John Kimball

Welcome to the forum. The basic rule of thumb for inserts is about 1x to 1.5x the diameter of the tube. So a 1.125" ID tube would be at least 1.125" and 1.7". It also depends on the use of the tube. If it's just a static load and you just want it stay in place, a shorter insert will be fine. But if you will see some shear, torque, or flex loading, you will want a longer insert. And as always, prep of both bonding surfaces is key to good adhesion. lightly abrade both surfaces (remove any shine so both surfaces are dull) and thoroughly clean with isopropyl alcohol.

Welcome to the forum! We get your question somewhat regularly. The answer is quite simple, but the math behind is a lot more complicated, as it all depends on the particular tube and how its made. While it's true that the fiber used in each tube may have a particular modulus, carbon fiber is considered anisotropic (as opposed to metals that are isotropic), so it only has strength properties in one direction, the direction of the fibers. When we make tubes, the fibers are oriented in a way that optimizes stiffness and reduces buckling. Because of this, the overall modulus of the tube is reduced. We call this a knockdown in performance. Most of the fibers are in the 0° orientation to create stiffness, but then the rest of the fibers are oriented in the 90° direction to decrease buckling (but these plies add nothing for the overall modulus of the tube). In some cases we may use +/-45° fibers to help with torsional requirements. In this case we should see a little bit higher tube modulus than with the 90° plies, but buckling is slightly increased. So, in a nutshell, if all the fibers ran in the 0° direction, you'd see a comparable tube / fiber modulus. But, when about 1/2 the fibers are not in the 0° orientation, but the tube tube dimensions are the same, you remove modulus from the tube as the 90° fibers add nothing, but they do take up space, so the tube modulus is reduced accordingly. Buckling (crushing, kinked garden hose affect, etc.) is high without the 90° fibers.

Make sure you are using the correct materials in the correct order. 1. Carbon fiber layup 2. Peel ply 3. Release film 4. Breather cloth 5. Vacuum bag The peel ply will help to evacuate any trapped air in the part. The release film will control the resin bleed and prevent the breather from sticking to the peel ply. The breather allows the vacuum to stay constant throughout the cure cycle. A general rule of thumb for me is that every layer of consumable vacuum system will be slightly larger than the previous layer. For example, if your layup is 12" x 12", then your peelply will be 13" x 13", Release film 14" x 14", etc. Without the proper materials and placement, the resin can bleed out too much and cause problems. And I can't stress enough the need for a leak proof bag.

This looks like a great start. My 3 observations: 1. As mentioned, you need to make sure the fiber is deliberately placed into the corners, one ply at a time. There is definitely bridging in all the corners. 2. Your vacuum port appears to be isolated from the breather on the part. You must have a vacuum path from the port to the breather on the part. This will help with the porosity on the surface and may help in the corners a bit too. Just add a strip of breather from the port to the part to achieve full vacuum on the part. Otherwise, the vacuum will seal itself off from the port and not pull vacuum on the part. In the video link above, you will notice that there is always a vacuum path the part. 3. It appears that you have enough bag and it's tucked in pretty good, but you may want to tailor fit the breather so there isn't too much overlap. too much breather can result in less vacuum pressure on the part. You could also use the the envelope bag method (from the video link) to use less bag and make the bagging easier.

