3D Printing 4” 3D Printed Nosecone for Madcow Cricket Clone

[user 35735]

Hello all! I just got a giant sheet of plywood and have some extra tubes lying around and I was thinking about building a clone of the now discontinued Madcow 4” Cricket. I still need a shorter oligave nosecone with some bbs and epoxy in the tip. I was thinking about printing a generic one in PLA but wasn’t sure how to secure the shock cord. I’m concerned a printed loop/screw hole/etc. wouldn’t hold up and was instead thinking about either epoxying a bulkhead with an eyebolt into the shoulder or epoxying the nylon shock cord right along the interior of the nose. Any ideas on how to best to keep the nosecone on?

 

[thzero]

Honestly, I'd use PETG... if you can print PLA you can do PETG, and it'll handle the outdoor heat better. cwbullet has been advocating PLA+ too.

If you have a shoulder like most plastic tubes, you can probably get a 4" bulkhead in there (the flexible plastics used in blow molded nose cones flex, whereas the print may not) you can use the shoulder lip as a mechanical aid as well as the epoxy. I've actually had some good luck with Bob Smith (oddly enough) and PETG, but I wouldn't trust any epoxy without mechanical aid. Also have used

For a 2.63, I just designed in an attachment point at the base of the shoulder. Then used t-nuts with JB Weld to attach a eyebolt or such to. The t-nut is on the backside of at least a 1/4" thick printed layer.

Here is a pic of my 2.63 that was done in sections (yes, it got a bit wobbly at the top )



Then for the shoulder section, you can see the designed in attachment point with the t-nuts. I actually used a standard LOC bulkhead with three bolts to attach to the nose cone, then the eyebolt is in the center of the bulkhead. Distribute the load a bit.




Keep in mind, the strength of printed nose cones is weakest where the layers are joined together. I had one snap, even across layers, from a bad landing. So I've started doing a layer of fiberglass on the outside.

 

[Arsenal78]

Honestly, I'd use PETG... if you can print PLA you can do PETG, and it'll handle the outdoor heat better. cwbullet has been advocating PLA+ too.

If you have a shoulder like most plastic tubes, you can probably get a 4" bulkhead in there (the flexible plastics used in blow molded nose cones flex, whereas the print may not) you can use the shoulder lip as a mechanical aid as well as the epoxy. I've actually had some good luck with Bob Smith (oddly enough) and PETG, but I wouldn't trust any epoxy without mechanical aid. Also have used

For a 2.63, I just designed in an attachment point at the base of the shoulder. Then used t-nuts with JB Weld to attach a eyebolt or such to. The t-nut is on the backside of at least a 1/4" thick printed layer.

Here is a pic of my 2.63 that was done in sections (yes, it got a bit wobbly at the top )

View attachment 496128

Then for the shoulder section, you can see the designed in attachment point with the t-nuts. I actually used a standard LOC bulkhead with three bolts to attach to the nose cone, then the eyebolt is in the center of the bulkhead. Distribute the load a bit.

View attachment 496127


Keep in mind, the strength of printed nose cones is weakest where the layers are joined together. I had one snap, even across layers, from a bad landing. So I've started doing a layer of fiberglass on the outside.

How do you glass a nose? I printed out a 4” HoJo nose that I wanted to do a layer of glass on.

 

[thzero]

This is all based on what others have done with fiberglassing tubes, and some blokes in Australia with their high power water rockets...

I measured the outline of the nose cone onto paper. Then depending on the size of the tube, either use that (i.e. for 2.56" it was fine) or cut it in half. Those are basically your strips. You may need to adjust at the top so as to not get too much overlap and therefore increase the diameter of the tip. I used 3 ounce cloth that I had.

Then do the same with the release fabric.

Now mix up your laminating epoxy (I used West Systems 105/205). Then section by section, coat epoxy with some overlap, apply the strips of fiberglass. I have been using small foam brushes (avoids any lose hairs) and just dab at the fiberglass to get it to laydown and impregnate with epoxy.

Now that you have the nose cone layered with the strips of fiberglass, do the same with the strips of release fabric.

