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Here is a design for a 42 inch belt grinder. This is my general design but there are no measurements, I plan on doing the measurements when I have the 42 inch belt so I can use it to see what I need exactly.

The frame is to be made of 2x4s

I do not have a welder available to me.

Questions: What feet per min should I have for the highest setting?

How strong does this need to be? I wouldn't think a 1/2 horse motor would put a lot of stress on it.

Any tips? I haven't made one of these before.

thank you

42 inch Grinder.png

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Why 2x42 inch?  Have you researched the belt sizes and availability?  I suggest you stop building and read a bit more about motor sizes and belt sizes, most suggest at least 1hp with 2 hp being ideal for a 2 inch width, and  if you  look around will notice few belt options for your chosen size, whereas 2x72 inch is the standard and has many options for about the same work to build.

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10 minutes ago, Steve Sells said:

Why 2x42 inch?  Have you researched the belt sizes and availability?  I suggest you stop building and read a bit more about motor sizes and belt sizes, most suggest at least 1hp with 2 hp being ideal, and  if you  look around will notice few belt options for your chosen size, whereas 2x72 inch is the standard and has many options for about the same work to build

42 inch belts are just as easy as any other ones for me to get thanks to the internet. I have not started to build yet I am making the plans first. I unfortunately only have access to a 1/2 hp motor. If I need to upgrade later to a larger motor that shouldn't be a problem. Maybe ill steal the one from my table saw... it is a 2 hp and I haven't used it in well over a year

 

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i think you missed my point about belts and  availability  I was talking about choices in grit and material    Also  I must warn you that your speed control will burn up shortly after you power it up with a 648  watt draw.

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I would be concerned with your wheel/ pulley design. With the speed the belt travels and the rpm the wheels turn generating heat, I'm afraid they may fail with disastrous consequences.

I made a wooden flat belt pulley for my power hammer and the motor only turned at 850 rpm, the pulley failed, luckily it was further away from me and turning slow enough no injury occurred.

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8 minutes ago, Steve Sells said:

i think you missed my point about belts and  availability  I was talking about choices in grit and materials

I am having a harder time finding the selection in 2x72 than I am in 2x42. A brief look at the assortment I see numerous options anywhere between 40 and 800 grit in the 2x42 size. Im not trying to argue with you.

https://www.amazon.com/Knife-Makers-Sanding-Belts-Assortment/dp/B01FIJMO2O

if you look at the product and the similar products you can see a lot of options.

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52 minutes ago, NickOHH said:

What kind of motor is it that your using a fan speed controller? Going to lose torque like crazy 

Do you suggest I have no speed adjustment in the grinder? I figured that the fan speed controller was a cheap way of doing that.

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I noticed that the 6 pack you linked to was about US$8 more expensive than a ten pack of 2x72 belts also on Amazon.

Can you explain how spending $4.66 per belt saves money over spending $2 per belt for belts that will last longer as well?  If you want to do blades on it you will be buying belts by the 10 pack not just 6...When I worked for a swordmaker making high end blades---$7000 in 1980's dollars!  He said one of the secrets was to use belts as if they were free as trying to get the last bit of work out of a used belt often ended up causing issues that would have paid for big stack of new ones----for example fresh belts cut cooler with less force!

As for using wood because you don't have a welder; well my lincoln tombstone cost me $40 used, probably around my age and good for another generation or so with maintenance.  I see them under $150 fairly regularly...  Would you replace parts on a car with wooden ones because you are used to working wood and not steel?

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8 hours ago, ThomasPowers said:

Would you replace parts on a car with wooden ones because you are used to working wood and not steel?

Dangerous question...

29C818E6-806D-478C-A807-17B335A5F1BE.jpeg

9 hours ago, Brian Evans said:

Do you suggest I have no speed adjustment in the grinder? I figured that the fan speed controller was a cheap way of doing that.

If your grinder doesn’t have enough power to push the grit through the metal, it doesn’t matter how much control you’ve got over the speed. 

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Having built the no weld grinder I can say that the plans do work without any welding required.  Since I do have a welder I have welded some sections on it, but it was functional without the welds.  I can also say that I found 1 hp to be underpowered at the fastest pulley arrangement I had on it. I'd recommend step pulleys over your speed control solution.  I'm much more satisfied with the 2hp variable speed I have on it now.  It costs more to go that route, but step pulleys, pillow block bearings, shaft material, and a drive belt all add up if you have to buy them retail.

A 2 inch wide belt will have roughly the same drag on it at the point where you grind whether the belt is 42 or 72 inches long, so I don't think you'll find that a 1/2 hp motor will be satisfactory.  If it's "geared down" to the point where the power is adequate, the belt speed will be slow and therefore so will stock removal.

