andro000

I'm having a really hard tome of it here. I need to cut ribs for an undercambered wing. I can't tell you how many I've wasted so far.

Will y'all share the easyest way you know to cut ribs?

Rodney

I make a template using thin aluminum then just use a sharp knife and cut arround the template. It helps to have a couple small holes thru the template so you can pin it in place to keep it from slipping while you cut around it.

BMatthews

I do much the same thing but I use 1/32 plywood. Punch a couple of small bits of very light music wire or a pin through the ply in a couple of places and cut them off with a set of small side cutters so there's a burr left. That'll keep it from sliding around. having the burr on both sides lets you cut from whichever side fits the wood best for the most economy. With the undercamber you can then "nest" them easier.

And keep dem fingers out of the way. Those undercambered ribs can often be narrow. Makes for flat fingernail profiles....

Chevelle

My Feedback: (2)

I'm not there yet but will be. I will need about 120 identical undercambered ribs. I was looking into just having them laser cut for me but if not, I figured I'd make an inverse template out of thin metal. One where the rib is the hole in the plate, not the shape of the rib. I would just deep score the rib outline and then cut it through without the template. But like I said, I'm a long way off at this point.

If you don't mind me asking, what are you building? I am designing a 1/6 (may end up 1/4) scale AVRO Triplane MkIV.

KJohn

I had a router table which required the router to be mounted underneath. A piece of ply could be used for a router table surface. Then I used a router bit that had cutting blades nearest the router body and it had a 'flush' bearing near the tip of the bit. I think these are used to flush cut laminates for sinktops, etc. I think the bit was about 3/4'' or 1'' in diameter.

I then made a template of the rib of interest (Eppler 193) out of 1/4'' aircraft ply and inserted a few dress pins through it to act as small spikes. I would then place the template over a piece of balsa a little larger than the ply template and the pins to kept the balsa from sliding out of alignment. I then adjusted the router bit depth to cut the balsa while allowing the bearing to ride against the ply template (which is on top). Once it is set up it is easy to make lots of ribs with very good repeatability and speed. I ended up making extras ribs since it was so easy to make them. You will find that it is best to slide the balsa against the cutting edge from certain directions so that the blade is cutting from the 'outside' edge of the balsa and moving toward the inside section. This means cutting from the thickest point of the airfoil toward the leading edge then from the thickest point of the airfoil to the trailing edge. It just seems to provide a smoother cut.

Care must be taken when using a router in this way. You are placing your finger on the cutting side of the router and near the bit's cutting edges. So be very cautious. You are saving lots of time and getting great results so just go at a casual pace and be careful.

BMatthews

Chevelle. For that many I'd sure look at the stacked block method. You couldn't make all 120 at one go but stacking 20 to 30 at a time and shapeing them between two ply templates would sure save a lot of time.

If you go with the female template be sure to give yourself enough allowance for the cutting thickness of the blade and a little more to allow for stacking the ribs and block sanding the lot to remove any slight irregularities.

Also I figure it'll be harder to cut the leading and trailing edge ends with the female template.

toy264

Haven't done it in a while (like 30 years!) but if you trace the rib outline on a suitable balsa block and cut it out with a band saw, you can then lay it down and slice the ribs off of the pre-shaped block with the saw. use a rip fence (guide parallel to the blade) to keep the ribs a uniform thickness.

Chevelle

My Feedback: (2)

At least in my case, the wings are very thin. I don't know how easily it would be to make multiple ribs from two male templates.

I did make a 1/12 model from a R/N kit 25 years ago. (I still have it.) I cut them all out individually. You would be surprised how many you get done when listening to a couple of Pink Floyd albums. The only interruption is to turn the albums over.

They would have been done faster with the Stones, Yes, ELP, etc. but they all wouldn't have looked the same. They would have all looked the same with the Moody Blues but that would have taken too long. With the Greatful Dead, they wouldn't be the same and they would have taken too long but I wouldn't have cared.

andro000

Chevelle

I'm trying to build a Gym Sparrow.

And I just relized I no longer nave the plans.

Any one got this one?

BMatthews

ROFLMAO....

Looks like we have the same music roots. And yeah those groups would pretty much have that effect....

I've done my share of big rib counts for my old free flight towline gliders. Drilling for long #4 screws lets the bolts act as reinforcing bars to hold the stack flat and straight. Fresh sandpaper used with a light and skilled touch avoids the ribs flexing undully in the overhangs. But I can't think on any good sandpaper music... Oh wait, I've got it..... Janis Joplin doing "Summertime".. the sanding block would just flow along with her equally abrasive tone Of course the ribs are liable to come off the stack looking like '60's flower stickers for a VW Microbus.....

CoosBayLumber

My Feedback: (1)

For that quantity of ribs, I think that unless you are an expert flyer and do not expect to crash, the ribs ought to be done commercially. My thought here is that once to building, many of those ribs are not going to be exactly identical in every way to the one beside it because of spar sizes, rib thicknesses, or substitution of plywood.

If you are going to replicate an early era A.V.Roe aircraft, then you need to give thought as to letting everyone see inside the wing a bit by using transparent covering. Show them how the centers of the ribs were cut out for lightening, and then make up for this loss of rigidity with rib capstrips. Instead of about 120 identical ribs to be made up, have about 160 made up with some in different thicknesses and thin plywood so that you can repair damage, or substitute materials during the building process.

Two years ago, I received a scan overnight from Prague, Czech Republic. A customer there wanted ribs for a new glider design with a HUGE wingspan. Was a bit difficult to understand his notes, but began work on Wed. afternoon, ribs were laser cut Thursday, and a box of them were mailed out on Friday. Never saw the fellow, nor talked to him, but his drawing was good, and included a few dimensions in mm to counteract distorion, he paid via credit card, and was happy except for the government intercepted his box and held it for a while. Never saw the completed A/C either. As can be gathered, all this can be done from your desktop and across several time zones.

If you need new plans made, see my paragraph in Product Announcements here at RCU.


Wm.