Teach me about grinders

[mimidood]

I am not sure if this has been mentioned before but I cannot find it using search function.
I am hoping people can teach me about grinders and what to look for why purchasing them.
For example why sometimes 1/4 hp will be better than 3/4 hp.
The benefits of single phase/three phase or amperage and rotation speed.
Thanks in advance.

 

[phy6]

I think there are some basic, non-grinder specific properties you'll want to consider when comparing grinders. One of these applies to all electronic motors like in air compressors, sanders, drills, etc:
Instead of looking at HP ratings (which can be measured at peak or after it's running), look at the Amp draw. I think the Amp draw is less likely to be twisted for marketing appeal. Amp draw * voltage gives you Watts. 746 Watts is equal to 1 HP at 100% efficiency. The motors that we use for tools are probably on the order of 75-85% efficient, so that would mean something like .75 * Amp Draw * voltage. Obviously this is very simplistic, but if you wanted to compare the relative power of two motors quickly, this is something you could calculate while standing in the store.

There are other factors like duty cycle and the build of the motor, which may not be advertised. Does the rotor have cooling fins on one end? Can you replace the commutator brushes?

 

[Hammell]

Most welders I know use Makita grinders, ive used a couple of them for years and would recomend them. Bosch makes good ones too.

 

[woody 73]

To the op are we talking about hand held grinders or are we talking about bench grinders or both? At first I thought hand held untill I saw the part about single or three phase...

I am not the one to talk about electrical but I can answer a few things about your question:

Speaking about Bench grinders 99.999% of homeowners will have single phase power as in 120V or they can be wired for 240V. But on the other hand only a small percentage and that would be a business will have a dedicated power line for three phase power.

So that leaves most people with three alternatives Static,VFD, or rotary phase power to start your three phase grinder. (do a google search for more information).

Now the benefits of both could fill up a ton of space, but lets just say most people will stick with the easy option of single phase power for ease of use and for a easy resale.

Someone else can speak of HP ratings but I find the more HP the less a chance of bogging down the bench grinder.

Hope that helps you out a little bit, but if you were thinking about hand held grinders that is another story.

 

[Greatwhitewing]

Most welders I know use Makita grinders, ive used a couple of them for years and would recomend them. Bosch makes good ones too.

Are you referring to handheld grinders? I don't see bench griders on the Bosch website???

Course we're not sure yet if the OP meant bench or hand held...

 

[Hammell]

Are you referring to handheld grinders? I don't see bench griders on the Bosch website???

Course we're not sure yet if the OP meant bench or hand held...

I thought it was hand held grinders. Oops.. The only bench grinder I have is a 6 inch Mastercraft, works fine, haven`t killed it yet.

 

[woody 73]

Pm sent to the op to tell us which kind of grinder he needs help with.

 

[mimidood]

I am talking about bench grinders.

 

[larry_g]

Any grinder will do you until you define and refine your skills enough to make a specific type or style of grinder a necessity. If you have no experience or specific need then any grinder will do. As you learn and use it you will be better able to define the specific size and characteristics YOU need in the tool. Like vehicles, what you need may not suit me at all and so many to chose from.

Above quoted from the anvil thread...with the word anvil changed to grinder. I have books devoted to abrasive metal removal. It is not a simple subject and you will soon find that you may need 4-10 different grinders to do all you may want to do. The easy answer is to get a 1/3 hp grinder and put some decent wheels on it and then learn if it will do what you want to do. What do you intend to grind?

lg
no neat sig line

 

[woody 73]

Above quoted from the anvil thread...with the word anvil changed to grinder. I have books devoted to abrasive metal removal. It is not a simple subject and you will soon find that you may need 4-10 different grinders to do all you may want to do. The easy answer is to get a 1/3 hp grinder and put some decent wheels on it and then learn if it will do what you want to do. What do you intend to grind?

lg
no neat sig line

good advice start with a single phase small 6inch chinese or a good used american small grinder, buy some good wheels and go from there.

 

[mimidood]

Thanks for the reply.
I am going to meet a guy to see a old craftsman grinder today
The picture is attached.

Can you explain why some grinders are better in a situation over others depending on their specifications?

 

[GeorgiaHybrid]

There a LOT of us that love and use those old Craftsman "block" grinders. If it runs smooth, buy it and it should last you for years.

 

[woody 73]

why some grinders are better in one situation over another:

I sharpen wood lathe tools 24/7 A slow speed grinder is ideal for sharpening tools without generating a lot of heat, (which kills the tool) that you get so quickley from a 3450 RPM grinder.

Cool running is 1725 RPM using a white Aluminum oxide grinding wheel which will cut faster and will not clog up so bad.

I am sure other GJ members can add more examples to help you out.

 

[Steinmetz]

Buy good quality wheels of suitable grit (I like Norton) and dress them periodically with a dresser.

 

[mimidood]

Thanks for the brand of grinding wheels.
I purchased the grinder.
The users said he put recently put new wheels on it.

Can you explain or provide a link about dressing the wheels?

 

[Steinmetz]

A wheel dresser is a device having a diamond surface that is held against the wheel while in motion to remove metal embedded in the surface of the wheel, and to generally restore the surface of the wheel. They are relatively inexpensive.

If you perform a search here, you may find photographs and other information.

 

[Steinmetz]

Here's a link:

http://en.wikipedia.org/wiki/Grinding_dresser

 

[larry_g]

http://www.nortonindustrial.com/documentfinder.aspx

Spend a couple of hours at the above site and you will become a bit better informed. Lots of good information.

lg
no neat sig line

 

[mimidood]

Thanks, I will check it out.

 

[pcmeiners]

"For example why sometimes 1/4 hp will be better than 3/4 hp."

The only advantages of a 1/4 hp over 3/4hp.. cheaper to run wattage wise if all you do is very light work such as sharpening chisels, and more forgiving when you do something stupid, if you purchase a recently manufactured small fractional hp unit you can easily get speed control.
On the other hand with a 3/4 hp you can do heavy work without bogging down, versus wishing you had not purchased an under powered 1/4 hp unit everytime you have slightly heavy work to do. The quality of the grinder goes up as hp goes up, but then again that is arguable with consumer grade grinders.

120v vs 240....on small fractional HP it does not matter much, with higher amperage draw, 240v generally has a less resistance losses (depending on the wiring). Lastly, for those going for the Darwin Awards, you have a much better chance at achieving your goal by miswiring or poor/no grounding with 240v.

 

[torqueman2002]

Follow the link below, if you are interested in: ".... the restoration, use, and maintenance of the classic Craftsman bench grinders that were manufactured for Sears by Paramount/Allegretti & Co. from the early 1960's to early 1980's. Affectionately known as "Block Motor" grinders because of their unique shape, these power tools have developed a large following among shop enthusiasts because of their legendary reliability, accuracy, and power."

There's also a link to a March 1990 Popular Mechanics article: "Bench Grinder Basics"; I posted in reply #2.

http://tinyurl.com/CM-Block-Grinders