020 - 06:51 PM

Thanks Ed.  That shows very well what you've said a couple of different ways earlier in this thread.  Now that I've played a little bit with the layouts of a few Chiefs (though I haven't built my first yet), I have more appreciation for your choice of a 2" plano convex lens of 300 mm focal length and a slightly longer (negative) focal length plano concave lens for these and similar mirrors.

 

This makes clearer how things deteriorate rapidly with increased tilt.

 

Well done! 



#381 ksdowd

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Posted 18 October 2020 - 09:46 PM

JT, Ed and team, looking for feedback on if this was a success.  Here's how my first serious 3d print on the Ultimaker 2 turned out:

 

NOTE:  I'm afraid the precision is higher than the accuracy.  I don't think I really have an accuracy of a hundredth of a mm in my digital caliper skills.  And I still need to get the angle measured.

 

Hope to get back to the Maker space on Monday or Tuesday and try this again on the Ultimaker 3.  Your feedback is appreciated.

 

MEASUREMENT mm
RIM THICKNESS CONVEX 3.04
RIM THICKNESS CONCAVE 6.75
INNER DIA. CONCAVE 50.32
INNER DIA. CONVEX 50.32
ANGLE?
THICK SIDE THICKNESS CONVEX 11.28
THICK SIDE THICKNESS CONCAVE 11.97
THIN SIDE THICKNESS CONVEX 9.96
THIN SIDE THICKNESS CONCAVE 11.4

 



#382 jtsenghas

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Posted 19 October 2020 - 02:42 AM

JT, Ed and team, looking for feedback on if this was a success. ...

 

MEASUREMENTS....

INNER DIA. CONCAVE 50.32
INNER DIA. CONVEX 50.32...

You may have to open those lens seats at least a half millimeter, or about 0.020" to get the lenses to seat properly, and without pinching. 

 

The 3d printer I used has software that allowed me to scale the object up in size.  For both PLA and nylon filament I had to print at 101 or 101.5%. It looks like you need about the same. 

 

The two Newport lenses I have are exactly 2.000", or 50.8 mm. Ed reported that the custom lenses are 1.999", which is only a couple hundredths of a mm smaller. 

 

At a scale of 101.5% your 50.32 mm would become 51.07 mm, which would give you about a quarter millimeter clearance if things were perfectly round and more likely just enough to avoid pinching, especially with temperature variation. All my printed samples were out of round by about a tenth of a millimeter, which strikes me as pretty darn good for such a process. 

 

I can't speak for the other dimensions, but I succeeded in printing within hundredths of a degree to the correct angle between faces and Mike has shown that using tolerances of about a tenth of a degree works fine. 

 

I bet you'll be fine if you get the lenses to fit loosely.  Screws with plastic washers is what Ed said he plans on using. I may cut circular retaining rings from plastic using a gasket cutting kit I have. 

 

Edit -  Mr. Ed Jones, If these results are consistent for various users, you may want to scale your Solidworks designs up more than 1% to avoid tight lenses. This might be easiest done after drawing as you have been to Zemax dimensions. 


Edited by jtsenghas, 19 October 2020 - 02:50 AM.

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#383 LarsMalmgren

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Posted 19 October 2020 - 05:54 AM


Edit -  Mr. Ed Jones, If these results are consistent for various users, you may want to scale your Solidworks designs up more than 1% to avoid tight lenses. This might be easiest done after drawing as you have been to Zemax dimensions. 

I would say don't scale the master drawing.

 

This is because the factor of 1% will be different for different printers/filament types etc.

Let the master drawing be made with exact dimensions.

 

Then each can scale if needed.

 

Btw. 3D printers has to be adjusted so it can print to exact dimensions.

This is done in the slicing software. This way it's entirely possible to make the printer match the dimensions correctly.

Each filament type will need it's own scaling due to different thermal properties.

Even PLA in different colors from same brand might need different scaling.


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#384 warehouse

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Posted 19 October 2020 - 02:32 PM

For anyone with Zemax, here's the file I used for designing the straight-through 8" f/7 Chief above.  There are subtleties in the file involving proper use of coordinate breaks in Zemax that I would be glad to discuss separately without cluttering up this thread.

