HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Oct 14, 2014, 04:55 PM
OAK
Registered User
OAK's Avatar
Norway
Joined Oct 2002
172 Posts
Discussion
Rhino5 - need help to create Decathlon wing tip

Hi.

I am newbie to Rhino. Trying to model a Bellanca Super Decathlon (8KCAB) wing tip. Plan is to mill positive foam plugs with my CNC mill to create fiberglass wingtips using lost mold process. They are going on to a EMHW Decathlon XL (3m ws)

I have created a skeleton of curves based on the actual profile of the wing I have, three view drawings found online, and lots of pictures of decathlons online.

I have been trying to create surfaces from the skeleton, but I do not quite get the results I want. Close, but not good enough.

If any more experienced rhino users out there would point me in the right direction I would greatly appreciate it.

It is the leading edge, and the area just where the tip has a sharp angle and a straight section that is problematic.

Below are some pictures of a few almost successful attempts. But I have tried a lot of different surfacing methods, splitting up curves etc. but these are the closest I have got so far.

The Rhinoceros file can be downloaded here
OAK is online now Find More Posts by OAK
Reply With Quote
Sign up now
to remove ads between posts
Old Oct 15, 2014, 03:30 PM
Registered User
Hegra, Norway
Joined Feb 2007
145 Posts
Long time no see, OAK, and welcome to the world of Rhino!
I have not used all your curves, and also done some smoothing of the sections.
The main part was made by 3 separate curve networks, and the nose was made with a patch. Sanding the foam plug will take care of the rest ;-)

A tip is to save file as 4.0, and there will be a lot more people to help you.

Lars
LN-JET is offline Find More Posts by LN-JET
Reply With Quote
Old Oct 15, 2014, 05:23 PM
OAK
Registered User
OAK's Avatar
Norway
Joined Oct 2002
172 Posts
Hi Lars.

That looks close to perfect for me. Your help is really appreciated.

So now I can move on to the next step. CAM. The extents of the part is approx. 450 x 100 x 65mm. My machine travel i Z direction is 60mm and clearance between bed and gantry is about 80mm. I am debating if I should mill one side, then flip it and do the other side (need to take care of alignment of course and it will be a good check of how square my machine is). That should work and I think I will try that.

But I could also slice it into 2 sections vertically along the chord line which would give me a inner and outer part that would need to be glued together after milling.

This will be my first real 3D milling. Up until now I have only been doing 2D and 2,5D. Looking forward to it :-)

Thanks again for your help!
OAK is online now Find More Posts by OAK
Reply With Quote
Old Oct 15, 2014, 10:11 PM
Registered User
Denver, CO
Joined Dec 2005
6,370 Posts
I usually mill one side, and flip it.
I start by zeroing the mill on the table.
Then on one side of the foam, drill locating holes. And mill it flat it I need a more accurate part. I might go ahead and mill that parts side, or if I need a more accurate part I might flip the foam, and surface that side first. If I'm going to milling both sides flat, I don't mill the part until both sides are surfaced. My table has threaded holes, that I put set screws in leaving them sticking up.
I usually use some dabs of hot glue on the edges of the foam to secure it. Try not to distort the foam, as it will pop back to shape after its released from the table. That would distort the part.
I take note of how high I jogged up from the table. Sometimes to make it easy I set it to a specific height, like 1 inch, to surface the foam to.
I can go into the cad software to align the center of the part, to the center of the height I surfaced the foam to. I drill alignment holes in the top, while milling the top half. Flip the foam, and mill the lower half.

So in the cad software I generate the cam for one side, rotate the part on the centerline to make the other sides cam. With my software I set a boundry, and often add a plane for limiting the depth. Here are a few examples of how I do it. Notice the one I put the tool path on. They call it a slice planar. It cuts across the part, repeating back and forth until it reached the other side. This works good in foam, as it leaves support for the foam until it reaches the end. I usually leave tabs to hold it in place. http://www.rcgroups.com/forums/showt...4#post23998633
And a short video clip of it milling
http://www.rcgroups.com/forums/showa...2&d=1352019431
Roto Rob is online now Find More Posts by Roto Rob
Last edited by Roto Rob; Oct 22, 2014 at 06:05 AM.
Reply With Quote
Old Oct 22, 2014, 04:00 AM
OAK
Registered User
OAK's Avatar
Norway
Joined Oct 2002
172 Posts
The first tip is now milled. It went very well. I followed more or less the same procedure as Roto Bob recommended:

1. Surface milled the foam block on both sides. Accurately measured the thickness of the block.
2. Mounted foam block with double sided tape to the bed. Zeroed Z on top of foam block.
3. Milled first side of the part and drilled two alignment holes (along Y zero).
4. Removed foam block and drilled two alignment holes in the MDF sacrifical board at same coordinates as in the foam block.
5. Flipped the board and monted with alignment pins in the holes previously drilled.
6. Milled the second side.

