CNC for Aircraft Parts

[ScaleBirdScott]

Hello Zone-goers,

I'm an Industrial Designer, and I have been working on a sort of 'dream project' to build my own fighter plane. To be specific, a 5/8 scale replica F6F Hellcat, built from aluminum sheet over a steel truss frame. My father a few engineers, and myself, have been designing and planning this project for about 3 1/2 years now, and we're getting to the point where we've begun cutting parts.

But paying someone to cut parts for a one-off project is prohibitively expensive: at the most bare minimum doubles the cost of a sheet. And we have so many sheets to make. Now, if it was just aluminum we could probably find a vendor that can do all our sheets at once for a reasonable price eventually. But! In addition to cutting our aluminum sheets, we also need 'forming blocks' to go with many of these sheets to let us hammer our flats into final shape.

It's all very basic work, and if we had the patience and time it can certainly all be done by hand. But over the hundreds of parts that must be cut and formed and so-on...

So anyway all that to say, I've finally persuaded our 'team' to bite the bullet and build our own CNC router table as it should ideally cost less in time and funds and shed tears than the 'old fashioned way' or the 'quick and simple sub-contraced' way. One of my engineers has built a small CNC table before, and I have machining and 3D printing experience, and have some exposure to routers from college. We have welders and presses and sheet metal breaks in our shop already so... So I'm not too concerned about being able to build a quality rig. But it also doesn't need to be perfect this first time: I mostly just need to be able to do a better job of making small shapes from big rectangles than one can with tin-snips in one hand and a beer in the other...

And to further drive home the idea that it shouldn't take much, if you look at this page, you can actually see someone doing basically all I've just described to you with a wood-frame unit:

Thatcher CX4

(and perhaps that fine fellow is a member here and I'd love to talk shop about our various aircraft as that page has been inspiring!)

So long story short: I'm convinced that building our machine in-house and without going overboard on it is the best current situation for the project.

The purpose of this thread here, then, is that I have built some requirements for our 'ideal machine' and I'm trying to get some feedback on what would be reasonable for this project and what is a good thought but maybe not now, and what is like... no way.

So thusly my requirements are:

• 4x8 cutting area, to use full sheets of MDF and Aluminum to their maximum potential. We have some parts that reach into the 7ft long zone, like wing spars and skin panels... I ain't getting by with some dinky 2x4 desktop mill.
• Enclosure so that errant dust doesn't get into other parts of the shop, and to keep noise down. As this machine is going to be in a house, it's not a good practice to get aluminum and mdf dust into the works any more than we already have been. Plus there's people who aren't crazy living there who like TV. I know that my little plexiglass enclosure won't do much for noise but it's more symbolic, and it'll at least look legit. I'm wondering if the enclosure by itself would preclude needing a high-power dust-vac system when running.
• A frame and drive system rigid and capable enough to cut through .032 2024 aluminum in single passes. (I can't imagine that is hard, but I read accounts of people building bots that would only take .005 cuts for al, and that's just way too lame for us to bother with. I know these routers will blow through the sheet on a hand-op router table.)
• Accurate enough that I can confidently match-hole drill pilot holes for clecos. (I will always be stepping up mated holes for rivets/whatever else, but I need some kind of starter holes to align things. For profile cuts and arcs the tolerances are generous. Generally in the +/- .015 range over 12-24" as a ballpark guess.)
• Looks awesome. (It's gonna be in a house, and we're gonna have people over to see the project and take lots of photos, and I'm an artist and designer damnit I have a reputation; I won't accept a kluge of a machine as part of my project. It should look at least semi professional. I wanna paint it nice and have somewhere on my gantry for 'nose art' if you can follow my logic there...)
• Space saving. (I've either gotta be able to stow this thing or use it as a work bench when I'm not cutting. So my thoughts are folding table style frame, or mount the CNC pretty-much on the floor and build a work-table directly on top of the machine so I can rivet wings or weld fuselage while its cutting away my happy parts.)

