Thread: Bench Grinders

Just one: Don't ever expect, even in your wildest dreams, that the stone wheels will last forever, certainly not in store fresh condition. Can you buy replacements? Can you buy options for buffing, etc?

Most bench grinders that I am familiar with are running 3,700rpm or so. That's fast and can cook the temper out of a tool edge in no time.
Bench grinders for sharpening (what?) have motor speeds of 1750rpm. That's certainly fast enough but you can still cook an edge.

Having said that, if you take your time and go very gently, you can repurpose tools with a fast bench grinder.
I started with a 12mm Narex skew chisel.
Squared off the entire end. (Why did everybody else go outside?)
Developed a basic 10 degree bevel on each face.
Refined that on a stationary belt sander.
Oil stones then water stones then a strop with chrome green.
Result = a very nice 1/12 carver's stop chisel.

Just a word of caution = don't ever stand in frond of a bench grinder when you start it up. If the stone is flawed and disintegrates, chunks coning off at 3750rpm will spoil your whole day.

Vibration on a grinder usually limits how smooth you can grind, and once you have tried a low vibe grinder you will find it difficult to tolerate any that have a higher level of vibe.

Cheap grinders are a bit of a raffle, some vibrate straight out of the box and some develop vibration over time and a few remain OK.

If the vibration is due to the wheel it may be possible to correct it by truing the wheel but if it is in the motor or shafts then there is little chance of correction.

I'd be looking at the Makita for starters but if you can find a second hand Abbot and Ashby grinder you will see what I mean. These grinders will last a lifetime.

Originally Posted by Robson Valley

Most bench grinders that I am familiar with are running 3,700rpm or so. That's fast and can cook the temper out of a tool edge in no time.
Bench grinders for sharpening (what?) have motor speeds of 1750rpm. That's certainly fast enough but you can still cook an edge. . . . .

RV in Australia we use 50Hz AC so our grinders typically run at 2850 or 1420 rpm, not that much of a difference but a 1420 grinder can be quite effective combined with a bit of cooling.

Originally Posted by Robson Valley

Refined that on a stationary belt sander.

Wow, that IS a slow speed.......................

Quickest way to establish whether the grinder is to blame for vibration is to take the wheels etc off and run it without them. If the vibration is still there it is the grinder, if not it is the wheels.

At one stage I was going to buy one of the Barbatec slow speed grinders (1400rpm) and asked them to run one for me.
It just about walked off the counter, they told me the wheels needed truing. OK said I, let's take the wheels off, almost as bad without the wheels. To this day I haven't found a decent slow speed grinder.

Picked up an old GMF grinder from a fellow forumite, it also vibrated badly, but without the wheels it was as smooth as. Replaced the wheels with decent quality new ones and it runs as smooth as. Takes ages to come to a stop after switching off.

One tack I am looking at is to get a slow speed grinder is to find a used 3 phase grinder and put a VSD on it.
As well as speed control, 3 phase motors are usually rugged, well made and smoother than single phase motors.
Of course this adds considerably to the the cost but it would be worth considering if someone already has such a grinder in their shed.

That's an interesting idea Bob, don't know whether the 3ph grinder motors are star or delta?

Most of it has been said... if you can, run it w/out the wheels to look for vibration.

I'm also an Abbott & Ashby fan. If you ever find a working one going cheap in a Garage Sale, I recommend that you fight your way over the horde of slavering woodies and grab that beasty!

A couple of other things you should allow for in your budget:

You will need a diamond dresser to keep your wheels in good trim. T-bars are good for a novice, diamond points are cheaper but need a bit of practice.

Considering what you want to sharpen I'd seriously look at purchasing a white (AlOx) wheel to replace one of the stock greys. The greys are good at 'reshaping' lumps of steel, generating a lot of heat. Whites don't run as hot and are better at sharpening 'em, with less risk of bluing the steel.

Originally Posted by Big Shed

That's an interesting idea Bob, don't know whether the 3ph grinder motors are star or delta?

If it was big enough it probably wouldn't matter that much.

Originally Posted by BobL

If it was big enough it probably wouldn't matter that much.

Originally Posted by Big Shed

My understanding is that both will work but the Star winding will give the optimum performance at 240V.

Sorry but I have missed several paragraphs.
What can grinder vibration have to do with the finished tool edge? Grinders are rough and rugged and FAST. I like that. Go easy and don't cook the tool.
I get the shape. I refine that by other means. The belt sander was (at that point) the answer to my needs.

Grinder/schminder, I got that part done without cooking the edge.
I'll do oil stones then water stones to 4K and hone on a strop with
chromium oxide & aluminum oxides to 50,000grit and call it a day.
In fact, I'll call it a top quality "carving-sharp" edge.
You can test these by slitting your own throats. I carve wood.

Originally Posted by Robson Valley

Sorry but I have missed several paragraphs.
What can grinder vibration have to do with the finished tool edge? Grinders are rough and rugged and FAST. I like that. Go easy and don't cook the tool.

I think you missed a couple of the OPs points too.

As well as chisels, the OP says he wants to sharpen drill bits and spades. The spade you can sharpen with anything but drill bits can really make use of a vibe free grinder. A low vibe wheel really helps, especially with small bits, otherwise the bit goes dancing around on wheel can generate an uneven tip which produced the incorrect hole size. Once you have used a low vibe grinder you don't want to use anything else, even on an axe.

BobL: Thank you. I did not know that. Thanks for offering the info.

Originally Posted by Skew ChiDAMN!!

Considering what you want to sharpen I'd seriously look at purchasing a white (AlOx) wheel to replace one of the stock greys. The greys are good at 'reshaping' lumps of steel, generating a lot of heat. Whites don't run as hot and are better at sharpening 'em, with less risk of bluing the steel.

I have four grinders, but am no expert. I have read all sorts of takes on this subject ...

My observation would suggest the grey wheel cuts faster and cooler. And the white slower/smoother but generates more heat. As if, you might say, the first cuts more than rubs and the second rubs more than cuts.
Just my understanding ... my 3-phase grinder has one of each.

Also I have had no trouble (now) truing with the carborundum stick. Flat enough to test with my thumb on the wheel.
Not flat enough for a surface grinder I am damn sure
(And they're cheap.)

A_n_d ... amen to the smooth running wheel. When I first bought a white 8" wheel I tried it on my 6" grinder.
Huh-humm.
Then I put it on the shelf for about 6 months.
Tried it again when the 3-phase grinder came along - had the carb stick this time - has been heaven since.

Cheers,
Paul