How to make perfect wing rib.... - RC Groups
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May 07, 2012, 06:48 PM
Registered User

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???
Last edited by schusterjo; May 08, 2012 at 08:17 AM.
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May 07, 2012, 11:28 PM
I'm a pilot, 100 yrs too late
Thermalin's Avatar
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
May 08, 2012, 04:02 AM
Registered User
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.

May 08, 2012, 08:18 AM
Registered User
Originally Posted by slipstick
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.

sorry, its the rib I would like to accomplish.. been a very long few days
May 08, 2012, 09:11 AM
Registered User
You may find this site to be interesting. The particular link is a way to make uniform ribs.

May 08, 2012, 01:56 PM
An itch?. Scratch build.
eflightray's Avatar
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.
Last edited by eflightray; May 08, 2012 at 02:01 PM. Reason: Addition.
May 08, 2012, 02:11 PM
An itch?. Scratch build.
eflightray's Avatar
I found some pictures and text of the sandwich method -
May 08, 2012, 02:45 PM
B for Bruce
BMatthews's Avatar
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.
May 08, 2012, 06:47 PM
Registered User
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?
May 08, 2012, 07:34 PM
Registered User
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.

Last edited by Captain Dunsel; May 08, 2012 at 07:40 PM. Reason: Forgot stuff
May 09, 2012, 12:51 AM
B for Bruce
BMatthews's Avatar
Originally Posted by schusterjo
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.
May 09, 2012, 05:09 PM
Registered User
rcav8r2's Avatar
Originally Posted by schusterjo
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
May 10, 2012, 05:32 AM
Balsa builder and balsa basher
RC Trainer plane's Avatar
This is a relatively cheap way to make wing ribs exactly the same it's explained fully in this link.

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

hope i helped
May 11, 2012, 01:05 PM
Hatters gonna hat.
madbomber's Avatar
Ive found this way to work wonderfully for hand cutting out wing ribs.
May 11, 2012, 01:31 PM
Registered User
rcav8r2's Avatar
I forgot about this web page I did YEARS ago.....
Cutting the Parts 1, 2, & 3 (left frame) show how I manually cut ribs....

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