bench grinders

Hello,

I'm looking to get a bench grinder to sharpen some chisels. I see some have discs six inches wide, others are eight inches; is one any better than the other?

Is there anything else to look for? Should the power be a certain number of Watts for example?

I see most grinders have two discs: a coarse and a fine one but a few are wet and dry. Is there any advantage to a wet and dry one, and if so, why aren't they more prevalent? Why is the wet disc always at right angles to the body?

Thanks, Stephen.

Reply to
Stephen
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Bigger is vaguely better, as the resultant grind has less of a hollow to it. However this is a very minor point.

I'd strongly recommend the sort with a 10" slow water cooled wheel.

Double-ended coarse/fine fast grinders with small wheels are OK for most metalworking applications, such as cold chisels and HSS lathe tools. However we now have angle grinders for many other tasks and there just aren't that many things for which is the best sort of grinder.

For woodworking tools, these grinders are much too fast, too hot and rather too coarse too. They're better than nothing if you want poor results on HSS woodworking tools in a hurry, but that's about it. I wouldn't even use them for woodturning tools (which are generally more robust to abuse in grinding). In particular, they'll ruin good edges in good steels by overheating them.

If you do see a woodworking grinder, then it's usually slow-speed, large wheel diameter and water cooled. I've a Record one (rebadged Scan) that's quite cheap, the popular Tormek is 200 quid+ and there are some Creusen grinders that are very similar to the typical metalworking grinder, except for running at half the speed (1425, not

3450).

A useful compromise for the DIY workshop is a cheap (I've seen 30 quid) double-ended grinder with a worm drive to a 10" wet wheel. They're noisy, the wheels are a bit too coarse and the dry wheel is on the small side, but they're 30 quid... These are useful for woodworking tools, the wet end at least. I use mine for the woodturning tools and for initial shaping of newly forged tools or refurbishing and reshaping of old damaged S/H chisels. Then it's the Record for rough grinding, then hand stones for actual sharpening.

Reply to
Andy Dingley

By wide I assume you mean diameter? It's easier to use larger diameter wheels on most materials - but that may have been because the large ones were used professionally so were always well dressed. (I must get round to doing mine...)

Not usually a problem unless you intend to grind thick stock.

Yes, for chisels and other hardened and tempered tools a slow, wet wheel is practically mandatory as you'll probably draw the temper using a fast, dry wheel, ruining the item being ground.

The wet wheel is usually at right angles to the high speed shaft to accommodate the gearing slowing it down considerably from the dry wheel speed, connected directly to the motor shaft.

Reply to
John Weston

Stephen formulated on Tuesday :

Wood chisels, or some other type of chisel?

Diameter, rather than wide?

The greater the diameter, the wider will be the edge face of the wheel and probably the more powerful it will be for grinding heavy materials.

No - the larger and heavier the wheels, the more power will be needed to make them turn and grind (see above).

A wet wheel will prevent the material being ground heating up and loosing it's temper. You can get the same by grinding gently and dipping the tool tip frequently in a water bath to keep it cool during grinding.

The important thing to remember is that the RPM of the grinder means little, what matters is the speed that the edge of the wheel will pass a tool which is being ground. The faster it moves and the more course it is, the hotter the tool tip will become.

For gentle grinding of wood chisels, the Plasplugs 4 in 1 unit is quite good for these and also does various types of drill bits and helps make sure you get the correct angles. The go for around £50, but I recently saw one in a shop for just under £25, special offer. I have one of these, a 6" and an 8" grinder.

Reply to
Harry Bloomfield

If its wood chisels .. then just use an oil stone (or diamond if you have money to burn) ... a grinder will be too fast & too coarse, and probably take temper out of chisel as well.

I bought a record plane & chisel guide for use on oilstones ... at least 25 years ago ... stills works perfect.

Reply to
Rick Hughes

Mostly agree with the above, although I was taught to grind chisels and plane irons on a fast dry wheel - but go gently and be really vigilant about overheating.

Possibly where a fast wheel is better is when you chip a tool and have to remove a bit of material - again being ultra-careful about overheating.

Oh and make sure the tool rests/jigs are to your liking and cover all the tools you're likely to want to grand.

Reply to
RubberBiker

Cold chisels and sds chisel bits were what I had in mind. It sounds as though for these types of chisel a dry grinder is ok but if I wanted to sharpen wood chisels I would need a water cooled one?

