I basically got told I was an old foggie in a discussion on this last night !!
My friend is of the opinion that chisels and plane blades are nowadays always sharpened with just one bevel - that the DIY FAQ for instance is out of date saying that there is a 25 deg. bevel and then a cutting edge at 30 deg. for a chisel and so on. His premise is that the 'modern thinking' is that the whole face is just set to 30 deg.
Such shaping would be in line with wood turning tools where a double bevel inhibits proper rubbing of the tool on the workpiece before cutting, and also with inexpensive chisels and plane blades where it is obviously cheaper just to do one grind.
The collective's opinion would be appreciated before we do battle again on this subject !
I like to have my chisels with an edge honed on 2000+ grit. The important thing is the flatness of the back. I like the back to be like a mirror for the final inch - again 2000+ grit does this.
So. I grind the bevel at 30 deg. then put a polish on the whole of it with successive grits to 2000. Then I finish with the minutest 25 deg. bevel - it's just a barely visible line. When the line gets to about
2mm wide, I regrind.
Mortice, turning and carving chisels are different, so are plane irons for hardwood. I need the sharpness, but also a strong, well-supported edge. Many of my irons are very old, some are Japanese, but modern irons can be very good - the ones from China in the 80s and 90s are useless though.
All that being said, if it was a plastic-handled chisel for building joinery, I'd probably just grind a 30 deg. every morning and have done with it.
I bought a cheap set of wood chisels from Wickes a while ago
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the pack it said; "Ready ground cutting edge for immediate use". Having looked at them & only seeing one angle I took them back & queried it.
Usual blank look from Wickesdroid who clearly had no idea what I was talking about.
I notice on their web page it says "Ready ground cutting edge to 30 Deg angle for immediate use. To re-sharpen or if finer edge is required, use Honing Guide".
Having said that, they are pretty sharp & OK for undemanding work.
Even expensive "ready for immediate use" chisels rarely are (unless it's the likes of Lee Nielson - though I suspect those just get admired and put away again, without getting used).
The main thing wrong is the backs haven't been ground, and need quite a bit of flatting on a stone, if they're ever going to take a really good edge. In fact I was taught to flat the backs a little every time they're retouched on a stone (critically important with plane irons).
Stick to the 'old fogies' ways - the 25 degree bevel gives the blade edge 'strength' and the 30 degree bevel gives the nice sharp edge and the 'clearance' to get rid of the waste.
The 30 degree edge is *NOT* a modern day thinking by the way! I experimented with this many years ago and found that whilst it had some uses in heavy, site work - it lacked (to me anyway) that extra 'cutting' edge which enabled fine and delicate works to be easily cut.
Machine cutting tools and hand tools are two different things - you wouldn't use lathe tool to cut or trim a hinge housing or dovetail joints and conversely, you would use a bevel edged wood chisel to turn a bowl on a lathe (at least I wouldn't).
Try and pick up a very old book with the title of Planecraft, published by C & J Hampton Ltd, Sheffield [1], which give a mass of information on how to look after and sharpen the blades of different types of planes - I have found it very useful when having the odd 'technical' discussion in site cabins on rainy days over the years.
[1] The diagram in this book states that the Grinding angle is 25 deg and the Honing angle is 30 deg and then goes on to describe the reasons for this (I have printed a very short excerpt below):
-------------------------------------------------- The cutting edge as left from the grindstone, whilst of the correct bevel, is far too coarse to do the fine work a woodworker requires. The craftsman knows that a keen edge is not only productive of better results, but that those results are more quickly obtained with less expenditure of energy, so he never begrudges the time taken up in sharpening. Whetting or honing the edge is undertaken much more frequently than grinding, and results in a little bit being honed off the blade each time until the blade assumes a shape such as that of a "thick" blade, Fig. 53, B. Then the blade is ready for grinding once again. It must not be assumed that the oilstone merely burnishes or presses the edge of the blade. The oilstone has a true cutting action like that of the grindstone, but it cuts more slowly and leaves a keener edge.
(From Planecraft, published by C & J Hampton Ltd, Sheffield )
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Bound to get a few differing and conflicting replies on this, so I'll end with:
But as usual, what is one mans way, may well not be another's - and both will often produce the same results.
I use the 30/25 for both types of wood and simply adjust the mouth of the plane [1] to get the best results (narrowed for hardwoods and widened for softwoods).
[1] This is for the modern day planes and not the old wooden smoothing/jointer/jack planes by the way.
There is another way which I have found to be very quick and efficient but given the high-quality tenor of the answers above will, I fear, and with some justification, be regarded as somewhat sacreligious but which does have the great advantage of speed and functionality. I grind the blade on a large diameter angle grinder at the preferred 30 degrees odd (not particularly accurately) and this produces a concave surface on the cutting edge which I merely put an edge on. As one gets to the end of the process a lip of metal hangs on the end which I progressively attack from back and front alternating the action on the stone until finally it floats off and hey presto both back and front of the blade is perfect chris
I don't have a grinder, and I put a nasty nick in the end of my plane iron trimming a door (there was a nail buried in it). I was doing this for a friend, so when she heard me curse she offered to pay to have it ground. When it came back from the shop it had been ground all the way across at 30°. Grrr. Aside from anything to do with cutting angle and clearance angle, this is a real pain because every time you want to perk up the edge a bit you have to grind the whole face. With 30/25 you can get away with doing a few quick sharpens at 30° and only doing 25° every third go or so.
Double bevel is cheaper. You rough grind with one pass, then fine grind to the second pass. Unless you're in the absolute bargain bucket and are leaving the finish from a coarse grind, this means you're taking two passes anyway.
If the second grind is at a slightly steeper angle, it has to remove far less metal. This is cheaper, as the grinding takes less time.
It is however common to describe the first pass ans "grinding" and the second as "honing". This allows cost-cutting by claiming the old canards that "proper woodworkers insist on doing their own honing" or "Honed tools go blunt / get damaged on the retailer's shelf". This is of course rubbish: buy a Veritas tool from Lee Valley and it's razor sharp out of the box. OTOH, Hock Tools (about as posh as plane irons in modern steels get) are infamously poorly ground and expect you to do half of the work for them.
Read Planecraft, and if you've read that, read Leonard Lee's book on Sharpening (that's Lee as in Lee Valley tools, so he does rather know what he's about).
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