Drillable Materials - ?'s

[skirk1975]

What makes some of the plastics drillable and not others. 1.67 and 1.70 can be drilled according to the manufacturer (with Seiko due to MR10 Polymer) but why not Spectralite, 1.56, or 1.60. I need some detailed explanations of this.

[Darryl Meister]

Very few, if any, materials are "not drillable," though certain materials stand up to the stresses of a drill-mount frame better than others. For instance, brittle materials or materials with low tensile strength (i.e., the ability to resist tearing and breakage) will break more easily from the mechanical stresses applied by the screw / mounting.

Glass is the most susceptible to breakage, followed by hard resin. High-index urethanes, including MR-6/8 (1.6) and MR-7/10 (1.67), have excellent tensile strength and mechanical rigidity. Polycarbonate has great tensile strength, but its sensitivity to certain chemicals, internal strain, and drilling technique needs to be considered. Most mid-index materials fall somewhere between hard resin and the high-index urethanes in terms of tensile strength -- with the exception of Trivex, which is more like Poly (though it does offer better chemical resistance).

Keep in mind that tensile strength is only one factor important to drill-mount durability. The use of recommended mounting hardware and the use of proper drilling technique are also crucial. The quality of the drill-point will have a significant effect upon the local tensile strength surrounding the hole. The application of brittle coatings can affect the strength of a lens material, as well.

[Chris Ryser]

Good post by Darryl, and very explanatory. I can go even further.....................

There is NO materials in our lens field that can not be drilled..............and there is No material that can not properly mounted and fitted.............if you know, and have learned hoW to do it.

[mshimp]

Which material would hold up under the most abused circumstance?

[Chris Ryser]

Which material would hold up under the most abused circumstance?

For above described circumstance you should and would totally refuse to sell customer any rimless drillmount and sell em some safety glasses.

[Darryl Meister]

A material like MR-7 or MR-10 may offer marginally better tensile strength than Trivex or Poly, but they are all at least in the same ballpark. If impact resistance is an issue, Trivex or Poly would be a better choice (Trivex if thickness is less of a concern, Poly if chemical resistance is less of a concern). I've never investigated this, but I suspect that Poly is probably more sensitive to drilling technique as well (producing excess heat during the drilling process or failing to ream the lens afterward may increase the likelihood of failure).

MR-7 and MR-10 offer excellent overall durability, thinness, and chemical resistance, but they will not be quite as impact-resistant as a material like Poly (which can literally let the lens flip itself inside-out). However, keep in mind that rimless mountings are not necessarily the best option for eye protection in the first place, and an impact strong enough to break a high-index urethane would probably send the frame into your face anyway. Since the lens serves as integral component of the frame in a rimless mounting, one could also argue that the flexural strength (or mechanical rigidity) of high-index urethanes provides for more structurally sound eyewear.

Nevertheless, a material like Poly should be recommended if providing the maximum level of impact-resistance is important, regardless of the actual performance of these materials.

[mshimp]

Darryl,thanks for the info