How much carbon fiber on insert runner bodies?
wnethercote:
I am looking at building a new set of insert runners. Three of the five sets of side-runner inserts I've built so far have relied on aluminum stiffeners. One runner set (3/16 x 3 in. SS316 insert) had a Baltic birch core with 3 x 9 oz. of unidirectional carbon for stiffening on each side (and no aluminum stiffeners). These runners were robust but tended to chatter at the leeward mark, so I was always suspicious of their stiffness. When I replaced them with a set of 440C inserts I simply glassed the wood core and went back to aluminum stiffeners. I am happy with this new runners, apart from the bulk of the aluminum stiffeners.
I'd like to give 'carbon only' stiffening another try. How much carbon fiber do people typically use to stiffen 36 in. side runners? 'As much as you can' is hardly an engineering answer. :)
So:
1. Has anyone got a static deflection measure for how stiff runners should be?
2. How much carbon did you use (press or vacuum bag layup, or ...) over what thickness/material wood core?
Warren Nethercote, DN 3786
Geoff Sobering:
The best description I've read is from Daan Schutte:
Quote
Plane the wood body of an insert runner to the minimum thickness (22.5 mm) to be able to laminate as much carbon on to the runner as possible. Use approximately 1000 grams per square metre of which at least 80 percent in the direction of the slot.
In English terms, this works out to be a 7/8" thick wood body with 1/16" carbon on either side.
Some people add "wings" of carbon or aluminum to add stiffness.
Of course, the final word on runners are the Official Class Specs:
https://ice.idniyra.org/Yearbook/Specifications/Runners
Cheers,
Geoff S.
wnethercote:
Geoff,
I rolled my eyes a bit at the 'as much as possible' but the at least 1000gm/m2 meant something. The handy-dandy internet said this is about 42 oz/yd2, which is coincidently near the maximum I would get if I redid my carbon only runners with a minimum core and assumed that I could get the same degree of packing as I achieved with 27 oz.
Warren
Geoff Sobering:
It's been a while since I did a layup of carbon sheet for a runner, but I just checked uni-carbon at Fibre Glast and they list 9.0 oz/sq yd at 0.014" thick:
http://www.fibreglast.com/product/Unidirectional_Carbon_Fabric_90_oz_2583/carbon-fiber-fabric-classic-styles
I'm not sure how thick each layer would be with resin, but that gives you some idea of what to expect.
Pre-preg is really the way to go, but you need a heated platten to cure it.
I tried both vacuum bagging and pressing between two sheets of plexiglass. If I were to do it again, I'd use a mold made from two flat sheets with a 1/16" spacer around the edge.
Ron Sherry and Jeff Kent used to sell 1/16" carbon sheets. I don't see them on either of their price-lists.
eric_anderson:
I use Baltic birch bodies. I laminate 2 pieces of ½ Baltic birch glued up between two pieces of plate glass. Then sand them to exactly 7/8 and shape the noses.
I then vacuum bag on 3 layers of 9 oz carbon Uni, (2 the long way and one vertical.) I then vacuum bag on a layer of 5.7oz glass. This should come out about 0.985 If there are any high spots I sand them flat.
I put on a final layer of carbon on the sides when I glue in the blade. I thicken the epoxy for the final layer with graphite powder so it is a nice slick surface. I glue it up between 2 pieces of ½ thick plate glass with aluminum spacers so that the blade is held parallel to the body , and the body comes out to 1.010 thick.
Make sure you wax the hell out of the glass with mold release- 6-10 coats so you dont bond the glass to the carbon, I made that mistake once.
Cheers,
Eric Anderson US 5193
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