• Versatility. So this is counter to what I said above but, ultimately, I'd hate to spend this time and money on a tool that just makes an airplane (I think many, however, would be extremely satisfied with a tool that could do half of an airplane?) so I'm thinking about some product development opportunities that would arise from such equipment
  
  • What would be needed beyond what I listed above, to use a machine like this for 3D milling of nylon blocks? I have a lot of widget parts that I've been trying to get quotes for low-cost molding or machining from plastics, and I'm running into that valley where I have maybe 100 customers for a niche good, but no way to get a vendor price low enough to make it realistic. I know why I'm getting these results but still, frustration! But if I could make my own...
  • So I'm thinking the ability to throw in a big slab of plastic and just have a router cut it to shape would be a reasonable solution. In this case we're talking handheld-size products and accessories, like adapters and grips and what-not. I've been 3D printing my prototypes on a Makerbot 2, and they work great, but the finish and build times are no good for production. But are the turnaround times for a decently finish-passed 3D part any better on these types of machines? Is there are reason almost all 3D work I see on youtube is in wood and foam and not in acrylic or nylon? I know that it comes to speeds and feeds but, imagine that I'm going with relatively budget drivers and a cheap spindle or router... what are my realistic options?

So I know this is a lot of text! And I have no reputation here yet... and I'm a bit new to all this for sure. But I've been doing a lot of homework and I have pages of sketches, I just figure I should start a thread here and make a toehold on this project. Speak it and it will become real.

-Scott

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[ger21]

I'm wondering if the enclosure by itself would preclude needing a high-power dust-vac system when running.

Absolutely not. But a good dust collection system may preclude the need for an enclosure.
Cutting without dust collection would literally fill every inch of your enclosure with a layer of dust. A good dust collection system will catch almost all airborne dust.

Space saving. (I've either gotta be able to stow this thing or use it as a work bench when I'm not cutting. So my thoughts are folding table style frame, or mount the CNC pretty-much on the floor and build a work-table directly on top of the machine so I can rivet wings or weld fuselage while its cutting away my happy parts.)

A folding table is not realistic.
As for building a workbench on top, keep in mind that a 4x8 cutting area machine will be at least 5'x9', so a removable top might be large, and rather awkward.
You may find it possible to work right on the machine bed itself.

What would be needed beyond what I listed above, to use a machine like this for 3D milling of nylon blocks?

Nothing, other than a method of holding the blocks down.

Is there are reason almost all 3D work I see on youtube is in wood and foam and not in acrylic or nylon?

No, there's no reason. Plenty of people are making plastic parts with CNC routers. Just be aware that not all plastics are easy to machine.

But are the turnaround times for a decently finish-passed 3D part any better on these types of machines?

Depends on the part, but should almost always be much faster than a 3D printed part. Unless the parts are very complex.

I know that it comes to speeds and feeds but, imagine that I'm going with relatively budget drivers and a cheap spindle or router... what are my realistic options?

I'm not really sure what you're asking for here?





There's a member on the MechMate forum that recently built a Mechmate specifically for building airplanes, and cutting aluminum sheets.

I'd probably recommend a Mechmate or CNC Router parts machine. What's you're budget? You should probably expect to spend somewhere in the $5000-$7000 range.

[ScaleBirdScott]

Absolutely not. But a good dust collection system may preclude the need for an enclosure.
Cutting without dust collection would literally fill every inch of your enclosure with a layer of dust. A good dust collection system will catch almost all airborne dust.

I'm sure it would go quite quickly into an abysmal state with no vac at all. I was thinking I'd still run a vac from the spindle but I figure I'd keep it minimal, and the enclosure slides would be more for keeping errant particles somewhat contained to at least the bot zone until after a job where I can go through and detail it. I guess I'm just used to running machines with enclosures.

A folding table is not realistic.
As for building a workbench on top, keep in mind that a 4x8 cutting area machine will be at least 5'x9', so a removable top might be large, and rather awkward.
You may find it possible to work right on the machine bed itself.

Yeah a folding table seems silly. As for the work-space, the 5' width is starting to get excessive for reaching the middle, but, our outer wing panels of the airplane actually take up almost the entire surface at that size, and so we will need a decent-size bench to at least that scale. Plus the fuse frames take up a good amount of that space if I were to weld those up on there as well. But maybe it would be best to make a way to protect the side rails and then run the gantry to one end, to use the remaining space for work surface?

Nothing, other than a method of holding the blocks down.
No, there's no reason. Plenty of people are making plastic parts with CNC routers. Just be aware that not all plastics are easy to machine.

I've got a feeling GRP Nylon is not the easiest machining, but, that would be sweet. I figure there's a few suitable materials for any given project.

Depends on the part, but should almost always be much faster than a 3D printed part. Unless the parts are very complex.

