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Thread: CNC Pietenpol Ribs & More

  1. #1

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    Question CNC Pietenpol Ribs & More

    Hello Everyone,

    I am considering building a Pietenpol and I have read through a decent amount of material related to the build.

    I was wondering, has anyone tried to utilize a CNC machine to cut out the wing ribs and other items requiring more than one nearly identical parts?

    I would think this would help cut down build time considerably especially at scale (multiple guys working on a Piet at once). I have not looked at how the plans are but I have seen many use a stencil for the ribs which should be able to be easily digitized.

    Would /could the wing rib be as strong or stronger?

    Any insights would be appreciated.

    Thanks,
    Charles

  2. #2
    rwanttaja's Avatar
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    I don't know if it's been done, but the same sort of thing has been proposed for the Fly Baby. Fly Baby wing ribs are 1/8" plywood and in three sections. The wing is untapered (until you get near the tip) so there are twenty identical copies of the center section and leading edge (trailing edge varies due to the ailerons).

    However, even when hand-cut, few builders make them one at a time. Many make a template out of thicker material as a template and use a router. Others stack multiple plywood sheets and cut them all at once with a bandsaw.

    I don't know how much it would cost to get this CNC machined instead, but it's easy enough to do it yourself and save that money. Most people building Piets or Fly Babies are looking to do it cheaper. Jake S. is an exception (Hi, Jake!).

    But if you want to do it, there's no reason NOT to do it. The templates exist for Fly Babies, and I'm sure they're out there for Piets, too.

    As to stronger, if you use the same material, it'll be the same strength. Ribs are rarely the weak point when it comes to wing strength, so a stronger rib buys you nothing.

    Ron Wanttaja

  3. #3

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    Thanks Ron,

    The idea would be to decrease build time for repetitive tasks or multiple items with only a marginal increase in price. I have seen many home built CNC Mills for around $350 - $500 dollars (Check out the MaslowCNC machine for an example). So I was thinking if I could build a rig and convert the files, one could rapidly (relatively) spit out a slew of these with greater precision.

  4. #4

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    Quote Originally Posted by Cunni5ac View Post
    Thanks Ron,

    The idea would be to decrease build time for repetitive tasks or multiple items with only a marginal increase in price. I have seen many home built CNC Mills for around $350 - $500 dollars (Check out the MaslowCNC machine for an example). So I was thinking if I could build a rig and convert the files, one could rapidly (relatively) spit out a slew of these with greater precision.
    The issue is that the router can make the ribs to very precise standards in a few hours. I'm not sure there are many other pieces in the FB where there are enough to justify pseudo-mass production.

    The real time saver would be to digitize the plans for the metal parts and have those cut for you (or CNC 'em yourself if you have the ability). Hacking stuff out using a bandsaw is really slow...

  5. #5
    rwanttaja's Avatar
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    Quote Originally Posted by Cunni5ac View Post
    Thanks Ron,

    The idea would be to decrease build time for repetitive tasks or multiple items with only a marginal increase in price. I have seen many home built CNC Mills for around $350 - $500 dollars (Check out the MaslowCNC machine for an example). So I was thinking if I could build a rig and convert the files, one could rapidly (relatively) spit out a slew of these with greater precision.
    In terms of the percentage of the build time for a plans-built plane like the Piet, the time required to build the ribs is in the noise. If several people are building the same type of airplane, it makes more sense.

    However, we build the airplanes for "education and recreation." So if it's something you WANT to do for the fun of it, or to learn how, have at it! I've made several decisions on my airplane that don't make sense, from the time expenditure or other logical reasons, but just because I wanted to.

    Ron Wanttaja
    Last edited by rwanttaja; 02-10-2018 at 02:28 AM.

  6. #6
    DaleB's Avatar
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    Charles, I know where you're coming from! I'll need to cut out a pile of plywood nose ribs. I already HAVE a CNC router, it would be child's play to cut them on that - if only I had the file. I have one, actually, but it's for a Shopbot (I think) in some oddball format that I haven't been able to translate into anything useful.

    I know it would be less tedious to cut them on the CNC machine, and I know they'd all be exactly the same. Plus, I like to play with the machine.
    Measure twice, cut once...
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  7. #7

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    Glad to head it Dale! I feel that with the significantly low prices of CNC machines, relatively low cost of computer software in 2018, why can't / haven't there been an effort to convert these plan's only aircraft to digital file formats that could be cut out on a CNC machine and assembled? I saw a good discussion going some years back discussing this concept and it took a turn towards creating an open source aircraft (not sure what came of that).

    Even if 1/4 - 1/3 of the time could be removed from a 1000hr build time it would be well worth it for the community. I would think EAA as an organization would even want to lead the charge on this concept increasing, consistency, decreasing cost and build time. It seems like it would lead to a larger pool of aircraft owners and increased safety.

    Thoughts?


    Quote Originally Posted by DaleB View Post
    Charles, I know where you're coming from! I'll need to cut out a pile of plywood nose ribs. I already HAVE a CNC router, it would be child's play to cut them on that - if only I had the file. I have one, actually, but it's for a Shopbot (I think) in some oddball format that I haven't been able to translate into anything useful.

