|
wozza
|
|
|
Group: Forum Members
Posts: 688,
Visits: 5.4K
|
As mentioned Kevlar can be a pain to cut. You really need a good pair of Kevlar shears as Chris says, even then it can be a slow inch by inch process depending on the weight of the cloth.
With aramid cloths once cured trimmed edges are always a bit "fluffy", you cant polish it like carbon edges. You can stop the aramid layers short of any seen edges, say 10-20mm and build up the remainder with strips of cf. On something like body armour I would probably increase the thickness around the edges anyway, that way you can put a nice radius on the edges of the finished part avoiding the knife edge of a thin laminate.
Warren
Carbon Copies Ltd
|
|
|
|
|
identiti66
|
|
|
Group: Forum Members
Posts: 8,
Visits: 20
|
Thanks chaps.. sounds like good, solid advice. I figured that the internal foam padding would be about 5mm thick. And if I sanded the edges round, that should minimise the risk further. I think I can probably get an idea of the materials best suited from the posts here, is there an idiots guide to actually getting the thing done once I have the mould? If anyone feels like estimating a cost to do it for me from the mould I make (not sure if that's allowed here, apologies if it's not cool) feel free to pm me.. 
|
|
|
|
|
wozza
|
|
|
Group: Forum Members
Posts: 688,
Visits: 5.4K
|
identiti66 (03/04/2014)
Thanks chaps.. sounds like good, solid advice. I figured that the internal foam padding would be about 5mm thick. And if I sanded the edges round, that should minimise the risk further. I think I can probably get an idea of the materials best suited from the posts here, is there an idiots guide to actually getting the thing done once I have the mould? If anyone feels like estimating a cost to do it for me from the mould I make (not sure if that's allowed here, apologies if it's not cool) feel free to pm me.. You really need to decide how you are going to make the final part before making the mould ie wet-lay, infusion or pre-preg as this will have a baring on how and what the mould is made from. Looking at your sketch, because of the wrap around design it will have to be a split mould otherwise you wont get the finished part out of the mould. With infusion or pre-preg you will need some flanges on there as well. If you plan on outsourcing the manufacture I would talk to whoever is going to make it as to what type of mould they suggest. One problem area of outsourcing is that the "fit for purpose" responsibility would fall on their shoulders and they may not want that risk. Warren
Carbon Copies Ltd
|
|
|
|
|
ajb100
|
|
|
Group: Forum Members
Posts: 346,
Visits: 4.4K
|
Just to add my 2p to the convo, have you considered the risk of immobilising your elbow? By locking it rigid, you are much more likely to break your wrist, arm or dislocate your shoulder with much less of an impact due to removing virtually all damping in your arm and transferring the load to joints which don't move in that way. It's the same with LEAT braces used in moto, they reduced neck injuries but were causing more rib damage and lower back problems as they just transfer the load elsewhere. Because of that issue, I personally would stay away. I don't mean to be critical, I just wanted to point it out
|
|
|
|
|
identiti66
|
|
|
Group: Forum Members
Posts: 8,
Visits: 20
|
ajb100 (03/04/2014)
Just to add my 2p to the convo, have you considered the risk of immobilising your elbow? By locking it rigid, you are much more likely to break your wrist, arm or dislocate your shoulder with much less of an impact due to removing virtually all damping in your arm and transferring the load to joints which don't move in that way. It's the same with LEAT braces used in moto, they reduced neck injuries but were causing more rib damage and lower back problems as they just transfer the load elsewhere. Because of that issue, I personally would stay away. I don't mean to be critical, I just wanted to point it out This is something I have considered, at great length.
The problem is that the elbow joint is completely knackered. After 3 unsuccessful rebuilds there's no actual joint left. It's just the ends of 3 bones, some ligaments and screws. Plus half my tricep is missing too.
Any load placed on the elbow runs a high risk of it falling apart which leaves me on a river of excrement in a native American craft with no means of propulsion.
Short of giving up any MTB aspirations I don't know what else to do.
|
|
|
|
|
tack talk
|
|
|
Group: Forum Members
Posts: 9,
Visits: 215
|
Like others have said if you make it too rigid and solid the loads will simply be transferred elsewhere through the part. Ideally some kind of energy absorbing material built into the part could help, e.g. honeycomb core, nomex etc. This would be crushed in an impact but absorb energy in the process of being destroyed.
|
|
|
|
|
wozza
|
|
|
Group: Forum Members
Posts: 688,
Visits: 5.4K
|
tack talk (04/04/2014)
Like others have said if you make it too rigid and solid the loads will simply be transferred elsewhere through the part. Ideally some kind of energy absorbing material built into the part could help, e.g. honeycomb core, nomex etc. This would be crushed in an impact but absorb energy in the process of being destroyed. This is just my opinion. To crush a honeycomb core between cf skins would require a very big impact. If you have hit something hard enough to do that then your in big trouble anyway so wont help the outcome. Many of the comments so far are valid and well directed but having had to give up various sports/hobbies due to injury I know how frustrating it can be. Careful design should result in something suitable but as mentioned by others be prepared for other potential injuries if you have a big off. All a case of calculated risk I suppose which is all part of extreme sports anyway. Warren
Carbon Copies Ltd
|
|
|
|
|
tack talk
|
|
|
Group: Forum Members
Posts: 9,
Visits: 215
|
"To crush a honeycomb core between cf skins would require a very big impact. If you have hit something hard enough to do that then your in big trouble anyway so wont help the outcome."
Point taken. Not a good recommendation for the core material from me.
Maybe the energy absorbing core concept could still add something though? How about using a thermoplastic foam core or even an EPS like Styrofoam.
|
|
|
|
|
identiti66
|
|
|
Group: Forum Members
Posts: 8,
Visits: 20
|
guys.. sorry I've been away from this for a while, the universe conspired against me. Had a bit of a rethink (and bought a road bike), since I'm a little less likely to need hard impact protection on the local, quiet, country roads, I'm wondering if I could mold a thermoplastic brace directly to my arm and achieve the result I want that way... From what I've read there's a little flex in them so they aren't 100% rigid. Any thoughts?
|
|
|
|
|
Romain Lussier
|
|
|
Group: Forum Members
Posts: 15,
Visits: 145
|
Hi everyone, I don't know if it's considered good or bad practice to dig up old threads, but I'm doing it, as this one is relevant. Of course, if it's bad practice, then please say so, and I'll change that right away  Anyways, my project is to essentially have a custom molded version of this:  I was thinking of making the mold out of this:  Which is some thermoplastic that would be shaped around my elbow/shin. On that I'd but a layer of carbon and a layer of kevlar, a layer of high density foam and that should pretty much do it. Except that I don't see either thermoplastics or HD foam listed on EC, if they are listed, could someone point them to me? Finally, if anyone in the community managed to complete such a project, I'd be very curious to gather all the info I can get! Cheers, Romain
|
|
|
|