When is a bench grinder's wheel too small ?

[Rhossydd]

I'm just coming back to turning after some years off. The jigs I made to sharpen my gouges are now all wrong as continued use of my bench grinder in the intervening years has worn the wheel diameter down too much.
Looking at it, the now 5" wheel, will give quite a hollow grind to tools.

When do you change wheels to something newer ?

The next question will be; Is there much difference between cheap wheels and expensive ones ?
It looks like I can buy a complete new grinder for less than the cost of some wheels.

 

[woodfarmer]

I am probably the last person who should give grinding advice.
I have just been reading the Keith Rowley book, in it he says it is best not to use a wheel of less than 5" diametre.

Personally I mostly use the face for grinding simply because I was taught to grind metal working tools that way. there are similarities and differences between the way wood and metal is cut.

The reason Keith gives for not using the face, is because by thinning the wheel it will become fragile. I use one of these wheels http://www.axminster.co.uk/wide-wheel-f ... ch-grinder these are stepped out so the outside is much wider than the middle bit. I would advise to stop using the face when it is about the same thickness all the way down. By using the face you will remove less metal from your tools because the form does not change shape by a reducing thickness unlike the way it does with a reducing diameter and always has exactly the same angles. Also the cutting edge is slightly better supported. Plus when you install a new wheel the angles will be the same so no great removal of metal to conform to a different diameter periphery of the new wheel.

I have seen scary you tube videos of people sharpening tools using jigs to hold the tool pointing into the oncoming wheel periphery. If the jig should slip a tad the likely result would be the tool cutting edge digging in and an exploding wheel. At least if you are at the face of an exploding wheel the bits are less likely to fly straight at you.
I realise face sharpening may be entirely contrary to what the majority of people believe and practice, so use your own judgement.

 

[Rhossydd]

I have seen scary you tube videos of people sharpening tools using jigs to hold the tool pointing into the oncoming wheel periphery.

It's difficult to find anything else.
I think your comment is the first I've read that doesn't say use the edge of the wheel, as per the fitted tool rests. You would have to be really ham fisted to 'dig in' to a grinding wheel. Surely the idea is to address the tool to the wheel gently, well supported and at the correct angle that a dig is almost impossible.

Having said that, I can see the merit in 'flat' grinding on the face of the wheel for some tools. Wider items might be difficult to sharpen, not only because of the lack of area, but also because of the different speeds of grinding across the face from centre to periphery.


Thanks for the interesting opinion though.

 

[MMUK]

FWIW, I find that as long as the BG has sufficient power (ie; 250w or more) to prevent it slowing under use, then all it takes is a decent pair of wheels. I use Norton wheels as I've found these to be the longest lasting and they are pretty well balanced out of the box.

 

[CHJ]

....Is there much difference between cheap wheels and expensive ones ?
It looks like I can buy a complete new grinder for less than the cost of some wheels.

When comparing price due notice should be made of the specification of the wheel.
Most reputable supplies like Peter Childs will only be stocking and supplying wheels of a specification suitable for the wood turner to sharpen HSS tools.

There are considerable differences in grit size, bonding material etc, that is covered by the coding on such wheels and it's a case of balancing required surface finish against wear rate and self sharpening characteristics of the wheels.
Price alone is not a true comparison, you must compare specs.
I find a good quality 80-100 grit White Oxide wheel and a Blue Ceramic wheel meet my needs.
The white wheel is the general dogs body and the blue ceramic is the rapidly cutting very much self sharpening wheel that never needs dressing but does need a light touch.
A correctly specified wheel cutting freely, used with a light touch should work for hand sharpening without a need for dressing for many months.

Some basic information on wheels here without too much marketing spiel and going into the full technical aspects.

Can't envision ever using a grinding wheel to the extent that I would wear one down that far in my lifetime in a hobby shop.

 

[Rhossydd]

Can't envision ever using a grinding wheel to the extent that I would wear one down that far in my lifetime in a hobby shop.