Reply to
Stephen

That explains it. Thanks.

Reply to
Stephen

Sorry, I was not very clear in my OP. I was talking about cold chisels, bolster chisels and sds chisel bits, and you and the other poster are quite right, I meant diameter.

Are they all induction motors, and if not, is induction preferable?

Why do you need both a 6" and an 8"? Is one more suited to one task than another?

Thanks.

Reply to
Stephen

I have been browsing a few online shops and it occurs to me you may have one machine with a 6" wet wheel and an 8" dry wheel. Is this right?

Reply to
Stephen

Stephen has brought this to us :

The bigger the better then, if you intend to do many. 8" as a minimum.

The SDS is a different beast. Probably a 6" would do for that, but it will need a special wheel called a green grit wheel. The normal blue/grey will not even mark the carbide edge.

Yes, certainly for this size of grinder.

The 6" is better suited for drill bits and HSS lathe bits. The 8" does the courser and heavier work and is twice the power.

No problem.

Reply to
Harry Bloomfield

Stephen formulated on Wednesday :

I have never heard of one, but there is no reason why not. Probably the best of both worlds - but you still need a means to grind the SDS.

Reply to
Harry Bloomfield

Stephen formulated on Wednesday :

Probably you could get away with a fine wheel, gentle grinding and dipping frequently in a water bath.

Reply to
Harry Bloomfield

Cold and SDS chisels will be OK as they are tempered differently from a wood chisel.

Cold and SDS chisels have a much greater mass to absorb the heat generated as well. However, they don't need heavy pressure on the wheel. Blueing them is not a crime, as that is what colour they are tempered to in manufacture.

Grinding anything is not about loading the grindstone wheel, but about getting a feel of grinding. If you want to grind something quickly, revert to the DIY favourite, the angle grinder.

In fact, what would the group's opinion be on that?

Wood chisels are tempered to a lower temperature of straw coloured. That gives them a much harder edge, but much more liable to chipping that edge. Blue one of those and you have 2 ways out.

Through it away, or start the hardening and tempering process all over again.

Not

Dave

Reply to
Dave

Dave explained :

No problem, I do it all the time.

Reply to
Harry Bloomfield

Go to your local 'shed' and look for one. If you find one, spin the smaller wheel with you finger and see how fast the other wheel spins. It must be slower, otherwise. you have got the wheels mixed up.

Wet wheels are usually larger and wider.

Dave

Reply to
Dave

Well, that is one comment :-)

Dave

Reply to
Dave

How many of these are you realistically planning on sharpening?

I have several "old style" grinders and rarely use them (lathe tools only). On the rare cases when I do need to sharpen a cold chisel, I'm usually on-site, up to my ears in plaster dust and have an angle grinder with me but not a bench grinder. You can imagine the rest...

Yes. This depends somewhat on the steel used and the quality of both chisel and the work you're planning for it, but broadly yes.

You'll see woodworking tools, particularly Stanley plane irons, advertised as using chrome molybdenum vanadium steels. This is a _bad_ thing in a plane iron - the steels are softer, "gummy" to sharpen and you can't get a good edge on them (my notion of "good" is pretty high here). These HSS-like alloys are used because they increase the softening temperature of the steel, thus allowing them to be ground in factories on fast, dry air-blast wheels, thus reducing costs. Note that you can't have a grinder like this yourself - you won't get the cooling air jet (serious HSE issues involving dust extraction), so you're going to be running even hotter.

The best chisels around are 50+ year old Sheffield-made chisels with very simple alloys of high carbon steel, particularly if you can find laminated ones. These are fairly easy to sharpen, but do need to be kept cool if they're not to draw the temper. Any powered grinding needs to be wet. For another thing, the angles are more acute, so an edge has much less "body" behind it to distribute heat by conduction. Then their final grinding (bevel & honing) really needs to be done by hand (only takes moments) because a mechanical wheel would have to have very expensive bearings to give the necessary stability.

I'd strongly recommend a starter sharpening kit for woodworking of a cheap powered wet wheel for resurrecting car-boot sale chisels, a cheap combination waterstone (1000 / 4000 grit on each side) and a read of Leonard Lee's "Sharpening" book. You might find Scary Sharp worth a look too (silicon carbide wet & dry paper stuck to glass). Oilstones are a pain, diamond and ceramic are expensive for good quality.

Reply to
Andy Dingley

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