After many months of lurking around this site and soaking up as much information as possible, I finally feel like I have something to offer back. I recently built a 2X72 belt grinder (thank you to everyone who ever posted a picture of their grinder on bladeforums, if its on the web, I probably looked at it when designing this one) and there are a few clever aspects of it that I havent seen anywhere else. These are:
1. A cheap way to make a simple drive wheel
2. A new tracking mechanism thats relatively simple and rock solid
3. A new take on the style of a 2X72 grinder designed with versatility in mind
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First, the story behind it. When I started making knives, I built myself a small grinder since I couldnt find anything decent for cheap. I designed it to have a solid built-in table and take anything from 1X30 to 2X48 belts with a ½ hp motor. I mainly use 1X42 belts and it has worked very well for everything except large kitchen knives. A friend who initially got me into knifemaking, finally sick of using his little 1X30 (you could probably stall the belt by grabbing it with your bare hands), asked me to build him one too. Initially he wanted one just like mine, but I argued that a 2X72 wouldnt cost all that much more and would be far more useful. I set out designing a 2X72 somewhat similar to the KMGs, but he still wasnt convinced he wanted a 2X72 since belts arent locally available. Then in a stroke of pure genius, I realised that the design of my little grinder with the built-in table and interchangeable belt sizes looked remarkably similar to the back end of my 2X72 design. With a $3 4-way switch, a reversible motor, and some clever wiring, I knew that I could build a grinder that does it all. Intrigued? Then skip to Point 3.
1. Drive wheel
In my searches I found a lot of interesting ideas for inexpensive idler wheels. Some of these were longboard wheels, bearings pressed into aluminum pipe (I opted for this one), or simply purchasing the real thing. However there were very few ideas out there for an inexpensive drive wheel. What I came up with was rather simple and easy. Take a 3.5 pulley, and press it into a 3 pvc pipe coupler. 3 pvc pipe has an outer diameter of 3.5. It follows that the coupler has an inner diameter of 3.5 and outer diameter of 4. Perfect for a drive wheel. The couplers even have a little ridge running the inner circumference that lets you know when your pulley is centered and ensures it is set straight. I found that while my idlers where a somewhat hokey solution that may not last forever, the drive wheel is solid, perfectly round, and while a little longer than necessary (about 3.5 instead of 2), works excellently.
2. Tracking mechanism
Im proud of this one. Most of the tracking mechanisms you see out there are essentially some type of hinge with a set bolt that controls how much your belt can pull down on the tracking wheel to control what angle the wheel is held at. I considered quite a few different methods including modifying an old door hinge or making a hinge like the KMGs. What I ended up doing was using a piece of round pipe for my tension arm, which serves as the inner part of the hinge. A 3 length of pipe with an inner diameter slightly larger than the outer diameter of the tension arm rotates over the tension arm pipe and holds the idler wheel mounting bolt. A bolt connected to the outer pipe pushes on a stationary bolt connected to the inner pipe in order to set the angle of the tracking wheel. The inner pipe has a hole drilled in it slightly larger than the diameter of the idler wheel mounting bolt so that the bolt can rotate with the outer pipe. Belt tension keeps constant downward pressure on the entire mechanism. Sorry for my unclear explanation, it really is pretty simple when you see it and rock solid. These pictures should explain it much clearer than I ever could.
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I like this design because it combines the tension arm and tracking mechanism into one part and holds the wheel at the same level as the tension arm (as opposed to above it like most do). It also has lots of adjustment capacity built in. I actually welded the pipe for the tension arm on this grinder inside a piece of square tubing since the pipe I had wasnt quite long enough, and I needed the tension arm to fit inside another piece of square tubing for one of the setups youll see in point 3.
