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:

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 don’t bond the glass to the carbon, I made that mistake once. 
Cheers,
Eric Anderson US 5193

[wnethercote]

Thank you Eric.  It would appear that you, Geoff and Daan Shute are in the same ball park - and more important, I seem to be headed in the same direction! 

[Geoff Sobering]

One technique I found helpful when I was making some wood/carbon slipper-plate runner stiffeners is to start with a piece of wood slightly over 1/2 the final thickness of the body without carbon/glass. Wet out the carbon/glass layers on a flat waxed sheet and then clamp the wood onto the composite layers. Let it cure and then plane the wood down to exactly 1/2 the final runner-body thickness. Then glue the two halves together.

This removes some of the variables in getting flat and parallel sides the right thickness.

I actually started with a single sheet of wood large enough to make both sides and cut it apart after the planning.

[glovejoy]

Could the carbon sheet below from Dragonplate.com be used?  They use a quasi-isotropic layup for the plate/sheet.  Its 1/16 in. thick and cost roughly $125 per runner if purchased enough for 3 sets of runners.

http://dragonplate.com/ecart/product.asp?pID=3628&cID=67

[wnethercote]

The Dragonplate  looks attractive at first glance but may not have enough fabric in the 0 degree direction for desired bending stiffness.  For other applications the 0/45/90 mix is a good idea.  They have uni-directional sheet as well, but only in 24 inch lengths.  Their web site also has pultruded CF strip of various dimensions so one could offset the off-axis fibers in the 0/45/90 sheet via a CF stiffener.  Of course, for the committed handyman using these pre-prepared sheets would considerably more expensive than buying the CF cloth and epoxy and doing it yourself - but much less prone to risk of project failure.

[Bob Rast DN1313]

Try Soller  composites , I recently used this for solid carbon Stiffeners
Specs: 50 inch wide 20.0oz. sq yard/680gsm Super High Quality, T700 711Ksi, 34Msi, 0.020" Thickness, 1.7ft/lb ******Huge Limited Time Sale******

http://www.sollercomposites.com/composites/carbon%20fiber%20uni-fabric.html

50 inches wide  by 3 ft cost me  about 40 bucks add some plain cloth on the outside and you have a Quasi Isotrobic layup  you need mostly uni

Bob Rast
DN1313

[Bob Rast DN1313]

For Bodies I prefer Hard rock Maple , I get a board cut down to 7/8 Strips  which I glue up with grain the way I want it,
 I do a dry layup carbon and wood clamped between 2   3/4 Aluminum plates to max carbon content  clamp down to 1" spacers  then if it is right   undo add epoxy  a nd clamp again to finished width

I think the maple is stiffer than Ply
My 2 cents
 wish wood spec was more like 3/4 or 5/8  width so you could add more exotic not really thayt  expensive carbon and have bodies that would never delam or bend and have to be redone

Rast
DN1313

[Bob Rast DN1313]

I do have some solid carbon stiffeners available $100 a pair  need 2 pair per runner these are 20 oz uni 6 inch wide piece of uni compressed in mold to 1/2 x1/2  30 inches epoxy to sides

can send photo if interested
Brastco@gmail.com

[wnethercote]

Thank you all!

Warren

[DonTyerman1]

Geoff

Your approach of laying up the bodies (wood and carbon combined in one go)  then glueing the two sides together sounds intersting.  I like the fact the wood core can be further machined to obtain optimal fit in the chocks before the blade is fully assembled.

When using this approach could you please provide specifics on how you machine the slot for the blade, drill for the blade pins and install the glass wrap around the upper portion of the blade?

Everyone -this discusssion thread is excellent for us "newbie blade-builders".  Thanks!

Don Tyerman

[Geoff Sobering]

When using this approach could you please provide specifics on how you machine the slot for the blade, drill for the blade pins and install the glass wrap around the upper portion of the blade?

I've only used that process for a plate slipper runner so I was able to cheat a bit. The two stiffeners were just glued on either side of the steel plate so I didn't need to machine a slot.

Because the stiffeners went on either side of the plate, I drilled the holes for the pins into the wood, stopping short of the carbon sheet. In then inserted the threaded-rod pins into the holes (with thickened epoxy) as I was clamping the stiffeners to the steel plate.

I'm not sure if that would be a better process for inserts than the usual procedure of gluing the body together, milling a slot in the bottom, and inserting the steel+fiberglass into the slot.

Cheers,

Geoff S.