matt_southward":2qxm0zxe said:
bugbear":2qxm0zxe said:
I can recommend diamond stones for this kind of grinding/tuning. About the right level of grit, and reliably flat. BugBear
This was my experience exactly. I
thought I'd tuned the cap iron before - on oilstones - but after buying some diamonds stones a few weeks ago (and after wading through this thread) I went back to it on the diamonds and they did seem to give me the results I wanted more easily. I'm certainly happy with it now. I tried it on some fairly coarse mahogany earlier, and the surface sheen was lovely.
Matt, just a mention and I think it's been touched on earlier. If/when tuning this close the cap becomes as critical as the cutting edge of course, and the leading edge of cap has to be perfect straight (assuming iron back is dead flat where they will mate). I think there are these essentials:
1] get a small degree of clearance behind the leading edge on the underside - aim for a line of contact with 'nil' area. We know nil is impossible but that is the target. The clearance angle can be small but there needs to be one to be certain the leading edge is contacting totally, right across.
2] Raise the leading edge angle of the cap - consensus here seems 50 degrees, I have been doing roughly 60 (by eye) but thereabouts. Just a ribbon along the edge, noting the shavings are v thin so this surface strip can be.
3] Important bit - use a medium you know to be flat (stones are not flat for this purpose) and get 2 flat planes/surfaces meeting at the leading edge of the cap. Only this way can you be sure to have a truly straight line of contact. Make the 2 surfaces fine, finishing on about the finest flat medium you have. Check and remove any wire edge that may have formed. I run a final 10 second check. A flat surface held to the edge and check no light through (I use a sine bar!, be careful if using a straight edge, a flat surface object is better).
Good news - once done well, you will hardly need to touch it again for a long time. And any appearance of micro-dust in that contact line is a sign it needs more work.
Sorry if this is obvious or covered in sections elsewhere, but I think this is the complete prep process.
edit: re diamond stones BB, good ones flat but many not I find. Just best to check.