# New kit lines

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#### George Sychrovsky

##### Banned
I would like to see the cost break down of those ribs machined from a solid block of one inch thick aluminum. From looking at it it seems to me it would take something in the order of a thousand pounds of aluminum for a set of ribs for one plane plus all the machining cost ???. That would probably cost as much for the ribs alone as all material for entire airframe of comparable plane, I wouldn’t be surprised to see a government agency to build a space shuttle this way but a kit plane ?

George

#### orion

##### Well-Known Member
The one inch aluminum plate is fairly pricey (about $2,300) but I can get all the airplane's components from one sheet, including all the fusleage frames, all the ribs, as well as several other miscellaneous bits of hardware. I'm not sure of the cost of using a router to get the parts but using a waterjet cutter approximately doubles the raw material cost. As such, all the framework components can be had for less than$5,000, give or take a bit.

Using the bent tube approach, the framework cost drops to less than $130, including the material, the bending, and the additional tube lengths that will comprise the diagonal braces. The investment casting approach will be a bit more as it will cost about$60 for the coating and casting process and maybe something over $100 for the machining of the wax. In volume, obviously these costs will decrease, thus showing good promise for keeping the kit prices at the level estimated earlier. I have however slightly redesigned the airplane (mainly to account for the bending requirements of the square tubes) so once I finish the lofting work I'll post the new pictures. #### sonex293 ##### Well-Known Member Thanks for the update. Looking forward to the new photos. --Michael Sonex #293 #### Jman ##### Site Developer Ditto - Exciting stuff! Jake #### CNCRouterman ##### Well-Known Member Stereo Lithography Bill, I checked into Stereo Lithography. The cost of admission to be able to lith` a 20" x 20" x 23" work area is around$300,000 or so. The published tolerances are .005" per inch per inch (.005/in^2). Pretty sloppy even for a wood worker. Now, the actual achievable accuracies are much better, but that is what the manufacturer is willing to stand behind. The rate of throughput for the S.L. equip is about 7 hours for a coffee cup sized item. Assuming you leased it, and wanted a 5 year payback, you would have to charge a pretty penny per hour to crack a $6000 per month nut. Then of course, the usual assortment of associated expenses are on top of that, like electric, consumables, operator expense, insurance, etc... Bottom line, for robust geometry items, a CNC Router like mine can rout things for much less money and in much less time than you could do with a laser cure/ laser sintering machine, not to mention that most CNC routers with have work volumes substantially larger in at least two if not all three dimensions. One huge advantage for stereo lith and laser sintering equipment is that the material induced limitations for thin wall machining do not exist. Also, internal or hidden features that would be impossible to machine in one block can be easily done with these fancy rapid prototyping innovations. Lucky for me, I do not expect any serious competition from this technology. The sales rep indicated that the typical buyer of these stereo lith machines is a company that needs it to support another process (such as investment casting) as opposed to a stand-alone profit center. He also said that improvements in the process are being made to facilitate single step - laser to application use in some plastics such as nylon. I don't expect to be in the market for one of these puppies for quite some time! I found two shops in my area that do investment casting, both of which also have one form or another of RPL equipment. --edit: I corrected my horrendous spelling.. Last edited: #### orion ##### Well-Known Member Good morning Eric; Sounds like the info you got on STL is about what I've seen. The only reason I mentioned it is because the local investment casting shop mentioned it as one possible approach - however he too indicated the possibility of some pretty impressively high costs. Once I get feedback and the samples from the tube bender (probably by the end of next week or so), I'll have a better idea as to which process will deliver the better results. If the investment casting idea comes out ahead, I'll go ahead and redesign the frames and send you the files so you can take a look at what will be involved in machining the patterns and also what your local investment casting outfits will want to do the parts. #### orion ##### Well-Known Member One of the drawbacks of trying to do something different from the norm is that despite the most dilligent of efforts, the best of conceptual approaches may not work due to more practical considerations. Such is the case in our latest approach to the framing of the fusleage. To review, the basic approach that I'm taking towards the configuration of our airplane is to develop a structural concept that is not only strong and durable, but one that is also easy to fabricate and assemble, thus allowing the design to be built quicker and cheaper. So far it has become clear that the first idea, cutting the fuse framework out of aluminum plate, is out of the question due to the cost of the aluminum, as well as those costs associated with the cutting of each structural framework. Although router cutting turned out to be the most cost effective, the parts still generated way too many chips for the concept to work effectively in a production setting. The follow-on idea was to fabricate the cross sections for the cockpit out of extruded square tubes. With today's CNC driven tube benders, several potential suppliers assured me that they would be able to maintain about a .020" accuracy and repeatability for each of the cross sectional members. Given the fact that extruded aluminum tubing is not all that expesive, and that the bending costs were quoted at$37 per cross section, this seemed like an ideal solution. The only unknown was the supplier's ability to bend the tube without significant wall distortion.

