I believe it means that the manufacturer is either incapable of manufacturing a perfectly flat plate or is trying to sell it at a price point that prohibits it.
In either case a "slight crown" is NOT preferable. NOTHING is better than perfectly flat. Period.
Save your money and invest in a quality plate by a reputable manufacturer like Kreg, JessEm, Woodpecker etc.

 

I agree get a plate that is flat, .008 mm crown???? my guess is that would be about a 1/32" bow or crown. Not the best for a router table.

 

I wonder how the phenolic plastic will flex when one hangs a 2-1/4 hp or 3 hp router under it.

 

:jester: The flex will be *downward*, Cassandra; the amount is a calculation left to the student. :jester:

 

Hi Jim:

Yes, the deflection is of course downward. My previous post was to stimulate the conversation on whether the slight crown would disappear once the router is hung.

Cassandra

 

Yep but being plastic, the deflection wouldn't stop at flat, it would continue downward over time and with heat then you would have a concave spot in the table.

 

Deflection is the key, Danny, and Cassandra's point... <going technical here all.. skip the rest if you don't want to read technical>

when you hang a weight on a flat plate, to exert its lifting force it bends downward slightly. It's the compression force on the top and the tensile force on the bottom that provides the "lift". Just how much it deflects depends upon many things such as thickness, distance to support and properties of the material used. As long as the weight doesn't exceed the "elastic deformation" range and move into the "plastic deformation" range, it will spring back when the weight is removed.

Thus technically, if you want it to be perfectly flat with a weight on it there should be some amount of crown on it without weight such that after the load is applied it becomes flat. In practice, for a rigid plate that's not excessively large and not too heavy of a weight, that amount is insignificant and can be ignored.

For an easily visualized example of this, consider a long overloaded bookshelf. It sags in the middle. If it were designed with a slight crown in the middle and the ends were constrained (held) from moving outward, it could hold a lot more weight. This principal is what makes arched entries so much stronger than square ones and why a lot of the Greek stonework (with arched brick construction) are still standing today.

<end technical>

 

Interesting, but why try to estimate such things?. Buy a high quality 3/8" plate that is flat and won't deflect from the weight of the heaviest router you plan on installing.

 

That's what I did, Joe.. As I said above, I considered it insignificant...

 

"Moulded with slight crown (0.8mm) for distortion free cuts"
That's the same text that can be found on Amazon in the description of the Trend RTI/Plate.

0.8 mm is 0.0315 inches or in fractions of an inch ..... can't remember how to do it.
Needless to say the Trend RTI is a recognised piece of kit and 0.0315 is not worth worrying about (for most folks).