Now sit and let dry. I did not vacuum bag or anything with mine - if you have it, its probably a good idea.

Oh make sure to cover the shoulder with mylar and plumbing tape so that you don't get epoxy on it.

Again, this is how I've done it - and I've only done it now a couple of times.

The HoJo may be a bit more challenging due to the shape.

 

[Kelly]

I'm getting close to needing to glass a 3" printed NC, and I'm thinking about maybe glassing it internally. It seems to me that one of the locations of possible layer separation/fracture is right where the shoulder ends, and there's no good way to glass over this juncture externally. By glassing internally, I also don't need to worry about getting good conformance of the glass to the cone, and I don't care if there are some gaps or overlaps in the fabric. I've glassed long, pointy-nosed cones before, but I think this would be tougher with a rounded nose , or the HOJO as you point out. The disadvantage is, well, having to work inside of a small cone.
What I'm thinking is, I'll print the cone, and cut out maybe 4 strips of glass cloth to cover the inside. I'd apply the epoxy with a long-handled brush, insert the glass and maybe a release fabric, and then inflate a latex balloon inside the cone.
Thoughts?

 

[thzero]

That should work... I did essentially that with a custom coupler.

 

[BigMacDaddy]

How thick do you guys print the shells of large nose cones like this?

 

[thzero]

I have been doing the same thickness as the tubing wall thickness, i.e. if its 1.1mm thick since I am using .4 nozzle size I do 1.2mm thickness

 

[BigMacDaddy]

I have been doing the same thickness as the tubing wall thickness, i.e. if its 1.1mm thick since I am using .4 nozzle size I do 1.2mm thickness

Cool thanks -- is that the total thickness of the walls of a nose cone or outer layers of the print?

I also usually do 1.25mm walls on my smaller models to assure 3 layers thick with a .4mm nozzle and 1.65mm if I want to make things a little stronger with 4 layers. However, I assumed you guys would do much thicker on the larger nose cones (although I guess if you were going to fiber glass it then maybe that is not necessary). I also worry less about weight on nose cones than I do on other parts since I am usually adding nose weight.

 

[BigMacDaddy]

I also wonder about where to attach shock chord in a large nose cone like this -- near the base of nose cone or up closer to the tip?

As you guys highlight the layers can rip away so I have been thinking of ways to attach the shock chord directly to the weights in the tip of nose cones for my larger models. I wonder for something as large as 4" if you could print a separate top section / tip of nose cone with compartment for weight and mounting nuts, etc... (great design @thzero) for shock chord mount. You could then put any weights in that tip portion and basically fill the whole tip of the nose cone with epoxy. This would mean your shock chord would feed through most of the nose cone and it might be a pain to reattach if it ever detached but this would direct pulling forces to strongest portion of the cone (rest of cone would just get some compression forces which 3D prints would be less vulnerable to).

 

[thzero]

I've only printed 2.56" and below at this point. Certainly there is a weight vs strength to consider, but at least for the smaller ones I just did 1.2mm and made sure that the slicer was showing the three layers.

Yeah, that was something I was considering also. The 2.56" rocket I put together initially clocks in around 42.2 ounces, and 67.1 in dual deployment mode. But its still down to any one of the layers letting go to cause an issue. In the several flights I have with it, I haven't seen any issues with it thus far as far as deployment attachment point goes. Theoretically it should only really have the weight of nose cone (and anything you have in it as payload) that is acting forces on it during 'deployment', which if you have a long enough shock chord should hopefully reduce the stresses.

But if I were printing something bigger, yeah I'd be looking at something like you propose. Create a shelf that is as deep as you want to go for attachment purposes so that you aren't filing the entire tip of nose cone with epoxy, with some sort of t-device as an attachment point. The t-device would have a rod horizontal through the nose cone and through the epoxy. Then a vertical rod attached to the horizontal rod as the attachment point. The t-device would be buried in epoxy. And the epoxy block would be mechanically connected to the surface of the nose cone via the horizontal rod, just as others have done with standard plastic nose cones. The compression forces then are acting through many layers, which is good. Even if the nose cone were to separate at a layer at or above the horizontal rod, you should still be fine.

https://www.rocketryforum.com/threads/my-l2-project.167503

In post 28 and 37, I did something like the t-device using a coupler and threaded rods. Had to drill through the coupler with a drill press and cutting oil. Then buried the coupler and horizontal rod in epoxy in the tip of the nose cone. Granted its a molded LOC nose cone. But think same should work for a printed one too.