I used wide skateboard (longboard) wheels for the tracking adjustment and flat platen idlers for a while.  They work ok, but you'll be changing out bearings more frequently than the "standard" options.  I still think that's a better solution than what you proposed.  For the drive wheel I started with a wooden wheel I made by gluing a couple pieces of oak 2x6 together,  cutting it to rough shape, then installing it on the motor and turning it to the final shape.  I'm not necessarily recommending that, but I used it for several months that way until I could buy an aluminum drive wheel.  Other than not being as comfortable with a drive wheel made of wood there really isn't that much difference imho.

Good luck with whatever you choose to do, but please understand that when you ask for opinions/tips, the ones you get may not line up with what you had planned.

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4 hours ago, Buzzkill said:

Good luck with whatever you choose to do, but please understand that when you ask for opinions/tips, the ones you get may not line up with what you had planned.

oh I am well aware of that. But that is something I prepared for, I have not yet started the project aside from acquiring pieces and gluing plywood together for the wheel.

I appreciate all the help and suggestions. I am now going to make it a 72 inch belt design and I have salvaged a 1 and 1/2 horse motor off my table saw that I have not used since I have started to make things in the shop. I am going to make the frame out of wood for several reasons: I would have to find all the metal pieces in a scrap yard or buy them, I do not have an efficient way to cut metal (4 inch angle grinder that heats up way to fast), and the power hammer that I made out of wood has had no issues (so far, probably with around 40 hours of use). If this decision ends up being a mistake then that is on me.

I still have not been able to find a speed (SFPM) that is recommended for grinding blades does anyone have an idea?  

17 hours ago, ThomasPowers said:

Can you explain how spending $4.66 per belt saves money over spending $2 per belt for belts that will last longer as well?  If you want to do blades on it you will be buying belts by the 10 pack not just 6...When I worked for a swordmaker making high end blades---$7000 in 1980's dollars!  He said one of the secrets was to use belts as if they were free as trying to get the last bit of work out of a used belt often ended up causing issues that would have paid for big stack of new ones----for example fresh belts cut cooler with less force!

I did not know that fresh belts cut cooler, that is good to know. When you worked for a swordmaker what was the SFPM of the grinder that you used?

By the way Steve Sells did convince me to move to a 72 inch.

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1 minute ago, Steve Sells said:

those are partially dependant on bearings and belts

Can you expand on that? I was under the impression that there would be an ideal speed to grind steel (probably different for each type of steel), apparently I am wrong. I am here to learn.

I was going to have the motor shaft directly attached to the grinding belt wheel. I need to know what SFPM to make it before i can determine the size of the wheel.

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FWIW, I have a 4 inch drive wheel and can turn my motor up to a little over 4000 rpm.  It's a 3600 rpm rated motor, but I can exceed that with the VFD.  Even at 3600 rpm, to me that's plenty of belt speed with the 4 inch wheel. The grit of the belt has a large impact on how fast you can remove material if you have the speed and power to handle it.

I think what Steve was getting at is that running a faster belt speed than the bearings or belts are rated for can cause premature and/or catastrophic failure of the components.  For instance the small contact wheel attachments usually have bearings that are not rated for as high speed as the 2 inch wheels.

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I've never bothered doing the calculations.  I only run full speed for quick hogging of material.  Other than that I adjust the speed so it feels right to me for the object I'm grinding, the grit of the belt, and the relative precision I'm trying to achieve. I do finish grinding on heat treated blades at a much slower speed than rough grinding prior to heat treating.

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the fastest i run my 2x72 at is 4710 sfpm. it is nice to be able to run it slower too. a 3600rpm motor with a 1 inch triple groove to a 1-2-3 inch v-pulley and a 5 inch drive wheel gets you roughly 4579,2289,and 1497 sfpm, which is a good range of speed for most things.

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With the caveat that I am NOT a bladesmith and my experience with grinders is limited, the short answer is that the limiting factor is FRICTION. In other words, the more friction the belt generates, the slower it should go. Fine grits and dull belts generate more friction, so they should be run at lower speeds to avoid ruining the blade’s temper. Coarse grits and sharp belts generate less friction, so they can be run at higher speeds. This is why variable speeds are good: you can adjust the speed to match the belt. 

@Steve Sells, is that about right?

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Ok I am getting a better idea of what I should be looking for when I am building it. I may end up adding a three step pulley to the design later if I need to. For now I want something that doesn't take as long as a hand file. I am going to have my drive wheel 5 and a half inches in diameter.

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