Grading
F Grade vs MGP Grading
Grading systems for timber can quickly become confusing. The standard and most common grading system that has been used with structural timber for many years is the F Grade system. Most timbers bar some of the plantation pines are F graded. This is done either visually or mechanically, using a stress grader. Alternatively, MGP grading can be used on specific plantation pines, and is done using a machine.
F GRADING
Giving an F grade to a piece of timber measures the bending strength of the timber. The ‘F’ stands for force, measured by MPa (megapascals), and gives a measurement of the amount of force a piece of timber can stand before bending beyond a certain threshold. An F9 piece of timber would be able to withstand 9 MPa.
|
Standard Trade Name |
Stress Grade (F Grade) |
|||
|
Douglas Fir |
F11 |
F8 |
F7 |
F5 |
|
Radiata Pine |
F8 |
F7 |
F5 |
F4 |
|
Slash Pine |
F14 |
F11 |
F8 |
F7 |
|
Cypress Pine |
F7 |
F5 |
F4 |
|
|
Hoop Pine |
F8 |
F7 |
F5 |
|
MGP GRADING
MGP grading, standing for Machine Graded Pine, is a system used for particular pines such as radiata, slash and Caribbean pines. MGP measures elasticity (MOE, modulus of elasticity) which considers other properties such as stiffness, compressive strength and shear strength.
A higher MOE means stiffer properties. Measured by an MGP machine, the grade the timber is given is simply an abbreviation of the MOE category that is falls under.
MGP 10 has an MOE of 10,000 megapascals (MPa)
MGP 12 has an MOE of 12,700 Mpa
MGP 15 has an MOE of 15,200 Mpa
USING MGP IN PLACE OF F GRADED TIMBER
An important consideration to make is that while MGP timber may be substituted for F graded material, F graded wood cannot be substituted the other way around.
The reason is that MGP grades have compatibility set for a range of properties, where F grades are based only on bending properties. Therefore, if an F graded piece is provided as a substitute, it may not take into account important factors such as shear or compressive strength where MGP wood is tested such.
MGP 10 can replace F5
MGP 12 can replace F8
MGP 15 can replace F11