JonPatrickHyde
3 years ago10,000+ Views
THE INSIDE LANE - Tech Talk - Chain Stay Protection - Kevlar-Steel Modification
First - a disclaimer - I do NOT recommend anyone do this unless they are certain they want to permanently modify their bicycle's frame. Depending on your frame maker - doing what I am going to show you MAY void your frame's warranty. Check with your frame maker BEFORE doing this. This is NOT meant to substitute repair work for a damaged frame. IF your frame's chain stay has been damaged due to the chain getting wedged between your crank and frame - failure to have your frame inspected and/or repaired by a certified carbon fiber frame tech can result in serious harm or death. NEVER guess or assume. When it comes to carbon fiber bicycle frames, always have ANY damage inspected. THE FIRST PHOTO OF THIS CARD - is for demonstration purposes - to show what chain damage CAN do to a carbon bicycle frame. --------------------------------------------------- I've become obsessed with what I consider a major failure of bicycle manufacturers - adequate protection for the delicate areas of a carbon fiber bicycle frame. First, I'm the son of an engineer and I've worked with fiberglass, carbon fiber, Kevlar, aluminum, steel, pvc, etc... and the list goes on. I have an advanced knowledge of everything from how vibration can indicate failure of a bearing system when tracked over time (vibration analysis) to how you can use ultrasonic detection units to find air leaks as small as 1 micron in size. All thanks to working for my dad during summers as a teen and young adult. Carbon Fiber has amazing strength in regards to it's ability to withstand stress and force. Unfortunately this is typically stress and force from one direction. The weaves work to create an incredibly strong bond directionally. Aluminum is a 10 - Steel is 30 - and Carbon Fiber is 20. BUT - Aluminum and steel have unidirectional strength - they can resist crushing and force from any direction. Carbon fiber will crush like plastic if force is applied in a direction that does not engage the directional strength of the fibers. ---------------------------------------- The danger of getting your chain wedged between the body of your bike's frame - either the stays or around the bottom bracket housing - is two fold - the metal chain is stronger than the epoxy covered carbon fiber weave. So it can saw into your frame like metal against plastic will do. The second, and more dangerous damage comes from crushing the frame where it gives before the chain does - if the space between your bike's frame and crank is less than the width of the chain the chain will crush the frame as it lodges into the space. This type of damage is very dangerous - if the frame's outer layers are not damaged visibly, the underlying damage can cause catastrophic failure without warning down the road. Surface damage that doesn't eat into the carbon fiber layers can still be fatal to the frame in a process called "delamination" - where like the layers of an onion skin, the initial damage can cause the layers beneath it to separate. ------------------------------------------ So why do frame makers not build extra protection into the design of the crank-side chain stay? I honestly don't know. Weight, manufacturing costs, etc... are the most likely reasons. But as I get more and more comfortable riding and caring for my carbon fiber bike - I have been looking for a solution that makes sense. There are chain stay protectors on the market - adhesives, Velcro and nylon, even a couple of thin aluminum items - but nothing that really addresses the crushing and cutting problems that are the reality of a full-speed chain slip. I found two very interesting things doing research - a company that makes molded carbon fiber sleeves that "snap" onto your frame - that's better. And then an individual who like me, was comfortable working with different composite materials who had used a carbon/Kevlar (the stuff bullet proof vests are made of) flexible weave with a steel reinforced epoxy to set it. Basically he made the down tubes and chain stays on his bike bullet-proof. In addition he only added about 1/2 pound in total weight doing it. I LIKE THIS! HECK YEAH! He didn't make his mod "pretty". The carbon/Kevlar weave is sort of a gold color and he just put it on his frame in clear epoxy and left it. ------------------------------------------ So I decided to do this for myself. Starting with the chain stay of my bike - I wanted to create "armor" for the area most likely to be damaged should my chain jump off and get past my chain drop guard. I purchased a unidirectional Aramid (Kevlar) and 3K carbon hybrid weave fabric - 2ft by 2ft - for $30 from a local fiberglass supply company (check your local business listings - if you live in a big enough city you'll find several). After discussing this project with my dad i decided to go with an epoxy base from JB Weld - which is steel reinforced. --------------------------- WHAT YOU WILL NEED - 1) Flexible - unidirectional Kevlar/carbon fiber fabric - buy from a reputable shop. You NEED to ensure you are really using Kevlar and not some fabric someone tells you is Kevlar. 2) Industrial-grade steel reinforced epoxy - I went with epoxy that takes an hour to set up - 24 hours to cure - this gives you plenty of time to work with it to get the shape of your "armor" fabric right. 3) Epoxy putty - for plastics 4) Stainless steel scissors (for cutting/shaping the fabric). 5) A variety of files and sandpaper. 