When sharpening a knife, using the SG-250 (220 grit) followed by the SJ-250 will leave a scratch around the heel. Is there a solution?
Did you follow the recommended procedure of grading the SG fine before using the SJ?
Ken
SJ wheel diameter appears to be slightly larger that your SG stone, leading to a mismatch in the angles. Probably too small to readjust, just hone that area a bit longer.
I recommend adjusting hte jig for SJ 1 or 2 degrees higher and justing honing the edge, not the full bevel.
The real issue isn't a problem with the SJ wheel, (or even the Tormek). The issue is the design of the knife where it meets the plunge line at the heel. That little "flare out" causes the sharpening medium to improperly contact the stone, resulting in an ever so slightly uneven grind in that area. It's also why you have a second area in front of the yellow circle that is similar, but smaller. The uneven grind isn't noticed until the polishing wheel, because the coarser wheel makes enough contact and grinds enough steel away to make it look OK, but since the finer wheel is just polishing, it doesn't remove enough steel to overcome the uneven grind.
The best solution is a "sharpening notch" or "sharpening choil" (an internet search will give you more info). 2nd is to grind a bit on the part where it flares out... this will result in a wider bevel in that area. But since neither option is a particularly good one... especially on a customer's knife, or if time is an issue... the best option is to try and insure that the edge of the coarse wheel stays in front of the area where it flares out... this will keep the bevel even. (Over time a slight "bump" will occur at the flare out point... this can be ground away at 90 deg. on the wheel).
In your example, since you've already sharpened it... you might try spending some more time on the polish wheel, and see if you can improve it... you can also use the microadjust to slightly raise the angle to help polish it out. And try and insure the wheel doesn't "ride up" on the part that flares out. (Also don't concentrate too much in one small area... make sure the bevel stays even).
Quote from: Ken S on November 06, 2017, 01:17:28 PM
Did you follow the recommended procedure of grading the SG fine before using the SJ?
Ken
No. My procedure is SG-250(220grit) -> SJ-250.
Quote from: stevebot on November 06, 2017, 01:21:28 PM
SJ wheel diameter appears to be slightly larger that your SG stone, leading to a mismatch in the angles. Probably too small to readjust, just hone that area a bit longer.
I recommend adjusting hte jig for SJ 1 or 2 degrees higher and justing honing the edge, not the full bevel.
You're right. My SG-250 is smaller than the SJ-250. However, the result is the same when using SB instead of SG. SB is larger than SJ.
And the results were worse when I honed the whole edge for the same amount of time. The photo is the result of honoring Heel a little longer.
The rest of the edge is normally honed, so I think the way to raise the US a little is not a complete solution.
Quote from: sharpco on November 07, 2017, 01:59:13 AM
...
And the results were worse when I honed the whole edge for the same amount of time. The photo is the result of honoring Heel a little longer.
While it's possible that a stone can become contaminated somehow, I highly doubt that is what is going on here. A contaminated stone won't show worse results the longer it hones. Honing... essentially polishing at this stage, requires that the edge/bevel be properly prepared, otherwise the polish level will "bring out" any imperfections from the previous grind. The scratch pattern from your photo is so typical of what I described earlier, I would be surprised if it were something else. A polish stone won't polish, then start scratching up the bevel... rather it will simply show or bring out the imperfections. (One reason leather won't do this is it adapts to the imperfections).
Quote from: sharpco on November 07, 2017, 12:07:27 AM
No. My procedure is SG-250(220grit) -> SJ-250.
If you're going for polish, it would be better to grade the SG stone "fine", prior to moving to the SJ stone. Not only will it make scratch removal easier, but it will provide a better surface for the polish stone.
Quote from: cbwx34 on November 06, 2017, 03:15:33 PM
The real issue isn't a problem with the SJ wheel, (or even the Tormek). The issue is the design of the knife where it meets the plunge line at the heel. That little "flare out" causes the sharpening medium to improperly contact the stone, resulting in an ever so slightly uneven grind in that area. It's also why you have a second area in front of the yellow circle that is similar, but smaller. The uneven grind isn't noticed until the polishing wheel, because the coarser wheel makes enough contact and grinds enough steel away to make it look OK, but since the finer wheel is just polishing, it doesn't remove enough steel to overcome the uneven grind.
The best solution is a "sharpening notch" or "sharpening choil" (an internet search will give you more info). 2nd is to grind a bit on the part where it flares out... this will result in a wider bevel in that area. But since neither option is a particularly good one... especially on a customer's knife, or if time is an issue... the best option is to try and insure that the edge of the coarse wheel stays in front of the area where it flares out... this will keep the bevel even. (Over time a slight "bump" will occur at the flare out point... this can be ground away at 90 deg. on the wheel).
In your example, since you've already sharpened it... you might try spending some more time on the polish wheel, and see if you can improve it... you can also use the microadjust to slightly raise the angle to help polish it out. And try and insure the wheel doesn't "ride up" on the part that flares out. (Also don't concentrate too much in one small area... make sure the bevel stays even).
The plunge line is not the only cause. This is because a similar phenomenon is seen in a knife without it. Around heel, there is always a tendency not to be honing properly.
Quote from: sharpco on November 08, 2017, 09:33:49 AM
The plunge line is not the only cause. This is because a similar phenomenon is seen in a knife without it. Around heel, there is always a tendency not to be honing properly.
1st, I still think it's a knife design issue, for which you'll have to adjust your technique. Whether or not you have an obvious plunge line... a bolster in the way, original grind, etc., all can contribute. Technique will solve it.
The 2nd thing to look at is sharpening technique. One thread you might take a look at is "Middle Overgrinding Problem (https://forum.tormek.com/index.php?topic=3055.msg16402)" by wootz... and see if there might be a clue in there that will help. (Nice sharpening notch shown in the 1st photo over there, btw).
I always "return to the basics" when checking technique.... mark edges with a Sharpie and make sure I'm properly removing metal where I want (at each step of the process except honing on leather), look at how the water flows over the knife to insure proper contact with the stone, etc. I would in particular, mark the edge with a marker, make a pass, and see what it going on, especially in the heel area of the knives you're sharpening. You might find you'll need to make a slight adjustment in the heel area, by slightly tipping up the knife, to insure you properly contact the area.
And 3rd, as mentioned in the other thread you started, check the equipment... true the stone, clamps working properly, blade clamped properly, double check angle settings at each step, etc.
Thank you so much cbwx34.