Plane question

I know that when tuning up an old plane [even a new one for that matter] we are to make sure the back of the blade is flat. What about the top of the blade, where the cap iron mates? Should I give attention to that as well? I know to make sure the cap iron is ground smooth, but my question is about the top of the blade. Lewis

That's a good question. I don't recall reading/seeing anyone doing the the top of the iron for this purpose. I have only seen that the back of the chipbreaker where it mates with the iron is dressed for this reason. That being said, isn't that the same thing in reverse? I'll be checking back to see if someone posts the answer.
ralph

I am guessing here:

On a bevel down plane the cap iron is mated to the flatten side.

A bevel up plane directs the chip up and away from the cap iron. So maybe flatting this side not as essential.

Lets hear from someone who knows. I want to know if I am in the ballpark.

The reason we flatten/hone/polish the non-bevel side of a plane iron is to insure that we have a sharp edge. Since the definition of a sharp edge has often been stated as the intersection of two planes, with a zero radius, it can be seen that the presence of grooves or ridges on the non-bevel side of an iron means that true sharpness cannot be achieved. In the case of a bench plane, flattening this area (and mating the chipbreaker) also acts to prevent chips from becoming wedged between the two.
Your question seems to ask whether it is desirable or necessary to flatten that part of the iron above/behind the bevel.
The answer is no.

As long as the chipbreaker and the blade mate well, I can't imagine needing to do this. That being said, I am no expert.

I am not sure what you mean by the "top of the blade."

A good mating between the blade and cap iron/chip breaker is essential for many reasons as stated above. Any flattening of the blade beyond the useable area is not important. The side of the blade bedded on the frog should be smooth, but 100% flatness isn't needed.

The chip breaker shouldn't have much other influence on the blade. If the chip breaker has too much "lift" it can cause a concave cove on the blade and keep it from seating well on the bed of the frog.

There are different opinions on this. Some feel as long as there is good contact at the base of the blade it doesn't matter if the rest of the blade is bedded. My feeling is the more contact between the blade and the frog the better. ymmv

jtk

I guess the question would be the area where a bevel down iron rests on the bed of the plane right where iron's edge comes through the sole. That area is "milled" smooth on the plane's base. Would polishing both the "milled" area on the base, and the bevel side of the iron make for a better fit? Maybe less "chatter" IF the iron is bedded smoothly to the base for support? IF one spends all that time to get a "mirror finish" ( that the chipbreaker will just scratch up when you slide it in place) on the "back side', a little extra work on the bevel side wouldn't hurt? NOW, IF there is a way to polish the area on the plane's bed where the iron rests?

thanks for all the input. My reason for asking this was to help eliminate chatter. I don't have the Lees just Stanleys and Stanleys look alikes. So every bit helps.

I did have a little Millers Falls 700 block that screamed at me when i used it. I checked UNDER the iron, well, well, a bit of wood stuff, maybe a grain sized or two. Just sitting there between the iron and the bed. Chatter? Nah, it screamed! Cleaned the metal bed back to bare, shiny metal, put things back together, and it is a very quiet, well-behaved little block plane. When i sharpen irons, I do tend to polish both sides. Makes thing a little better when moving the iron in and out for depth settings. I also try to keep the bed area clean. Amazing what a couple little grains of dirt can do....