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Old May 07, 2012, 06:48 PM
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United States, IN, Lebanon
Joined Oct 2011
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How to make perfect wing rib....

Is there a relatively cheap way to make perfect rib every time (scratch built with a pattern)? Mine to seem to be inconsistent as well have nicks... I know back in the day in shop I used a pattern an had some kind of router device that I could just run around the outer edge of the patter an it would cut what ever shape the patter was underneath. Anyways i need to make many spars an would like for them to be all the exact same preferably making many all at once.. a machine? a router way? ???? any???
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Old May 07, 2012, 11:28 PM
I'm a pilot... 100 yrs to late
Thermalin's Avatar
USA, FL, Palm Harbor
Joined Jan 2005
3,520 Posts
I dont think you will easily beat what you can get at te LHS for dimensional accuracy across spars. A router is more used for edge design. A table saw would be a better choice but a bit dangerous as your basically shaving 1/4" or whatever size strips off te main piece. Also when you do that you usually end up with some bowing as they cure due to the drying rate of the outside portion of the piece compared to the inside portion.

How many do you need and of what size
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Old May 08, 2012, 04:02 AM
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Staffs, UK
Joined Nov 2003
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Are you sure you mean spars ? A spar is normally just a long straight piece of wood and as Thermalin says it's much easier just to buy the correct size rather than "make" it.

Steve
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Old May 08, 2012, 08:18 AM
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United States, IN, Lebanon
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Quote:
Originally Posted by slipstick View Post
Are you sure you mean spars ? A spar is normally just a long straight piece of wood and as Thermalin says it's much easier just to buy the correct size rather than "make" it.

Steve
sorry, its the rib I would like to accomplish.. been a very long few days
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Old May 08, 2012, 09:11 AM
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Boston, MA subburb
Joined Sep 2004
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You may find this site to be interesting. The particular link http://www.airfieldmodels.com/inform...ribs/index.htm is a way to make uniform ribs.

Alan
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Old May 08, 2012, 01:56 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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For parallel chord wings, (all ribs the same), the sandwich method is probably the easiest without using special machinery.

You need two templates with a number of slightly over size blanks in between, then just sand to shape, and cut-out the spar slots with a junior hacksaw.

I have created sets of balsa ribs that way for years, now everyone seems to have their own personal CNC machine, or knows someone who has one.


Addition. - It can also be done for tapered wings, but the ribs will need individual truing as they will likely have angled edges. But it's still an easy method.
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Old May 08, 2012, 02:11 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
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I found some pictures and text of the sandwich method - http://www.scale-models.co.uk/tutori...wing-ribs.html
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Old May 08, 2012, 02:45 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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Small shaping errors are not as important as having a smooth progression from one rib to the next... .at least small errors are not important unless you're making a high performance sailplane. For regular sport models the airfoil shape only has to be "close enough". By this I mean within the thickness of a pencil line or so.

For myself I cut out a hard sheet stock or plywood template which is purposely cut out about a pencil line out from the final desired shape. I cut out all the ribs using this template for the outline with no spar notches at that point.

Once I have enough blanks they are stacked and either pinned or bolted through some drilled holes with long machine screws. The hard templates being on either end. I sand down this block of ribs so they are smooth and as accurate as I can given the use of hand tools and bleary eyeballs filled with balsa dust. Usually this means being able to decently split the line on the templates for the final shape. At that point the spar notches are rough cut with a Zona or similar saw and some small coarse cut metal files that have non cutting smooth edges on one or more sides are used to trim the notches to a nice firm finger push fit to the spar stock.

As the ribs come off the stack I number them from one end to the other so they can go into the wing in the same order. This automatically graduates any final slight errors evenly along the span so the spar notches at least are in a straight line the whole way.

If you want or need anything more accurate than this you're looking at laser cutting or CNC routering. But unless you're doing something very exotic you really don't need anything better.
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Old May 08, 2012, 06:47 PM
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how much a small cnc cost? including software or whatever is needed to complete? another words everything to be able to have it making ribs?
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Old May 08, 2012, 07:34 PM
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United States, NJ, Browns Mills
Joined May 2005
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For constant chord wings, I make a stack of blanks bigger than the pattern (which is glued to the top blank), then jig saw almost down to the line. I then use a sanding block made from a scrap of spar stock with sandpaper glued to it to get the spar slots open.

