[Goemon]

From the pictures it looks like the Multicams are well made for the most part but those gantry beams just look spindly to me. For the most part gantry beams are the weak links in most router designs (this includes the beam supports). This is one reason why I'm following your thread closely to better understand how your beam design will work. Generally you would want a rather large cross sectional area, a big box beam if you will, to get the required stiffness. This is the same no matter what material you make the beam out of.

When it comes to a laminated carbon fiber beam I simply don't have the experience to say how one with a thin cross section will work in real life. You really can't tolerate much twist or deflection in the beam else you compromise with respect to the amount of driving force you can apply. That is you end up having to lower feed rate or more likely cut depth to avoid beam deflection.

In any event keep posting, I'm learning something new overtime I view this thread.

In some respects carbon fiber is like any other material in that a thicker part will be stiffer than the same part design with fewer layers but it differs greatly from metals and woods in how the part design, choice of weave and orientation of the lay-up effects strength and stiffness.

Essentially, it is easily possible for a 2" thick cf part to be stiffer than a 3" thick part that uses the same volume of cf.

My finished gantry beam will end up being around 3" or maybe 4" thick. It is being designed in a way that maximizes stiffness and strength in the direction of the forces it will be subjected to.

I will find out for sure when I start testing but my assumption is that forces hitting the center of the gantry at 90 degrees would present the greatest stiffness challenge. I.e. You don't want it to bend in the middle. This is why I am using carbon fiber tubes to reinforce the beam at 0 and 90 degrees.

The other thing that is key to my design is the choice of using random matrix fabric for at least half of the thickness. Woven fabrics provide superior tensile strength and directional stiffness but the random matrix fiber's provide multi-directional stiffness. The mix of both types of cf produces really strong and stiff parts. I'm a huge fan of this approach. It's really cost effective too as the random matrix fabric costs 4 times less than woven 2x2 twill.

Another important area where cf differs from most metals is that it doesn't bend much before it breaks. With steel, there is a noticeable flex / bend as a warning before a part breaks. Cf parts just snap if the load exceeds their capability so it's important to build in more strength than is necessary so there is a good margin of safety. If there is any noticeable flex at all then the part is almost certainly too weak to be safe imo.