CNC Pietenpol Ribs & More

[Cunni5ac]

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

[rwanttaja]

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

[Cunni5ac]

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.

[Kyle Boatright]

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...

[rwanttaja]

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

[DaleB]

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.

[Cunni5ac]

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?

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.

[Fritz]

...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?

Hi Charles,

...I only mention this because you asked about CNC ribs for a Pietenpol specifically.

I made a set of CNC'd plywood replacement ribs for an old Pietenpol that was damaged in a landing accident.

If it was a whole new "per the plans" wing it would have been very quick and simple to make the CAD and CAM files and cut the ribs (I've done several all CNC'd "per the plans" rib sets), but for this airplane I had to scan one of the old ribs and go from there. There's a short thread on the process here: http://www.homebuiltairplanes.com/fo...ad.php?t=23156

IMHO you can build light, strong wings ...very quickly using a CNC machine. http://www.homebuiltairplanes.com/fo...ad.php?t=20101

[Cunni5ac]

Hi Charles,

...I only mention this because you asked about CNC ribs for a Pietenpol specifically.

I made a set of CNC'd plywood replacement ribs for an old Pietenpol that was damaged in a landing accident.

If it was a whole new "per the plans" wing it would have been very quick and simple to make the CAD and CAM files and cut the ribs (I've done several all CNC'd "per the plans" rib sets), but for this airplane I had to scan one of the old ribs and go from there. There's a short thread on the process here: http://www.homebuiltairplanes.com/fo...ad.php?t=23156

IMHO you can build light, strong wings ...very quickly using a CNC machine. http://www.homebuiltairplanes.com/fo...ad.php?t=20101

Hi Fritz,

Thanks for sending these links. You and mmarien look like you have successfully utilized this process for building aircraft components. Do you think it would be possible to digitize the Pietenpol's plans and have the majority of the aircraft cut out?

Yes, I know for 1 builder it may or may not be a good use of time. I am looking at the long run. My thought is if a collection of individuals get together to fund this project, they could take a 1000hr project down to a 400-500hour project that are looking to get into homebuilding an aircraft.

I could see this being a situation where the project is crowd funded and the plans are given to a small group of people that can determine what parts of the aircraft can be CNC'd and what parts will need to be built traditionally, digitize the CNC eligible parts into workable files.

[SaltedTailfeathers]

I'm new to this.

One of the things I expected to see, (maybe I haven't looked in the right place yet) but haven't, is rental tooling.

If someone is building a tail feather for a Cub there is a fair bit of layout and lofting (boat building term I don't know if it applies) before the metal gets cut and welded together. Building the tools to build the parts is a significant amount of the work. The hydroform process for making ribs is another case.

For a few hundred$ you can ship a pallet box of tooling almost anywhere. I kind of hoped to find that there would be a rotation among the chapters. (Chapter 1, would build the dies and hydroform boxes for ribs and control surfaces. Chapter 2. Tail jigs. Chapter 3, engine mount jigs..........)

I understand that would require a significant number of people to want to build the same aircraft and have the faith to accept the next guys tool construction of a design that probably only a few folks could agree to.

At the least builders who have completed stages and tools could have an exchange?