Mike

 

attachicon.gif8f7 Chief - MIJ opt custom CDGM H-K9L PCC, Newport KPX205 fold after L1L2.zmx

I used OSLO-LT since I don't have ZEMAX using the straight through formula here: ?Attached File  Chief8f7_MIJ_mod.len   1018bytes   2 downloads

 

I couldn't get a coherent spot diagram until I tweaked some parameters. Can any OSLO experts QC this file please.

 

Some changes were primary at 3.1 degrees tilt since it seams to clear the lenses and diagonal.


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#385 warehouse

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Posted 19 October 2020 - 06:24 PM

I used OSLO-LT since I don't have ZEMAX using the straight through formula here: ?attachicon.gifChief8f7_MIJ_mod.len

 

I couldn't get a coherent spot diagram until I tweaked some parameters. Can any OSLO experts QC this file please.

 

Some changes were primary at 3.1 degrees tilt since it seams to clear the lenses and diagonal.

This version implements tilt then decenter on both lenses with tighter spot diagrams:

Attached File  Chief8f7_MIJ_mod2.len   1018bytes   2 downloads



#386 scooke

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Posted 20 October 2020 - 02:56 PM

There is an 8"F8 available in classifieds.

 

https://www.cloudyni...”-f8-newtonian/



#387 ksdowd

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Posted 22 October 2020 - 08:26 AM

I bet you'll be fine if you get the lenses to fit loosely.  Screws with plastic washers is what Ed said he plans on using. I may cut circular retaining rings from plastic using a gasket cutting kit I have. 

...

 

Edit -  Mr. Ed Jones, If these results are consistent for various users, you may want to scale your Solidworks designs up more than 1% to avoid tight lenses. This might be easiest done after drawing as you have been to Zemax dimensions. 

JT,

 

I can cut a gasket/ring with the laser cutter, so that's no problem.  May use Ed's plastic washer approach to begin with, since it' works and is already done for us by Ed in the Solidworks file. (Thanks, Ed!)

 

I opened the file in Solidworks last night (which is about the limit of my Solidworks skill set) and the diameter of the lens holes is 2.00".  So what you said about changing the Solidworks design to open up the diameter of the lens sockets makes sense to me.

  • If we have to account for thermal expansion effects, increasing the diameter to -
  • A) avoid pinching &/or long term deformation of the printed lens holder with contraction/expansion of the assembly
  • B) making it possible for clumsy fingered people like me to insert the lens
  • C) minimize the negative impact of any variances from circles caused by the X/Y printing process - examining my print shows the "circle" to be about a 37sided approximation of a circle, so it has a range of diameters.

So I'll have to acquire some basic Solidworks skills so I can modify that.

 

Additionally, I like your idea of changing design from 2.00" to a slightly larger diameter rather than scaling as it addresses design issues in design rather than in "manufacturing".  I am still a couple steps behind you on how to realize a 3d print to correctly match the design; which is where I plan to follow your approach on comparing the materials I have available against the resulting measurements and then scale from that point to a usable result.

 

QUESTIONS: 

1.  JT suggested a quarter mm clearance (so a half mm dia. increase).  I'm going to run with that, but are there any additional thoughts?

2.  Am I overthinking this and I should just sand out the lens "sockets" until the lenses fit?  Or would that wreck the de-centering?



#388 jtsenghas

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Posted 22 October 2020 - 09:56 AM

QUESTIONS: 

1.  JT suggested a quarter mm clearance (so a half mm dia. increase).  I'm going to run with that, but are there any additional thoughts?

2.  Am I overthinking this and I should just sand out the lens "sockets" until the lenses fit?  Or would that wreck the de-centering?

Actually, I'd recommend only about a quarter millimeter clearance on the diameter, not twice that. I'm talking about the measured minimum diameter minus the lens diameter.  It should allow for dimensional variation with temperature as it is about 0.5% of the diameter. That's still plenty even for ABS.

 

If you open it slightly in diameter it should remain pretty well centered if you use a hand made reamer or sanding drum eased into the hole. You could even wrap tape and sandpaper around a smaller cylinder. 

 

Your printer parameters for the stl file should allow for finer resolution and thinner layers at the expense of time.  A 37 sided polygon is almost 10 degrees a facet.  WAAAY too coarse!


Edited by jtsenghas, 22 October 2020 - 11:11 AM.



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