Thread: Lapping help requested

I have a Norton 4k/8k stone and the Norton flattening stone. My questions are:

1. Should I use the flattening stone on a new stone?

2. How often should it be lapped?

3. I have seen people posting about drawing a grid on the stone but I've not been able to find any posts describing the method. I presume this is done to demonstrate that the stone is flat.

4. Is there some way to know when the stone is not flat enough for sharpening?

Right now I am able to get my TI blade sharp enough to shave albeit with a bit of pull but it's not getting as sharp as it should be. I figure its either my technique, the stone, or both. Time I will need to improve technique but if there is a problem with the stone I've lost before I've begun.

TIA

Not an expert, but can share my experience. I did find that I had much better results after my stones were lapped even though they were new (referring to a Norton 4K/8K).

1. Yes. Often they are not flat out of the box. You should also round the edges.

2. Difficult for me to answer, but I probably lap my stones more often than I should. I lap the nortons more often than my belgians.

3. I just freehand draw a grid on the stone. You rub the stone together (wet, not dry) with the lapping stone until all the lines are gone. Provided your lapping stone is flat, when the lines are gone, your stone is flat.

4. Howard (Howard Schecter of the Perfect Edge) recommended using a machinists ruler. Hold the rulers edge on the stone and hold it up to a light to see if there are gaps between the stone and the ruler.

cabo_,

For the grid lines, take a #2 pencil and with it draw lines spaced about 1/2" - 1" (1-2 cm) apart and parallel to both the long and short sides of the stone. When you rub the stone on the flattening stone, alternate between circular and long axis rubbing motions and do this until the grid lines are rubbed away. Bring the abrasive stone to the flattening stone (flattening or lapping stone on the bottom - lapped stone on top) and rub the two together under a stream of running water. When you have lapped the abrasive stone, tilt the stone up on its edge at about a 45 degree angle and rub the edges of the stone on the lapping stone for a few strokes. This will create an "eased" or chamfered edge that will make the stone much more honing friendly.

And yes, the surfaces of the stones out of the box are not necessarily perfect and need to be lapped to ensure flatness and to remove any glaze that may interfere with their ability to hone.

good luck, Bruce

There is a lot to what you have asked. I did a demonstration of hone flattening at the recent Bladesmithing Conference in NY and flattened a coticule one of the guys had inherited from his grandfather. The process is easily learned when you can see it done in front of you! I'll try to describe it anyway.

I always check with a straightedge before I start lapping any stone. Hold a straightedge on its edge in the middle of the stone lengthwise. Hold the stone and straightedge up to the light and see if you can see any light between the straightedge and the stone. If you can, you know you should lap the stone flat. Usually the stones are dished in the middle. It would be very unusual to have a stone high in the center and lower on the two ends. This is due to human nature concentrating the honing in the center of the stone.

Put either the Norton4k8k or the flattening stone in the kitchen sink and adjust a stream of water over one end to wash away the swarf. This is very important as a buildup of swarf in the flattening stone will not allow lapping to occur. Rub the stones lengthwise to flatten. Check the stone after about 20 seconds. If it's a coticule, you'll see a light colored area where it has been lapped and those were the high spots. Keep at it until you get the light color evenly across the stone. Same deal with the Norton. You don't need a lot of pressure in doing this either! You also shouldn't need to lap very often if you use the whole stone when you're honing.

Also, you didn't mention whether or not you're stropping on leather as a final step. That's critical.

The last question is: how flat is flat? Flat is a specification and not a quality inherent to anything. I have granite surface plates that are flat to .0001" across the whole 18"x 24" surface. That's flat at a specific temperature and humidity and when supported by a steel stand with support at specific intervals to prevent flex. These things are certified and tracked by NIST. At that level of flatness, if you put your hand on the stone, you'll be able to measure the difference in height in the stone created by the warmth from your hand.

So, how flat does flat have to be to hone a straight razor? It certainly doesn't have to be .0001" across the length of the stone. As a practical matter, I flatten the coticules I ship to the flatness of the DMT stones on which I flatten them and that's flat enough for this application. If you use a quality straightedge like the Starrett Machinist's rulers I use (and sell for $3) and can't see light between the straightedge and the stone, you're flat enough. BTW, I think way too much is made of "perfect" lapping for stones and more time should be spent on honing technique. Lap your stones, keep them flat, but focus more on what you're actively doing to the edge.

Howard