stack and taper

[Crooked Stic]

What exactly is prepeg

[Kirkll]

What exactly is prepeg

Here ya go Mike…. This is the most common material used laying up carbon sheets…… the problem is…. Every roll is a wee bit different, and can cause quite a bit of difference in strength…. So unless you are buying large quantities, or the whole roll at a time. Every time you have some made it’s a different strength.

The aerospace industry has standards that must be met. But if the material is a bit stronger than the minimum, that’s fine…. As bowyers we require more consistency than that to hit our draw weights constantly.

As a custom bowyer buying small quantities of carbon, building just a few sets of carbon limbs here and there is a nightmare. You end up building 2-3 sets for every bow to hit your draw weight perfectly, and hope you can sell the other ones down the road.

I suppose if you are just building bows and selling them as-is , your exact draw weight doesn’t bother you much. Build em, mark the weight, and sell the product.
It would sure be a lot easier to do it that way.

https://www.fibreglast.com/category/PrePreg_Fabrics?gclid=CjwKCAjw_YShBhAiEiwAMomsEOidQf0kLQ9NLyVAM-2nEKbin9oHqL18ITFd5BjKBiHVDpQxxtJzkhoCIDIQAvD_BwE

[Crooked Stic]

If you are getting the stuff from Mark Tom it is already laid up and shinny both sides and it needs sanding before glue. He said use 180 I used 120 what smooth on recommends. And measured it inseveral spots and was .019.

[Kirkll]

Here is some interesting carbon weave material info.

Plain Weave. The simplest carbon fiber weave is known as a plain weave. The plain weave is formed by crossing tows in a one-over, one-under pattern, creating the checkerboard seen on many woven fabrics. These materials are strong and highly stable, but they are not very pliable. Plain woven carbon fiber is best for components that are flat or only slightly contoured.

Twill Weave. Like the plain weave, the twill weave comes from passing tows in an even over/under pattern. However, rather than passing over a single tow, each strand passes over multiple tows, then under the same number of tows. This is typically done in a two-over, two-under pattern, but 4 x 4 twills are also common. In either case, the resulting pattern appears to form rows of rectangles proceeding diagonally up the fabric. Twill weaves are more formable than plain weaves, so they can be used with more complex shapes. However, this means that they are not as stiff and stable as plain weaves.

After reading this, it makes me wonder if the compression characteristics are different using this Twill weave, and possibly more user friendly on the belly side of the bow. I've always use the plain bias weave in the past with one layer of uni in the center. XOX  = 45/45 / Uni / 45/45 plain weave. One of the better lay ups we used was XOXF  with a layer of glass in the matrix assembly. This allowed you to run it through a drum sander to get exact thickness specs and sand the glass.

Just a bit more info on carbon if you are interested.    Kirk

https://prepregs.com/prepreg-carbon-fiber/#:~:text=Prepreg%20Carbon%20Fiber%20Applications%20Prepreg%20materials%20are%20easy,and%20resistance%20to%20both%20chemicals%20and%20extreme%20temperatures.

[Crooked Stic]

Rosewood has a 6 ply twill that has uni. Pretty sure that is what Widow uses on the front and the two ply twill on the belly. No glass.

[Kirkll]

That doesn't surprise me that Black Widow would use it belly and back. They stamp out large quantiles of limbs and dont need to sweat actual draw weight on each set they build. Mix and match, and out the door...


Mark Tom got back to me on the product he uses, and it is "pre preg" material. But I haven't got any specifications yet on the carbon weave type... Still fishing for that info...   Kirk

[Crooked Stic]

T has may be prepeg hen I am confused. The stuff Mark Tom has may be prepend before he lays it up but you have to add glue when you use it.

[Kirkll]

T has may be prepeg hen I am confused. The stuff Mark Tom has may be prepend before he lays it up but you have to add glue when you use it.

I think you are miss informed on how pre impregnated carbon lay ups are done Mike…. That is the beauty of this material. It’s pre impregnated with epoxy resin and doesn’t need any resin while assembled….only needs to be air bagged or pressed and cooked….



Check this out….

https://www.easycomposites.co.uk/learning/introduction-to-out-of-autoclave-prepreg-carbon-fibre


Of course what we get from manufacturers is already cured, and we need to use epoxy to put them together. The pre preg itself could not be used in a bow form easily.  The temps needed to cure pre preg carbon exceed our standard 160 degrees by quite a bit, and is cured at higher temps than the fiberglass is. 

You could find other videos showing  how flat lay ups are done and different curing methods, autoclaves, and ovens used… it’s pretty fascinating….   Kirk

[Crooked Stic]

Now I am clear. Sometimes$50 words don't Pentwater this brain

[Kirkll]

Now I am clear. Sometimes$50 words don't Pentwater this brain

I’m surprised you didn’t get into the carbon limb prototype craze that went on in the bowyers gallery on POA years ago Mike. There were several guys on that forum that were seriously well versed on carbon products. Had a few that actually laid up their own sheets with cloth and poured their own micro spheres for foam cores….. That was a talented group of innovative bowyers… it was sad to see it fade away like it did…..  but….. there was some wild and crazy guys on that forum too…..  Kirk