I’m having a heck of a time getting that nice first-time polish on my plane iron backs and can’t find any resources to help me figure out what I’m doing wrong (the Sharp-fast article in FW I got a day or two ago was well-timed, but didn’t help me). I have a couple of Stanley blades and a couple of Groz blades and they both do similar things… I’ve gotten them flat using a combination of sandpaper and/or emery cloth on a granite stone, diamond stones, and water stones – generally in that order. When I’m on my finer abrasives – the 4000 and 8000 water stones – I can only get spots of polish on the back and the remainder stays a dull sheen. The polished areas change from one viewing to the next – I check progress, see some polished spots and think I’m on the right track, then work a bit more and check again and find either the polish is gone altogether or has moved.
I have a high quality Pinnacle straight edge that I’ve used to check all my equipment to make sure it’s flat and have been flattening my water stones during use to make sure that isn’t the problem (not so often as to lose all the slurry, but maybe every 5-10 minutes). I’ve tried high pressure and light pressure, long strokes, short circular strokes, keeping the stones very wet, letting them get a little dry, returning to coarser stones thinking the blades weren’t actually flat yet, and still no luck. When I flattened the soles of my planes, I did it all with sandpaper and am guessing I could have similar success with the plane irons… but at this point it’s as much of an issue out of principle as anything else (not to mention that I’d like to get more value out of my water stones and not spend more money on sandpaper).
Any ideas or pointers?
Replies
Lapping
Buck,
You only need to get about a half inch of the back flat. The purpose of this lapping is to provide an even edge all the way across the iron. The rest of the iron does not touch the wood and getting it shiny would have no affect on its performance.
Jim
back polish
I agree with Jim's post regarding limiting the area one attempts to flatten and polish. Enlarging that area adds only frustration to the process without adding any actual benefits.
As to the meandering mirror effect, I suspect you may not be spending enough time with the coarser grits to get the iron really flat before moving on to the fine grits for polishing. Remember, the primary purpose of the finer grits is simply to remove the microscopic grooves left by the coarser grits, not to further flatten the iron.
How meticulous are you at maintaining the flatness of the waterstones? It won't take much out of flatness to show up in the polishing effect.
I agree that you need only polish the last 1/2", but you need to flatten more of the surface to ensure good mating with the frog. That is don't create a "bevel" on the last half inch by concentrating on just that area with coarser grits.
For that matter, I'm a bit leary of using sandpaper on granite, etc. Unless VERY good technique is used it's more possible to dub the edge a bit, making it very difficult to get a really flat edge where it counts with the finer grits.
Thank you and good points
Thanks to everyone so far for their thoughts. I should better explain that my motivation for this is to understand what is really possible in terms of sharpness and sharp longevity. I have gotten good results planing with blades that were not perfectly mirrored, but then I felt like the blade dulled rather quickly and want to see how much better that gets with a sharper edge (i.e. better polish indicates fineness of the surface finish and therefore sharpness). And of course, the other motivation is that when I finally get through my plane blades, there's a set of chisels waiting to be flattened and sharpened.
I am working on only about 1/2-1" worth of the back depending on the iron - two are relatively small, one is medium, and the other irons are larger. I have not worked the entire blade back flat, but like was mentioned I did want to get a good seating on the frog - plus it's practically easier (at least for me) to work an area that size than to get much smaller. I can try the ruler trick Puchalski covers in the recent FWW issue and circumvent a lot of this... but like I said originally, I'd like to understand the principle as much as anything else at this point. For the Groz blades I wonder if the material quality is part of the problem; these are obviously not the top shelf tools, but I was shocked when I put my straightedge to the blade back. It made me wonder how much material hardness varies across the blade and if that's contributing to the uneven sheen.
Especially after the replies here, I tend to think I must not be truly flat coming off the 1000 grit stone, but I've only moved past that after getting as uniform a finish on the blade as I can detect.
I'll take another stab at it when I get some time, hopefully this weekend. If I think of it, I'll take a few pictures and post them.
mirror polishing...
some other methodology that you might want to employ are the use of buffing wheels (don't bear down on them or you'll actually dull you blade- a gentle touch is best...
turn an MDF circle on yer lathe, charge it with green buffing compound and use that as a grinding wheel to get the mirror finish...I think Sorby markets a similar methodology as the "ultimate" sharpening system for lathe tools.
and if you can get a sharp cutting edge on a tool, that is the most important, you don't have to re-hab the entire tool all at once. sometimes it takes a while...
focus on achieving the required result, and then augment/expand the methodology.
When I'm rehabbing edge tools, I realize that sometimes I ain't gonna achieve Nirvana all at once, and I'm a patient fella.
Like friendship, it don't happen perfectly all at once, you gotta work at it in stages sometimes...
Eric in cowtown.
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