I bought my first one(by Elu) in about 1987 and it's lost an inch in diameter with pretty light use since then. I hope I'll wear at least one more out yet

Yes, I understand about spec being important, but price for apparently the same spec can vary by huge amounts. Do the cheap ones wear faster ? more unevenly ? fall apart ? less well balanced ? clog up more ?

 

[CHJ]

Wheels made to the same specification and carrying the same international code should respond the same.

 

[Rhossydd]

Wheels made to the same specification and carrying the same international code should respond the same.

Er 'should' ???
Come on, we all know that things made to the same specifications by different companies can perform differently. What I'm trying to find out is why some cost more than others, surely it can't all be down to overheads and packaging.

 

[CHJ]

Wheels made to the same specification and carrying the same international code should respond the same.

Er 'should' ???
Come on, we all know that things made to the same specifications by different companies can perform differently. What I'm trying to find out is why some cost more than others, surely it can't all be down to overheads and packaging.

You tell me, your the expert that needs to know if a 5" wheel is usable.

 

[Rhossydd]

You tell me, your the expert that needs to know if a 5" wheel is usable.

I'm no expert, that's why I'm asking here.

You're confusing two different questions;
1. When do people think a wheel needs changing, ie is the hollow grind from a 5" wheel too great ?
I'm just seeking others opinions, experience and ideas.

2. What are the differences in quality between cheap and expensive grinding wheels ?
Has anyone found cheap wheels to be a problem in use ?

 

[winemaker]

I am probably the last person who should give grinding advice.
I have just been reading the Keith Rowley book, in it he says it is best not to use a wheel of less than 5" diametre.
Personally I mostly use the face for grinding simply because I was taught to grind metal working tools that way. there are similarities and differences between the way wood and metal


You should never use the side of a grind stone it can shatter :!:

 

[woodfarmer]

I am probably the last person who should give grinding advice.
I have just been reading the Keith Rowley book, in it he says it is best not to use a wheel of less than 5" diametre.
Personally I mostly use the face for grinding simply because I was taught to grind metal working tools that way. there are similarities and differences between the way wood and metal


You should never use the side of a grind stone it can shatter :!:

True, but they can also shatter when being used on the outer rim. The difference is if you are using the outer rim you are in the line of fire. When face grinding its a bit like standing at the tailstock, not so likely to get hit if the workpiece flys apart on the lathe.

All of the tools from Crown were face ground at the factory as they were absolutely straight and not concave at all. Which is why when I sharpened them on by face grinding they just to about 3 light wipes as I wanted to remove as little metal as possible. So maintained the original angles. If they had been concave at all the first wipes would have touched only the cutting edge and the ends of the bevels. In the factory where I was taught the grinding machines had flat work spaces on the end faces and water on those faces. However that was 50 years ago and times and practices change. The wheel I have is made wider at the outsides.

 

[Richard Findley]

I'm no expert on grinding wheels, just a woodturner. As far as I'm concerned, grinding on the side of the wheel is considered bad practice, and with proper guarding should be virtually impossible. Standard bench grinders aren't designed to be used like this.

Tool manufacturers generally use a very large grinding wheel to sharpen (like 5ft diameter) although they could possibly have used a flat wheel, I suppose?? If you are determined to get a flat grind, then get a belt sharpener like the Sorby.

The other thing to remember is that tool manufactures have no idea how to sharpen turning tools!! Don't worry about initially grinding away steel. Once you have a good shape then all you will do is clean the bevel each time you sharpen.

Hope this helps

Richard

 

[Richard Findley]

Just to answer the original question. I would think 5" is about as small as you'd want to go but I always take the heel off of my tools so it matters less. I use an 8" grinder and over the last 5 years I've used about 2" of it. I do know one pro that reckons he uses an 8" white Record stone per year. I reckon he either grinds waaaay too much or Record make their wheels from cheese!

Richard

 

[SVB]

To add another thought - it could be said there is an advantage to a worn wheel in that the peripheral speed will be less so reduced chance of overheading tool but that is really only relevent with bad sharpening practice that will struggle with the smaller wheel so, given cost of the rest of your kit I'd just bite the bullent and buy a new wheel!

S