Selecting a Lapping Plate for Waterstones
What is a lapping plate and why do I need one?
A lapping plate or flattening stone is a coarse stone used to flatten other sharpening stones. In order to keep flat and straight edges on cutting tools, it is necessary to have a flat stone to sharpen on.
Stones such as water stones cut very quickly because the binder that holds them together breaks down very quickly, constantly exposing fresh grit. While this results in fast metal removal, it also means that the stone wears relatively quickly and will lose its flatness through continued use.
The rate of this wear varies by both grit and grade of the stone. In general, the coarser the stone, the faster the wear. Also, the higher the grade of the stone (for instance Naniwa Professional series as compared to the Traditional Series) the harder the binder and therefore the slower the wear.
What are the options in Flattening stones?
There are two main types of flattening stones available, diamond lapping plates and abrasive flattening stones.
are available from Naniwa, Norton and Sharpening Supplies. They are most often made from silicon carbide abrasive. These stones use water for a cutting fluid and do a fine job of flattening all grits and types of Water stones. They have large grooves for waste removal which help keep them from clogging during use. They are available in different sizes. These flattening stones do wear over time. When this happens they require flattening themselves, often on a diamond lapping plate. These are generally more economical than diamond lapping plates
The Naniwa Flattening Stone is a smaller stone. Indeed it is smaller than most waterstones it is intended to flatten. This means that it is often necessary to move it over the waterstone being flattened. While inexpensive, its size can make it harder to produce a dead flat surface on the waterstone.
The Naniwa Extra Large Flattening Stone is indeed much larger than the regular flattening stone. While the size may be cumbersome, it would make an excellent permanent fixture on a dedicated sharpening bench.
Diamond Lapping Plates
are available from DMT and Shapton. These stones offer the advantages of extreme flatness, translating to reliably flat waterstones, and durability, never requiring re-flattening. There are different grits and sizes available and diamond lapping plates are an excellent choice if your budget permits.
The DMT Dia-Flat Lapping Plate is very handy for flattening all waterstones. A large surface area and very aggressive 120 mesh grit make this our fastest lapping plate. The DMT Hardcoat technology makes this lapping plate wear more slowly and last longer than ordinary diamond stones.
The DMT Dia-Flat 95 Lapping Plate at 160 mesh is a finer grit version of the DMT Dia-Flat. This is our most popular lapping plate, and it also incorporates the DMT Hardcoat technology, giving it a long working life. While slightly slower cutting than the coarser plate, it still makes fast work of flattening. The Dia-Flat 95 leaves smoother finish on the waterstone being flattened and is preferred by many for surfacing very fine stones. The DMT Dia-Flat 95 is available in 10" x 4" or 8"x 3".
The DMT 8” Dia-Sharp Extra Coarse Stone is a bit finer yet at 220 mesh. While not as fast or as large as the DMT Lapping Plates, it will work well on finer Waterstones. The Dia-Sharp 220 also has the advantage of being usable as a coarse stone for other sharpening needs, and can be a cost efficient option.
The Shapton Diamond Lapping Plate is a very precisely engineered surface for flattening waterstones. A specialized tool developed for the Shapton stones, it is not intended for use on any stone under 500 grit.
Which lapping plate is the best?
While no one flattening stone will fit every sharpener’s needs, we have found the DMT Dia-Flat 95 to be the best option when cost isn't a factor. The best value option is the Double-Time Flattening Stone.
All of the lapping plate options are capable of giving you flat, ready to use water stones. When choosing, keep in mind the size of the stones you need to flatten. A lapping plate larger than the stone to be flattened is generally preferable. Also think about the amount of sharpening you do, a good quality abrasive flattening stone may be a good value but a quality diamond lapping plate may be more cost effective if you need to regularly flatten water stones.