Originally Posted by
IanW
Well, this thread has ceratinly drawn some strong opinions from the crowd, and gone off at a few tangents, so perhaps a bit of summing-up is called for? As I see it, the original post shows that that simply moving a cap iron over some pretty small distances, all else being equal, can make a significant difference to both the appearance of the shavings, and the surface quality. As a (former?)believer in the cap-iron-as-stiffener-only theory, I find that an interesting result, at odds with my own views and experiences, and it begs some sort of explanation, whatever it may be (I certainbly don't have one at this stage).
I will have to trawl through the links to see if there are any plausible suggestions as to exactly what the cap-iron is doing at its 'sweet spot', but so far no-one has offered what I could accept as a full explantion in this thread, unles I missed it.
To me, it was demonstrated clearly that you can set too close (this is definitely my own experience, too, & obviously that of others), which to my reasoning, doesn't sem to fit with the chip-bending theory. Someone worked out (can't remember where I read it) that the average beam-strength of a shaving is so small, that the bend would have to be starting right at the cutting edge to have any effect, not 0.3 of a mm back from it, which is about 10-12 times the thickness of a fine shaving. So if bending of the fibres to break them at the blade contaact point is the explantion, either their calculations were wrong, or wood fibres have a much higher stiffness in micro sections than they have in thicker sections (which is quite possible, as many materials are 'stronger' in ultra-thin sections than thicker section strengths indicate).
As some other posters do, I rely on experience and guess-work when setting cap irons. I was taught as a lad to set at a 'fat 32nd', which is around 1mm, for general work, and a 'fine 32nd', which is perhaps .6-.7mm, for fine work. This seems to work for me for the majority of situations. I have never had much luck setting finer than about 0.5mm, and then only for very fine shavings. If I dial for a coarser cut, I am soon getting crinkly shavings that jam the thoat and work under the cap iron, which defeats the exercise utterly. Having highly polished cap-irons helps, but doesn't eliminate the problem, for me. I expend a good deal of effort in getting my cap-irons & blade backs mating as perfectly as I can, but admit they may not be absloute, so there is one area that could be improved.
I think the message from the 'experienced' set is that cap-iron settingss are important, but just one factor in a complex equation. Blade sharpness, cap-iron fit, general seaworthiness of the plane itself, and of course the wood being atacked, all make a big contribution to results. Not only that, but we all have different ideas of what will do "off-plane", based on our personal skill, equipment, and need to get the job done in a time that will pay the rent. Some strive to get a polishable surface with planes only, while others are happy to knock the rough off, and finish with scrapers, abrasives, or whatever is their weapon of choice. (And please don't get into the argument about which leaves the perfect surface in this thread - start another! :U)
If I were instructing a beginner in hand-plane use, I think I would still advise sticking with the settings I was given, as a good starting point, until the person became proficient with sharpening & general plane use. Once you are happy with your general abilities with the tool, if you are the inquisitive kind, start playing about with specific settings for specific purposes. Which is of course, where Derek is at........
Cheers,