Bench grinder size

[shamrock12]

Just curious why it seems to me that 8" bench grinder is a popular choice? From what I understand, the ideal speed is approximately 5000 to 5500 "linear" feet per minute. Many of them are available with 1800 and 3600 RPM motors. At 3600 RPM, the 8" grinding stone would be spinning at 7540 FPM (86 MPH) which is pretty high but only at 3770 FPM with 1800 RPM motor. If the grinder stone is spinning too slow, it does not cleans well and loads up. If it is spinning too fast, there are two dangers: you risk the chance of burning up (overheating) the tool you are sharpening, but that can be controlled if you know what you are doing. The other danger is an increased chance of grinding stone disintegrating and potentially cause injury to the operator.

So therefore, a 6" grinder with 3600 RPM motor is perfect and so is a 12" grinder with 1800 RPM motor. A 10" grinder with 1800 RPM will be a bit slow (4710 FPM) but still is a good speed.

 

[2oolhound]

Not everyone just wants to sharpen tools. Some of us want to eat metal then weld it. Boo Hoo for temper. Bigger is better.

 

[R W]

I wouldn't buy less than an 8", bought a 6" once but found it to small, fortunatly I found a buyer and were able to get rid of it and get an 8".

 

[retrobuilder]

Agree. 8" also give a better contour for edge tools. If you are only sharpening there are even better grinders with "platter' grinding disks for flat surfaces and bevels. 8" will likely have better motor power as well. Utilize a speed controller if needed. As usual depends on what you are doing with the tool.

 

[goodysgotacuda]

I bog down my 6" every time I use it, shouldn't have ever bought it. 8" I think is my new minimum, I'd really like a larger one though..

 

[Jack Olsen]

Some of it has to do with the size of the motor housing itself. The nice thing about an 8" wheel is that you'll have more access from more angles. On my 6" grinder, the wheels are just about the same size as the motor case.

 

[JASTECH]

^This, like Jack wrote. Your issue with a 6" grinder was most likely a 1/6 HP motor or some Chinese motor used for grinding doggie toe nails. Like most have learned from GJ members, the old USA made bench grinders are far better then what is glued together from China. If you like 6" then fine, get an old C'man block grinder 1/2 HP.

 

[shamrock12]

I think maybe my question was not clear enough. My question is more toward the proper speed of grinding stone rather than the ease of using a certain size grinder. What I am saying is that 8" has one of the "worst" speed for proper grinding, whether if you are sharping a tool or just deburring some piece of metal. Also, spinning the wire brush at 7500 FPM is gonna sting quite some. As mentioned earlier, the chance of grinding stone disintegrating is greater at this speed. Safety wise, the 6" and 10" would seems to be the more ideal choices rather than 8". And they would not burn up the tool or material as much as 8" would do. It just seems like every other person have a 8" which makes me wonder if they just don't care or if I am just crazy. Hopefully that gives you a better idea of what I am asking here.

 

[R W]

I have 2 x 8" grinders, 1 is fitted with a coarse wheel and a wire brush, the other a fine wheel and a Multi-Tool sanding belt, from memory they run @ 2850 RPM, I have not encountered the problems you are referring to.
No doubt a 10" would be great in many applications, but as stated before a 6" is way
to small for any serious applications. Wheel dosn't have to wear much and all you have
is a 4" or 5".

 

[Carla]

Hi, Shamrock,

Actually, the higher peripheral speed of an 8" wheel running at 3450 is desirable for many varieties of the work for which the usual type of bench/pedestal grinder will be used. The higher peripheral speed, compared to the common 6" or 7" wheels at 3450, simply gets more work done in the same time.......if.....the operator is using the correct wheel for the job.

The important consideration is to use the optimal grade and grit of wheel for the work to be done. The reputable grinding wheel manufacturers provide 'application charts' for the selection of wheels, and make wheels which are designed to run safely at 3450 in the 8" size.

Yes, low-quality wheels from 'cheap labour countries' are a serious hazard, and will fail, with possible very serious danger to the operator. This is as true of any size/shape of wheel, to be sure.

As a practical matter, its desirable to keep a number of grinders and polishing motors set up with different wheels for different varieties of work. (granted, it may take a while to find good deals on older, best quality, American-made grinders, but they are not all that difficult to obtain, with a bit of looking)

As an example, the ones in our little shop here are a 12"x1750 Cincinnati, an ex-Navy maintenence shop grinder with flood coolant on one side for tool grinding, an 8"x3450 Baldor grinder, 8"x3450 Baldor polishing motor, two 6"x3450 polishing motors, and one 7"x1750 grinding/polishing motor, used for delicate work. The idea is to have several different varieties and grades of grinding, buffing, and polishing wheels readily available, saving the time which would otherwise be wasted in changing wheels to suit the work.

The 8"x3450 units have been in service for 30+ years, and have never had a wheel failure, but we've taken care to use only best quality wheels. A minor cost-effectiveness detail is to use wheels on the 8" grinders until they are worn to 7" dia,, at which point they are suitable for use on a 7" grinder.

cheers

Carla

 

[dirtydogintex]

Hi, Shamrock,

Actually, the higher peripheral speed of an 8" wheel running at 3450 is desirable for many varieties of the work for which the usual type of bench/pedestal grinder will be used. The higher peripheral speed, compared to the common 6" or 7" wheels at 3450, simply gets more work done in the same time.......if.....the operator is using the correct wheel for the job.

The important consideration is to use the optimal grade and grit of wheel for the work to be done. The reputable grinding wheel manufacturers provide 'application charts' for the selection of wheels, and make wheels which are designed to run safely at 3450 in the 8" size.

Yes, low-quality wheels from 'cheap labour countries' are a serious hazard, and will fail, with possible very serious danger to the operator. This is as true of any size/shape of wheel, to be sure.

As a practical matter, its desirable to keep a number of grinders and polishing motors set up with different wheels for different varieties of work. (granted, it may take a while to find good deals on older, best quality, American-made grinders, but they are not all that difficult to obtain, with a bit of looking)

As an example, the ones in our little shop here are a 12"x1750 Cincinnati, an ex-Navy maintenence shop grinder with flood coolant on one side for tool grinding, an 8"x3450 Baldor grinder, 8"x3450 Baldor polishing motor, two 6"x3450 polishing motors, and one 7"x1750 grinding/polishing motor, used for delicate work. The idea is to have several different varieties and grades of grinding, buffing, and polishing wheels readily available, saving the time which would otherwise be wasted in changing wheels to suit the work.

The 8"x3450 units have been in service for 30+ years, and have never had a wheel failure, but we've taken care to use only best quality wheels. A minor cost-effectiveness detail is to use wheels on the 8" grinders until they are worn to 7" dia,, at which point they are suitable for use on a 7" grinder.

cheers

Carla

Well said.... esp the section I highlighted (bold, underlined).

 

[autopts]

I've got a Baldor 8100W that I might be selling. If it fits your needs get back to me. Shipping could be a bit high. They go about 100 lbs.