In my experience it goes like this:

Aluminum Fixture boards are for being able to cut into and modify while doing one off jobs until the board looks like swiss cheese, then you get another. Aluminum is very soft. Put a pin in a reamed hole, tap it on the side with a hammer and see the result. Even with a hard anodized surface that is only a very thin “crust” that will crack rather quickly under minimal stress.

6061-T6 Aluminum-      Brinell Hardness = 95       Tensile Strength = 40000 psi

 

1045 Steel Fixture Boards are for Hobbyist and semi Pro machinists. Steel will last a long time and its worth helicoiling and bushing as the years go on. Many of the shops I have worked in during my 30+ years in industry use this type of plate.

1045 Steel –     Brinell Hardness 210                Tensile Strength = 81900 psi

 

4140PH (aka 4142) steel Modular Plates are awesome for long lasting, low maintenance and high endurance, For the Pro or the semi pro who wants quality and durability.  I decided on this material for the first Tormach modular plate I made for John Saunders of NYC CNC fame. Its almost indestructible nature has made it a popular choice for Tormach users over the years.

4142 Steel –   Brinell Hardness = 300             Tensile Strength = 125,000 psi

 

2″thick high carbon Steel, finish ground with AA headed bushings in every dowel hole and CMM certified is full CNC Professional. These plates generally cost upwards of $20,000, I know, I used to buy them for our CNC machines in the mid 90’s. Nice to have, but silly expensive.