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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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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, 10:57 AM
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Quote:
Originally Posted by sandman
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".

I have one in a damaged package if that will help. I can easily take it out.
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Old 05-07-2020, 02:13 PM
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Quote:
Originally Posted by sandman
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".

Gordy, I presume that height measurement is at the base of the sharpener, since the ridges taper down as they go towards the top.

Hopefully the OP will pop back in now that we have actual numbers for him to use to refine is 3D print model with.
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Old 05-07-2020, 03:31 PM
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Quote:
Originally Posted by BEC
Gordy, I presume that height measurement is at the base of the sharpener, since the ridges taper down as they go towards the top.

Hopefully the OP will pop back in now that we have actual numbers for him to use to refine is 3D print model with.


Yes, that is correct. T measured the height of the ridge at the base.

They taper down to nothing towards the top at 1.15" long.

So the ridges are actually quite small.

Everything from our childhood is actually smaller then we remember.
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Old 05-07-2020, 04:33 PM
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Is that 1.15 inches the long ones or the short ones? They alternate at two different lengths, 5 of each, around the circumference.

I sure get that “smaller than we remember” bit!
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