3. Overall belt grinder design
Ill never really understand why most of the home built grinders Ive seen are usually built in just one plane. By this I mean that their basically two dimensional with a motor that is mounted next to the grinder. Why not build a three dimensional frame that houses the motor within? I understand that the commercial grinders are designed in one plane for shipping reasons but this isnt really an issue in a home job. Both of the ones Ive built have built in frames and I think theyre stronger for it. The top of the frame also works great as a worktable in a pinch. The grinders are a unit that can be picked up and moved wherever you want without remounting the motor. The motor (1725 rpm) drives a shaft that is mounted with two pillowblock bearings. The pulleys are geared so that the drive wheel spins at double the rpm of the motor, but could be used at a few different rpms if step pulleys were used. All elements of the frame are made with 1.5 (0.120 walled) or 1.25 square tubing. This is so that the smaller square tubing fits in the larger beautifully when used with a set bolt for a receiver type setup. As far as what all this grinder can do, Pictures say more than words can:
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I havent actually tried the one on the bottom right, but I think it would be great for sharpening if the drive wheel is ever able to be slowed down with step pulleys. For the times when a table is in the way, the motor can be reversed at the flip of a switch and the back side of the grinder becomes your work area. A full height platen as you see in the below picture can be installed with the two idlers in place or if I ever figure out a way to make a contact wheel, it can be mounted to a tooling arm made from 1.25 square tubing (again with the motor reversed of course). The idler you see mounted on the bottom right side of any of the above pictures is mounted to 1.5 square tubing. This square tubing also serves as a receiver for any attachment you want (like the multi-way adjustable table you see in the below picture). When the table is used with the flat platen its locked at a set distance from the platen since the bolt for the lower idler wheel goes directly through the tooling arm of the table, but it can be set at any distance when used with a contact wheel since that idler would then be removed.
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Since I know somebody will probably ask, the entire machine cost my friend about $300 in materials and a cup of coffee in labour. I work cheap, but it was a Tim Horton's coffee, so it was worth it
. Most of the cost went to the driveline stuff (including making the idler wheels). Bearings, keyed shaft, and pulleys arent cheap. The motor (1hp) was bought used and most of the steel plate was scrap I had laying around.
Thanks for reading through my post, and feel free to use any of my ideas for your own grinder builds (Just use common sense and dont hurt yourself; belt grinders can be dangerous). I hope Ive helped a few people out there. One thing I love about this design is that its not like anything else out there. Most homemade grinders are KMG clones and I like that mine is something new. Finally, in the off chance that this style of grinder ever catches on and because Im a vain jerk, Im calling it an OBS grinder:
Person 1: I made a grinder that can take almost any size belt, can take a contact wheel, and has a solid built in table.
Person 2: Oh, BS!
Person 1: Exactly, an OBS!
It has nothing to do with the fact that my initials are obs
Please, give me your feedback, Id love to hear your criticisms and ways that I could improve it. Ive got pretty thick skin and Ill probably be making myself one before too long so it would be great to make it even better.
1. A cheap way to make a simple drive wheel
2. A new tracking mechanism thats relatively simple and rock solid
3. A new take on the style of a 2X72 grinder designed with versatility in mind
First, the story behind it. When I started making knives, I built myself a small grinder since I couldnt find anything decent for cheap. I designed it to have a solid built-in table and take anything from 1X30 to 2X48 belts with a ½ hp motor. I mainly use 1X42 belts and it has worked very well for everything except large kitchen knives. A friend who initially got me into knifemaking, finally sick of using his little 1X30 (you could probably stall the belt by grabbing it with your bare hands), asked me to build him one too. Initially he wanted one just like mine, but I argued that a 2X72 wouldnt cost all that much more and would be far more useful. I set out designing a 2X72 somewhat similar to the KMGs, but he still wasnt convinced he wanted a 2X72 since belts arent locally available. Then in a stroke of pure genius, I realised that the design of my little grinder with the built-in table and interchangeable belt sizes looked remarkably similar to the back end of my 2X72 design. With a $3 4-way switch, a reversible motor, and some clever wiring, I knew that I could build a grinder that does it all. Intrigued? Then skip to Point 3.
1. Drive wheel
In my searches I found a lot of interesting ideas for inexpensive idler wheels. Some of these were longboard wheels, bearings pressed into aluminum pipe (I opted for this one), or simply purchasing the real thing. However there were very few ideas out there for an inexpensive drive wheel. What I came up with was rather simple and easy. Take a 3.5 pulley, and press it into a 3 pvc pipe coupler. 3 pvc pipe has an outer diameter of 3.5. It follows that the coupler has an inner diameter of 3.5 and outer diameter of 4. Perfect for a drive wheel. The couplers even have a little ridge running the inner circumference that lets you know when your pulley is centered and ensures it is set straight. I found that while my idlers where a somewhat hokey solution that may not last forever, the drive wheel is solid, perfectly round, and while a little longer than necessary (about 3.5 instead of 2), works excellently.
