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Flat as a pancake, A quick guide to Lapping and Trueing

Updated: Nov 27, 2023


(Pictured is Sharpeningsupplies double time flattening stone both green and pink)


Lapping stones and grading tools are used to resurface and smooth out sharpening stones and water wheels. These are easily distinguishable from sharpening stones by some key features. They are very abrasive, ranging from a low 24 grit up to the 300+ range. They need be more abrasive than the material they are working against. Because these stones remove a lot of material, there is an excess amount of slurry created by the action of lapping. these stones often have deep channels or grooves, allowing them to drain off this build up of waste. A majority of flattening stones with the exception of diamond and glass plates will be a lot softer than your sharpening stones and grinding wheels. Black silicon carbide stones for example are very light and almost feel hollow.





There are several different shapes and types of trueing stones. Common materials used to make these stones include silicon carbide and aluminum oxide. The grains of silicon carbide are much more sharper, harder and jagged than the grains of aluminum oxide. Silicon carbide stones are found in two forms, black SiC and green SiC. Green SiC has a higher purity than black SiC and tends to be more durable with a slower wear rate. Yet both forms of silicon carbide are less durable than alumina. Aluminum oxide is what many sharpening stones are made from. Silicon carbide and alumina are ceramic materials. Silicon carbide is better used for non-metallic objects with a low tensile strength (tensile strength is defined as the maximum strength a material can bear, before breaking) which is why silicon carbide is more commonly used to correct sharpening stones and not so much as a material for making them. In contrast aluminum oxide is better suited for materials with a high tensil strength, as we previously mentioned; Its a good material used for sharpening stones.


Not all lapping and gradding tools are made of stone. One of the most popular materials is diamond abrasives, diamond coated lapping plates and grading tools are loved for their high wear resistance, speed and highly agressive cutting power. Another type of lapping plate thats in use is a sure flat glass plate. This glass plate requires an adhesive backed abrasive sheet, with alumina and Silicon carbide being common abrasive used in these papers.


The term lapping can be used to describe a process of surface finishing where abrasives are used as the grinding agent at a relatively low speed. How does this process work? As you move your sharpening stone across the lapping plate the abrasive particles carried by a liquid vehicle (in this case water) remove materials at the highest surface points of the surface making contact with the lapping plate. The goal is to produce a uniformly flat surface .



(Pictured: A 36 grit diamond trueing tool (left), you can see the very course diamond head used for cutting away material from the wheel)


Trueing tools come as jigs or as small T shaped tools with abrasive heads and points. The action or definition of trueing can be defined by the act of restoring the grinding face of a wheel by removing the abrasive material from the cutting face and sides of the wheel so that it runs smoothly with respect to its axis of rotation. Trueing makes the periphery (outer limits or edge of an object) of the grinding wheel concentric (In geometry, two or more objects are said to be concentric when they share the same center) with its axis. These tools are just about always made from diamond abrasives or diamond points, this allows them to cut quickly and very agressively remove material in rather short amount of time.



(Pictured: The surface of a water cooled sharpening wheel after being trued. The diamond tool leaves track lines and groves through out the stone wheel. To finish the job this wheel will need to be dressed)



The one .thing all of these lapping plates and stones have in common, is that they are virtually flat. This a crucial element of any of these stones and plates, if they are not flat your stones and wheels will not be flat. A wonky sharpening stone or one that is not flat will provide an uneven cutting edge. An uneven stone can also damage a knife and the stone itself. This is because when you have hills and valleys on your sharpening stone, as your running the knife across it, the edge may bite into one of the higher points of the stone. This will put a nick or gouge in your sharpening stone and can also chip the knife or ding the edge. A wonky sharpening wheel will be out of sqaure and will often woble, this will transfer to the items your sharpening resulting in uneven wear spots along the cutting edge. This is especially important on tools like chisels and planers were level precision is required, The bed angle on a chisel is important to its function, with out it the tool will not perform correctly. The same with Japanese knives, you will not be able to properly sharpen a single bevel knife, not only will the cutting edge be inconsistent but this will also affect the uraoshi on the back of the knife.


So how do you find out if your stone is actually flat? there are several tests that can be used. These tests ensure that both our sharpening stones and our lapping stones are flat.


  • Straight edge test, a straight edge is a metal measuring instrument of various sizes that is completely flat, lay it acrosss the stone length wise and width wise to see if your stone is dead flat. Alternitively a solid combination sqaure can be used. Dont use a flimsy ruler or other thin instrument as these can be off.