Welcome to the forum. Sounds like a great project. We'd love to see your project. Post pictures if you can. The most important suggestions I can give when working with prepreg vacuum bagging are as follows: 1. Patience is a virtue. 2. Carbon fiber NEVER stretches. 3. The vacuum bag is not a magic wand for perfect parts. Having said that, the proper method for your application is centered around getting proper placement of the plies in the corners. Female molds are especially hard to get all the plies snugly placed in the corners without bridging (when plies don't touch each other in the corners and create a bridge or gap in the corner). Every ply needs to be deliberately and carefully placed into each corner. Start in the corners and work the material out to the edges. You are allowed to cut the prepreg and overlap slightly if it won't conform to the mold surface, just try not to have seams on top of seams, try to stagger them from ply to ply. The next step is to place your vacuum bagging plies as carefully as the prepreg plies. 1. Peelply - Peelply will not stretch, so place it the same way you place the prepreg, cutting the material where it won't conform. 2. Release Film - The release film can be placed without cutting it by folding the material on top of it's self, but if you need to cut it, use flash tape to hold it in place. 3. Breather fabric - It will need the same attention as the peelply, but it does stretch a little bit, so you can less careful. The most important step is the vacuum bag. You will need a much larger bag than the part to allow the bag to get into all the corners. The bag will most likely have wrinkles in it, and that's OK. After assuring that you have a leak free bag, let some air back in the bag and then carefully work the bag into the corners using your fingers or a dull pusher stick to push the bag into the corners as tight as possible. Attach the vacuum again and then check the corners for bridging. If you see bridging, repeat the process of letting air back in the bag and pushing the bag in the corner. Having too much bag is a blessing, and having a crease in the corner will allow for bridge free corners. You can watch the video below to see some of the bagging techniques. You can see how placement of the breather is important. Here are some other pointers that may help: Air leaks in the vacuum bag will reduce the amount of compaction the bag provides. Always find and seal any leaks in the sealant or vacuum bag. A simple crease in the bag on the sealant tape will cause a leak. Also, pin holes in the bag will cause leaks. NEVER place the vacuum port directly on top of the part. Always place it off to the side, but provide a vacuum path from the part to the vacuum port. Always place the prepreg or wet layup materials in the mold as tight to the surface as possible, especially in the corners. If you have thick laminates with more than 8 plies, a debulk operation may be required. Debulk is an intermediary step of vacuum bagging the part to compress the plies before adding more plies. In most cases, a debulk can be added every 4 plies if the part is very thick. Darting or cutting the prepreg to get it to conform to the surface is acceptable, but keep it to a minimum. ¼” to ½” overlaps at the seams is preferred. Try to not place seams on top of each other ( from one ply to the next). Think of brick a wall. The bricks are staggered to prevent cracking at the seams. NEVER assume that the vacuum bag will stretch the material or bag into corners. It won’t. Ever. Wrinkles in the vacuum bag are acceptable. Larger tools may require more vacuum ports to provide enough compaction for the entire part. About 10 ft2 per vacuum port is a good standard to use. A release agent on the tool (mold) surface is required. If not, you will bond the material to the surface. Sometimes permanently. Chemical release agents work best. A vacuum bag/Oven only cure will provide about 12-14 psi of equivalent pressure to the part surface. The addition of an autoclave can add an additional 40-150 psi to the surface. The more pressure you can get on the surface, the better the part will be structurally and aesthetically. It is also acceptable to press mold prepregs, but the thickness must be controlled to ensure that the resin is not pressed out of the material, and the press must be heated to cure the prepreg.

I'm not new here, but I should introduce myself. I'm John and I've been in the advanced composite industry for almost 38 years. I've experienced just about every aspect of composite manufacturing from grinding and sanding all the way through design, costing, and program management. Feel free to hit me up with any questions you may have.

David, As mentioned, repairing woven fabric is pretty easy, but cosmetically, extremely difficult. The first issue is finding the exact fiber and then matching the weave so you don't see any seams is a very time intensive project. The best possible outcome is to repair it properly for structural integrity, then skin the entire diffuser for a cosmetic look. Looking closely at the picture, you have a 3k plain weave fabric. Skinning is a time intensive project and takes some patience, but done correctly, you can get fantastic results. You can use the same fabric and resin for repair and skinning. You can find the fabric here: https://www.rockwestcomposites.com/13006-d-group. A good resin can be found here: https://www.rockwestcomposites.com/shop/pro-set-laminating-resins And Hardener here: https://www.rockwestcomposites.com/shop/pro-set-laminating-hardeners. I recommend the Pro-Set LAM-135 Resin with LAM-226 Hardener

Isaiah, The amount of load a tube can take will greatly depend on a lot of factors. Mainly, how it's loaded, how many tubes are loaded, how is the tube fixed, static loads, etc. For instance, if you are using the tubes as legs, then it would be a mostly compression load and would be spread around through all the other legs. But a cross member would take a bending load. The more you can share with the group, the better.

