Need ideas for making cross sections

[JESTER]

I'm making a fin that I will use as a master to cast 4 other fins.

I'm thinking I make it similar to an airplane wing where I cut out the vertical sections and glue them to the main shape. I guess I will fill it with Bondo and shape it according to the cross sections.

Is there any tutorials for something similar to this? Does anyone have any recommendations or ideas???
I'm not sure how to get the cross sections correct. I don't do 3D so I can't go that route.

I drew this to show what I'm trying to accomplish. The squared off tab on the fin profile drawing will insert into a tube.
It's convex on the top section and concave on the lower section.



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[JESTER]

Nevermind.

[Gordon Ferguson]

Jester,

late in throwing my ideas, little problem with op on hand.

Here is how i would approach it ---- using card or plastic card

draw out the largest profile, end one ? as accurate to the shape you want , mark and cut out rectangular slot from centre line to one edge .... where one of your corners are.

Now if you have a scale, or full-size drawing of the piece you can mark on that where you have the rest of your profiles ..... suggest a regular spacing. from that you will have details of the maximum width and height at each profile station

cut these out as rectangles, place the first rectangle on top of your accurately cut first profile. Using a pair of compasses open them to the distance from the edge of the profile to a corner of the rectangle then use point of compass to follow curve of profile to draw curve on the rectangle .... do for the 4 ? edges . Cut out and also cut out rectangle slot on same plan as the first one

Follow this procedure for each profile station.

Cut out the shape of the fin in plan marking out the station points and cutting out the slots in these to correspond with slots already cut in the profiles slide on/glues your cross sections together

I would use something like blue foam to fill in the missing pieces as it is easy to sand

Sorry no pics for SBS and I hope it makes some sense ... having to type left handed seems to have confused the brain even more than normal

Just occurred to me  that if you type in via search engine "carving blue foam glider fuselage" which is what I have used this process for before you should find some more info/photos.

[JESTER]

Thanks Gordon!! I'll post my progress.

I have a friend who does CAD and he's printing out all the cross sections.
I drew this out in Illustrator after I did that sketch. If I didn't get the CAD done, I was going to try to draw the cross sections using the skills I learned in 10th Grade Drafting class! If I could still remember!

I was told that if I use Bondo as the filler that I should use Basswood because the Styrene might warp as the bondo dries. What is Blue Foam? My friend used the expanding spray foam with good results.



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[Gordon Ferguson]

Jester , with CAD you should have no trouble plotting all the sections ......... and it will be a lot more accurate than my old fashioned steam powered method ............ especially as the form curves as well .

Blue foam ............ there is some info on it on this thread

http://www.finescalerr.com/smf/index.php?topic=404.0

about a third of the way down first page


But the spray foam will work just as well and probably a bit quicker ............ a suggestion I would make is to glue a piece of fine but reasonably stiff wire across the profiles along the line of the crest and the other edges  .......... think you will find this will give a good sanding line and keep those edges "straight", protect the foam as well as letting you have a uniform curve at these corners

[JESTER]

a suggestion I would make is to glue a piece of fine but reasonably stiff wire across the profiles along the line of the crest and the other edges  .......... think you will find this will give a good sanding line and keep those edges "straight", protect the foam as well as letting you have a uniform curve at these corners

Good Idea! Thanks for the link.

[JESTER]

[Gordon Ferguson]

Looking good Jester, look forward to watching you work this one up ............. reminds me of the fins in Tintin's rocket ship

[jacq01]

Jester,

you can built it up lke they do modelship hulls, Very thin waterline shapes glued together. Sand the protruding edges after the model is formed and the glue is dry.
Advantage is no warping.

Jacq

[JESTER]

 jacq01, do you have a link to that type of build?

gfadvance, due to time constraints, my friend is building this off my plans so it's not me doing the work.
I'm working on the rocket and will be casting the fins once I get the master.

Here's the fin with spray foam added and roughed out.

[JESTER]

Here's the final fin before casting:



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[Gordon Ferguson]

Well Jester , your friend has done a nice job for you

Would be interested to know what paint/primer he used to get that surface finish.


Glad you got it sorted out, let me know if you are going to do a production run ............... think I could have a bit of fun with paint on this 

Gordon

[finescalerr]

Gosharootie, that turned out nicely! -- Russ

[JESTER]

I know he used bondo on top of the foam but I'll get the specifics.

He is currently making a studio scale Betty from Aliens Resurection.

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[Gordon Ferguson]

Thanks,

out of interest is this based on or inspired by the Raygun Gothic Rocket Ship ?

Gordon