The hardness of some of the Arkansas stones means that they require particular attention to lap flat. The good news is that same hardness means that once lapped flat, you are unlikely to have to do it again anytime soon.
Most of the information on this page is derived from this great thread by @captaincaed : Lapping an Arkansas in Excruciating Detail. Excruciating in the sense of both the level of detail, and in how your sore your arms will feel once you are done.
Most of the information on this page is derived from this great thread by @captaincaed : Lapping an Arkansas in Excruciating Detail. Excruciating in the sense of both the level of detail, and in how your sore your arms will feel once you are done.
What you'll need
First, in addition to a hard Ark (also encompassing Surgical and Translucent), you will need the following lapping equipment:
Alternatively, depending upon availability, you could simplify with: 90 → 220 but expect a lot more work.
In addition, it is helpful to have:
Similarly, just using Wet & Dry will see you go through reams of the stuff, and it is likely that your arms will give out long before you make enough progress on the stone. The W&D is used to help hold the SiC in place, and for the final fininshing of the stone at much higher grits, not to do the actual cutting work.
- Silicon Carbide powder, in a range of grits, starting from as low as 60. You can get away with starting higher, but be prepared to work a lot longer.
- Wet and Dry paper, again in a range of complementary grits to the SiC.
- A known flat surface to work on. A piece of granite or the like
- A Sharpie to mark a grid on the stone's face
- Time. This isn't a quick process.
Alternatively, depending upon availability, you could simplify with: 90 → 220 but expect a lot more work.
In addition, it is helpful to have:
- A flat steel baking (cookie) tray, to contain the mess
- A straight edge to determine flatness (the edge of a diamond plate will work here)
- An atomiser/water sprayer
Similarly, just using Wet & Dry will see you go through reams of the stuff, and it is likely that your arms will give out long before you make enough progress on the stone. The W&D is used to help hold the SiC in place, and for the final fininshing of the stone at much higher grits, not to do the actual cutting work.
SiC Process
Place your lowest grit W&D paper onto the flat surface, (or on to the cookie tray on said surface), after lightly wetting it. Wet the top of the paper lightly and then sprinkle a ½ teaspoon of the lowest grit SiC across the paper, ensuring it is evenly distributed. Wet it down lightly: an atomiser is great for this. Then place the surface of your Ark (with a Sharpie grid) onto the paper and begin to lap it. Bear down on it and you want the force to generate friction and scour the surface of the stone.
Over time, the SiC will break down and form a slurry with the shed novaculite. At this point you will no longer be cuttting, so you will add more SiC. The W&D will help hold the SiC in place, but this will also start to perish and will need replacing. Budget for around 4 sheets for each of the lower grits.
One important conisderation is that, over time and grits, you will inevitably remove more of the material around the edges of the Ark, so you will be convexing the stone. You can monitor progress by replacing the Sharpie grid, or with a straight edge.
Note that it is important to clean off the surface, or the baking tray, completely between grits. You do not want to contaminate the higher grits with any of the lower grades.
Keep replacing the Sharpie grid until it is being removed uniformly across the stone. By the time you get to the higher grits, this should be in increasingly fewer laps (around a dozen is a decent benchmark for flatness: confirm with your straight edge before proceeding).
Once you have gone through the SiC progression, and prior to turning to the W&D for finishing, if there is any residual convexity shown by your straight edge, you can use a worn diamond plate to complete the lapping.
Over time, the SiC will break down and form a slurry with the shed novaculite. At this point you will no longer be cuttting, so you will add more SiC. The W&D will help hold the SiC in place, but this will also start to perish and will need replacing. Budget for around 4 sheets for each of the lower grits.
One important conisderation is that, over time and grits, you will inevitably remove more of the material around the edges of the Ark, so you will be convexing the stone. You can monitor progress by replacing the Sharpie grid, or with a straight edge.
Note that it is important to clean off the surface, or the baking tray, completely between grits. You do not want to contaminate the higher grits with any of the lower grades.
Keep replacing the Sharpie grid until it is being removed uniformly across the stone. By the time you get to the higher grits, this should be in increasingly fewer laps (around a dozen is a decent benchmark for flatness: confirm with your straight edge before proceeding).
Once you have gone through the SiC progression, and prior to turning to the W&D for finishing, if there is any residual convexity shown by your straight edge, you can use a worn diamond plate to complete the lapping.
Finishing
Now that you have completed the SiC grit progression, you can finish the flattened surface(s) with Wet & Dry. A common approach is to finish to 600 on one side, and between 1000 and 2000 on the other. This is done exactly as above, only without the SiC powder on the paper.
Before honing your precious grail, run a beater over the stone's face to ensure there are no irregularities or protrusions left. If it feels glassy smooth, you are good to go.
Some people advocate burnishing the face with a kitchen knife or chisel, but that is outside the scope of this article. A search on the forums will provide the details.
Before honing your precious grail, run a beater over the stone's face to ensure there are no irregularities or protrusions left. If it feels glassy smooth, you are good to go.
Some people advocate burnishing the face with a kitchen knife or chisel, but that is outside the scope of this article. A search on the forums will provide the details.
Images
See Also
There are a number of helpful forum threads worth reading:
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