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Whether you are looking for your very first belt grinder or want to upgrade your existing one, what contact wheel size do you need for a knife grinder is an important question. You most likely shouldn’t obsess over it, but you should at least understand how it will affect your knife grinding process.
If you are a hobbyist, then you could pick one wheel size and stick to it for the rest of your life. But if you are making knives professionally, then you would want to be more flexible.
No matter what you need, below, you’ll find some helpful information on why contact wheel size is important in belt grinders and how to choose it!
Why Is Contact Wheel Size Important For Knife Grinding?
Usually, contact wheels on belt grinders are used when you want to do hollow grinding. With hollow grinding, contact wheel size is important because it determines the shape of the grind. The radius of the wheel will be translated into the material you are grinding.
If we were to talk more precisely, a smaller contact wheel would make for a more pronounced, deeper hollow grind. The grind would be shorter as well because of the small size of the wheel.
In contrast, if you were to go for a larger wheel, the hollow grind would be less noticeable and more gradual. If you were to go bigger and bigger, the grind would eventually simply flat out, making it seem that the knife has no hollow grind at all.
Now, we only took into account the size of the contact wheel. But what about the knife itself?
Well, when picking a contact wheel, you need to consider its size against the size of your knife.
If you have a teeny-tiny knife, then you would certainly want a smaller contact wheel. If you try to grind a small knife on a large wheel, then you may not be able to achieve any kind of hollow grind whatsoever. A large wheel would also just eat away all the material if you tried to apply force to the knife.
Small wheels don’t work well with wider and longer blades as well. Small wheels produce a deeper hollow grind that may not look good on larger blades. Although you can achieve a hollow grind this way, the aesthetic results of a small wheel & large blade combo probably won’t be too good.
With that in mind, you should pick a smaller wheel for small, narrow blades and a large wheel for big, wide blades.
Personal Preference Is Important Too
So we’ve just covered the rationale behind combining different contact wheel sizes with knives. However, although you would generally want to somehow match knife and wheel sizes, your preference is important as well.
Hollow grinds can be different – they can be more subtle and gradual on some knives and more aggressive and dramatic on others. Furthermore, some knives may be hollow-grinded from both sides.
For a given knife size, the smaller the contact wheel, the shorter and more dramatic the hollow grind gets. Conversely, if you make the wheel larger, the hollow grind will cover more of the blade’s length and will look more subtle as well.
With that in mind, there are some aesthetics involved in wheel size too. You’ll need to figure out on your own what works the best for your blade style and goals.
Contact Wheel Size & Belt Speed Are Connected As Well
Finally, you should also keep in mind that contact wheels’ size and belt speed are connected as well. However, this will only hold true if the contact wheel is also the drive wheel.
Belt speed is measured in surface feet per minute (SFPM) and is calculated as follows:
SFPM = (π x drive wheel diameter) x motor rpm
Generally, for knives, you want the SFPM to be somewhere between 4,100 and 7,000. How fast the belt should move depends on the density of the material. Denser materials like steel or cast iron need very fast-moving belts.
You’ll need to do more research to figure out the right SFPM for you. But do remember that higher belt speed leads to heat generation, which can damage the blade.
Another thing to keep in mind with drive contact wheels is that they typically cannot be replaced. So if your belt grinder has a 4-inch drive contact wheel, you’ll be stuck with it until you get another belt grinder.
What Contact Wheel Size do you need for a knife grinder As A Beginner?
Most people seem to opt for 8- to 10-inch contact wheels. These appear to work the best for most people’s needs. If you have zero idea as to what contact wheel size to choose, then stick to the 8- to 10- inch range.
8 to 10 inches won’t necessarily be perfect for you, but you will at least get a baseline to compare other wheel sizes against. If you feel that your wheel is too small for your needs, then you could switch to a bigger wheel any time in the future. Well, as long as your belt grinder’s contact wheel isn’t also the driving wheel.
So in the end, here are the key takeaways from above:
- Smaller contact wheels produce deeper and shorter hollow grinds. In contrast, larger wheels make more gradual grinds.
- Smaller wheels would work better with small and narrow knives.
- The choice of contact wheel size somewhat depends on your preference.
- Larger drive contact wheels increase belt speed.
If you are looking for a knife grinder for beginners, then you should probably get yourself a tool with an 8- to 10-inch contact wheel. The contact wheel should ideally be replaceable so that you can adjust the grinder to your needs as time goes on.
Once you’ve got a baseline for comparison, you could try switching to a larger or smaller contact wheel. Play around with your options to see what works best for you.
And lastly, remember that a contact wheel isn’t the only important thing in a belt grinder. Consider SFPM, adjustability, dimensions, and price as well to choose the right tool.