Grinder Talk

Let’s talk about grinders!

The centerpiece of a knife shop is the grinder. We would like to think it is the anvil but most time is spent grinding and polishing. Who knows why the industry standard has become the 2”x72” abrasive belt, it’s probably a combination of brand popularity, abrasive availability, and happenstance but here we are. When I was starting knifemaking I used tools that I already had from woodworking. My 6”x36” bench tip belt sander from Ryobi was already one of my most used tools so I instinctively went to it for knife grinding. The main problem I had was that the steel backer or “platen” was wider than the belt itself so I could not use the edge of the belt. This means that I could not create a distinct plunge line for my bevels. The shorter belt length generated more heat and wore out belts faster. 

I solved this problem by picking up a 1”x30” grinder at a yard sale. I would do most of the bevel grinding on the larger sander then finish the plunges on the smaller, which had enough relief on either side of the belt for making the bevel terminate cleanly near the handle. Neither of these tools was variable speed which reduces versatility quite a bit. There are many more options now outside of the main 2x72 market than there were 10 years ago. There are several 1”x30” and 2”x48” options that come in well below the price of a 2”x72” grinder nowadays but I’ll just be talking about the big boys because that is the tool all knife makers end up going with. The abrasives selection, tooling versatility, and drive motor options to make this format the clear choice in not only knife-making applications but also most modern fabrication shops. 

Abrasives

Once an abrasive size is standardized in the industry, all manufacturers rush to offer their products in that format. All the top abrasive companies have offered their full lines in 2”x72” belts for many years. These include international companies like 3M, Norton, Klingspor, Hermes, and VSM. In recent years many smaller manufacturers and distributors have popped up to serve the knifemaking and specialty fabrication shop world. These include Preferred, Combat, Red Label, Benchmark, and Maverick among others.  Some of these smaller companies manufacture their own and others buy abrasives in bulk and then cut and size belts and sheets for their customers. We have to spend years testing out and refining which companies and belt types are best. Everyone in the knife industry has their favorites and many of us like to use multiple different brands based on their strong points. I have settled on Klingspor as my supplier and although their belts are on par with other leading companies, the real reason is the service I get from my local company rep Craig. For me, in a world where there are many good choices, service makes all the difference. I’ll take a deep dive into abrasives specifically in the next post. 

The Machine

The main grinder companies that were originally available were Bader and Burr King which had housings around them. They were built for machine shops and heavy fabrication so the housings and shrouds were helpful to keep the dust down and meet occupational safety standards. This makes for slower belt changes and a bit less room around the platen area. Beaumont metalworks came out with their skeletonized version called the KMG grinder and that became the standard machine for most knife shops. Their design spawned a whole specialty industry of a 2x72” grinder for knifemaking. 

Grizzly tools came out with a grinder which is based on a buffer housing. This machine comes in at half the cost but has no changeable tool arms and is not variable speed. This brings me to the variable speed issue. It is critical. Once you can run abrasives at the appropriate speed, there’s no going back. I’m all for getting started with the tools that you have. I’ve written previously about the error of over-investing before putting any effort into actual knife-making. But once you become serious about making, you have to be willing to reinvest your earnings into good equipment. Having the ability to have an infinite adjustment from 0-100% over speed will give you the maximum amount of control over not only your grinder but over the knife project itself. 

The most popular VFD (variable frequency drive) is made by KB Electronics and has a Nema-4 enclosure. This means that it can be sprayed down with water and not short circuit and more importantly, no dust can get in. The cheaper VFDs have open housings and the fine metal dust that we produce tends to get into the circuit board and fry the components. A fully sealed enclosure is critical to make the drive components last in a harsh environment. Similarly, grinder motors have to be TEFC - Enclosed Fan Cooled. This keeps the detrimental dust out of the important bits. To run a VFD, you must have a 3-phase motor. Most buildings don’t have 3-phase power but a VFD can convert 120 or 240 power to 3-phase. For reasons above my pay grade, single-phase motors cannot be operated with a VFD. If you have a single-phase motor, you can use it as a one-speed drive with an on/off switch. There are generally two speeds of standard motors. 3600 rpm is the most common motor and the best to use with speed control. If you are outfitting a grinder with a single-speed motor, the 1750 rpm slower-speed motor is the best choice. Most grinder frames on the market are interchangeable when it comes to the drive motor so starting with a slower single speed and upgrading to variable speed in the future is a great option. 

Tooling 

A very important component of the 2x72 grinder is the versatility of the tooling attachments. The standard platen consists of a 2x8” steel backer plate with a 2” wheel at the top and bottom of the platen. This is where most of the work is done. The next most used feature is the contact wheel. A small wheel attachment will hold anything from 1 ½” down to ¼” contact wheels. Larger contact wheels start at 4” and go in 2” increments up to 14” in diameter. The capabilities of these different radii are critical in a production shop. Most contact wheels are turned aluminum bodies with bearing at the mounting point and high-density rubber on the contact surface. 

