Canaboo

I think you would have been better off just buying aluminum close to the final shape needed and drilled and bolted them to the existing forks. If they worked you could then take them apart and refine the shape a bit.

scottfsmith

Maybe for experimenting I could do that. I could get a bunch of fork shapes cut in aluminum and try different setups until I hit the optimal, then do that one in carbon. I think the carbon will save around 200g on the weight and it should be much stronger. At the sendcutsend place it looks like fork shapes will be $1.25 each.. so I could get a large number of them.

The O.L.D on the wheel would have to be different since the aluminum bolted to the outside would widen the gap, but I could just put some washers on the axle to compensate.

squirtdad

While not a frame builder yet, I have built a lot of things over the years (included hacked roller set up so a luge sled could be used for training on roads).

My concern, especially i used for skate style vs classic nordic style, that there will be a lot of lateral forces in play, and with the amount on length added to fit the larger wheels that unless using really thick plate, there will be way to much flex, especially with 16 in wheels

maybe flat, with stiffener welded on outside, but that sound's like it is going beyond OP's current shop toolset

Doesn't hurt to try,

Darth Lefty 

As you design, don’t conflate stiffness with strength and don’t forget about either. You need more of both just because it’s a longer arm from the platform to the wheel. If you replace steel with carbon the carbon has to be thicker… it’s “stronger” and “stiffer” per weight but much less dense.

scottfsmith

My impression was the modulus of elasticity (stiffness) and tensile strength (strength) were not scaled by density, they were absolute numbers. Specific stiffness and specific strength are the per-density ones. Carbon has similar stiffness to aluminum and more than 2x the strength. I am mainly worried about strength in my design as I don't think there will be much unwanted elasticity. So, it seems like with the same thickness of carbon as with the current aluminum I should get 2x the strength which should be OK for the longer forks. This is for the 12" wheels, for 16" wheels it may need something thicker.

Or so is my impression of this stuff.. I'm no expert. I am using this page as a reference.

Re: how much stiffness is needed, I don't think it matters all that much as there are not many side-to-side forces on these skates. You are not twisting in NCS, it is not like downhill skiing. Having less stiffness will in fact be good I think, for the up-and-down forces for which some dampening would be good.

guy153

The two are related in this case because lack of stiffness can cause the structure to deform meaning it's loaded differently and therefore breaks. Basically if it bends it might break (in the case of CF) or yield (if Al).

It's a bit like if you do the math you will find that in theory you could stand up vertically on a piece of TIG wire. In theory the strength is there. But a tiny perturbation and you won't be loading it straight down any more so of course it will bend.

dsaul

This seems to have really gone into the weeds with all the theoretical discussion of strength and stiffness. Sometimes you just have to build it and see if it works.

scottfsmith

Indeed. I decided to order some full side panels in aluminum and use those to prototype. Its $12 a panel including materials, cutting, shipping, and tax .. it seems worth the cost to get a realistic prototype. Here is my simple design if you are curious. I had to learn a few more features of my CAD program to get this done.