I used Cut3D, 6mm ball nose mill, cut speed 3500mm/min, depth of cut 15mm, stepover 50% for rough cut, and 30% for finish cut. Rough cut was planar along X. Finish cut parallel along Y. Tried different spindle speeds during cut, 10000-24000rpm, didn't really notice any difference. Total cut time each side approximately 20 minutes (5+15).

One mistake I did is that I did not take into account that the total milling depth was deeper than the length of my mill, so the collar nut started to rub on the foam some places. So halfway through I had to cut away some foam using a knife to avoid rubbing. On the next tip I will probably add an extra rough cut to ensure clearance to the nut.

The small hole you see in the finished part is just a defect in the block that was there before I started milling.
OAK is online now Find More Posts by OAK
Last edited by OAK; Oct 22, 2014 at 04:28 AM.
Reply With Quote
Old Oct 22, 2014, 06:04 AM
Registered User
Denver, CO
Joined Dec 2005
6,370 Posts
Looks good.
I get some foam melting, and sticking to the end mill, if I have too high of rpm for the feed rate. So I set the feed where I wanted, then turned down the rpm until I get small ribbons of foam slicing off.
When I have an end mill long enough, I only do one full depth pass. That way the foam is better supported for most of the cutting.
Roto Rob is online now Find More Posts by Roto Rob
Reply With Quote
Old Oct 30, 2014, 06:09 PM
Registered User
Hegra, Norway
Joined Feb 2007
145 Posts
Nice, OAK!
I have done wing tips, and other two sided objects like that before. Latest foam project is this 1/6 Saab J32. I had to make some extra long tools, to reach as much as possible of the fuselage half-sides.
Lars
LN-JET is offline Find More Posts by LN-JET
Reply With Quote
Old Oct 30, 2014, 07:03 PM
OAK
Registered User
OAK's Avatar
Norway
Joined Oct 2002
172 Posts
Nice jet Lars, and creative long reach mills.

I have now milled the second one. Went slightly better due to rough cut removed a bit more to clear the collet nut on the deepest cuts.

Have you done a lot of lost foam? I am considering wrapping the plugs in glad pack to ease removal. Or would you recommend laying the fibreglass on the plugs directly and carve/acetone everything out?

Will have to experiment with layup as well. Do you think 200+200+50g would be ok? Have not done much research or experiments on this yet.
OAK is online now Find More Posts by OAK
Last edited by OAK; Nov 04, 2014 at 09:06 AM.
Reply With Quote
Old Oct 31, 2014, 05:57 AM
Registered User
Hegra, Norway
Joined Feb 2007
145 Posts
Not a lot of parts, but some wing tips, nose cones, ducting, and fuel tanks. The jet will be the first complete fuselage.
I don't recommend glassing directly on the foam, unless you are leaving it in place afterwards. Gladpack can be used, but it is not easy to get the wrinkles out. I have used either ordinary covering film, thinned spackle and acrylic paint, or covering with paper, and then acrylic paint. Then wax and PVA release coat.

Your layup sound heavy, but with lost foam there is always the need to sand away some bumps. Maybe lay down 200g first, and sand before the next layer.
Remember that the wing tip has curvature everywhere, and will be rigid mounted, so no reason to overdo. A test layup is a good idea. Search for user "J Morgan", he is king of lost foam!

Lars

Quote:
Originally Posted by OAK View Post
Have you done a lot of lost foam? I am considering wrapping the plugs in glad pack to ease removal. Or would you recommend laying the fibreglass on the plugs directly and carve/acetone everything out?

Will have to experiment with layup as well. Do you think 200+200+50g would be ok? Have not done much research or experiments on this yet.
LN-JET is offline Find More Posts by LN-JET
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion New to fixed wing...need battery selection help and other ?'s Jimbo45 3D Flying 5 Sep 26, 2014 09:45 AM
Discussion Need help interpreting washout in wing design. T.D. Modeling Science 4 Sep 25, 2014 06:11 AM
Help! Help needed! Wing tip repair on Hangar 9 Cub 40 bangolange Crash Discussion 4 Jul 23, 2014 09:50 PM
Discussion Need help creating circular airfoil in Solidworks lance.plater1 CAD/CAM 4 Jun 13, 2014 04:24 AM
How do I create wing ribs from only root and tip profiles?? rcminiman Scale Kit/Scratch Built 6 Dec 22, 2004 01:56 PM