DIY Belt Grinder Build Questions

devils4ever

devils4ever

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I'm thinking about building a 2X72 belt grinder for shaping/sharpening HSS lathe tooling and general shaping/deburring metal parts. I have a 6" bench grinder now and it works, but it's slow. But, I have some questions on the design and construction.
  1. Why are most belt grinders 3 or 4 wheels? I'm thinking 2 vertical wheels would be simpler to build and easier to keep the belt tracking. It would also take up less bench space.
  2. Is variable speed really needed? Why would you not keep the speed maxed out at all times?
  3. Can this be made from aluminum instead of steel? Aluminum is lighter, corrosion resistant, and easier to machine.
  4. A lot of designs allow the belt to be placed horizontally. When would this be useful?
  5. I see a lot of designs that allow the belt to be tilted as well as the rest. Why do you need both to tilt? Isn't one tilting enough?
  6. I understand a glass platen is better than steel. Is it because it is flatter and more wear resistant?
  7. I would probably buy the wheels as a set since it would push my mini-lathe to the limit. What are good diameters for the drive wheel?
  8. What SFM is desirable on the belt?
  9. If I do go with variable speed, I'm guessing a 3-phase motor and VFD are the way to go?
  10. I know mikey recommends ceramic belts. Looking at MSC, they go from 36 grit to 220. Is 220 fine enough for lathe bits? What is the equivalent grinding wheel grit?
That's all for now! Thanks all!
 
Thake a look at the Burr King grinders. They are essentially the Cadillac of belt grinders. They are the best built longest lasting machines of this type I am aware of. They have dozens of different models and belt sizes. The type of work you want it for generally dictates the size and style you want. Each machine has a short description as to it's features.

Belt Grinders

www.burrking.com www.burrking.com
 
I've built a couple 2x72's out of treadmills that work really well. takes some patience to get everything aligned for tracking is all. Longboard skateboard wheels are excellent idler wheels. Last one I built has less than $35 in cost in it withholding my time and runs like a screaming demon. If $$ wasn't an object I'd buy a Bader but I digress, I'm a cheepo where I can be.

2 wheel setup can be done, going to sit pretty high, Grizzly uses this design.
Variable speed isn't a necessity, but very useful for finer grit belts to keep the heat transfer minimized.
Aluminum? Wheels for sure, suppose the rest could be made out of it too.
Horizontal, mine aren't, again suppose it would be useful just so far haven't had the need for it.
Glass platen, less belt wear on the back, cooler running, nice and flat.
Drive wheel size determined by rpm of your drive source, mine runs at ~4500 rpm max, faster than it needs to.
SFM?, guess I never got that technical about it.
Variable speed motor source, I'll take the DC motor anytime.
I make knives and sharpen them. My belts go from 36 to 2500.

Hope that helps.
 
I’m very slowly working on one. My design:

targeting 7k FPM as the max surface speed; and

using TEFC 3-phase motor to avoid issues with ferrous grinding dust and a permanent-magnet motor.

I think the configuration for tilting axes (belt, work support, platen) is mostly about convenience for whatever shape work you happen to be working on.
 
I also built my own and here are some of my own opinions:

1) A large space in the middle allows for more attachments than just the flat platen, like a large and small contact wheels, or even a surface grinder attachment on the bottom. I also have mine on a bench rather than free standing, so it lowers the overall height.
2) YES. I use slow speeds all the time for delicate work. Even if the motor itself isn't variable speed, just using a step pulley like on a drill press is enough.
3) People have made them out of aluminum. There are even some plywood designs. Steel is usually just the cheapest and easiest to weld in any shape.
4) I've never really desired it myself, but it helps with burrs. When you grind perpendicular to a face, you can get a massive burr on the bottom. IT also gives you a larger strip of the flat platen to work with.
6) Generally wear resistance. I'm using a piece of ceramic glass for mine, though the static buildup can be pretty insane if you don't hold a finger to the metal frame. There are countermeasures for this though, just like with dust collector static buildup.
7) Like Daffy said, 2" wide longboard wheels work well, they're what I'm using right now. You could also just glue some MDF sheets together and turn them on your mini lathe. My main drive wheel is MDF laminate.
9) I'm using a 3ph motor I got for about $30. If you're doing this on the cheap, just scan ebay for used ones, they're not uncommon. If you have a single phase motor available to you, just make some stepped pulleys out of plywood. I like to have pulleys with my 3ph motor because it gives me torque options.
10) Very opinionated, but I wouldn't go over 60 or 120 grit with ceramic. Over that just isn't cost effective. You'll get a lot of use out of the 36 and 60 grits though. If you're grinding HSS lathe tools, 220 is fine before a quick stoning.
 
