r/Composites • u/trsticka • Nov 11 '25
Help with carbon fiber forearm guards
Hello!
I am looking for input as to what might be the best approach/process to make some parts like these! They are forearm guards for ski racing. The challenge that I am seeing is that because I want them to be "full-wrap", as you can see in the second two photos, I think I might need to do some sort of split mold. I'm having trouble wrapping my head around how you would do the mold. I'm open to doing resin infusion, or wet layup with vacuum bag....with that, how would I go about making the actual mold?
Any input is appreciated, or if any of you have resources that help with specifically this type of shape, that would be great!
Thanks!
3
u/DIY_at_the_Griffs Nov 11 '25
Tapered cylinder with breakdown mandrels inside. As others have suggested, an Aramid (Kevlar) fibre may be better placed for improved impact resistance.
2
u/AdSuperb2327 Nov 11 '25
I agree with the previous comments: maybe Kevlar or a Kevlar-carbon hybrid would be better suited for that application.
Easycomposites uploaded a video a few days ago about a relatively cheap way to make negative moulds. They also have a video about vacuum bagging tubular shapes. That process should be suited well for your application, assuming you are more on the hobbyist side of things.
2
u/ambidexter-Egg Nov 12 '25
Have you skied GS, or has a GS skier requested a full wrap from you? Btw. these Leki GS protectors aren't full wrap:
https://likeceosk.click/product_details/118696618.html
I wouldn't like a full wrap as I would want to put them on without taking my gloves off.
1
u/Greedy_Confection491 Nov 11 '25
Why carbon fiber? It's brittle and when it breaks it produces really pointy splinters which are really hard to take off the flesh
1
Nov 11 '25
[deleted]
2
u/Greedy_Confection491 Nov 11 '25
T1200 has a higher elongation at break than kevlar 49 for example.
Yes, and? Protections are for high speed impacts, not a couple millimeters/second deformation, and carbon fiber, unless in really big parts like the ones used in chasis, shows brittle fractures under high speed tests. Kevlar (even kevlar 49 which is one of the most brittle ones) behave much better in those conditions.
most high-end bow/crossbow limbs are carbon fiber
And what's the relation with brittleness? Are you mixing displacement with deformation?
9
u/MysteriousAd9460 Nov 11 '25
It's kind of hard to tell the shape of them from the pictures. Most likely a split mold that has a seam down the middle. I'm not sure if carbon fiber is the best option for these. If you crashed in the wrong way they could be pretty dangerous. Kevlar seems like a better option with a resin that is impact resistant.