The locking mechanisms are positive lock, but with any multi-jointed system, you will get some play that you wouldn't get with a bonded or continuous assembly. You also get the fishing pole affect with telescoping assemblies. The smaller the tubes get, the more flex it will produce towards the tip. For large radio antennas, they need to use guy wires to control sway.

Carbon fiber can actually be very reflective to RF signals. Most space and airborne antenna reflectors are made of carbon fiber due to the reflective nature of carbon fiber and of course it's weight and stiffness properties. However, depending on the location of the antenna in relation to your signal, you may be OK. The biggest question is how stationary you need the antenna to be at full extension. Telescoping poles are a bit more flexible due to the joints. While 5 lbs is not a lot of weight, extended 100 inches in the air, you can expect to see some swaying. The bigger you can make the tubes (larger diameter tubes), the stiffer it will be. If some swaying is not an issue, then a telescoping system may be the answer. It should also be noted that the fewer joints you have, the stiffer the assembly. In your case, if you can allow for longer compressed length, you will reduce cost and make a stiffer assembly. For example, if you need 21" collapsed X 100" Extended, then you will need 9 sections. However, if you can extend your compressed length to about 36", you can cut it down to just 3 sections.

The basic response to this question is, The bigger the diameter and the thicker the wall, the stiffer the tube becomes. 150kg is not a light load, and loading only in the center makes is more difficult. Also assuming that the load will never be truly static as the person will be shifting weight and possibly bouncing a bit, the load could be more than that momentarily. If you have an aluminum tube that works, you can simply replicate it with carbon fiber and it will perform better and will be 2x lighter. As this a potentially life critical situation, we don't want to recommend or tell you what will work. We do recommend that you do some physical testing to ensure that the tube you choose will work in a dangerous situation.

An interesting question for sure. It really depends on how involved your chassis is. Most chassis are made from several pieces then welded or bonded together. In the case of a carbon fiber chassis, depending on the type of chassis, it may take 4 or more molds for the basic chassis, and possibly numerous stiffener molds, and several bonding fixtures to get a complete chassis. My guess is that if you were doing it full time and had access to proper software and design tools, you could expect to spend 6 months designing parts and then designing the molds and other tooling needed. Actually making the tooling could take even longer than that, as you would need to make a bunch of different molds. And to be clear, making molds also involves making master tools before you can make a mold. I just want you to understand the amount of time and dedication it will take to complete this undertaking.

The debulk process is just vacuum bagging the part for a few minutes to consolidate the plies before moving on. the more plies you have, the more loft the part will have. Debulking decreases the loft. On contoured parts it's very a very important step. The only difference in debulking and curing is the heat. Debulking can be as short as 15 minutes under vacuum or overnight. Sometimes a pressure debulk is needed in the autoclave, and sometimes a heated debulk is needed to help the resin flow a little bit. Typically, debulks are used every 4 plies, but depends on the thickness of the part. The bag can be reused for the debulks, but aren't usually used again for the cure.

Welcome. Hopefully the community can give you the help you need.

You may want to use epoxy resin to saturate the fiberglass. Wood glue is not meant to be used for laminating and may be too flexible in the end. Also, at thicknesses like that, it will shrink a lot, creating other issues.

