Grinding is fun the first time you do it, but it quickly becomes a chore as many projects will require grinding. The difference between a cheap grinder with a cheap belt and a high quality grinder with a high quality belt is astonishing. A high quality setup will remove anywhere from 8-16 times the amount of material that a cheap setup will in a given amount of time.
Buying a high quality grinder with a high quality belt will save you A LOT of time and frustration, especially if you are a power user that will use your belt grinder on a regular basis.
Factors To Consider When Buying A Belt Grinder
Grinders come in all shapes and sizes, what factors are worth focusing on?
Grinder Size
The first thing you will want to consider is the size of your grinder. 2″x72″ grinders are the industry standard for knife making, and the majority of belt grinders made are this size. These grinders will have more accessories, attachments, and wheel attachments than other sizes.
Compared to shorter belts, the long 72″ belt will reduce wear and tear and will disperse heat build up across a longer surface. This will keep your stock cooler and will make your belts last longer. This is important if you are trying to preserve any heat treatment that has been applied to a material.
At 2″ across it has more working area for larger pieces of work.
It is for these reasons that the 2″x 72″ grinders are industry standard.
However nothing is free, these grinders – and the belts that they use – tend to be more expensive. As I mentioned earlier, if you are planning on making more than a couple knives, you will get your money’s worth paying up for a better grinder. Small grinders with weak motors are a pain in the butt to use.
If you are on a budget, I wouldn’t buy anything smaller than a 2″x48″ belt grinder. These tend to be a few hundred dollars cheaper, and are a good starting point if you are not sure if you want to make the investment in a good grinder. Although many people have started on smaller grinders than a 2″x48″ belt grinder, I wouldn’t recommend it, as you will just replace your weak small one after 3 knives anyways as they are not very good for the task.
Another belt to watch out for and avoid is the 4″x36″ belt grinders. These are generally made for woodworking and are not well suited to knife making. They tend to have weak motors that will slow down when grinding steel.
How Much Horsepower Does My Belt Grinder Need For Knife Making?
As you would expect, more horse power is better. Stronger motors allow you to run at higher speeds and allows you to run coarser paper. A common rule of thumb is to have 1hp for every 1″ of belt. This means for knife making on a 2″x72″ grinder you will want a motor that has around 2hp. That being said, I wouldn’t take this rule of thumb too seriously, as I know a lot of talented knife makers that use a 1hp or 1.5hp motor on their 2″x72″grinder, and they make phenomenal knives.
How Much Belt Speed Does My Belt Grinder Need For Knife Making?
Steel oriented grinders will want a higher belt speed than wood oriented grinders. You will want a belt speed somewhere in the range of 4,100 surface feet per minute and 7,000 surface feet per minute. You can calculate the sfpm with the following formula: sfpm = (pi * drive-wheel-diameter) * motor-rpm / 12
Variable Speed
Not all belt grinders allow you to change the speed of your grinder while working. You can make due without a variable speed grinder if it’s powerful enough, but having a grinder that can go faster for stock removal and can slow down for detail work is useful.
A Sturdy Frame To Minimize Chatter
When you push a piece of steel against the cutting surface of your belt, the steel will have a tendency to vibrate or wiggle around while it’s in contact with the cutting surface. Chatter makes delicate or accurate work (like bevels on a knife) more difficult to accomplish. Heavy duty frames can help cut down on chatter. Heavy frames will also last longer. Now when you hear heavy in the machine world, you should think expensive. Belt Sanders are no different. I won’t focus on the frame as much when I recommend a belt grinder later on in the article for this reason(sturdy frames are expensive), but it’s still worth keeping this in the back of your mind.
3 Basic Types Of Belt Grinding Contact Surfaces For Knife Making
There are basically 3 common types of contact surfaces for knife grinding, they are:
- Platen
- Contact Wheel
- Slack Belt
A platen is a flat piece of steel that is placed behind the belt and acts as a force of resistance as you push in while grinding. Platens are one of the most common contact surfaces in use in knife making as they are used for flat bevels.
A contact wheel allows you to cut circular cuts such as a hollow ground (concave) cut. Hollow ground edges are incredibly sharp, but they lose durability as a price for their sharpness. The radius of the contact wheel will directly affect the radius of your concave cuts.
