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Cleaning old tools these days is okay. Want to extend the life of your old tools and make them look new again? CNC (Computerized Numerical Control) sharpening can make that happen. You buy a bench grinder that can easily handle almost any sharpening task. What are the advantages of CNC tool sharpening? How to do it? We write about it below!

The most important rule when using a bench grinder

The key step to take first is to prioritize safety. The most important thing is to protect your eyes, hence you should wear approved safety glasses, and right after that, decent tight gloves to protect your hands. In addition, use both hands when sharpening tools to make sure you don’t apply too much or too little pressure. To learn more regarding tool sharpening, read our post to the end!

Using a bench grinder to sharpen tools

If your tools are very dull or severely damaged, skip the files and other hand tool sharpening options and go straight to a bench grinder. It can easily handle any tool sharpening task and save you valuable time.

Here are some tips to help you sharpen old tools on a bench grinder:

  • Match the wheel to the metal you want to sharpen – the right tool for the job is always applicable. You can use an aluminum oxide wheel of 60 grit and medium hardness for older tools.
  • Put the tools in a not-too-hot oven – the optimal temperature is about 350 degrees – and let it sit for 2 hours. This treatment will help prevent cracking during sharpening.
  • Mushroom tip – will help you feel the sharpening. Use the edge of the wheel to make a short work of resembling a mushroom, then start from there.
  • Patience – try to remove only some of the metal at a time. Take your time and make several passes. Watch out for any flakes of hot metal that will fall off during grinding.
  • Try to get a good edge when sharpening and don’t use too much pressure. 
  • Remember to dip it in cold water, oil or another cool lubricant. Overheating the tool will only work against you.
  • Use a wire brush at the beginning and end to remove rust from old tools, and to prevent bumps.

Bench grinder for sharpening lathe tools

A tip that can help you when grinding lathe tools is that using a grinder is very similar to using a lathe. The techniques are also very similar, almost the same. However, you will find that sharpening lathe tools requires a lot of accessories and can be done meticulously.

Required tools:

  • A 6- or 8-inch slow-speed bench grinder
  • V tool tray
  • An 80 grit grinding wheel
  • Diamond wheel dresser.
  • Angle gauge
  • Permanent marker

It should be noted that different turning tools require slightly different techniques. This is due to the purpose of each tool. The following instructions apply to diamond-cutting tools.

  • Use a protractor to set the tool’s support angle so that the bevel coincides with the circle.
  • Place the parting tool on top of the rest and align it with the circle.
  • Mark the straight lines with a permanent marker. This helps keep the device straight while grinding.
  • Press the tool directly into the circle.
  • Continue until you get the correct edge angle.

For the lathe scraper:

  • Match the lathe knife holder to the angle of the blade.
  • Use a permanent marker to color the edge of the spatula.
  • Touch the wheel with the scraper. Adjust the tool holder until the wheel is in the middle of the bevel.
  • Holding the scraper flat, gently push it into the circle. Follow the shape of the edge.
  • It’s all over when the sparks start flying and falling on the scraper blade, and you feel the edge.

For the bevel chisel:

  • It would help if you had flat bevels on both sides of the tool.
  • Let the bottom part of the tool touch the circle first, then the top part.
  • Do this on both sides of the chisel.
  • You want to end up with a slope of 35 to 40 degrees on both sides.
  • Pressure is not critical, so gently move the chisel toward the wheel.


This takes practice if you want to slide the gouges into the wheel simultaneously as you move it up the wheel. Don’t use a tool holder to stabilize the lathe tool for the best results. It would be best to have a bevel of 25 to 30 degrees with concave edges.

Rough spindle gouging:

  • You’re looking for a counterbore between 40 and 55 degrees.
  • To do this, position the rest so that the tool’s angle matches the grinding wheel.
  • When the chisel touches the wheel, hold the tool with one hand and slowly turn it with the other.
  • When you get to the other side, reverse the direction and do it again.
  • All the time, keep the tip perpendicular to the circle.

Sharpening lathe tools takes some practice. You will need patience and a steady hand to sharpen the tool again. The key is ensuring the angle is correct and constantly adjusting the knife holder.

Sharpen CNC tools safely

Always keep yourself and those around you safe when sharpening tools on CNC machines. Proper use will help you avoid injury to yourself, those around you, and your equipment. Here are some of the safety tips:

  • Remember to have enough space – you will need it to properly sharpen a tool that is too long, for example. After all, it would be best if you move freely. 
  • Remove debris and flammable particles – to keep yourself, your workplace, and your friends safe, clean the grinding area. Sparks can start a fire and damage the area around you.
  • Earplugs are in order – Bench grinders can be noisy, so it’s best to wear earplugs or muffling headphones to mute the noise. We’ve talked about protecting your hands, eyes, and face. It’s also essential to protect your hearing.

What is a CNC grinder?

It is a machine that uses computer numerical control (CNC) to create precision parts and tools. Various rotating matched grinding wheels to remove material from a part or tool is often used to sharpen and refine the edges of drills, end mills, and other custom cutting tools.

How does a CNC grinding machine work?

The grinding wheel is mounted on a rotating shaft, moving up and down to achieve the desired cutting angle. The wheels, assisted by a motor, allow the material to be cut at very high speeds. When the grinding wheel cuts into the material, it generates a lot of heat. To prevent this, abrasive oil is sprayed to maintain a constant low temperature, protecting the integrity of the cutting tools. In doing so, it is constantly filtered and cooled during each cycle to ensure trouble-free and proper operation.

 What are the benefits of using a CNC grinder to sharpen tools?

CNC grinders offer four main advantages over traditional tool sharpening and finishing methods:

  • They provide more precise and repeatable results than manual sharpeners.
  • They allow you to quickly and easily adjust the sharpening angle to achieve the desired result.
  • A CNC grinder produces less waste than other methods, saving you money, especially when working with carbide or other expensive metals.
  • Tool or part damage caused by heat is less likely due to the grinding wheel and grinding oil.
  • The operation relies on making the most of the whole geometry of the tools.

How to get the most out of your CNC grinder

Here are some basic tips to help you get the most out of your CNC grinder’s strengths:

  • Try using a dedicated CNC grinder to sharpen your tools. This will help you achieve better results and avoid potential damage to your machine.
  • Always use the same wheel for sharpening tools. Switching between wheels can lead to inconsistent results and damage mechanisms.
  • Use coolant when grinding metal. This will help keep tools at the right temperature and prevent heat damage.
  • Always inspect or test a sharp tool on scrap metal before using it on a workpiece. This will help ensure the tool works as expected and does not require further adjustments.

Do I need to buy my CNC grinder to sharpen my tools?

Buying your CNC grinder is a worthwhile investment, but it is crucial to answer the most important questions before deciding.

Here are some of them:

  • Does your workshop have enough space for the grinder and a cooling system?
  • Do you have the resources to cover the price and operating costs? Buying and operating a CNC grinder can be very expensive.
  • Do you have the qualifications and skills to use the machine comfortably, safely, and efficiently?
  • Is there someone at your facility who can help with operation and maintenance?

If you answered no to any of these questions, tool sharpening is best left to a professional company.