6) Krylon ColorMaster *get the plastic safe version - in the colors to match your bike - or if you want to get really fancy and take your bike to a professional painter you can - but it'll probably cost a nice amount. 7) Painter's Tape (blue) - won't hurt your frame and you'll want/need to tape it off. 8) Nitril Gloves - you DO NOT want to get the epoxy on your hands - although the putty is perfectly safe - check the instructions of each product you purchase to be sure! 9) THICK black vinyl sheet - cut into 2 inch wide by 12 inch long strips. 10) Duct Tape 11) A sewing needle 12) MOST IMPORTANT - patience - this process will take no less than 5 full days. I don't believe in short cuts. ------------------------- THE PROCESS - DAY 1 - 1) First I would use some old fabric like a white cotton t-shirt - to make a pattern of how you want to cut your Kevlar/carbon weave. You can even use paper. You need to ensure that whatever area you want to protect is adequately covered. ONCE YOU'VE DECIDED THE PATTERN'S SIZE AND PLACEMENT - tape your bike frame off with the blue painter's tape - leaving about 1/4 of an inch from the edge of your pattern uncovered. I decided to wrap the new "armor" all the way around the chain stay to the back - adding additional strength to the new covering as a whole. At first I was going to cover the entire chain stay - but in reality I only need to protect the area under the crank and chain rings. Your chain won't really damage your stays beyond them because there's nothing to pinch it against the stay. You can use available store-purchased nylon or adhesive covers for that. YOU WILL MOST LIKELY NEED TO REMOVE YOUR BICYCLE'S CRANK! Be sure you are comfortable with this and have the right tools before attempting this mod. 2) Prep the area of your bike by taking 100 grit sand paper and VERY carefully roughing up the paint. If you are unsure how thick your paint or clear-coat is - use 220 grit paper. This is where the patience comes in. You want whatever finish your bike manufacturer installed to be rough or gone - but you don't want to eat into the carbon weave of your bike's frame. It's a VERY fine line. If you are unsure - don't do it. I mean - this entire process. I would sand and stop. Sand and stop. Sand and stop. Checking between each to see where I was. It took several hours to get down to the outer epoxy layers of my frame - above the carbon weave and below the bike's painted finish. 3) Test your fabric pattern - use double sided tape if you need - and make sure your pattern is good. 4) Trace your finished pattern onto your Kevlar/carbon weave fabric with a sharpie and cut it out. 5) Test your Kevlar/carbon armor template on your bike for fit and make any adjustments as needed. Try to make your edges align and NOT overlap. 6) You are going to mix enough steel reinforced epoxy to cover your bike's frame in the area you've prepped for your pattern. Be liberal but try not to drip the epoxy. You'll want the epoxy to soak INTO the areas between your Kevlar/carbon pattern's weave. APPLY IT TO THE FRAME. 7) Carefully place your pattern into the position you will want it over the epoxy you've just placed. MAKE SURE ALL EDGES ARE AS FLUSH WITH YOUR FRAME AS POSSIBLE! 8) Cover the pattern with ANOTHER layer of steel reinforced epoxy. Try and cover every area. 9) Use your THICK BLACK VINYL STRIPS and starting on one end of your pattern - attach a strip to the painter's tape with a small strip of duct tape - make sure it is secure. Then carefully WIND the VINYL around your pattern and epoxy cover - stretch the VINYL and overlap it to ensure it is pressing the pattern firmly against the frame. Secure it with more duct tape - either to itself or the painter's tape. 10) Once you've completely covered the epoxy and armor pattern tightly - take the sewing needle and poke small holes in the VINYL - about 1 every 1/2 inch. Epoxy may leak out and this is OK. BE SURE TO COVER your frame or work area to prevent excess epoxy from dripping onto it. YOU WILL LET THIS SIT FOR 24 HOURS. Epoxy/composite fiber combinations typically are cured in a vacuum - in small applications such as this one, you can simulate a vacuum by using a material that the epoxy will not adhere to *THICK VINYL - and using it to compress the pattern. DAY 2 - 1) Carefully remove the VINYL - you should see what looks like a chain metal cover on your bike. The steel in the epoxy, once set - retains it metallic color and sheen. Your new armor plating should look like PICTURE 6 of this card. BE VERY CAREFUL - any edges of this armor plating can potentially be sharp. 2) Inspect it to ensure the pattern doesn't have any areas that didn't conform to your bike frame - check the edges for lifting - and make sure the seam in the pattern is connected and doesn't have gaps. 3) Take a small metal file and CAREFULLY file down any areas that are lifted, sharp, or sit above the main pattern - ONLY ALONG THE EDGES of the pattern. REMEMBER! You are basically working with metal that's been reinforced with the same stuff used in bullet proof vests. It is going to be VERY hard and filing may take some time. DO NOT RUSH IT! 3) You can do one of two things at this point. If you need to add more steel reinforced epoxy - you can - then repeat the curing procedure (with the thick vinyl strips) from the day before. IF YOU ARE SATISFIED with the coverage and fit of the pattern - you can get the EPOXY PUTTY out. BEFORE YOU APPLY ANY EPOXY PUTTY - BE SURE TO CHECK THE AREA/SPACE BETWEEN YOUR INNERMOST CHAIN RING AND THE STAY - Some frames only have a few millimeters - very small tolerances - for the passage of the inner chain ring and the stay. DO NOT BUILD YOUR ARMOR UP SO HEAVY THAT YOU PREVENT THE CRANK FROM FITTING!!!! 