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Discussion Starter #1
And so it begins. This is a thread away from my bike rebuild one that has been going on for...……. well too long. So this is the beginning of a new thread toi specifically cover off the building of the first of what I hapoe will be many, Carbon fibre swing arms to suit the 91-97 Supersports.
First up has been the design. After a lot of umming and rrrring I came up with the design that I am going to use bt a process of elimination of what was required to make it a reality. Going with a slab sided design with a cut out in the both sides that are symmetrical meant that I would get the same sort of stress responses for both sides. Adding additional surface area also means that I can play around with laminates as I please once I do the moulds for the finished item. This first one is going to be made on a light shell made of a number of different portions off the plug. Each part over laps another part for bonding and sealing purposes. and there are some internal structures that have to be made as well specifically around the mounting point for the rear shock. As this first one is going to be built as a test/road use item it is anticipated that it will finish up being heavier than future ones will be. For the fittings I have them being machined at the moment though I do have the top shock mount to sort out over the next couple of days. manufactured from 7068t6511 they are a lot stronger than I could have possibly imagined so it is really the transition from metal to alloy that I am really concerned with. The assebl is compatable with all other components from the original bike though I have been updating parts of the assembly as I go.
So where we are up to now is that the plug has been completed and I have made the first part of the shell. Just need to wait for it to cure before removing it , cleaning it up and then get ready for the next part.
 

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exceedingly cool project. can't wait to see the first test unit in use.

but, this - "manufactured from 7068t6511 they are a lot stronger than I could have possibly imagined so it is really the transition from metal to alloy that I am really concerned with."

lost me there. what?
 

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Discussion Starter #6
Bonding Composites to aluminium presents a number of issues. Firstly aluminium and carbon fibre causes corrosion issues. The way around it is to anodise and have a barrier between the carbon portion and the aluminium which I have solved. Next is that the design of the area where you do the bond needs to be free of any flexing. Reason is that if the composite portion can move in any way over a period of time and a number of flexing cycles it will eventually separate from each other. Carbon fibre has a grain so to speak similar to wood. In one direction it can be extremely stiff . In another it can be flexible. But ever apparent is that if you hit it hard enough it will shatter so you have to have a degree of structural redundancy in the laminate design to over come the issue. This is where the type of resin that you use can help. I have gone away from the use of epoxy for the simple reason that I have access to some pretty tough vinyester resins that are vastly superior in there mechanical properties. The resin that I am using these days allows me to reduce the amount of carbon but still retain the same strength. In turn this makes the component lighter thinner in cross sectional area and makes the component more resilient. When combined with some of the other special materials that I am using I get it even stronger again. Some of the components that I have been building as of late are half the weight there epoxy/carbon counterparts were when I first started doing all of this. All the trials and failures have led me to this component. If this turns out sucessfull I will then start on the frame replacement though I do have a desire to build a replacement composite swing arm for a Moto Guzzi Sport 1200 at some stage...
 

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exceedingly cool project. can't wait to see the first test unit in use.

but, this - "manufactured from 7068t6511 they are a lot stronger than I could have possibly imagined so it is really the transition from metal to alloy that I am really concerned with."

lost me there. what?
Bonding Composites to aluminium presents a number of issues. Firstly aluminium and carbon fibre causes corrosion issues. The way around it is to anodise and have a barrier between the carbon portion and the aluminium which I have solved.

From reading your full response, I am left to assume you meant to say 'transition from metal to composite' or some such. That's the bit that had me scratching my head.

I haven't read about (or worked with) composites construction in any depth for a very long time. Your moving away from epoxies is interesting. I was going to say not to worry about the corrosion issue but, most of the aluminum:carbon items I worked with in the past were joined with epoxy. Machined bulkheads joined to the carbon monocoques, for example. What are you using for core material(s)?

Following with a high level of interest!
 

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Discussion Starter #9
I have seen too many composite components that corroded badly in the marine industry when in direct contact with carbon. Move to vinylester was based on the testing that I did with various adhesives both epoxy and vinylester - vinyester always came out miles ahead. Use mostly Soric core matts and Nomex honeycombe though this first swing arm is going to be core free for the first one.
 

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Discussion Starter #11
I have a plug for one that is designed for the fuel injection system as fitted to the latter models with straight shot ram tubes that I am in the process of getting ready for making a mould of. I did make a couple of them and have been asked to make more. If you have a look at my other thread you will see what it looks like.
When I get to the carbon frame there is only a top and bottom plate - the frame acts as the airbox with a carbon top and bottom plate that acts as a stiffener for the frame.
 

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Discussion Starter #13
Well if it was easy everyone would have done it. Disaster has hit during the removal of the first part of the lightweight skin having to destroy it to get it off. The peel ply came off perfect bare one small place that had a bit of tack tape touching it, great I thought so far so good. Not sure what has happened but everything pretty much turned toes up from that point on. I damaged the plug getting the skin off and had to throw away tit away. The bright side has revealed that I have made a bit of an error with the radius of a few edges in critical places which would have resulted in a failure of the finished item had I gone any further anyway. I had far too tight a curve in critical parts and they just gave way when I started to try to remove them from the plug.
So I have already started the remodelling of the plug straight away and will modify and repair it over the next couple of days. Hope to have another crack at it later in the week. I also came to the conclusion that I had made it too light as well which I will fix for next time as well. The complex shape is going to require me to rethink the number of parts that I need to make it out of as well but during the removal process I did get to see a plan for the moulds in the future if I decide to do a production run. Shit happens but in this case there has been a silver lining in the cloud in that some valuable lessons have been learnt for the future.
 

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Discussion Starter #14
Received the components for the rear swing arm though there is an issue in that the pinch bolt threads have not been machined. Will sort that out latter. but the rest of it looks the part. Managed to get a coat of clear on the plug for the composite stuff so will have to leave it for a couple of days before getting into the laminateing again. Noe just need to get the top shock mount designed and machined.
 

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Yes pretty pissed about it to be honest - another set back that I have to deal with but have resolved it with the company that manufactured it for me.
 

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thinking out loud here. i cant help thinking two things. you would be better (easier) off with a two piece tool. a inner and outer. then both skins bonded together. seeing how thin it is i think it needs some internal support or webbing. i see to many unsupported, thin flat areas that can crack due to twisting sheer. make one from thin balsa sheets glued together laminated with fine weave glass. then you can flex it and watch where it begins to fail. out of the three benelli carbon swingers that came to the country, all failed and im sorry to say they were made in a not so dissimilar fashion by of all people a boutique (hand made) carbon pushbike maker. please feel free to slap my if you think im an idiot.
 

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Discussion Starter #19
You have just described the whole process that I am going t use to make it. Unfortunately I have to make it in no less than 7 different sections due to the complex shape but each section will be bonded together with all the hard points to form a light weight internal skin. From that point on it is a case of laying up the outer laminate and orientating the fibres correctly. I am on the lookout for a small quantity of 20mm Nomex honeycomb for the internal structure at the moment. I was not planning to use it on this one as I want to test the structure without the internal core to see if the simulations that I did on the computer are the same as what happens in real life.
 

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Sorry Combi. Forgot to ask why you’re not using unidirectional for strength and then over layered with cloth for cosmetics.
How is the bond strength to anodised Al compared to textured raw?
One last thing. At the axle, why not a small simple plate bonded internally for crush resistance and externally sandwiched with interference fit and bonded plates for the axle adjusters. That way there’s no compromise in strength compared to the carbon trying to hold the Al in place, even with all the keys drilled in current adjusters. Again, just thinking out loud😃
 
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