Yeah I figured as much. Between having to run at ridiculously small layer heights and all the zig-zagging, there's a lot of parts that take me 12 hours to print that have 10 minute cut times on a HAAS. I know this isn't a VFC, but even 2 hours vs 12 is a massive leap.

I'm not really sure what you're asking for here?

I was just stating that anyone could build a machine capable of plowing through styrofoam with some old 2x4s, printer parts, a salvaged dremel and a Gameboy Color for a drive; and maybe you could still eventually carve your way through a billet of aluminum to the statue hiding within: but it won't be practical for any halfway serious work that I would imagine. The key for me is to not go too-far beyond what serves the immediate purpose, its real easy to justify each part up a few dollars and turn a $4k build into a $7k build.

There's a member on the MechMate forum that recently built a Mechmate specifically for building airplanes, and cutting aluminum sheets.

I'd probably recommend a Mechmate or CNC Router parts machine. What's you're budget? You should probably expect to spend somewhere in the $5000-$7000 range.

I will look for that member.

The kits I am inspired by, but I'm not sure I want to buy a full kit; maybe an electronics package. My budget has been in the 4-6 range, including new bits and accessories, having some computers and drivers already from another CNC project.

[nlancaster]

I am in the process of assembling a CNC RouterParts standard 4848, 49ishx49ish x 6 cutting area. I went for the DIY Nema 34 electronics and I am in for about $6k with all the other bits and bobs to assemble the machine. Many people really like them and they seem to do very good work.

[ScaleBirdScott]

nlancaster: did you go for the structural kit from them or building most things from scratch, simply based on their plans and buying an electronics package? If from scratch are there parts you'd be changing for your needs?

I'm about halfway through designing my concept table/frame hybrid with true 3D dimensions, to see if it is a viable form factor. I'll attach screenshots below. (And I'm planning on continuing down this path so I don't know if this all belongs in another area of the forums if it's becoming a design/build thread or maybe I'll start something else?) Either way, as my design is shaping in 3D, it seems everything fits; the only main concern is how to run vac hose for dust collection without going up and over the unit as I still want a work surface above it: I'd need some kind of horizontal service loop setup suspended from the 'ceiling' over the gantry, and then runs to a 90' elbow at the Z-axis. I bet that will have an impact on efficiency but I'm not a fluid dynamics guy so I'll consult the engineers on that one!

I'm thinking that from a design standpoint, it seems that the only reason most gantry routers are setup the way they are, is to minimize structure needed to build the table: you can combine your table supports with your rail/track support and save from redundant strong beams that stretch the length of your unit. But you end up with a gantry that has rollers and drives far down near the bed surface, and then sometimes rather long arms to raise the actual gantry rails. This seems like it'd create a lot of moment on the gantry, even if it is supported in plane with your cutting.

Looking at my Makerbot it has a suspended gantry design, and I'm wondering if not the same is viable here? Certainly a 3D printer is seeing zero tool load vs a cutting router, and a moving Z platform is not practical at 4x8 feet: but I don't see why I couldn't have my X-axis rails and drive at the same level as the Y-axis if I'm willing to construct the proper structure for it; and use only the Z-axis to drop down to my part. It seems like how some5-axis machines are setup, and there's examples such as this:



That uses X rails definitely above the bed plane; But that example has almost no Z-clearance because it's still a direct connection to the frame at the bottom. I would still raise the whole system a good distance above the bed using a strong steel frame, with trusses if required, to get maybe 10 inches of gantry clearance.

Also note how the Z-axis is centered between the Y-rails, vs being cantilevered out over the part. Both that design and the gantry on my Makerbot put the tool between the gantry rails. Other than eating up extra space, is there any reason to avoid that setup? It seems that it could save weight overall if designed properly.

The only thing I've read that would suggest against having the X-axis raised up above the bed, is that there would be more twisting load on the gantry by not being supported where the cutting tip is. I figure though if the cutting tool is centered and not cantilevered, it would balance the side loads. I also thought about how cool it would be to have a 3rd set of rollers and a bottom rail that would not be load bearing but might help with some anti-racking action, and give me a perfect place to put a cool side panel and that nose-art I was talking about. The side arm panels would be very lightweight, made of bent 6061 sheet and riveted gusset construction, so it should function to stiffen the assembly and keep some 'cutting plane' contact without a lot of mass. They weigh a paltry 4 lbs in total. Also the lower roller rail will double as a track for my bed to slide out from under the table for loading/unloading, like an oven rack. I know that feature will likely kill my ability to hold zero between jobs, however it should be fine.