    I know it would be less tedious to cut them on the CNC machine, and I know they'd all be exactly the same. Plus, I like to play with the machine.

  8. #8
    Sam Buchanan's Avatar
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    Quote Originally Posted by Cunni5ac View Post
    Glad to head it Dale! I feel that with the significantly low prices of CNC machines, relatively low cost of computer software in 2018, why can't / haven't there been an effort to convert these plan's only aircraft to digital file formats that could be cut out on a CNC machine and assembled? I saw a good discussion going some years back discussing this concept and it took a turn towards creating an open source aircraft (not sure what came of that).

    Even if 1/4 - 1/3 of the time could be removed from a 1000hr build time it would be well worth it for the community. I would think EAA as an organization would even want to lead the charge on this concept increasing, consistency, decreasing cost and build time. It seems like it would lead to a larger pool of aircraft owners and increased safety.

    Thoughts?
    You asked for thoughts......

    Compared to the entire custom-built aircraft community, there is an insignificant number of wood aircraft such as the Piet and FlyBaby being built. I am assisting a friend who is building a FlyBaby and he is only aware of one other plane currently under construction. There would be a few more Piets...but very few.

    I can't think of any other wood components of the FlyBaby other than ribs that would lend themselves to quantity reproduction. As Ron stated, rib construction time doesn't even register compared to total build time. These are custom-built planes in the strictest sense which means components are built to fit each other, not necessarily to fit the plans. Tolerances can accumulate, and by the time fabrication reached the point of needing prefab parts, they may not fit what has been previously constructed. I realize this may be difficult to understand if one has never built one of these wood aircraft and doesn't appreciate the uniqueness of each particular airframe.

    In regard to total time savings, as a general rule the airframe comprises about 1/2 of total build time. In other words, when you have something that looks like the bones of an aircraft, you are only half way to a flying aircraft. This means saving a little time on prefab ribs is meaningless in total build time.

    However....if you want to take the time to set up production of ribs and enjoy that process, then do it for the educational and recreational benefit. But I doubt the CNC-capable builder will save any time, precision or gain any safety over the builder who is handy with a bandsaw.

    The only wood aircraft I've seen that relied heavily on CNC process was a wood version of the TEAM Airbike but I don't know if that kit ever came to market. It was a totally different design from the Piet or Flybaby consisting primarily of plywood for the entire airframe. While I was building and flying a Legal Eagle a builder geared up for milling the nose ribs, but again there was no saving of time, just the fun of knowing it could be done.
    Last edited by Sam Buchanan; 02-10-2018 at 11:06 PM.
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  9. #9

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    Quote Originally Posted by Sam Buchanan View Post
    You asked for thoughts......

    Compared to the entire custom-built aircraft community, there is an insignificant number of wood aircraft such as the Piet and FlyBaby being built. I am assisting a friend who is building a FlyBaby and he is only aware of one other plane currently under construction. There would be a few more Piets...but very few.

    I can't think of any other wood components of the FlyBaby other than ribs that would lend themselves to quantity reproduction. As Ron stated, rib construction time doesn't even register compared to total build time. These are custom-built planes in the strictest sense which means components are built to fit each other, not necessarily to fit the plans. Tolerances can accumulate, and by the time fabrication reached the point of needing prefab parts, they may not fit what has been previously constructed. I realize this may be difficult to understand if one has never built one of these wood aircraft and doesn't appreciate the uniqueness of each particular airframe.

    In regard to total time savings, as a general rule the airframe comprises about 1/2 of total build time. In other words, when you have something that looks like the bones of an aircraft, you are only half way to a flying aircraft. This means saving a little time on prefab ribs is meaningless in total build time.

    However....if you want to take the time to set up production of ribs and enjoy that process, then do it for the educational and recreational benefit. But I doubt the CNC-capable builder will save any time, precision or gain any safety over the builder who is handy with a bandsaw.

    The only wood aircraft I've seen that relied heavily on CNC process was a wood version of the TEAM Airbike but I don't know if that kit ever came to market. It was a totally different design from the Piet or Flybaby consisting primarily of plywood for the entire airframe. While I was building and flying a Legal Eagle a builder geared up for milling the nose ribs, but again there was no saving of time, just the fun of knowing it could be done.
    Thanks Sam,

    I think you are right that since I have never built an aircraft, there are some elements of the build I am envisioning that likely doesn't match up with reality.

  10. #10

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    If you can come up with the files to cut them, check with your local college, technical college, or community college. You might find that you have access to their CNC equipment for free, or nearly free. The instructor might even give the project to a student to generate the cutting file for you. My local community college has a nearly new 'fab lab' that already has a half dozen Dremel 3d printers, a MarkForged *carbon filament* 3d printer, a large format (3' x 3' x 20") 3d printer, a 30 watt laser (unfortunately the bed is too small for wing ribs), etc etc, and they are expanding rapidly. On the way is a blue/white light scanner (you just walk around the object you want to scan), and a 3d printer for concrete. I'm a senior citizen, so I can audit courses for free, and the fab lab is open to the public in general, for just the cost of materials.

    All this, and I live in one of those backwater states that's behind the rest of the country. You might be shocked at what's available to you in your area.

    Charlie

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