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I'm no expert, but I'm learning....
I recently took on the task (finally) of doing a better job of flattening/polishing the backs of my chisels. Also, very recently (last night), I received my Lee Valley medium shoulder plane (sideways gloat!), which comes with a blade having an already-lapped back side (the new standard for Veritas).
Since I have access to a sweet optical microscope, I thought I'd snap a few pics to show what I'm learning about sharpening. Although I didn't take the time to set this up as a nice before/after sharpening experiment, I think you can get the idea by regarding the shoulder plane blade as the "before", and the chisel as the "after".
First, here's a photo of the backs of two blades. The 1/2" Marples chisel is on the left, and the lapped, but not yet polished medium shoulder plane (MSP) blade is on the right:
My backside lapping/polishing routine (Scary Sharp) for the chisel started at 150 grit (and stayed there for way too long for flattening), and progressed up to 2000 (by way of 240, 320, 400, 600, and 1200), finishing with green polishing compound on a leather strop. In comparison, I plan to polish the back of the MSP starting with ~600 grit, and working very quickly up to 2000.
Here's a couple micrographs of the 1/2" chisel backside (see scales in photos for an idea of the magnification):
Low mag:
High mag:
In the high mag photo, you can just make out the starting of edge breakdown. (This chisel has been used some since the last sharpening.) But stand by to contrast that amount of edge break-down with the MSP blade.
As I said, the MSP blade came pre-lapped, which is a huge bonus IMO, but it was not polished backside, and the bevel was sharpened an unknown amount, and not honed. That having been said, with absolutely no polishing/sharpening/honing by me, after popping the blade in, it cut a fairly nice shaving with the grain.
But, between that, and banging it into some edge grain, the edge is very quickly breaking down, as shown in the following three micrographs; the first one being low mag, the second (high mag) focussed higher up on an edge fold, and the third (high mag) being focussed on the backside:
Low mag:
High mag, focussed up on the fold:
High mag, focussed down on the backside:
I think this breakdown is either attributable to using the edge before doing a better job of sharpening/honing, and perhaps leaving some remaining amount of burr which is folding, or perhaps the bevel angle is too acute to support the edge. If the latter, I'll need to put on a micro bevel. If the former, I'll be good to go once I correctly sharpen this thing. Either way, I should be slapped for punishing such an awesome blade like this; I don't expect to see it in this shape again.
But, I think there's still a take-away message here about doing a good job of lapping the backside to remove the sharpening burr, and to sharpen to higher grit to lengthen the time between sharpening. Hmmm, seems like a mantra I've heard before....
And, if you don't have access to a $100k+ optical microscope, may I suggest my home version:
Radio Shack, 60-100x optical loupe, $10. I tricked mine out with a white LED for much better illumination.
Regards,
Tom
I recently took on the task (finally) of doing a better job of flattening/polishing the backs of my chisels. Also, very recently (last night), I received my Lee Valley medium shoulder plane (sideways gloat!), which comes with a blade having an already-lapped back side (the new standard for Veritas).
Since I have access to a sweet optical microscope, I thought I'd snap a few pics to show what I'm learning about sharpening. Although I didn't take the time to set this up as a nice before/after sharpening experiment, I think you can get the idea by regarding the shoulder plane blade as the "before", and the chisel as the "after".
First, here's a photo of the backs of two blades. The 1/2" Marples chisel is on the left, and the lapped, but not yet polished medium shoulder plane (MSP) blade is on the right:
My backside lapping/polishing routine (Scary Sharp) for the chisel started at 150 grit (and stayed there for way too long for flattening), and progressed up to 2000 (by way of 240, 320, 400, 600, and 1200), finishing with green polishing compound on a leather strop. In comparison, I plan to polish the back of the MSP starting with ~600 grit, and working very quickly up to 2000.
Here's a couple micrographs of the 1/2" chisel backside (see scales in photos for an idea of the magnification):
Low mag:
High mag:
In the high mag photo, you can just make out the starting of edge breakdown. (This chisel has been used some since the last sharpening.) But stand by to contrast that amount of edge break-down with the MSP blade.
As I said, the MSP blade came pre-lapped, which is a huge bonus IMO, but it was not polished backside, and the bevel was sharpened an unknown amount, and not honed. That having been said, with absolutely no polishing/sharpening/honing by me, after popping the blade in, it cut a fairly nice shaving with the grain.
But, between that, and banging it into some edge grain, the edge is very quickly breaking down, as shown in the following three micrographs; the first one being low mag, the second (high mag) focussed higher up on an edge fold, and the third (high mag) being focussed on the backside:
Low mag:
High mag, focussed up on the fold:
High mag, focussed down on the backside:
I think this breakdown is either attributable to using the edge before doing a better job of sharpening/honing, and perhaps leaving some remaining amount of burr which is folding, or perhaps the bevel angle is too acute to support the edge. If the latter, I'll need to put on a micro bevel. If the former, I'll be good to go once I correctly sharpen this thing. Either way, I should be slapped for punishing such an awesome blade like this; I don't expect to see it in this shape again.
But, I think there's still a take-away message here about doing a good job of lapping the backside to remove the sharpening burr, and to sharpen to higher grit to lengthen the time between sharpening. Hmmm, seems like a mantra I've heard before....
And, if you don't have access to a $100k+ optical microscope, may I suggest my home version:
Radio Shack, 60-100x optical loupe, $10. I tricked mine out with a white LED for much better illumination.
Regards,
Tom
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