Anyway, like I said, I'm still kinda new at all this, and my ideas may be mostly nothing new and maybe long-proven bad from the pioneers. But there's no single features here that I havn't found used elsewhere, just not all of them in this config.

[nlancaster]

I bought the entire kit, i know I could have saved money by sourcing my own 8020 extrusion. But I just didn't want the hassle of having to track down and probably cut the correct lengths. I did build my own table from Timberstrand lumber and plywood.

[ScaleBirdScott]

Hi guys a quick update:

I've continued the design on my own router table, I'm calling the "Hellcat" after my favorite WWII fighter.

However I have a stronger need for parts than I do to use my own router design. Plus, to do the machine I want right, I diddn't want to be hacking and templating and filing parts to shape without a CNC to start with. So I will call the custom design a 'stage 2 upgrade' shall we say; and our project went looking for a CNC kit that will get us to the point of building the "Hellcat" and also making some other parts in the meantime.

I was looking at a CRP4896, but that would be a serious machine and wouldn't warrant replacing by design, and the price was steep. I had been looking at the CNC mogul stuff, but it was out of stock and reviews have ranged from satisfied to 'ok but with serious flaws' to downright scathing. Well a week ago I noticed they had updated their page with a new '6.0' model that is in stock, and the price for the mechanics-only kit was astonishingly good, and the improvements in the design actually seem to be a step in the right direction for helping to beef up their very minimal design.

So we said screw it, and ordered the new CNCMogul kit in 4x8. We still havn't gotten the electronics/drive package, but i'm thinking a G540 driving NEMA34 is the recommended 'high end' for this machine and from what I'm reading should be alright in terms of speeds and capabilities.

I was also thinking I'd just suffer through the noise of my PC690 router for the next couple months, but Mike at CNC Mogul was letting me know that a spindle would probably handle the aluminum work with better results, and from my milling experience I'd agree, so now I'm looking at budgeting for a 2.2kw spindle setup!

So yeah, I havn't found any info on the new CNC Mogul 6.0 kits as they are very new, but also scant little with the older CNC mogul kits other than a few discussions which, ultimately leave me neutral on the company between the pros and cons. But a whole moving 3 axis platform for my router for the cost of just a Z-axis on some other machines, while I know one gets what they pay for especially in this world, I'm making a bet that 'good enough' will get me to the next step with better results.

[alan_3301]

I had never heard of cncmogul had to look it up, I don't think you will be impressed at all with how it performs.
That design looks like it should max out at 2ft x 2ft, I can't imaging a 4x8 ft one.
The extrusions looks fairly flimsy, and delrin wheels are not rated for any serious load.
$685 for a machine that size is a good indication of what you are getting.


No disrespect if the creator of that kit is on here, just my thoughts.

[alan_3301]

Also, don't bother with the extra money for nema 23 stuff, it is way overpowered for that machine frame.

[ger21]

I think he meant don't bother with the Nema 34. Nema 23's properly matched to a G540 are more than powerful enough for that machine. I wouldn't even bother with the spindle. The frame of that machine will be the limiting factor, not motors and spindle.

[alan_3301]

oops, yeah that what I meant.

[ScaleBirdScott]

From what I've seen of it on youtube for the older ones, it should get through the basics. I know I'm not getting a steel frame, steel rollers, or anything fancy. But it's the bare essentials of moving a cutting bit around in 2-3 axis with computer control at a reasonable price and from what I've seen on youtube videos it's going to be a solid-ish starting point towards the next step... which is another reason I'd rather buy one solid set of NEMA motors to pass along. I mostly just want to be able to design and cut gantry plates, Z-axis plates, etc without eyeballin' it, or borrowing shop time from someone. I want to learn this stuff myself at any rate.

I'm thinking once I get a nicer table built, I'd move the motors and spindle to that and then depending on how I feel about the design, pick up some parts and cut the mogul in half; into two 2x4 frames using lower-cost motors and spindles and use them to cut the smaller 'prototype plastic parts' I need made. Or, keep it big and use it for cutting vinyl or laser work where it doesn't have nearly the tool loading. Doesn't seem terribly outrageous a plan in either case.

Oh, and for composites work, seems I could cut cloth to shape with the right cutting tools, maybe a dragknife.

[bconn]

Make an enclosure out of 8020 with canopy door hinges. Add table top vac system


Bruce Connally
Woodone US Corporation