Slackbelts are when you place your stock into contact with the belt without any structure supporting the belt.These allow you to make soft convex cuts – which are the inverse to the type of cuts the contact wheel makes.
What Is The Best Belt Grinder For Knife Making?
So by now you are probably going to expect me to recommend a variable speed 2″x72″ grinder with a 2hp motor and the appropriate spm, right? Well, not quite. The problem is that no such grinder exists that sells for under $1,000 dollars that is reliably made. I have seen a few models that try to fill that role, but the reviews I have seen make them seem too unreliable for me to feel comfortable recommending them.
I also don’t feel comfortable making a $1k+ grinder my primary recommendation, as I know that is out of the budget range for most people. And OF COURSE a thousand dollar machine will run better than a cheaper model – at least it better!
So I’m going to compromise.
My pick for the “best” belt grinder is the Grizzly G1015 Belt Sander. This grinder is well known in the knife making community and is referenced all across various knife making and metalworking forums.This model has been in production for a long time and there are no surprises with it at this point.
It’s one of the best belt grinders in that price range between $400-$900.
The machine itself (not the belt) is 30.5″ x 16.25″ x 15″. It has a maximum rotational speed of 1725 RPM and has a belt speed of 3600 FPM. It has an auxiliary arbor that accepts buffing wheels, sanding drums, or flap wheels. The belt has a quick-release mechanism making for quick belt changes. It has a belt arm that can be full tilted. It has a cast-iron body which makes it hard and heavy, but brittle; So don’t go smacking it. It is made with a ball bearing construction. It weighs a manageable 60 pounds.
Now that I”m done with the sales pitch, I want to stress that it’s not perfect. This model doesn’t have variable speed and has well documented tracking issues that can be fixed – there are a million different hacks for doing this, just google it. It also has less horsepower than is ideal. It’s also notoriously fast. It has a small work rest which many people modify to make it bigger. Finally, this belt sander has a two wheel design. Two wheel grinders generally have less configuration options than grinders with 3 or more wheels. It’s also – as far as I know – not possible to change out the contact wheel to a wheel of a different radius, which can be helpful for certain types of cuts where you may want to change the radius of your cuts to make them steeper or flatter.
It may seem like that is a big list of cons, but I”m really leaving no stone unturned here in an effort to be thorough. The biggest obstacle for you is not some mythical design where everything is perfect, the biggest obstacle is price. The more you pay, the fewer obstacles you (should) have. For its price range,the Grizzly G1015 is one of the best grinders/sanders out there.
There are cheaper options, but I really think they are a waste of time and money as you will replace them much faster than you now think you will. There are more expensive options, but I don’t personally own them and will save my review for the 1k+ grinders for when I own one myself.
Once you have a good solid grinder, you will want to put good belts on them. I will go over the different types of belts below:
4 types of abrasive belts:
- aluminum oxide
- zirconium
- silicon carbide
- ceramic belts
These are the MOST COMMON types of belts, but it’s not an exhaustive list.
Aluminum oxide belts are cheap but dull quickly. Aluminum oxide – also called AO – belts are good for higher grit finishing when knife making. They do not make good low grit belts, especially when you need to do a lot of stock removal.
Zircuonium can handle steel better than aluminum oxide belts, but they wear out faster than ceramic belts.
silicon carbide is a specialty abrasive and is often used for finish work on materials such as wood,resins,epoxy, and other heat sensitive applications. It is also used for materials such as marble, garnet, glass, and other hard materials.
Ceramic is fantastic for hardened steel as these belts like high speed and pressure. I use almost exclusively ceramic for my lower grit belts.
There are also belts that have their abrasive materials glued onto the belt in little piles that can continue to cut effectively as the abrasive material is grinded off. These belts are said to have structured abrasives. Structured abrasives are often made of AO or aluminum oxide, but this is not always the case. Belts made out of structured AO will last longer than unstructured AO.
I don’t have much personal experience with structured abrasives – I’ll get around to testing them eventually, I swear! My understanding is that they are not great for big rough cuts, but they can be very effective for high grit finishing operations.