 

[thzero]

I know some manufacturers are using 3d printed nose cones on bigger rockets, but have no idea how they are attaching. One I know that was called out recently was the Fusion Rocket (https://www.fusionrocket.biz) with their Nike Smoke and Diablo... if you can get some hands on their instructions, might be interesting to find out their suggested method.

I do have a 3D resin printer on the way - there are just some parts that I want to print for other purposes that need the detail - however I'm curious to see if like a Strong-X or Tough-X resin will print a nose cone in parts and how it compares.

Also thinking of printing horizontally instead of vertically. Printing horizontally on my FDM has never given me a nice rounded object (probably my setup, hobby grade printer, gravity, etc) but maybe the resin printer would do better. Printing horizontally would mean layers wouldn't separate based on the pulling forces with attachments.

 

[thzero]

Just saw in a Thor thread under HPR section, about coating the inside of nose cone with epoxy too. Epoxy does soak into the print (at least with PLA and PETG it seems to) as I mentioned in the other thread.

Also, not sure the design, but you could go a lot less complex and just have a bulkhead sitting on the shelf formed by the coupler? Granted, some issues with layer splitting, but again forces acting against multiple layers. And hey if the nose cone breaks off above the bulkhead, um, not good but at least anything attached to bulkhead will get returned.

 

[Scottydog1]

I know some manufacturers are using 3d printed nose cones on bigger rockets, but have no idea how they are attaching. One I know that was called out recently was the Fusion Rocket (https://www.fusionrocket.biz) with their Nike Smoke and Diablo... if you can get some hands on their instructions, might be interesting to find out their suggested method.

Or better yet.... I'll tell you. On the Nike Smoke, there is a lip printed into the base of the nose cone - a laser-cut bulkhead is epoxied into the base at the lip. On the Diablo, we use a 2-piece cone with a lip printed into the top of the base, and it uses a standard 3" coupler for the shoulder. The cone again comes with a laser-cut bulkhead plate that is epoxied into the nose cone base before the 2 pieces are epoxied together. There is a slot in the plate that allows the shock cord to be passed through, then a knot is tied in end of the shock cord before the nose cone tip is glued on..... From the drawing you can see that there are provisions for bulkhead plates in the coupler, as well.....

And yes - we recommend coating the inside and outside of EVERY 3D-Printed part we make. They're just simply not ready to fly until that's been done. We use 12 minute epoxy thinned with 70% isopropyl rubbing alcohol, or West System 105 resin with 206 hardener, which dries rock-hard and is sandable the next day.

 

[thzero]

Yeah.. that works. Sorta what I do a lot with the plastic madcow, loc, etc. nose cones.

 

[boomtube-mk2]

Long ago, somebody from this forum 3D printed the above nosecone for me. It is a BT-101 Big Bertha style.
Powered by 3 D-12's, fiber-glassing it would have been massive overkill.

Good luck on your build.

 

[dr wogz]

Does epoxy really stick to the plastics? or does it just hold onto it by sheer love & the imperfections of the 3D prints..

PLA has been notoriously hard to 'glue to'.. and most epoxies I know of rarely stick to plastics.

 

[0011001100]

Does epoxy really stick to the plastics? or does it just hold onto it by sheer love & the imperfections of the 3D prints..

PLA has been notoriously hard to 'glue to'.. and most epoxies I know of rarely stick to plastics.

I've had good luck with abs and asa but those can also be dissolved in acetone and so they may actually react with epoxies. Petg on the other hand has been harder but doable though I believe it is more of a mechanical bond and if the surface isnt sanded then it can flack off.