  • Flashlight test, one test we often do here at our shop is the flash light test, to do this you will need turn the stone upside down so the side you use is facing down, you will also need a pen light or a flashlight thats beam of light sights no higher than the top of the stone, next place yourself so your eyes are level with the stone, then move the flashlight from one side of the stone to the other. Light will shine through or can show you spots were your lapping stone is uneven.

  • Visual Test, carefully examine the stone for uneveness or patterns of wear. It helps to have good lighting when doing this. if an area is poorly lit it may be hard to notice any deffects

  • Surface test, Another test you can do it to place your stone on a surface you know for sure is completely flat such as a glass lapping plate and inspecting the stone carefully. To do this you will need to put the side of the stone you are using facing down.


When to use a lapping plate or grading tool, you may be thinking you only need to use one if there is dishing present or your wheel is way out of square. The best time to use a lapping or grading tool is every time you sharpen. Regularly maintaining your stones and wheels prevents excessive wear and defects. If you are consistent you will save more time in the future. This practice is better for your stones and extends their lifespan, if you wait until you have a deep valley in your stones you will now have to remove a larger amount of material from the entire stone to correct it. This also put excessive wear on your lapping tools and shortens their life.


Now that you have an understanding of lapping tools, you may be asking which lapping stone is best or which one should I get? we of course have done the work for you. From having the hands on experience of using many lapping stones over the years and some others we have gotten to try more recently, We have compiled a list for which ones work the best and which ones are good for average use and which ones are good for heavier use.


here are our top choices:


Best overall:

The double time flattening stone from sharpening supplies, this was a more recent one for us. After using this stone for over a year we decided it deserved the best over all spot on this list. Most importantly its flat right of the box. The DTFS is made of green silicon carbide which gives it agressive cutting power and speed with a moderate wear rate. We put it through several hard tests and through repeated daily use it only diminshed slightly. One thing that we always appreciate when it comes to flattening is size and surface area. This stone definitely has both, it measures at 10"Lx4"W by 1" thick hence why we nicknamed it the Hulk. It has a very reasonable price for such a high quality stone. aside from the generous size it also comes in two grits, 120/320. Having dual grits is must for us, some times 120 is just to rough for finer stones in the range of 5,000-12,000 and removes an unecessary amount of material, it can also be quite harsh on softer stones of lower grits. As an added bonus it has deep channels that rapidly drain off waste material. Sharpening supplies puts in the extra work to ensure only the best for their customers.


Best budget friendly stone:

This one goes to sharp pebbles dual grit lapping stone, it costs about $27 USD on amazon. We had used these stones many time and got fairly good results and feedback from it. Its measures 7.8"Lx2.8"W and sits at 1.2" thick. This more compact size allows it to be easily stored in the kitchen without taking up to much drawer space. This stone is made from black silicon carbide and therefore did not hold up for us with heavy usage seen daily. Dont let the smaller size or durability discourage you though, this a great dual grit stone with 120/320 combo. It has deep channels that send of excess material. is the perfect stone for at home use or for the avid home sharpener. It has fair cutting power that makes quick work of dished sharpening stones.



Best Stone For Professionals and the avid sharpening need:

The double time flattening stone/pink oxide. This was another recent stone we were fortunate enough to recieve to test out., The DTFS pink oxide stone was a pink alumina version of sharpeningsupplies classic DTFS. We did several tests like leaving it fully submerged in water for 2 days and it showed no signs of deterioratio. It was near identical to the original green SiC stone except the pink stone has far more strength and durability as we mentioned earlier. The other key difference is this stone has 120 grit side and a 280 grit side. It also had a faster water absorption rate and was ready to use in less than a minute. This stone cut some what slower than the silicon carbide version but that was expected due to the original being made of a more sharper material. This pink stone was released on a limited run and may no longer be available so we included a contender or second option, the DMT Dia-Flat 95 Plus Lapping Plate, DMT is the leader in diamond sharpeners, making just about the best products available and this stone is no exception. It has decent channels to send off excess material and holds up quite well to wear. There are two plates available and those are single sided at either 120 or 160 grit You get the generous 10"Lx4"W with plenty of surface area to work on. In our opinion these stones are pretty agressive and very fast cutting so do becareful not to over do it when flattening your stones.



