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Cutting Carbon Fiber with a Cricut Vinyl Cutter

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watheyak

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So I've been struggling with how to keep leading edges and tip to tip reinforcements intact during high speed (M2.7+) flights. Mach 3.7 in this particular project. I've been doing lots of combing through threads here, a flight or two of my own that illustrated what not to do, and some laying awake at night pondering.

I finally decided that I really liked someone else's idea, including what they learned, and what they would do differently. I am shamelessly stealing A5tr0 An0n's method outlined in this post and the thread that led up to it-


So my fins start with a high temperature core, and are one piece, rather than a separate leading edge. In this case it's Garolite G-11, just like in his thread. As illustrated in the link above, the tip to tip reinforcement sits in a pocket machined into the face of the fin. This project started by modelling the fin in Fusion 360.

Fin in Fusion.png


This pocket, plus the bevels, made for some complex machining requirements. Thanks to a very talented co-worker, I have four fins that are straight-up rocket art.
IMG-2707.JPG


IMG-2709.JPG


Because of that curve in the corner of the pocket, it occurred to me that it would be nice to have a very precise and accurate shape for the tip to tip reinforcement. Having a nice clean edge at the border of the pocket would help making sure it stays in place. Plus better aesthetics and style points, right?

More pondering and laying awake happened. I finally decided that I might be able to cut the carbon fiber on our Cricut Maker. The Maker has a cutting wheel attachment that is similar to what I'd be using to cut it anyway. It's also capable of adding quite a bit of pressure to the wheel.

de60a6f3617440d9eea96d3a31b891a5.jpg

This method wouldn't work for all carbon fiber, as it has to be stuck down to a carrier sheet to be cut, then peeled off after the cutting is complete. Regular carbon fiber would come off in shreds. But some of the newer, more modern products come on a carrier of their own. Some of the Hexcel spread tow products that are becoming more popular would be a good candidate. In this case I'll be using unidirectional prepreg that comes stuck to it's own carrier paper. Due to this fact, I peel the carbon fiber and it's carrier off the Cricut carrier sheet in one piece.

So next I modeled the whole thing in Fusion. I used the sheet metal tool to simulate the carbon fiber in order to be able to convert it to a flat pattern. I'm pretty new to Fusion still, so a big thanks to Bob Heninger for helping me figure the sheet metal part out. The flat pattern can be exported as a .DXF file, which can be imported into the Cricut Design Space software. Here's a few pics of that process.

Whole Enchilada.png


Template.png


Cricut.png


The other issue that keeps me up at night is that none of this is going to work at all if the fins aren't on exactly straight or if the fillets aren't exactly the radius (.25") that was specified in Fusion. I'll elaborate on how I'm trying to control that in my next post. The jury is still out as to whether I was successful in this regard or not. All this extra work might be for not. But still fun.
 

neil_w

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Super interesting! Looking forward to seeing this progress.
 

rharshberger

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Looking forward to your results, not sure how well it will work as the CriCut Maker seems to need lots of extra "sticky" to cut things without them pulling up on normal materials. Here's hoping for your success!
 

manixFan

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Wow, I like what you are doing. Those fins are very impressive. Using the sheet metal tool is very clever to be able to create the cutting pattern.

One thing I've been doing for fin alignment is using a two part, 3D printed alignment jig to keep the fins as perfectly aligned as possible. All three fins are mounted at the same time and under tension. I've done them for 38mm up to 98mm CF Mongoose kits. It's not perfect, but it seems to be a pretty good start on getting good alignment. Please keep us posted on what you do.


Tony

example test fit of the jigs:
completed-jig.jpg
 

FredA

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The fin jog looks great, but how do you keep the aft one from being glued on?
 

manixFan

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The fin jog looks great, but how do you keep the aft one from being glued on?
Ha! I learned that lesson the hard way with with a foam core jig I had made. So I added a chamfer to provide clearance for the epoxy, as shown below.

Another club member down here had a small pocket, much like on the fins above, machined into the body tube as a guide for the fin root. I think he also had small pins in the fin root that mated to holes in the body tube. However that was for a very stout 6" diameter body tube. In fact I'm pretty sure I saw him also use a fin jig similar to mine on a prior rocket which is where I got the idea.

BTW, those are some of the nicest looking fins I've ever seen, they are "straight-up rocket art."

Tony


(one thing I would do differently is add an extra perimeter for stiffness, not needed for smaller diameter for four the 4 inch I think it would have helped)
fin-align-jig-02.jpg
 
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watheyak

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Yeah Tony, that's a cool set of jigs. I especially like the rubber band tensioners. I may steal that idea too.

Here's what I did, yet another stolen idea. I think a university did it this way first, then A5tr0 and a few others, allegedly.

I had Nat at Upscale CNC make a pretty traditional set of fin alignment guides. They were put together with an array of all-thread. It's supposed to be able to be adjustable enough to get them parallel and what not...

Jig Cropped.jpg


But I guess I'm just not smart enough to make this setup work. I could make the plates parallel, but I couldn't get the two plates reliably centered over one another.

Ok back to the drawing board. Sacrificed a fin beveling jig, some shims... And boom... Not as slick as Tony's but it got the job done pretty well.

IMG-2715.JPG
 
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manixFan

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watheyak, as you mention the key is to come up with a jig that solves exactly the issue you described, keeping the jigs centered over each other. With my jig if the fit wasn't nice and snug over the fins, there was some play - I could twist the top jig relative to the bottom one. However that was mostly solved by adding a layer of tape on the fins, being careful to keep them all symmetrical. Doing some tests with the 38mm fins, the deeper the engagement of the jig (i.e., the longer the length of the fin held by the jig) the less twist I could apply to the top jig relative to the bottom. But at least it appeared they were all in alignment, even if a bit twisted. For my next 38mm MD, I am going to extend the length of the jigs to cover nearly the entire fin, that should prevent any twisting as long as I have a good width of the fin slot. One thing I have found with 3D prints, there are definite steps to certain dimensions based on the width of the extrusion.

Based on my measurements my 98mm fins appear to be very straight. I plan on putting a camera on the rocket and I figure that no spin = good alignment.

Tony
 
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watheyak

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Success!

I needed to make a new tube for this fin can after I had an issue with the Cotronics I was using. That's been addressed in another thread. But since I had the prepreg out of the freezer I thought I'd use a piece of scrap I had to test this.

For the material in Cricut Design Space I used "Monk's Fabric" which specified a pressure of ~3200 (near the maximum, not sure what the units are) and the wheel cutter. I used a standard grip mat.

Even though this was with prepreg, it could also be done with any non-prepreg so long as it comes on a carrier. All the Textreme spread-tow and many uni-directional fabrics would be good candidates.


IMG-2940.jpg


IMG-2941.jpg


IMG-2942.jpg
 

manixFan

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Wow, those turned out nicely! Thanks for the update.


Tony
 

JohnCoker

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Wow, very cool. I didn't even know those existed, but it totally makes sense.
 
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