Laminated Panels

[Asleep Helmsman]

Hey Guys,
I'm building some small panels and trying to eliminate flex in multiple directions.
It will have some point loads and will need to be lighter than using solid aluminum.

Inner Skin will be 1/4" (6.35mm) 6061 T65 Aluminum Plate
Core will be end grain western red cedar approximately 1.5" (38mm)
The question is the outer skin.
I'm thinking of using trydirectional glass from Jamestown.
Vectorply Fiberglass Cloth - Triaxial | E-TLX 2200 https://www.jamestowndistributors.com/userportal/product.do?part=391912&engine=adwords&gclid=Cj0KCQiAvKzhBRC1ARIsANEXdgxiyUltFCS-CR0qil9V1-FNa-SIvBQolrl70Qv2WjVYarKoGPL44mMaAqmMEALw_wcB
Reviews on their site talk about it laying very flat. I will be vacuum bagging it to a granite mold because flatness is important.
Thanks for reading this entire description.
Question: Is there any reason to use another type of glass in this panel?

 

[JamesG123]

With 1/4" AL plate bucked by 1.5" of wood you would need a LOT of glass to make any noticeable impact upon the panel's rigidity. What is the application for these?

 

[Asleep Helmsman]

With 1/4" AL plate bucked by 1.5" of wood you would need a LOT of glass to make any noticeable impact upon the panel's rigidity. What is the application for these?

The core is end grain, so the out panel will be in almost pure tensile loads, the inherent stiffness, as you said, won't have much effect. The skin also serves to create a harder, damage resistance, surface than the relatively soft cedar.

This will be used for constructing a light weight CNC router gantry assembly.

 

[fallguy]

How large are the panels dimensionally x & y planes?

You run the 0 strands of triax out and consider the stresses for the direction.

Triax would not be my choice for a covering glass. I would prefer 1708 or 1808.

 

[Asleep Helmsman]

How large are the panels dimensionally x & y planes?

You run the 0 strands of triax out and consider the stresses for the direction.

Triax would not be my choice for a covering glass. I would prefer 1708 or 1808.

The panels are roughly triangular, with an 18" base and 24" height. I think I am in overkill territory anyway. So maybe other consideration should come into play. For example, impact resistance, and final finish.

What is your motivation for using one of the bi-axial clothes?. And, do you think there should be 2 layers?

I'm planing on using West System 105 on the Glass Lamination and G Flex as the adhesive for the Aluminum/Cedar connection.

 

[fallguy]

the only reason for using a triaxial cloth would be to gain directional strength.. It is more about motivation away from something unnecessary and 1708 is sort of a common cloth, ought to cost less, etc. It is also 25 ounces a yard and would cover in a single go. Two layers only if the thing is going to get a lot of common use and handling, otherwise a single layer is great plenty I'd say

 

[Asleep Helmsman]

the only reason for using a triaxial cloth would be to gain directional strength.. It is less about motivation away from something unnecessary and 1708 is sort of a common cloth, ought to cost less, etc. It is also 25 ounces a yard and would cover in a single go. Two layers only if the thing is going to get a lot of common use and handling, otherwise a single layer is great plenty I'd say

Yup. it will get abused, it's in our shop. Thanks for the heads up. No use spending more than I need, especially for no real gain.
Fiberglass DBM 1708 Knytex Biaxial +/- 45 Degree Fabric 17oz/576.4gsm https://compositeenvisions.com/fiberglass-dbm-1708-knytex-biaxial-45-degree-fabric-17oz-576-4gsm/
Fiberglass DBM 1808 Knytex Biaxial +/- 90 Degree Fabric 50"/127cm 18oz/610.31gsm https://compositeenvisions.com/fiberglass-dbm-1808-knytex-biaxial-90-degree-fabric-50-127cm-18oz-610-31gsm/

 

[fallguy]

Make sure to do both layers in a single go; it'll be much better and if you are hitting edges, you need a little more radius than a milled 2x4..

 

[fastwave]

I would be very careful with your proposed changes. The assymetric nature of your layup means that with any load or temperature change the beam will band out of plane. Not what you want for a CNC machine

 

[Mr Efficiency]

I'm not au fait with what is being proposed here, but my first impulse was to wonder why one skin would be a completely different material to the other.

 

[Asleep Helmsman]

I'm not au fait with what is being proposed here, but my first impulse was to wonder why one skin would be a completely different material to the other.

The aluminum inner skin will be flat in the range of a 1/1000 th of an inch. Plus it will be suited for hard points and treaded holes. The outer skin will be primarily subjected to tensile and compressive loads.
The whole panel could be solid aluminum, they mostly are for DIY CNC Routers. I just wanted to design one that would be stiffer for the same weight.
This maybe a wild goose chase. But it also provides a good way to test the load carrying capabilities of aluminum-wood-FRP sandwiched panels. We can very easily determining loads and deflection in this machine. Epoxies have gotten much better ate adhering to aluminum, and end grain sandwiched panels have been around since the 60s.
So we will see.

 

[fallguy]

How to prep the aluminum?

Wire brush perhaps?

 

[Asleep Helmsman]

How to prep the aluminum?

Wire brush perhaps?

According to the latest from West System that's all that is needed if you are using their GFlex product. They discontinued their aluminum prep solution. Their test indicate 2600 psi for aluminum.