Yesterday we discovered that this requirement was virtually impossible to meet. Although the fabricator was not able to generate the small corner radius to the magnitude I specified, they did come close. Close enough as a matter of fact that I was willing to reloft the airframe to take the larger bend radius into consideration. The problem though was that the bending process caused serious distortion of the tube walls. Since the distortion is virtually impossible to eliminate, and at times is responsible for cracks in the faces, it looks lke this idea is going by the wayside also.

Oh well, back to the drawing board. I still have three other ideas so there's still a chance one of them will deliver the properties and low cost fabrication that I'm after. Back to the testing.

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#### Midniteoyl

##### Well-Known Member
Would a couple relief cuts on the inside radius help with that? Course, the tig welding required afterwards would prolly defeat the low-cost... just a thought.

#### orion

##### Well-Known Member
The only idea I've been able to come up with is something similar to what is used for forming tubing for trumpets and trombones - the tube is filled with a special liquid, which is then frozen solid. After that the tube is put on the bending tool and formed to the necessary shapes. The frozen interor keeps the tube from forming any distortions.

For this case I thought to fill the tube with sand and water, then freeze it solid. That mix should provide sufficient resistance to the distortion, however how much, I don't know. The problem though is the cost - I don't know how much it would add but off the top of my head I'm guessing it might again make the parts a bitt too prohibitive.

But as of today, I'm off onto some of my other ideas, so we'll see. (Boy, composites are a lot easier.)

#### Midniteoyl

##### Well-Known Member
(Boy, composites are a lot easier.)
Ok, how about composite? At least for this? A way of fastening the skin would be needed... Like a aluminum 90 degree angle or 'T' molded/sandwiched along the edge of each composite frame to allow for riveting of the skin...?

#### orion

##### Well-Known Member
Well, the original idea behind this approach was to come up with a design that was not only strong, durable and easy to assemble, but also one that would allow the company to bring in reasonably priced components from outside vendors. In that way the company is not saddled with the costs and floor requirements of producing laminated components.

Yes, I know there are companies out there that are setup to produce laminated parts for their customers, but having seen the success of that (or lack thereof) at companies like Glasair, I really did not want to take that road. Metal parts are easier since once you provide the specific drawings to a fabrictor, all he has to do is maintain the tolerances. After all, "tin-bashing" is a well known and established process.

One would think that that could be done for composites also however the reality seems to be that there are several more issues to deal with which make the process a bit more difficult (and costly).

The other issue of that is that if I went to the compsites, I would want to substantially refine the loft of the body. But in doing that, I would now of course have to make the tools. I have done that on many occasions before, and I really did not want to do that now. The only two choices of that route are to either spend the next six months building a plug and molds, or spend about \$10,000 and have them machined. Not my favorite choices.

The other drawback of doing the latter is that once you're done with the tools, you can only produce that aircraft. The idea behind what I'm trying to do with this airplane is to develop a structural approach that would allow the company to produce a line of airplanes that had the major parts in common.

Yes, I know - picky, picky. But then if one is starting from scratch and spending his own money, one can be picky to meet the desired goals.

So now I'm going through the process of evaluating the variables. Is it more important to meet the original goals or can I relax a few ideals and take a more compromised approach. I sure wish I had more funding for this to play around more with several of my ideas.

Well, I still have three other ideas to try before I change the goals - we'll see.

#### whirlybomber

##### Well-Known Member
orion,

perhaps this wont suit your low cost approach, but harley-davidson have a method of forming complex al. tube shapes very accurately (well i saw them doing it, don't know if anyone else does).

Basically they get the shape roughly correct with a tube (bent, cut and welded), then put the pipe in a steel machined mould. They close the mold around the pipe and whack HIGH pressure fluid through it, to swell the tube out to the shape of the steel mold.

AFAIK they get +/- .5mm tolerances on it.

Only problem is going to be the cost of tooling.

Cheers,