Rotary attachments have recently become common in knife shops. This incorporates a tool arm that has 4 wheels which are connected by a rubber belt. This rotates the belt behind the abrasive material, giving the grinding surface a soft forgiving backer. This allows for the use of fine grit belts that were previously not viable with a hard platen backer. The surface grinding attachment has quickly become a popular addition to the knife shop. With a contact wheel incorporated with a magnetic sled, this tool can deliver precision flattened results without the need for an expensive stand-alone machine. Broadbeck Ironworks has taken the 2x72 platform a step further with attachments that include a disc sander, buffing wheels, and a highly adjustable work rest. They also include a tilt feature that allows the machine to turn 90° and become a horizontal grinder rather than a vertical one. Other companies like Ameribrade and KMG have this option as well. I find that I rarely turn my grinder horizontally even though it is quite easy to do. 99% of my grinder work is done vertically so I would not let the tilt function sway my decision on buying a grinder. 

The 1 ½” tool arm has become the industry standard. I have multiple brands of grinder in my shop and I can share tooling among all of them because they all take the same size tool arm. All grinder companies use this format except for Ameribrade which uses a 2” tool arm and AMK which uses its own extruded aluminum track system. Both systems work fine but they lock you into that company’s parts and tooling. This can be a big drawback when compared to the freedom to incorporate multiple company attachment options. 

The rotary platen has been a big game changer, the addition of a rubber backing belt allows for the use of higher grit belts without the associated problems. Flat platens are great for all rough-in work and the main grinding tasks but once a high degree of surface conditioning is required, smooth and thin abrasive belts tend to transfer any subtle texture from the platen through the belt into the workpiece. The rubber belt backer works as a buffer between the hard steel platen and the hard steel surface of the blade. It gives a much more uniform finish. The Moen platen is the top-of-the-line version of this which comes complete with a carbide platen, contact wheel option, and a built-in cooling fan. This is a great tool but costs about $3500. Ameribrade has a more basic version for about $400 which is what I run. Although I’m sure I would prefer the Moen version, I’m very happy to have the Ameribrade rotary attachment for a fraction of the price. It works with their 2” tool arm but can be easily outfitted with a 1 ½” arm. 

Basic or Fancy?

There are two main groups of grinder styles, the basic workhorse and the hyper-versatile. Brands like KMG, Pheer, Wilmont, and OBM offer sturdy grinders that do not tilt and have simple and reliable builds. The fancy end of the market is made up of grinders that have more of an all-in-one aspect. Broadbeck Ironworks is the best example of a machine that can take the place of multiple tools in a small shop. As stated before there are buffing, surface grinding, and disc sanding attachments that eliminate the need for extra stand-alone machines. The TW-90 by Travis Weurtz is known for its high quality but also operates with its tool arm size and dedicated attachments. KMG offers its standard grinder as well as the TX model which has the tilting feature along with a few other upgraded features. 

 When it comes to grinder choice price, quality, and versatility are the main determinants but there are a few other things to think about. The tension arm is something to think about. Some grinders use a coil spring which is very reliable but requires more effort and strength to compress when changing belts. A popular alternative is the piston tensioner. This is a much easier system to compress during belt changes but the pistons wear out and sometimes they don’t give quite enough tension for good tracking. The third option is the ratcheting system of tension like the TW-90 has. This version requires the operator to push up on the arm until the desired tension is achieved and required a separate lever to release the ratchet teeth - somewhat like a ratchet strap. In my experience, the ratcheting and piston systems have potential problems but the coil spring never fails. I have seen the ratchet system come apart when too much force is applied and we are constantly replacing pistons around the shop. 

In my shop, I prefer simple workhorse grinders like the KMG and Pheer grinders. There is just less that can go wrong with them, the heavier build and bolt-down construction cut down on vibration. All of the grinders with a tilt function on them inherently have a bit more movement to the body of the frame. This leads to somewhat more instability and vibration compared to the simple models. While not a deal breaker, I do prefer the more stable of the two. It is my opinion that the grinder market has been more focused on the higher end leaving a gap at the entry-level. OBM and Pheer have a good basic variable speed grinder for around $1600 but companies like OBM sell just the main chassis for about $600. This allows you to add your motor which is a potential cost-saving. 

Some are capable of building their grinder. For those, several companies offer plans and kits for the purpose. Polar Bear Forge has had to build-it-yourself kits for years now and House Made has either kits or digital plans that you can buy. Anyone making a frame from scratch will find it most economical and time-wise to buy an aluminum wheel set from one of the grinder manufacturers. OBM and KMG are the most accessible options out there. I have a homemade grinder and it has always been the last grinder that anyone wants to use. The manufactured machines have had more testing and design refinement than we can do on our designs. If you happen to be a professional tool and machine designed then please forgive my presumption. 

In conclusion, I think about the grinder question quite a bit because in teaching knife making classes, I get asked about them often. Most people balk at the $1500 entry price and I don’t blame them but keep in mind that these machines hold their value well. Much like anvils, they can truly be considered an investment. I hope this article helps explain some of the finer points and ultimately leads you to the right choice of machine for you. I have used KMG, Pheer, OBM, Broadbeck, Ameribrade, TW-90, and Wilmont grinders as well as multiple homemade rigs. I am not sponsored by any of these companies but I do have respect for them all. Each one brings something unique to the table and has helped to build the knife making industry in its way.