Honorable Mentions:

Large naniwa flattening stone, Sharpal diamond lapping plate, Scottchen flat glass lapping plate with abrasive sheets and the 400 atoma diamond plate (one of my favorite stones for lapping and repairs)


Best grading tool for stone wheels:

This spot goes to the Tormek tt-50, this very affordable diamond tipped attatchment from tormek costs $110 USD. From our experience its just about the fastest way to true up an out of square wheel. You dont need to have a Tormek for this tool to work, like with many of Tormeks attatchments we have found it also fits on the WEN, Jet, triton and Grizzly sharpening systems railing. Im guessing it would fit on similar systems too, Pretty universal!



Best budget friendly grading tool:

This one goes to the ATLIN dressing tool, this hammer or t-shaped tool does its job very well with out breaking the bank. It comes with 2 grits, 36 and 120. They cut aggresively and quickly fix your grinding wheels. They hold up and last fairly well before needing to be replaced. It takes less than 2 minutes to have a newly restored stone. These guys are perfect for both bench grinders and water cooled sharpening systems. as an added bonus the heads are replaceable!



Runner up pick:

This spot goes to Powertec's grinding wheel dresser, the heads on these have a good amount of densley packed diamond abrasives that quickly cut away material to form clean a wheel. The diamond abrasives have an even wear rate and break down modestly continously exposing fresh new abrasive. These come in a 2 pack for around $20 USD making them another great bang for your buck.



Just wait it gets better, theres a kicker, at some point you will need a flattening stone to flatten your flattening stone, yeah try say to say that ten times fast. Sharpening is an art and like with any art there is hardwork and dedication that goes into each piece. Its tedious to all of us but we love what we do, so its not a burden for us. Sharpening and lapping can be peaceful and relaxing if you make it so. Now what exactly do you use to flatten a flattening stone? thats a great question we get from our customers often, the answer is, A diamond plate. I personally use either a 120 grit diamond plate or my 400 grit atoma plate. Now you may say "I thought they needed to be more abrasive than the material they work against?" Well this true for flattening sharpening stones and wheels, however its not the same for flattening flattening stones, in this case its more of using an even harder material to break down the softer material and expose a fresh leveled surface. Diamonds remain the undisputed king of hardness and are far harder than the ceramic mateiral that silicon carbide and aluminum oxide are made from. Another reason I prefer to use diamond stones is because they are guaranteed flat down to spec. were not all stones are made equal, some stones are not completely flat and sometimes this may not be noticeable to the human eye.


When you use a lapping stone to correct your sharpening stones be sure to follow up with a nagura stone (So many stones. I know, it can get exhausting) , the courser grit stone and diamond particles can impregnate your sharpening stones. This is called grit contamination. It can easily ruin a polishing job or scratch up your knives. A scratch on a knife with an acid or laser etched finish can be fatal to the cosmetics of the knife. How it works, a nagura stone dresses the surface of your sharpening stones essentially smoothing the surface and removing some of the metal swarf that gets embeded during the sharpening process. Nagura stones also help build up mudd (a naturaly accuring slurry of the stone particles and water) used for better sharpening and polishing. These stones range from 220 grit up to 20,000 grit, they should be identical to the stone your using it on, for example 1000 grit water stone to 1000 grit nagura. Keep in mind these stones cannot be used to effectively flatten other stones.


The same goes for your water cooled wheel, you will need to follow up with a dressing stone, to smooth out the rough surface left by the diamond trueing tool. This can be one of your lapping stones so theres no need to get another stone just for your wheel.



(Pictured: A Water cooled grinding wheel on the WEN system that has been dressed with a 120 grit lapping stone. You can see here all of the grooves and track marks from the diamond tool have been smoothed out. This how you want your finished wheel to look, its smooth with plenty of fresh grains showing. It does not wobble and there are no high spots when checked with a speed level)


Though its important to have a flattening stone, lappening plate or grading stone its not as important to buy the absolute most exspensive one on the market. Like with knives and sharpening stones it depends on You and how much you sharpen. for at home use you dont need anything more than $60. Professionals will have their favorites and will either spend the least or the most. It really comes down to what fits our needs. If you would like to learn how to use or try out flattening stones and grading tools you can sign up for our sharpening lessons at:



Thank you for taking the time to read this. We hope you found this article helpful, be sure to leave a like and the comments are always open and as always stay sharp!




 
 
 

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