I forgot to mention that I don't have a welder. So, my design has to be bolted together!

I do like the design that Phil Vandelay uses on YT except his is metric and I would have to convert it. See it here.
 
devils4ever said:
I'm thinking about building a 2X72 belt grinder for shaping/sharpening HSS lathe tooling and general shaping/deburring metal parts. I have a 6" bench grinder now and it works, but it's slow. But, I have some questions on the design and construction.
  1. Why are most belt grinders 3 or 4 wheels? I'm thinking 2 vertical wheels would be simpler to build and easier to keep the belt tracking. It would also take up less bench space.
  2. Is variable speed really needed? Why would you not keep the speed maxed out at all times?
  3. Can this be made from aluminum instead of steel? Aluminum is lighter, corrosion resistant, and easier to machine.
  4. A lot of designs allow the belt to be placed horizontally. When would this be useful?
  5. I see a lot of designs that allow the belt to be tilted as well as the rest. Why do you need both to tilt? Isn't one tilting enough?
  6. I understand a glass platen is better than steel. Is it because it is flatter and more wear resistant?
  7. I would probably buy the wheels as a set since it would push my mini-lathe to the limit. What are good diameters for the drive wheel?
  8. What SFM is desirable on the belt?
  9. If I do go with variable speed, I'm guessing a 3-phase motor and VFD are the way to go?
  10. I know mikey recommends ceramic belts. Looking at MSC, they go from 36 grit to 220. Is 220 fine enough for lathe bits? What is the equivalent grinding wheel grit?
That's all for now! Thanks all!
Click to expand...

1. You actually do not need to go with a 2X72. There are a lot of other common belt sizes and a 42 or 48" belt would do fine while allowing you to use two wheels instead of four. The 72 belt is commonly used by knifemakers and are readily available. Each wheel has a job - drive, tracking and on a platen, two wheels support the belt as it runs over a platen. Contact wheels have an obvious function.
2. VS is nice to have when using fine grit belts. High speeds tends to eat up the abrasive quickly and also causes the splice to thump annoyingly under the work.
3. You can go with aluminum; others have. The thing to consider is the modulus of elasticity of aluminum is 1/3 that of steel so for parts that are under tension, steel is a better option. The chassis, if properly braced, can be aluminum.
4. Horizontal positioning is useful for grinding wood, knife handles, edges and so on. Not necessary but nice if you can design it in.
5. Tilt is good for grinding bevels while keeping the tool rest flat. Think beveling the edges of square tubing before welding.
6. Yes. A ceramic glass platen will remain flat for years in a hobby shop. When grinding tools, a flat platen is critical to controlling your geometry. Of all the mods you can do to a belt sander, I consider a glass platen to be #1.
7. 5-6" is common.
8. For metal grinding, supposedly somewhere near 6K or more is desirable. I have gotten along fine with much slower belt speeds but if you have a VS motor that can hit those speeds then you'll be grinding, not sanding.
9. VFD's are commonly used on these belt sanders. However, if you are going to be doing a lot of detail work at slower speeds then a DC motor might be a good option because you will retain torque at lower speeds.
10. For shaping, a 36 grit ceramic belt is really good, while 80-120 is good for smoothing out the coarse grind marks. You can step up through the grits to put a near mirror finish on a lathe tool if you desire. I would look at the Red Label ceramic belts on Amazon if I were you.
 
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Ok, so looking at the motor, I'm thinking a 3-phase, 1-1/2 HP, totally enclosed fan cooled unit such as this would work? It is 3,470 RPMs. If I calculate this correctly for a 6 inch drive wheel, the max SFM is RPM X (drive wheel diameter in inches X PI) * (1 ft/12in) = 3470 X (6 X 3.14) / 12 = 5,448 SFM. To hit above 6K, I would need a 7 in drive wheel.

I'm not sure on VFDs since I've never used one. I'll have to look at those units as well.

I'm thinking of staying with the 4 wheel design and using steel for the parts.
 
With a VFD you can drive the motor past it’s rated speed. Increased speed would mean increased power of torque is constant, so I believe typically it would run with constant power (decreasing torque as speed exceeds rated speed). I am not sure what the practical limits are but I went with a 6” drive wheel and 3600 rpm, 2hp motor.
 
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