How to roll perfect cones?

[theOshkoshModeler]

Hello all!

I'm currently tackling P.Model's Mitsubishi F-1 after a long hiatus due to college; after studying several build threads by some more advanced builders on this forum in the meantime I'm starting to notice a lot more issues in my current building technique.

One issue especially peeves me to no end; every time a part needs to be rolled into a cone with a point I end up with an open 'loop' where the point should be.
Shown below is an example from the nose cone of the F-1 at 10x zoom (the squares on the cutting board show 1/2 inch); the 'loop' is very small at but I'd much rather prefer a perfect point.
It doesn't look bad at 1:50 scale but is a lot more noticeable on the 1:144 Talon from my SCA build thread (I still have plans to continue that build in a different thread as I'm working on modifying/correcting De Vries' SCA recolor).

My current method is to roll the cone around a toothpick angled towards the point. Perhaps there's a more effective way? Is my card (Walmart brand, 199gsm) too thick for a good cone?
Suggestions are very appreciated.

Thanks!

[SteveB]

Hi, I think maybe your card is a bit thick. If you managed to roll a cone with no gap whatsoever at the tip, the point would be the width of two thicknesses of card - the thicker the card the wider the tip. Thinner paper would give a sharper point. The cocktail stick sounds fine.

[mbauer]

Same issue:
1) Bamboo skewers work really well when working with cones
2) Use a finger nail to force the top of the glue tab to bend for about 1/4", make sure to tuck this under the top layer-this bottom edge usually catches to cause what you are experiencing.
3) Pinch the top part flat after lining it up, don't let the glue dry completely, just enough attachment to force the cone back to proper shape after it grips. Be careful: too much glue and it will glue the top closed/flat.


4) Not necessary but I always add a blob of glue to inside of the tip, letting it dry. This allows pinching the nosecone to remove from the models that have the removable nose cones.

Question: Thinking you are, but are you pre-shaping the cones?

Hope this helps.

Mike

[ReynoldsSlumber]

If you approach it in terms of geometric topology, a paper of finite thickness cannot ever come to an absolutely perfect conical point. Even if you had perfect control of what shape the paper takes, as you get toward the tip you'd have to sharpen edges of the paper to reduce the edge thickness.

Maybe it would look better if you cut off the tip so that the rolled diameter is about twice the paper thickness? Any finer of a point than that, and I think the non-conical effects you're talking about become topologically unavoidable.

To get a perfect conical point, maybe best to resort to lathing it out of a wood dowel or toothpick. Or, more simply, chuck it up on a drill and "lathe" it.

Or you could use thinner paper, ~200 gsm is indeed thick. Something 100 gsm or less may get the tip irregularity down to a size where it's not noticeable with the naked eye.

[theOshkoshModeler]

Originally Posted by ReynoldsSlumber

If you approach it in terms of geometric topology, a paper of finite thickness cannot ever come to an absolutely perfect conical point.

Oh, absolutely. My focus is to eliminate the gap as seen in my photo as much as physically possible.

[Knife]

I use the round file from the small file set available at Harbor Freight Tools. The teeth of the file grips the paper just enough to give it a bit more bend than a smooth tool such as a bamboo skewer. A lick of saliva on your fingers applied to the tip of paper will provide just enough moister to the paper to allow it to be flexible enough to get a fine point on the end.

[Siwi]

Counter-intuitive as it may sound, trimming a fraction off the tip of the cone in an arc can actually get a better point. This is because you don't have all the micro-bends in the surface of a cone converging on a 'zero point' and the thickness of the paper will fill in the final space.
If there is any visible gap, I go back over with glue and/or paint to fill them. Done nose cones for a MiG-21, F-5 and Drakken using this method and they are actually sharp enough that I need to watch my fingers!

[theOshkoshModeler]

Originally Posted by Siwi

Counter-intuitive as it may sound, trimming a fraction off the tip of the cone in an arc can actually get a better point. This is because you don't have all the micro-bends in the surface of a cone converging on a 'zero point' and the thickness of the paper will fill in the final space.

A rough test of this method using the same part (A1) from the F-1 (with slightly thinner card) shows favorable results compared to the initial attempt and negates the gap pretty much entirely. The recessed glue tab had to be trimmed to allow the two edges of the cone to touch, however.
Thanks, Siwi!

[Siwi]

Glad it worked out for you. I would love to take all the credit for this idea, but in reality I'm sure I came across it in a kit! I think it was one of the Hermercraft airliners, or the Ralph Currell Concorde.