Step 3: Scan Original Blueprints

I was given the sheet of blueprints (actually white zeroxed copies) to work from.  I taped the relevant portions together and traced the image to be cut on white butcher paper. Then took it to a local architectural copy shop (FedX-Kinkos would do) and had them make a digital file. They also sized it a bit to match the dimension given on the plans. I was enlarged 1.6%.
I suggest that a comparative load test should be done between that CNC-ed rib and ordinarry build up rib from spruce sticks. Ordinary rib will be superior as grain orientation and strength of the spruce (or douglas fir..) is way higher than of the plywood. The backdraw of the plywood is also the grain orientation, and it can not be used to its best strenght. <br>Pure plywood ribs should be designed for that lower strength of the material. Caps and diagonals should be much wider. And this will resulted in heaviest ribs, than odf classic design. <br> <br>Othervise it is clever idea to simplify ribs manufacturing and to speed up the process. The newest design from team AeroMax use many CNC done wooden plywood parts in the aeroplane structure.
I see the concern but ribs on most airplanes are not heavily loaded and even aerobatic airplanes are using routed ribs now. <br> <br>I've noticed that many times we get buried in conventional thinking that is based on a theory nobody fully understands in aviation. Many theories are just rumors even. Sometimes it's better to just see if you can get something to work since everything is a great compromise in design anyway. Most great advances come from trying something new.
What airplane is it for? I've done some ribs for people too. Kitfoxes have routed wood ribs but the factory does them by hand. Sad huh? haha.
I would like to know more about how you faired the rib profile before you created the &quot;G&quot; code. I have never been able to make a rib that I could use right off the CNC table without doing a lot of hand work to get the profile fair. By that time I have lost the exact shape and the rib is worthless. <br> <br>I hope you can help me. I have two Marske Flying wings that I want to build. 70% of the work is in making the ribs and making them to the correct size. <br> <br>Thanks. <br> <br>Wally <br> <br>
I'm building a flying wing right now too. I use Rhino 3D which has a feature in the view menu to place a background bitmap, jpeg also works. I then use the control point curve to trace the outline and then scale it to the right size in the &quot;transform 2D&quot; function. <br> <br>I've owned a shopbot for 15 years and after you have the machine it's all about the CAD skills isn't it :) Have fun, I'll post my project &quot;floater wing&quot; soon.
Just a CNC tip - We often for complicated cuts used to print out the drawing - full sized - and the lightly tack glue to the material. that way we could see a) that the material is big enough - b) where to put the hold down clamps that is going to be out of the way.<br><br>We always used a piece of sacrificial MDF under the material so we could cut all the way through. this also allowed us to pin the material - usually wood - down with panel pins. Much better than double sided tape and easier than various clamping systems.
One could make a wooden vacuum table, with countersunk holes underneath the spar parts and waste bits, while avoiding the tool path. <br> <br>A 30mm hole grid, 5mm holes, counter sunk to about 10 - 15mm in diameter?
We tried a vacuum table but couldn't get it to work - although they are made commercially. <br> <br>The hole size is critical not too big but not too small. <br> <br>
Naaa the hole size if BS...<br><br>Drill your thick plywood wood where the router cuts don't go close by and then counter sink them out.. to about 20mm in diameter.<br><br>Holding power = force x area. <br><br>And maybe route away one end and then apply a clamp to that, and perhaps a couple more as you go.<br><br>If I had to make any more than one or two of the spars like this, I'd make a table to suit the spar.<br><br>Make the table the exact same size and shape as the spar, perhaps add a couple of square &quot;tabs&quot; to clamp the sheet down and then lay the sheets on it.<br><br>The other thing is too, that you can make them in the stencil pattern. <br><br>Cut all of the shape out - except for a few connectors, that hold all of the pieces in place.<br><br>That way you can scrap the vacuum table and not have your timber and bits flying around everywhere around the router bit, when the cuts are made.<br><br>Once all of the cutting is made, then take a small hand saw of some description and cut the tabs.<br><br>Look up stuff on stencils.<br><br>And design it so the long thin bits are restrained as well as the thick bits and keep an eye on the cutting speeds... not too high.<br><br>
I'd be curious to run a stress test to failure on this and a traditional built-up rib. In standard rib building (as I understand it) the wood grain runs parallel to each member, whereas with plywood the grain is going every which way. Then again, plywood would have increased strength in other directions, and wouldn't have failure-prone joints. Have you looked into this?<br><br>Please don't take this as a disparaging comment, it's a great use for a CNC router, especially if it gets another airplane in the air. Well done!
I'd be thinking that a UNIFORM construction from one sheet, if properly designed would be better. <br> <br>Most of the traditional construction techniques, while they are good, there may also be other considerations that come under cost, wartime and efficient use of the resources - such as timber. <br> <br>There was also the technical angle of the limitations of the equipment and the speed of production..... <br> <br>It was deemed to be better to use a little glue and all the offcuts etc.. and to really minimise waste, than to be throwing out huge amounts of material, and it probably would have been far easier to cut lots of little straight bits from the one sheet, to assemble a spar from, than to try and cut out one as a single piece. <br> <br>Not that they could not be pressed out with a knife press, but the smart people really factor in ALL of the considerations to get the most suitable product out the door at the best price relative to the market and circumstances. <br> <br>
Oh yes, it's absolutely much faster and very likely better use of materials. But if you're making something like a Pitts that puts heavy loads on the wing ribs, ultimate failure strength is by far the top priority. Mostly I'm just curious. :)
Yeah, but plywood can be a generalist product or a specialist product.<br> <br> There is some really great informaiton about designing and creating plywood and products from it.<br> <br> The types of glues, the types of timber, they direction of the grain in the layers, in some regards plywood is the ultimate in wood porn.....<br> <br> I guess that premium aircraft grade plywood is expesive, and if one were to knife presss and cut out, or route out or laser out whole spars from one single piece of ply, while I really like the idea totally - the amount of timber left from the sort of rectangular shape, would I guess, be about 5 to 8 times the amount of timber in the actual spar.<br> <br> So I know that really GOOD aircraft grade plywood, that is free from knots and defects etc., IS really expensive, so with wages etc., it may actually be enormously cheaper, to cut that sheet up into lots of little straight bits and gussets, and to lick and stick them into a jig and then profile the finished component, than to throw away heaps of expensive timber.<br> <br>
Having dealt with wooden wing ribs I can see where this will save the builder lots of time and money. Good job.

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