Should you round corners on sharp edges?

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J

jprconsulting

Well-known member
I was recently talking with someone who I respect in finishing business.  He indicated that on a piece like a Federal table with tapered legs, that it is good to slightly round the corners.  I am talking about just a slight touch with sandpaper type rounding.  That the finish will work better.  It makes sense that if the edge is knife like, there is less area to hold the finish.

I would appreciate any comments or ideas.

Thanks.
 
Well, I guess I'll jump in - though my response has nothing to do with any theory about holding finish.

When I "apprenticed" in the cabinet shop at the Ohio Village, it was standard practice to VERY LIGHTLY round any exposed arrises with the finest grade of abrasive paper used in preparing to apply the finish. Tom Clark, who I apprenticed under, felt this provided a small surface to reflect light (helping to visually define the arris, somewhat paradoxically), helped minimize the visual impact of subsequnt wear-and-tear, and softened the keenness of the arris when people came into contact with them.

Don McConnell
Eureka Springs, AR
 
My understanding about breaking the corners and finishing is this.
The sharp edge will cause finish to be drawn to it and cause a ridge. I don't remember the physics involved. Break the corners and no ridge in the finish. It also makes the piece nicer to touch.
Mike
 
It's interesting how "convential wisdom" turns to "fact". I too have learned that edges should be "broken" but the reason I was given (and I believe to be true) is that sharp edges allow the finish film to be broken more easily by the microtrauma of day to day use and to earlier finish failure. But just because I believe it doesn't mean that it's so.

Howard Steier
 
Well...close, but for the wrong reason. Did you ever overfill a glass to the point the water is actually higher than the rim of the glass? It's the surface tension. Instead of being pulled to the edge it's trying to get away from it and puddling right beside it. Liquids don't like square corners, inside or out. When you were filling that glass the water was curling up the sides until you got to the top. Obviously a sharp corner is easier to damage. As much as we all love crisp lines, really most corners aren't broken enough for an even film thickness to wrap around. Ideally (for the finish) every edge should have at least a 1/16 radius on it! Feel free to tell me I'm all wet!!!
Mark
 
Your're not exactly all wet, but your explanation of surface tension could use a bit of refinement from the scientific perspective.  The reason the water "crawls up the sides of the glass" before it gets to the top is that the water is a polar compound, and so is the surface of the glass, so they attract each other.  When the water gets to the top, it is still attracted to the glass, so the surface of the water will bend down to contact the rim. 

When the wieght of the water that is above the rim of the glass exceeds the attractive forces of the water to the glass rim and to itself (the actual surface tension), the film breaks and the water spills over the side. 

Not a terribly interesting experiment, but if you coat the inside of the glass with a hydrophobic substance, such as an oil or teflon lubricating spray, you'll find that instead of the water surface crawling up the side, it will instead be higher in the middle.
 
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