CD's and DVD's as Fins

[nukemmcssret]

I saw a thread about using CD's or DVD's as fins for a rocket. I have tried cutting a CD in half and all I get is melting material. Even at slow speed. Does anyone know how the CD's were cut? I have not tried 10,000 hobby knife blades. This seems a hassle. Any suggestions would be helpfull. Thanks NukeMMC

 

[jeff_in_AZ]

There are some suggestions here:

https://www.rocketryforumarchive.com/showthread.php?t=3614&highlight=CD+fins

 

[Bone Daddy]

This was probably one of my threads.

I use a really lousy band saw with a wood cutting blade. It will melt the edges a bit, but it's easily cleaned up with some sandpaper. My general response to precision cuts is sandpaper and files.

A scroll saw would be pretty sweet. A fine toothed hacksaw would work also.

There are two threads that I remember.

Disco Queen and Disco Bird.

Disco Queen is a 3 cluster with standard size CDs Disco Bird uses Mini CDs.

Anyway, they fly really nicely and I like the look.

Let me know if I can help.

 

[Micromeister]

I have to say the use of CD or DVDs as fins is not a good idea, While both are a laminated form of polycarbonate the process used to produce the media makes them quite brittle and shatter nicely with even moderate impacts.

I learned this the hard way with CD spool rockets which broke on every flight. A much better Idea is to buy and use clear Polycarbonate sheet. .030" to .080" makes Great nearly unbreakable fins or spool discs. the CD spool model below suffered a C6-0 Cato in November distroying the model but the discs are intact to be used again. Beware of LOW temperatures...below freezing Polycarbonate can and will crack and shatter just like most other "plastics".

Ps. I use a lot of Clear Polycarbonate for fins on Scale, Odd-roc and Plastic model conversions. Beleive me when I suggest Polycarbonate....Clear unprocessed Polycarbonate is the very best choice for "plastic" fins on any micro, Model or MPR rocket.
Hope this helps.

 

[RocketT.Coyote]

I used to work in plastics R&D. Polycarbonate usually melts at about 300C and has to be conditioned in a drying oven for 2 hrs at 102C before being fed into a molder.

 

[Micromeister]

I used to work in plastics R&D. Polycarbonate usually melts at about 300C and has to be conditioned in a drying oven for 2 hrs at 102C before being fed into a molder.

Did you mean degrees F not C? Still those numbers are above and below the actual working temperatures used outside the lab.
I'm in the Sign buisness, we use (vacuum form) Polycarbonates and other plastics almost daily.
Drying Polycarb sheeting is done in a 260°F (126°C) oven for 4-24 hours dependent on thickness sheet thickness .030" - .250". 4 hours for .063" to .125", 12 hours on .187" and 24 hours for .250". Forming is done between 340-400°F with the best average right at 375°F (191°c) for the sharpest detail defination for most .080" to .250" applications.

None of the above however have much at all to do with the Laminating/heating process used to produce CD/DVD media, which also involves a chemical etch and other processes that dramatically chance the structure of the finished material.
That is why the suggestion was for straight clear S-100 Polycarbonate be used instead. I'd be a little leary of even pigmented S-400 Sign grade White or colored polycarbonate as fins since the simple addition of color pigments change the impact resistance of the sheeting.

NukeMMC: if you really think you must use CD/DVD's I've had fair luck cutting them on a band saw with 1/8" x 18T blade at about 2500-3000fpm. or on a mini table saw with an 80T carbide tip blade at about 6000rpm. Drilling holes with standard metal bits at 1750rpm for 1/8" holes and much lower as the hole size increases trying to use as little pressure on the drill or bit as possible. Please ware gloves and face/eye protection while drilling or sawing because if the bit or blade snags the disc will shatter with shards flying....Please be safe.

 

[Zack Lau]

CDs are easily cut in a sheet metal shear. I've cut Lexan up to 1/8 inch thick. Polycarbonate doesn't shatter like acrylic or Lucite.

 

[Micromeister]

CDs are easily cut in a sheet metal shear. I've cut Lexan up to 1/8 inch thick. Polycarbonate doesn't shatter like acrylic or Lucite.

CD's and DVD's crack, break and shatter if bent.

 

[Zack Lau]

I had no trouble cutting up a 700MB Sony CD-R--nice clean cuts with the Pexto sheet metal shear. The shear also works great on G-10 fiberglass.

 

[new2hpr]

In the process of destroying CDs for security reasons, I found a huge variety in the materials. Most of the commercial CDs (not CDR or CDRW) shattered upon bending. Most of the CDRs were a bear to break up. Some would require repeated folding until they finally broke through. Must be a different recording layer in the CDRs vs. stamped ones.

-Ken

 

[Micromeister]

In the process of destroying CDs for security reasons, I found a huge variety in the materials. Most of the commercial CDs (not CDR or CDRW) shattered upon bending. Most of the CDRs were a bear to break up. Some would require repeated folding until they finally broke through. Must be a different recording layer in the CDRs vs. stamped ones.

-Ken

Very possibly Ken..
I've had a couple that needed to be folded, but the vast majority have shattered.

 

[dragon_rider10]

Micro,

What's the best adhesive for the poly to the body tubes? Epoxy?

 

[Micromeister]

Micro,

What's the best adhesive for the poly to the body tubes? Epoxy?

Yes: Over time i've found the very best method for joining clear Polycarb fins, dissimilar materials and/or unknown plastics to be the (Epoxy Rivet Method).
We just had a club demo on working with plastics last month. the Text of that demo is now in the library section as Tech Tip-017 on the narhams.org website if your interested. has a bunch of how and whys on a bunch of plastic types, suggested methods and materials. Epoxy rivets are explained in detail. I'm currently trying to finish up the photos that should accompany that article. Here's a couple referencing epoxy rivets.

 

[Zack Lau]

I've always wondered why string isn't used to attach fins to rockets--seems to me that string laced through a wooden support structure would be more impact resistant than epoxy rivets--maybe it doesn't look like a "real rocket" :confused2:

 

[Micromeister]

I've always wondered why string isn't used to attach fins to rockets--seems to me that string laced through a wooden support structure would be more impact resistant than epoxy rivets--maybe it doesn't look like a "real rocket" :confused2:

Not at all Zack:
Just more work then necessary Lacing or bolting with Nylon or other non-matallic fasteners for the matter could be a pretty decent fin mounting method, but the extra time and mass involved make them less attractive options then methods that have been tried and proven true for decades. The Epoxy Rivet Method has been employed in and on just about every conceivable fin type and body/fin material combination with superb results in all but the most extreme sweptback fin configurations.

You'll note the fin I'm showing in the demo mock-up photos have no overhang. These and similar fin shapes, clipped delta and others have proven over the years to be superior to fins that generally make first contact with the ground on landing, thus reducing the Landing load impact on the glue or epoxy joints. Other Swept fin configurations work but there is always the possiblity that enough landing force may flex the joint beyond the epoxies or Lexan's elastic limits.
Hope this helps

 

[Bone Daddy]

I remain a fan of CD fins. It's the easiest way to get a perfect semicircular fin.

This one has 12 flights, so far. One with an undersized streamer resulted in a hard hit and the body tube crumpling, but no damage to the fins. I just added a new piece of body tube. Not the prettiest, but I wanted to try a longer body tube anyway. The plan is to repair the body tube properly, but since she flies so well as is, it will probably never happen. I used superglue and epoxy fillets.

As far as drilling goes, make sure you use a piece of wood underneath. I also recommend clamping it to the wood so it won't ride up the drill bit when the hole is drilled.

I say go for it and post pictures so we can see what you came up with.