Next, scraps of spar stock are wedged into the spar slots, and the whole sandwich gets block sanded on a power sander.

As a side note, when I use the ribs, I alternate them from one end of the stack, so if the stack is not perfectly square, any taper that snuck in is matched on both wing panels.

Tools requried: Jig saw (Mine is a 30+ year-old Dremel), power sander, and sanding blocks.

Almost forgot: I print my plans out on an old LASER printer, then glue the templates in place with a glue stick.

CD
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Old May 09, 2012, 12:51 AM
B for Bruce
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The 'Wack, BC, Canada
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Quote:
Originally Posted by schusterjo View Post
how much a small cnc cost? including software or whatever is needed to complete? another words everything to be able to have it making ribs?
A helluva lot more than an Xacto knife, a couple of sanding blocks some pins or long bolts, a little harder balsa or plywood for templates, a few other handtools mentioned already and about an hour of your time.

Compared to building the rest of the model cutting out and shaping the ribs isn't that big a deal. You want painful and difficult? Making up and installing the servo mounts and pushrods is WAY more time consumning and difficult.
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Old May 09, 2012, 05:09 PM
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United States, PA, Beaver
Joined Sep 2001
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Quote:
Originally Posted by schusterjo View Post
how much a small cnc cost? including software or whatever is needed to complete? another words everything to be able to have it making ribs?
Bare Bones machine ~ $400 to ~ $1000 and more depending on size, speed, etc.
Driver software Free (need Linux) , or about ~$150 for Mach3 (Windows).
Driver board - ~$100-$500 depending on a lot of factors
Steppers - Typically 3 needed. ~$20 to ~$ 100 a piece.
CAD software... Free to thousands of $$
CAM software - Free to Thousands of $$
Motor tool --- ~$50 - ~$300
PC to run it. You will want a dedicated one with a parallel port . ~$50-100 used
Other Misc stuff (stand for it, limit switches, wiring, cutting bits, etc) - ~$100 - $200


I built a CNC machine because it's something I always wanted to build. They always fascinated me. It was actually easier that I though and works really well. I didn't built it to save time or for more accurate parts. I still manually cut out simple shapes and parts I forgot to add to my drawings as it is easier than setting up just one or 2 parts for CNC.

But before that I hand cut everthing, and as BMatthews said, cutting the ribs out are a cake walk compared to other tasks you will need to do. Also most wood is only nominally dimentioned... That is an 1/4" x 1/4" spar stock isn't always 1/4" square. When cutting by hand you can adjust for a nice fitting spar. With CNC you need cut smaller than what you think it will be and sand to fit anyway. At least that's what I do as I draw first, then order the wood so I have no idea what it REALLY is.
Unless you want to do CNC for the fun of it, it really won't save you any time for cutting out parts for a plane. This is particularly true when building from a physical set of plans. YOu need to digitize them, and if your not careful, the sizing can be way off. Now tab and slot stuff for a keel built self designed fuselage... Yea, a CNC is real nice
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Old May 10, 2012, 05:32 AM
Balsa builder and balsa basher
RC Trainer plane's Avatar
Joined Apr 2012
683 Posts
This is a relatively cheap way to make wing ribs exactly the same it's explained fully in this link. http://www.airfieldmodels.com/inform...ribs/index.htm

also to make exact spars here's a product you might be interested in from my local hobby store avicraft.
Avicraft - Balsa Cutter demo (5 min 18 sec)


if you want to buy it here's the link to their store http://www.avicraft.co.uk/tools/hand...-to-58mm-.html

hope i helped
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Old May 11, 2012, 01:05 PM
Hatters gonna hat.
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United States, CO, Denver
Joined Apr 2011
359 Posts
Ive found this way to work wonderfully for hand cutting out wing ribs.

http://www.rcgroups.com/forums/showp...&postcount=101
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Old May 11, 2012, 01:31 PM
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United States, PA, Beaver
Joined Sep 2001
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I forgot about this web page I did YEARS ago.....
http://home.comcast.net/~daverc102/spookmain.htm
Cutting the Parts 1, 2, & 3 (left frame) show how I manually cut ribs....
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