4) EPOXY PUTTY is a non-toxic filler that feels and acts like clay for about 5 minutes once it is activated. Once it sets it can become as hard as PVC, steel, or whatever it contains in it's compound. Because I wanted a "BRIDGE MATERIAL" to make the edges/seams of my armor plating seamless with the frame - I chose a PLASTIC-BASED epoxy putty. This will create a stronger bond with the epoxy of the frame and allow me to "SCULPT" it to make my new addition to the frame appear to be part of the design. 5) EPOXY PUTTY - use small amounts until you are comfortable working with it. Once you feel it start to get warm, the chemical reaction to set it has started and whatever you haven't applied is now activated and set - and not useable. I found I had about 4 minutes to work before whatever I hadn't applied was useless. So like I said, small amounts. YOU WANT TO FILL IN ANY GAPS, EDGES, ROUGH OR UNEVEN AREAS. You'll then let this sit for 24 hours. No need to cover it. DAY 3 - Check your EPOXY PUTTY CAST and make sure it is hard. You'll be shocked how hard it is going to be. It will have the consistency and strength of PVC plastic. But NOT be as brittle. BEFORE YOU START FILING/SANDING - BE SURE TO NOT FILE OR SAND INTO YOUR KEVLAR/CARBON WEAVE! It defeats the point of using it if you do that. 1) SHAPE - starting with 220 grit sand paper - start shaping and carefully sanding your epoxy putty cast to get it uniform, even, and smooth. Work with files, different grit sandpapers, etc... until you are satisfied that your armor is the shape smoothness you want. FOR ME - I WANTED THE ARMOR TO MATCH MY BIKE'S FRAME - I wanted it to look as if it was a part of the original design. This meant contouring it all the way around the stay and underneath the bottom bracket mount. 2) APPLY MORE PUTTY IF NEEDED! If you have major uneven areas - add more putty! BE CAREFUL NOT TO BUILD THE PUTTY/FILLER LAYER UP TOO THICK OR YOU MIGHT NOT BE ABLE TO PUT YOUR CRANK BACK ON! 3) If you are happy with the shape and smoothness of the armor - BEFORE you paint, do a dry run with installing your crank - to be sure your new addition fits and doesn't interfere with the crank or chain ring in any way. 4) Once you are certain you are not going to have fitting issues with your crank - double check your painter's tape and be sure to add new/replacement for any areas that have been damaged through this process. Go ahead and prepare the frame for painting. 5) Paint the armor to the desired color(s) or to match your frame - and let sit for 24 hours. DAY 4 So long as you are happy with the final result, put your bicycle back together and go forth knowing that your bike will more likely break/snap your chain off than allow it to get stuck between the crank and frame. Your bike now has "ARMOR PLATING" consisting of steel-reinforced Kevlar. *** I'm prepping my bike for painting and will post photos of the final result tomorrow!
2 comments
Why did you initially decide to go down this route? I'm personally a believer in the old saying "if it ain't broke don't fix it". Although I have heard of people's frames getting damaged in this area I would first take the steps of adjusting the derailleurs hi/low settings and make sure everything is properly tuned ever few weeks. In most cases the frame will not see much if any damage to the chainstay if you are diligent about tuning and take proper precautions. On the other hand if the bike does get small amounts of damage in this area I would begin to consider it
3 years ago·Reply
The reason was 3-fold - 1) Having a road bike with a bunch of mods for flat bar riding - I've had issues with the front derailleur - It has jumped off twice - both times I knew immediately - stopped pedaling and because of the chain drop guard I have - nothing happened to the frame - the chain didn't touch it - at least during the first incident. The second the issue was a faulty cable and the derailleur snapped back - that big spring grabbing it - the whole braze moved - because stupid me assumed the bike shop knew to tighten the braze down - so the chain drop guard moved, and I had chain over my frame - but because I didn't pedal nothing other than grease and dirt getting on it happened. 2) I have another project - a design I am applying for a patent on - not related to cycling. And I've been thinking about using carbon fiber and or Kevlar for it. So I've been playing with these materials. They are on my mind - which brings me to - 3) I wanted to see how well Kevlar/Carbon - and steel epoxy would bond with an existing carbon structure. In other words I was testing the materials on my bike - because I know them well enough that so long as the bond took - there's no way they'd do anything but add to the functionality of the bike. And I wanted to see if adding a much more robust chain stay on the chain-ring side of things would affect anything else with the bike. I keep my equipment in tuned/working condition at all times - but I am also an experimenter and I don't mind testing things. So this means sometimes I put my bike through more than it would normally go through. In this case, the new Derailleur I ordered and this addition - which will be painted tomorrow and really - looks like part of the bike's design now - with the chain drop guard - should really solve the issue. Which goes back to my original statement - barring this modification changing the way the bike rides - which I can't see how 7 ounces of material to a chain stay would - why don't frame builders do this when they are designing/building a bike?
3 years ago·Reply
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