2. Tracking mechanism
Im proud of this one. Most of the tracking mechanisms you see out there are essentially some type of hinge with a set bolt that controls how much your belt can pull down on the tracking wheel to control what angle the wheel is held at. I considered quite a few different methods including modifying an old door hinge or making a hinge like the KMGs. What I ended up doing was using a piece of round pipe for my tension arm, which serves as the inner part of the hinge. A 3 length of pipe with an inner diameter slightly larger than the outer diameter of the tension arm rotates over the tension arm pipe and holds the idler wheel mounting bolt. A bolt connected to the outer pipe pushes on a stationary bolt connected to the inner pipe in order to set the angle of the tracking wheel. The inner pipe has a hole drilled in it slightly larger than the diameter of the idler wheel mounting bolt so that the bolt can rotate with the outer pipe. Belt tension keeps constant downward pressure on the entire mechanism. Sorry for my unclear explanation, it really is pretty simple when you see it and rock solid. These pictures should explain it much clearer than I ever could.
I like this design because it combines the tension arm and tracking mechanism into one part and holds the wheel at the same level as the tension arm (as opposed to above it like most do). It also has lots of adjustment capacity built in. I actually welded the pipe for the tension arm on this grinder inside a piece of square tubing since the pipe I had wasnt quite long enough, and I needed the tension arm to fit inside another piece of square tubing for one of the setups youll see in point 3.
3. Overall belt grinder design
Ill never really understand why most of the home built grinders Ive seen are usually built in just one plane. By this I mean that their basically two dimensional with a motor that is mounted next to the grinder. Why not build a three dimensional frame that houses the motor within? I understand that the commercial grinders are designed in one plane for shipping reasons but this isnt really an issue in a home job. Both of the ones Ive built have built in frames and I think theyre stronger for it. The top of the frame also works great as a worktable in a pinch. The grinders are a unit that can be picked up and moved wherever you want without remounting the motor. The motor (1725 rpm) drives a shaft that is mounted with two pillowblock bearings. The pulleys are geared so that the drive wheel spins at double the rpm of the motor, but could be used at a few different rpms if step pulleys were used. All elements of the frame are made with 1.5 (0.120 walled) or 1.25 square tubing. This is so that the smaller square tubing fits in the larger beautifully when used with a set bolt for a receiver type setup. As far as what all this grinder can do, Pictures say more than words can:
I havent actually tried the one on the bottom right, but I think it would be great for sharpening if the drive wheel is ever able to be slowed down with step pulleys. For the times when a table is in the way, the motor can be reversed at the flip of a switch and the back side of the grinder becomes your work area. A full height platen as you see in the below picture can be installed with the two idlers in place or if I ever figure out a way to make a contact wheel, it can be mounted to a tooling arm made from 1.25 square tubing (again with the motor reversed of course). The idler you see mounted on the bottom right side of any of the above pictures is mounted to 1.5 square tubing. This square tubing also serves as a receiver for any attachment you want (like the multi-way adjustable table you see in the below picture). When the table is used with the flat platen its locked at a set distance from the platen since the bolt for the lower idler wheel goes directly through the tooling arm of the table, but it can be set at any distance when used with a contact wheel since that idler would then be removed.
Since I know somebody will probably ask, the entire machine cost my friend about $300 in materials and a cup of coffee in labour. I work cheap, but it was a Tim Horton's coffee, so it was worth it
. Most of the cost went to the driveline stuff (including making the idler wheels). Bearings, keyed shaft, and pulleys arent cheap. The motor (1hp) was bought used and most of the steel plate was scrap I had laying around. Thanks for reading through my post, and feel free to use any of my ideas for your own grinder builds (Just use common sense and dont hurt yourself; belt grinders can be dangerous). I hope Ive helped a few people out there. One thing I love about this design is that its not like anything else out there. Most homemade grinders are KMG clones and I like that mine is something new. Finally, in the off chance that this style of grinder ever catches on and because Im a vain jerk, Im calling it an OBS grinder:
Person 1: I made a grinder that can take almost any size belt, can take a contact wheel, and has a solid built in table.
Person 2: Oh, BS!
Person 1: Exactly, an OBS!
It has nothing to do with the fact that my initials are obs
Please, give me your feedback, Id love to hear your criticisms and ways that I could improve it. Ive got pretty thick skin and Ill probably be making myself one before too long so it would be great to make it even better.
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