Machinable non-conductive structural material recommendations

[erik3000]

Looking for a material to use for a structural component of dimensions roughly 5x5x5"

Hard brittle plastics are out do to bending loads. Wood too fibrous, plus it may get wet.

- Must be machinable
- Rigid
- Electrically non-conductive
- The more isotropic the better
- Can support tapped threads

Right now considering G10 FR4 fiberglass. Link
Though the directional properties due to the sheet layup are not ideal. Though it is machinable and can be had in thick blocks

 

[CoryPad]

http://www.corning.com/specialtymaterials/products_capabilites/macor.aspx

 

[erik3000]

That's really interesting thanks for the link. Cool material. I'll look into it. It has a lot of the properties I'm looking for, but a bit concerned about the hardness and fracture toughness as this part will be dynamically loaded.

 

[RPstress]

A bit short in info, so a very large number of possibilities exist.

You've posted here so a short glass fiber bulk or sheet molding compound springs to mind (may be called 'long' fibres but they're not continuous). The SMCs tend to be quite layered but won't be as layered as GR10 FR4. Injection moldable materials are also available. Matrixes of more pricey higher peformance plastic such as PEEK or PPS are available or engineering thermoplastics like Nylon may be good enough, and good performance from thermosets like epoxy or vinyl ester can be had.

Quantum Composites (

http://www.quantumcomposites.com/)

might well have something suitable. You could also try TenCate, but I find their website quite confusing (they've eaten a lot of the older companies such as CCS). Victrex advertise a lot of short glass reinforced grades of PEEK (

http://www.victrex.com/en/datasheets/datasheets.php).

There are a million glass reinforced Nylons (at random via Google

http://catalog.ides.com/datasheet.aspx?culture=en&I=64840&PS=ASTM&E=27531).

The Macor courtesy of CoryPad is certainly interesting but it is rather frangible (fracture toughness under 5 MPa√m or ksi√in). If 'hard brittle plastics' are out then Macor won't be any better. Is this part subject to shock loads?

It depends quite a bit on what your requirements really are: is weight important or cost? What sort of quantity? And so on. Your requirements as listed seem a bit confusing: a 5"x5"x5" cube and bending might be a problem? Also I'd seek to quantify your 'rigidity' (some sort of strength or stiffness in psi/MPa) and 'electrically non-conductive' (dielectric strength in V/length or resistivity in ohm-m) properties. Also you'd like it isotropic and yet are considering a G10 FR4 laminate. If you can't quantify the degree of isotropicity then perhaps say why it needs to be 'The more isotropic the better'.

If you refine your needs a bit (the strength needed and temperature extremes are probably the most important) I'm sure you'll get good advice from our associates in the Polymer engineering forum (

http://www.eng-tips.com/threadminder.cfm?pid=334).

Also, I take it that you've no constraints on manufacturing method? Or do you want to make whatever it is in-house?