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Jun 08, 2017, 10:17 AM
Flying in OZ.
iflylilplanes's Avatar
Thread OP
Mini-HowTo

A Wing Rib Cutting Jig For Constant Cord Wings.


My rib cutting jig is made of a few scrap pieces of ply and a piece of sand paper, simple system using simple tools.

First, I glue the rib template to a 1.5mm ply piece with spray adhesive and cut the top of the rib, leading and trailing edges only,
not the bottom, (see pic 1) when I’m happy the edge is smooth I rub CA into the edge to strengthen the ply so the #11 blade will
slide smoothly when cutting, this is the time where you make the spar notches the correct size so when you cut a notch with the
blade vertical the notch is just right for the spar size (see pic 1). I now glue the sand paper to the back of the ply template just to
the bottom of the rib (see pic 2).

A straight edged spacer is cut just a little thicker than the rib material, in this case 3/32” plus the thickness of the sandpaper
whatever that may be, now glue the spacer to the tabs level with the bottom of the rib (see pic 3). Now glue the spacer to another
ply plate, you now have a rib template raised 3/32” from the base, now a strip of 3/32” balsa can slide under the template and
when you press down on the template the sand paper holds onto the balsa and stops it from sliding around while cutting, another
small piece of ply is glued to the base as a stop at the leading edge (see pic 4, 5 &6).

The round leading edge shape is cut to the size of the dowel with a piece tubing with a ruff edge, I just use a knife blade to mark
the edge of the tube, and you just put the tube in place in the cut away and spin, this tube being the same diameter as the dowel
cuts quick and a perfect curve for the dowel.

I cut 16 ribs in 15 minutes, I've posted a short video as well showing me cutting a couple of ribs along with the photos.

I've used this technique to cut ribs for a Vic Smeed "Tomboy", and the featured jig here is for the Dave Robelen "Playmate",
the build log can be viewed here https://www.rcgroups.com/forums/show...elen)-Playmate


The Bakers Dozen Build Off 2 (3 min 56 sec)
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Jun 08, 2017, 12:56 PM
Registered User
absolutely brilliant!
Jun 08, 2017, 03:28 PM
Registered User
Ifly-

Looks great for flat bottom airfoils but how about symmetrical airfoils?
Jun 08, 2017, 04:33 PM
Flying in OZ.
iflylilplanes's Avatar
Thread OP
Quote:
Originally Posted by 049flyer
Ifly-

Looks great for flat bottom airfoils but how about symmetrical airfoils?
Have not got that far yet with this method, but have thought about it and, as I see it the tabs that hold the template to the base will be a lot smaller so you can still use a similar jig. A simpler method will be to just make a ply template with a lot of pins sticking out of it, as long as the template can't move/slid about you can position the template the best ways to save on waste balsa. I've used this method to cut ribs out of foam using a vertical hot wire like a band saw cutting a foam blank an inch and a half thick then slicing the ribs off with another hot wire mounted parallel to a surface, I used a 1/4" gap on the last funfly wing I built. I'll post photos later today, it's worked well using both the blue fan-fold foam and the standard white polystyrene foam, and, the wings come out nice and strong and still light.
Jun 08, 2017, 05:06 PM
Registered User
:-0 Lotsa ways to cut ribs "en Masse"
Whatever works for you is Good.
There are other simpler ways though.

PS: as heads up... a fully flat bottom " Sorta " airfoil is Nowhere near as good at Flying as a decent imitation of a Clark Y is.
Jun 08, 2017, 06:10 PM
Flying in OZ.
iflylilplanes's Avatar
Thread OP
You are right, but, the rib in this thread is as the original plan for the Playmate, and if it flys as good as the Pronto (same designer Dave Robelen) I built back in the 80's it wont disappoint me.
Jun 09, 2017, 07:47 AM
UAS Pilot - FAA# *******HRK
CryHavoc's Avatar
Quote:
Originally Posted by iflylilplanes
Have not got that far yet with this method, but have thought about it and, as I see it the tabs that hold the template to the base will be a lot smaller so you can still use a similar jig. A simpler method will be to just make a ply template with a lot of pins sticking out of it, as long as the template can't move/slid about you can position the template the best ways to save on waste balsa. I've used this method to cut ribs out of foam using a vertical hot wire like a band saw cutting a foam blank an inch and a half thick then slicing the ribs off with another hot wire mounted parallel to a surface, I used a 1/4" gap on the last funfly wing I built. I'll post photos later today, it's worked well using both the blue fan-fold foam and the standard white polystyrene foam, and, the wings come out nice and strong and still light.
Just make a top half and bottom half jig. Slide the straight balsa blank into one of the jigs you designate as the first cut, make the cut, then take it out and slide the blank into the other jig. Key it to whatever you make as the register and make the final cut. That way if you ever decide to change either the top or bottom half airfoil shape, you wont have to make an entirely new jig.

Mike
May 26, 2019, 09:23 PM
Registered User
Thank you for this tip! I was able to use it to cut some very small ribs with good repeatability.

Next time I do this I will replace the screws with "pins" (steel or dowels) so that I can use my hand to squeeze/release the stock as I go. I made it with a fixed gap and the pressure was too fiddly.
May 27, 2019, 10:44 AM
B for Bruce
BMatthews's Avatar
CG, try a shim at the screws to raise the template. But keep the shim sort so pressure at the template can flex it down to hold the rib stock secure. A layer or two of regular paper should be enough to let the stock move easily but thin enough that the cutting template can be pressed down firmly against the wood.

TO make this shim idea work best it would likely also help if the screws and raising shim were further away from the working template so the "flex to lock" pressure only needs to be quite light to lock the wood well.

For flat bottom airfoils like this I might just copy this jig. But for more complex shapes I think I'll stick with the simple template that has a couple of dots of sandpaper on each side so I can flip the template to get the best usage of the wood. I can see how a fancier jig could cut complex shapes quickly. But making the jig itself would be more work than it saved.
May 27, 2019, 05:28 PM
Registered User
There actually is a shim under there. But I didn't think it through much and glued it to the main (back) section. I can see a serious version of this where I decide on a standard rib template "card" and make it easy to swap these cards out (like for a tapered wing).

I figured this rib was too small for my fingers to hold down a regular plywood/sandpaper template well, and I wanted to try this idea out. It does seem ideal for a simple flat bottom airfoil.

An alternative to this whole jig though, for using regular plywood templates, would be magnets. A thin cutting surface on top of a steel plate, and then some strong magnets on top of your rib templates, and you'd have a hands free pressure and nothing in your way (including your own hand).


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