Is this normal (sharpening question)

[Eric Rathhaus]

Hi - I've been working to flatten the back of an iron. I got to the point where only the corners reflected a little light, and looking at the iron from another angle, I could see a consistent scratch pattern except for the small area at the corners. More strokes, and I had worked out the corners. But as I brought the corners into shape, a bunch of small, faint lines appeared running perpendicular to the scratch pattern I was making. Is this normal?

Eric

[Andrew Pitonyak]

I am having a difficult time following what you are saying. If you are unsure if things are uniformly flat, you can color the area of interest (use a marker) and then flatten until you remove the marker.

Be careful, because as you move back and forth, you might end up tilting (or putting more pressure) on certain areas and then you are again out of flat.

Also remember that you do not need to flatten the entire back, just some portion behind the cutting edge. I have a plane where one corner goes in very far so I would need to grind the blade back more than i wanted to to get rid of the problem. So, I used "the ruler trick", end of problem.

[Jim Koepke]

Hi Eric, This is a case where images can be an immense help.

My confusion is to whether the perpendicular lines are in the corners or in the central areas. My experience with something like this turned out to be a laminated blade with a crack in the lamination.

Also sometimes the back corners have been given a few swipes on the back as a quick way to camber. Here is an old post of mine using this technique to produce the effect of a camber on a blade > https://sawmillcreek.org/showthread.php?158373

Many of my planes came to me with this kind of blade modification.

In the long run what matters is the quality of surface your blade leaves when doing its work. A Scrub plane doesn't need to leave a finished surface as nice a Jointer, Jack or Smoother.

The real determination of "is the back flat enough" is how it works in the plane. It has to be flat enough to mate with the chip breaker so it doesn't jam shavings.

Many of my blades after initial flattening enough to work have been given a bit of back work every time they get sharpened.

One thing that has helped immensely in this is my Veritas Mk.II Power Sharpening System (https://www.leevalley.com/en-us/shop/tools/sharpening/power-systems/48435-veritas-mk-ii-power-sharpening-system).

This set up works for my wide range of needs. Others might prefer a belt sander or many other methods.

At one time my buying of lots of old tools kept the Mk.II humming. After first use it became clear my use would need multiple tool holders. Batches of five blades could be worked at a time. The first one would be cool by the time the fifth one would be set aside to cool.

The thickness of the different abrasives causes a tendency to produce a micro bevel. This can be counter acted by adding the abrasive backing sheets under the platters.

jtk

[Jim Koepke]

Andrew makes an important point:


Be careful, because as you move back and forth, you might end up tilting (or putting more pressure) on certain areas and then you are again out of flat.

For many tasks a circle template helps on my projects:

428695

The smallest one here and an even smaller one are very useful when flattening the back of a blade. One of these is set on top of a blade so downward pressure can be placed evenly on the blade while it is worked. A block of scrap could likely be made into such a helper without having to make it into a circle.

jtk

[Eric Rathhaus]

I'll try and take a picture. it's an old, laminated blade. The lines appear in the middle for the blade, not just the corners. The lines appear fairly uniform. Almost running straight referenced to the blade's sides. It's hard to believe it's a crack because the lines are all pretty straight. Here's a drawing - the first being the corners I was working on and the second after I had finished the corners and the lines appeared. The lines are straight despite my drawing but not all of same length. I will add that except for these lines, there's a mirror finish. 428697

[Jim Koepke]

[edited]
The lines are straight despite my drawing but not all of same length. I will add that except for these lines, there's a mirror finish.

It could be staining. The best test may be to install it into a plane. Set it to take the thinnest shaving possible. If the shaving is solid over the width, you should be fine. If the shaving looks like ribbons, then the lines are a problem. This wouldn't be a big problem for some purposes but would be a big problem for a smoother.

jtk

[Jim Matthews]

See: David Charlesworth, "Ruler trick".

I use Sharpie markers as a visual aid on irons.
Some prefer Dykem for this task.

https://woodandshop.com/woodworking-hand-tool-buying-guide-sharpening-honing-supplies/

[Robert Hazelwood]

It might be the factory grind marks.

[Eric Rathhaus]

Thanks for all your suggestions. I took the blade down to a coarser grit of sandpaper and worked out those marks. I think the problem was cause by contamination.