G10/FR4 Glass Epoxy Rod

Flame-retardant glass-epoxy rod is machining stock for insulating pins, studs, standoffs, shafts and spacers that have to carry a flammability rating. It is produced from stock certified to NEMA FR-4 and MIL-I-24768/27 Type GEE-F. Published lengthwise flexural strength for that material runs 65,000 to 80,000 psi and tensile strength 40,000 to 62,000 psi depending on the maker, with a temperature index of 130 to 140C, volume resistivity around 3 x 10^15 ohm-cm and a dielectric constant of 4.4 to 5.0 at 1 MHz.

There is an important caveat on the certification, and it applies to every supplier's glass-epoxy rod rather than just ours. Neither NEMA LI-1 nor MIL-I-24768 sets requirements for sheet-ground rod - one major maker says in terms that there is no industry standard for it - so the certification travels with the sheet the rod was cut from rather than with the rod form itself. If your drawing calls out a certified FR-4 rod, that is worth a conversation before you order, because what can actually be supplied is rod made from certified sheet.

Rod is also made two ways, and it changes which numbers apply. Smaller diameters are commonly moulded from prepreg; larger diameters and some small ones are cut from sheet and ground or turned. Sheet-ground rod generally carries the properties of the sheet it came from, which is why the figures above are the sheet figures. On flammability, the US makers we buy from publish UL 94 V-0 for FR-4; ask us for the certificate if the rating is a requirement. And heating this grade above 300C decomposes the flame-retardant package and releases hydrogen bromide, which G-10 and G-11 cannot do.

It is turned and milled into insulating pins and dowels, threaded standoffs, studs and spacers, non-conductive shafts and linkages, test fixturing and switchgear hardware. Natural stock is light green.

Machining and handling. The glass abrades tooling, so carbide is the floor and diamond-coated or PCD cutters are what hold tolerance in production; run high spindle speeds with secure workholding and design in generous internal radii, because small tools wear out fast against glass. Threaded holes are normally milled rather than tapped and external threads turned or thread-milled, since the plies can delaminate. The laminate has no hazards as shipped, but cutting it releases a fine dust, and the epoxy resin in that dust is classified as a skin and respiratory sensitiser - use local exhaust, a dust respirator, eye protection and gloves, and work to your own site's exposure limit, because published limits for glass dust differ by jurisdiction and by whether total or respirable dust is measured. It comes off as powder rather than chips, so vacuum it up rather than blowing it airborne. These are our shop notes, not a manufacturer specification.