No longer achieving shaving sharp
- This topic has 4 replies, 2 voices, and was last updated 05/02/2016 at 2:28 am by
.
-
Your problem is one that gets asked once or twice per year here on the forum. It’s likely that something has changed – maybe your technique or the set-up, but I’d bet that you aren’t quite touching the apex of the edge with your final grits. Depending on the type of stones used, all it takes is about one or two tenths of a degree change (decrease) in the angle to keep you from reaching the apex. You think you’re refining the edge but you actually are not.
Which pivot arms do you have? The simple pin joints or the ball joints with the micro-adjusts?
Do you have a loupe?
You can try the Sharpie method on your final grit, then examine it closely with a loupe to see if you’re leaving a little black right at the edge. I do the alternating direction method. With my USB microscope I can see if the scratch pattern for the direction I just used doesn’t go all the way to the edge. A good loupe should reveal the same thing.
How can technique do it? If your grip placement has moved down on the blocks, the difference can rock the stones down to a slightly lower angle. This can also be contributed to by some source of “slop” in the pivot or the rods. Try to always keep your grip point below the height of the apex – for all the grits. This will tend to keep the angles more consistent.
Depending on how many knives you’ve done over the year, I suppose it’s possible that your higher grits are getting worn. Josh of Razor Edge Knives reports that he gets 400-500 knives of life from his stones.
6 users thanked author for this post.
great! You’ve got the PP2 ball joints with the microadjustments. If with your loupe you see that the scratch lines don’t seem to quite reach the apex, you can make small adjustments to correct this.
In the 20 degree range, the micro-adjusts make just under 0.4 degrees per turn. If the scratches seem to stop near the edge, try turning the screw CCW about 1/4-turn at a time, until you get full coverage with the scratch pattern. For me, the 1/4-turn usually does it.
BTW, the thickness of the stone can change its effective angle. About 0.010″ difference in the height of a stone surface from the rod centerline can account for a 0.1 degree error. It’s possible that one or more of your platens have lifted from their intended positions. I check for this by inserting a 1/4″ rod thru the block, laying it on my granite plate and measuring the height of the rod right where it comes out of the block. I use one of those cheap bridge guages used to set saw blade height on your table saw to measure the height of the rod off the granite face. Record the distance, flip the block over a check the opposite side. Then go to the other end and do the same. Check all your hard stones – not your strops. Should only take you about 4 or 5 minutes per block.
I’ve got a batch of home-made blocks which differ from side to side, so I use the Variable Stone Thickness Adapters (sometimes referred to by the name “SWAT”) and make micro-adjustments with every stone change. It repeats to within +/- 0.1 degree or better and takes only a few seconds.
3 users thanked author for this post.
Thank you so much! I tried the sharpie with every stone change you were 100% correct a quarter turn (or thereabouts) did the trick I redid the knife starting at 1000 grit and now a hair whittling edge again. I do believe a SWAT would be a good investment. Thanks again have a good day.
2 users thanked author for this post.
- You must be logged in to reply to this topic.