Belt Backing Material
Most belts will have a cloth backing, but you can find other materials as well. Some of these alternatives include cork and soft plastic mesh. I have only ever used belts that have abrasives glued to cloth belts, so I can’t comment on the effectiveness of these other types.
Belt Backing Types
In addition to the type of backing material your belt has, there is also a letter designation on the backside of your belt. Heavier belts with less flexibility are towards the end of the alphabet such as the letter Y. Softer more flexible belts have a letter designation closer to the beginning of the alphabet such J. J is a very common backing, although I will recommend a Y backing later on in this article. Some belts are given additional treatment, which will often be labeled in addition to the letter. For example : x-flex or j-flex.
What Grit Belt Should I use for Knife Making?
I would use a ceramic 36 grit or 40 grit for your first initial cuts. These belts remove material very quickly and the ceramic variety last longer than zirconium or aluminum oxide. I think it’s worthwhile to use ceramic belts up to 120 grit or so. Above 120 grit you can make a good argument for switching materials, as ceramics do not work as well at higher grits – ceramics also tend to come on stiffer belt cloths, which is not always ideal for finishing work. Above 120 it makes sense to switch to zirconium belts, as they still last longer than aluminum oxide belts and they work well with higher grits. Zirconium can also be placed on more flexible belts than ceramics can. That being said, some knife makers just like the feel of AO belts better than zirconium, and will use AO for their high grit finishing work. You should try both and develop your own opinion if your budget allows.
Lower grit belts tend to see more vigorous use, but higher grit belts tend to gunk up faster than lower grit belts.
It might seem like I have presented a lot of different options for belts – and I have – but we are only scratching the surface. A quick look at wikipedia: https://en.wikipedia.org/wiki/Abrasive will show that abrasives can become a never ending rabbit hole of options. I will present in clear terms what I recommend to new knife makers later on in this article.
How Long Can I Expect A Belt For my Belt Grinder To Last?
A cheap aluminum oxide 60 grit belt will make maybe 2-3 knives for you before it begins to crap out. A high quality 40 grit ceramic belt may make anywhere from 10-15+ knives before it becomes ineffective. But these are just rough numbers to give you an estimate…
In reality, it can vary wildly. If you are doing heavy stock removal to make your knives you will go through more belts per knife. If you forge your general knife outline first, and are just using your grinder to make the bevels and to remove scratches, they may last longer. If you are an experienced belt sander user, you will spend less time at the grinder and it will last longer. Longer belts will last longer than shorter belts, the flexibility of the backing material will affect it’s longevity as well.
In short, it’s hard to estimate, and the only real way to answer this question is to get into your shop and make a bunch of knives.
You will have to get used to the idea that belts wear out. Ineffective belts cause a number of problems. A worn out belt causes longer grinding times, and it causes your stock to run hotter while grinding. This heat can have an unwanted effect on the strength/hardness of the material you are working on and will destroy any heat treatments you may have applied. In short, don’t drag your feet when it comes to throwing out old belts.
You need to view belts the same way you view your steel stock, they are a fundamental material cost for knife making, and you will go through a lot of them.
When you grind, three things are happening that degrade your belt:
- The abrasives on your belt become rounded off and less sharp
- Abrasive fall off altogether
- Steel and wood debris builds up in between the grains, this is called loading. Wood and plastic do more loading than steel.
Starting grits for knife making
You can save money by buying in bulk, 10 packs are common. You can buy singles, but you will pay more per belt, and you will be running to the store to buy more just as you are getting past your beginner-wtf-am-I-doing stage of learning to make knives.
Low budget starter pack:
10 60 ceramic belts,
5 120 AO belts,
5 220 AO belts,
5 320-400 AO Belts
If you have more money, the following list will work even better
10 40 ceramic belts
10 60 ceramic belts
5 120 AO belts
5 220 AO belts
10 320-400 AO belts
I would buy belts with different flexibilities for your higher grit belts. It may also be worthwhile grabbing a 120 grit zirconium belt to give you an opportunity to work with different materials.
Good finishing requires that you develop your “touch”, and different belt backing will provide a different “touch”. I know that’s vague, but I hope it makes sense.
There is nothing magic about the quantities above, it’s just an attempt to give you a shopping list with specific quantities. Many of the belts I recommend below are only sold in packs of 3 or 6, so don’t take the above suggestion as gospel.
