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  #1  
Old 05-06-2020, 01:25 PM
Jack Hydrazine Jack Hydrazine is offline
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Default Rock-A-Chute Mark II Nose Cone

I recently designed and posted this design on Thingiverse which you can download for free and print.

This nose cone is designed to fit BT-50 tubing, but you can always upscale or downscale in your CAD or slicing software to suit your needs.

https://www.thingiverse.com/thing:4332295
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Old 05-06-2020, 05:40 PM
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BEC BEC is offline
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Interesting. That will certainly suggest what the Leedes Sweete sharpener nose cone looks like.

Attached is a closeup (slightly out of focus) that shows the ribs are not as wide, of two different lengths, and that there are more of them. Since you've posted an image I took of G. Harry Stine's Mark II at the Museum of Flight back in 2010 on your Thingiverse page, it would make sense that another view, taken on the the same visit, would be useful....
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Old 05-06-2020, 07:15 PM
Jack Hydrazine Jack Hydrazine is offline
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If the sharpener pic was a little closer and more in focus and taken from a another angle it would helped to figure out exactly how to design it. I've looked online for other pictures, but they were out of their packaging and too far away and if up close they were in their packaging.

In the photo it's difficult to say what the exact dims are of any part of it. I inferred everything from knowing the OD of the airframe tubing and gave it my best shot.

I'd love to hold it in my hands and actually measure it and get some good photos of it.
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Old 05-06-2020, 09:45 PM
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I agree. That picture is lousy, and the pictures I have of another Mark II (taken at NSL 2013) don't show the ribs very well either.

I can try (if I remember) to get a better-focused picture of the one in the MoF next time I'm up there. I have a much better camera in my phone now than I did that December 2010 day when I took the pictures you have.

John Brohm, who is very detail oriented, wrote an article for a club newsletter detailing how to make the balsa Semroc reproduction nose cone that comes in the Mark II retro-retro kit look much more correct. It contains much detail about number, length and spacing, and is attached. I got it from him in another Mark II thread on here (more just below).

I've done a couple of Mark IIs this way, using 1/32nd basswood as the strips, and it is easy to overdo it. The ribs on the actual sharpener are not that prominent....

Added: Here are some pictures from a Mark II thread on here:

https://www.oldrocketforum.com/show...90&postcount=47
https://www.oldrocketforum.com/show...65&postcount=53
https://www.oldrocketforum.com/show...21&postcount=64
https://www.oldrocketforum.com/show...29&postcount=70

Heck, why not just cruise the entire thread for yourself. LOTS of pictures of both the actual crayon sharpeners and John Brohm's reproduction idea....
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File Type: pdf Nose Job.pdf (284.2 KB, 15 views)
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Old 05-07-2020, 07:02 AM
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Gosh Bernard; that's some digging. Had entirely forgotten about that thread.

As my note in the thread says, the ridges on the actual artefact are a little more subtle than what I had reproduced on the model, so with a thinner strip stock one could arrive at an almost identical reproduction nose with some care.

The model pictured below I built and presented as a gift to Carl and Miss Sheryl, for all their help over the years. Remembered fondly, missed badly.
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Old 05-07-2020, 08:09 AM
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I have an original Lead's Crayon Sharpener so I measured the ridges.

They are 1.27mm or 0.05" wide and 0.50mm, or 0.02" high.

Very subtle ridges.

It would be a easier to see if I took it out of the package...but I do want to do that.

The only place it says "leads" is on the bottom. It says, "A Leads Sweete Product".
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Old 05-07-2020, 05:49 PM
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Quote:
Originally Posted by John Brohm
The model pictured below I built and presented as a gift to Carl and Miss Sheryl, for all their help over the years. Remembered fondly, missed badly.

I'm sure both Carl and Sheryl appreciated the gesture as well as the craftsmanship that went into that model. Sure looked nice!
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  #8  
Old 05-08-2020, 05:43 PM
Jack Hydrazine Jack Hydrazine is offline
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Quote:
Originally Posted by BEC
I agree. That picture is lousy, and the pictures I have of another Mark II (taken at NSL 2013) don't show the ribs very well either.

I can try (if I remember) to get a better-focused picture of the one in the MoF next time I'm up there. I have a much better camera in my phone now than I did that December 2010 day when I took the pictures you have.

John Brohm, who is very detail oriented, wrote an article for a club newsletter detailing how to make the balsa Semroc reproduction nose cone that comes in the Mark II retro-retro kit look much more correct. It contains much detail about number, length and spacing, and is attached. I got it from him in another Mark II thread on here (more just below).

I've done a couple of Mark IIs this way, using 1/32nd basswood as the strips, and it is easy to overdo it. The ribs on the actual sharpener are not that prominent....

Added: Here are some pictures from a Mark II thread on here:

https://www.oldrocketforum.com/show...90&postcount=47
https://www.oldrocketforum.com/show...65&postcount=53
https://www.oldrocketforum.com/show...21&postcount=64
https://www.oldrocketforum.com/show...29&postcount=70

Heck, why not just cruise the entire thread for yourself. LOTS of pictures of both the actual crayon sharpeners and John Brohm's reproduction idea....


I've updated the design based on the input from those with the numbers, which helps a lot. Thanks to everyone for your help. Take a look at the design and let me know what you think. If I need to I will go back and create a third version.
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Old 05-08-2020, 05:58 PM
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That second picture on the thingiverse link looks MUCH better. I'm glad we were able to flush out some real dimensions for you.
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  #10  
Old 05-10-2020, 12:59 AM
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Quote:
Originally Posted by Jack Hydrazine
If the sharpener pic was a little closer and more in focus and taken from a another angle it would helped to figure out exactly how to design it. I've looked online for other pictures, but they were out of their packaging and too far away and if up close they were in their packaging.

In the photo it's difficult to say what the exact dims are of any part of it. I inferred everything from knowing the OD of the airframe tubing and gave it my best shot.

I'd love to hold it in my hands and actually measure it and get some good photos of it.


my sharpener is in storage somewhere, but note that there is a slight "flare" at the bottom (and possibly a circumferal ridge at the very bottom, but that I'm not sure if it is part of the shell or the base.
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