The thing you should first consider is how the composite material will affect the acoustics of the drum. Different composite materials have very different resonance qualities. I'm not a drummer, so I don't know how the drum body affects sound, but I would guess that resonance and acoustics are a pretty big deal. Carbon fiber has higher damping properties than other materials including wood and even metal. It would be fascinating to see how this affects the sound. In theory, you could replace the wood with solid composite plates, but your time consuming efforts might be greater than with wood. The best option would be to redesign the process to take advantage of the composite materials and processes.

Yes, this is possible. You would just use epoxy laminating resin and some clamping force or a vacuum bag to get good consolidation. You would want to make your wood pieces larger so you can trim it to size after it's cured.

As with any design that requires precision and specific loads, an engineering analysis and design is critical to prevent failure or potential safety concerns. It's understood that in your world, the damage mitigation is mostly centered around impact and collision (with the ground and other kinetic energy whirling weapons), which makes it even more critical to design properly. Most composite cylinders that are used for hydraulic pumps use a somewhat flexible, but compliant seal on the piston to build pressure without allowing leaking. Most composite tubes are made on polished mandrels, so they may be smooth enough, but if the mandrel is old, it may introduce some scoring on the interior. Long story short, It's not wise to use an off-the-shelf solution unless it's specifically designed for the internal pressures required. Do you know what those loads are?

I was able to check some configurations, and we can definitely help. To get to 50', it would take a 10 section system with the smallest tube at 1.48" OD and the largest at 2.61" OD. The compressed length would be 72" and the entire system would be about 12 lbs. The only consideration is that our compression fittings are designed to lock into place to hold the pole in an extended position. But they can be loose to do what you are looking to do. However, the pole won't be as stiff as it would be if the fittings were tightened. I don't know how much stability you require for your imaging. The assembly if used correctly will not separate when extended.

From what I understand, billiard shafts are a little more difficult to make as they need to be very balanced and very straight. Fiber orientation and curing methods will have an affect on how the parts will be after curing and mandrel removal. We have found it to be fairly difficult to meet the standards using a roll wrapping method which is a good process to control resin content and fiber orientation. RTM may have issues with fiber wash and resin content.

Also, You can use either 3k plain weave or 3k 2x2 twill for the fix. I'd probably prefer the plain weave for this application. Check our dry fabrics samples for the material you need.

You may need to contact the bike manufacturer to get that info. Any automotive paint should fine, but matching colors and finish will be super fun.

Rock West does sell sample packs of West System 105/205 that come pre-measured pouches for easy use. This is really fast curing, so you need to work quickly and deliberately. https://www.rockwestcomposites.com/shop/materials-tools/resins-adhesives/101-t

Mark, That isn't terrible, but there could still be some hidden damage (delamination) lurking below the surface. Removing the fractured fibers will reveal more. But in this case, you may just want to remove any burrs or slivers, sand the paint away and apply a single layer of woven carbon fabric/epoxy resin over the area. Overlap the fractured area by about 1" on all sides. Use the shrink tape to get good compaction. The resin will weep into the wound and somewhat prevent the fracturing from propagating further. Kind of like a windshield repair. Not perfect, but adequate. Otherwise, a full repair would require specialized sanding and layered patches to repair the area. You can use a quarter to perform a tap test to see how far the fracture is under the surface. Tap the quarter in an area that you know isn't damaged and then compare the sound to the damaged area. A good laminate will have a sharp "ping" sound, where delaminated areas will have a "thunk" sound.

Bike repair is a very fluid topic as each injury and subsequent repair will be based on the location and severity of the damage. Your frame is most likely made from unidirectional carbon fiber prepreg, but repairing with a similar material would require special equipment to cure the prepreg. There are professional outfits that provide this service, but the typical DIYer won't be able to do this. In your situation, it sounds like you have minor damage on a tube section. If that's the case, you would need to remove any paint from the surface, prep the surface for bonding, then use a dry woven fabric and 2 part epoxy resin or adhesive to cover the damage. Using shrink tape will give good consolidation and help with the cosmetic finishing. The number of layers depends on the size and extent of the damage. Posting a picture of the damage will help us provide better feedback.