Best Belts For Grinding Knives
I’m currently really liking norton brand ceramic abrasives, and I will recommend a number of them below. For higher grits I try and recommend products that have a good value/price ratio, however subjective that may be.
Best ceramic 36 grit belt for knives
These 36 grit ceramic belts will chew threw steel faster than you can believe.
Best ceramic 80 grit belt for knives
These are high quality 80 grit ceramic belts, they will still chew through steel but will give you a more refined grind than the 36 grit belts.
Best Ceramic 120 grit belt for knives
I still use ceramics at 120 grit, but a number of knife makers I know begin to switch to zirconium or AO belts at this grit. The choice is ultimately up to you.
Best Aluminum oxide 220 grit belt for knives
As I alluded to earlier, grits above 220 I switch to AO.
Best Aluminum oxide 320 grit belt for knives
Same brand as before, they make good high grit AO belts.
Best Aluminum oxide 400 grit belt for knives
There 400 grit is just as good as their 320 and 220 grit belts.
Best high grit finishing belts for knives
These are also made by the Red Label Abrasive Store. They are great for putting that final shine on your knives.
How To Use A Belt Grinder For Knife Making
Outline the contour of the knife on your piece of stock with a marker or sharpie.
Start with lower grit belts for stock removal. Switch to higher grit belts for surface refinement. A Common mistake beginners make is moving to a higher grit belt too quickly. Really try to eliminate all scratches and scuffs on the surface of your knife before moving up to a higher grit belt. This will save you time and money, and will make better looking knives as a result.
Biomechanically, you should use 2 hands and keep your arms close to your body. This helps you have a flat grind. You don’t want the stock to start “wobbling” in front and behind of the belt surface. This creates bad curvatures in the knife blade. Don’t let your fingers get close to the belt, this will rip you to the bone. Be wary of heat on your knife and on your fingers, even with a fresh belt. Cool your stock in cold water if it gets too hot.
Safety When Using A Belt Grinder
For the love of god please wear your safety glasses. While grinding, little bits of steel will be flying all over the place. If these tiny pieces of steel land in your eye, they begin rusting immediately and will cause serious health issues with your eyesight should you not get prompt treatment. A face shield is not a bad idea. You will want a pair of steel toed boots w/ a metatarsal guard. Grinders can throw a blade at your feet with surprising speed – ouch!
Please wear a respirator while you grind. I’m not enough of an expert to recommend the optimal setup, but I wear a 3m p100 filter while grinding. Both the steel shavings from your knife stock and the tiny abrasives are absolutely terrible for your lungs. Silicosis has been killing people for thousands of years, please take it seriously and wear a respirator while grinding.
What Is The Difference Between A Belt Grinder and A Belt Sander?
There is no centralized source of truth for these terms. Manufacturers of these machines will often refer to them as sanders. People in the abrasives industry will often refer to grinders as machines that use wheels, rather than belts. Knife makers will refer to these tools as belt grinders – I have heard some knife makers say that belt sanders refer to tools designed for woodworking. Who’s right? What terminology should you use? Hell if I know, I just know knife makers generally call these machines belt grinders.
Belt Grinder Accessories
In addition to the belt grinder and the belt itself, there are a number of tools designed to prolong the life of your belts and to improve your grinds. These tools are not necessary to make high quality knives, but it’s worth knowing about them
grinding belt eraser
These erasers are cheap and help you clean up the debris that builds up on your belt through use.
grease stick for belt grinders
I have never used these, but they are supposed to reduce heat build up while working. Most knife supply store sell them and they may be looking into if you are having issues with heat.
misters for belt grinders
There are a number of tools that will spray a gentle mist over your belt work surface in an effort to keep your stock cool. I don’t think these are necessary for beginners, but again, it’s worth mentioning that they exist should you run into heat problems further down the line.
Grinding Jig For Knife Making
If you find yourself making bevel cuts of a certain degree over and over again, it may be worthwhile to either make or buy a jig to help you make those cuts consistently across many production runs. I won’t go into detail on this, as it’s a topic onto itself, but it’s worth noting that these exist as they can make grinding tricky bevels much easier.