Compensating for tilted blade
- This topic has 23 replies, 7 voices, and was last updated 02/01/2016 at 7:16 am by
.
-
Actually, Josh has two math errors in the video. He subtracted the left reading (+0.70) from the right (-4.00) when he should have added them. The object is to find the angular displacement between one side of the blade and the other. Imagine that you have the AngleCube on the left side, reading +0.70. Now rotate the ‘cube to the left to -4.00. To do so, you have to rotate the ‘cube 4.70 degrees, not 3.30. This means the median (centerline) is displaced 2.35 degrees from each face. If the blade were perfectly vertical, it would read +2.35 on the left side and -2.35 on the right side. Since the left side reads +0.70 instead of +2.35, the centerline is canted 1.65 degrees to the left. To compensate, you deduct 1.65 from the left setting and add 1.65 to the right.
So, is it just a coincidence that you get the same result of 1.65 if you take 4-.7=3.3/2=1.65 vs what you posted here? 4+.7=4.7/2=2.35-.7=1.65
2 users thanked author for this post.
Yup.
1 user thanked author for this post.
Yup.
Are you sure? ‘Cause no matter what two numbers you use, either way you do the math, you get the same answer…. seems awfully coincidental. 😉
A couple points/questions… Tom, So how would the math work if you had two positive numbers something like 1+ on the left and 6+ on the right? You would actually subtract them then, correct?
Yes, +1 and +6 would mean the faces are displaced by 5 degrees. The centerline is 2.5 degrees and the blade is leaning 3.5 degrees (2.5 + 1) to the right.
The object of my method is to find the displacement between the two faces so that you know what the centerline is, so you can calculate the amount of cant/lean. In your video, you measured 3.3 degrees, with what you thought was a centerline of 1.65 degrees. The real centerline is 2.35 degrees (4.7 / 2). While your method ends up with the correct offset, for this clamping instance, you can’t use that centerline again when you remount the blade.
For example, if the next time you mount the blade, you measure +1.30 degrees on the left and you subtract that from your old 1.65 centerline, you’ll deduct 0.35 degrees (1.65 – 1.30) from your left rod setting when you should deduct 1.05 degrees (2.35 – 1.30). Your bevels will be off by 0.70 degrees.
So long as you use your complete procedure, you’ll be OK, but you’ll have an incorrect value for the primary grind angles, because your formula is convoluted.
Perhaps this is a big deal for me, because my EDC Delica gets touched up about once a month, and I depend on knowing that the primary FFG angles are 3.75 degrees inclusive. I just read the left face of the blade and bingo – I’m done. Whereas you (Josh) don’t think in terms of the centerline angle – you just depend on the procedure getting you to the correct answer (which it does) and I think this is confusing to those who are trying to understand what and how you are doing this.
2 users thanked author for this post.
- Topics: 14
- Replies: 427
One thing I found interesting to day.. Having a sharp knife, spoils you.
Here is my observation: Formerly, I have been use to semi sharp knives, and because they are semi sharp, they keep the same level of sharpness for a longer time. So you are use to the ability of that edge. So over time you take that edge for granted.
Now that I know what a really sharp edge actually is. I noticed today one of my sharpened kitchen knives was not as sharp as it was two weeks ago. It was noticeable enough, that a Newbie like me, could notice the difference.. ( the less than wicked sharp edge. ) I took it down on my WE and touched it up, ad now it is scary again.
My point to all this, is, When you don’t know any better ( ignorance is Bliss ) you could be happy with a poor edge.
I once owed a 200 dollar Stereo system, I was Happy with it …….. That is, Until I heard a 5,000 dollar stereo system.
I use to be happy with an 8 or 10 dollar bottle of wine. That turned into 15 dollars and 20 dollars, and 30 dollars, and then there is Chateau La fête Rothschild. ( 600 to 1200 dollars a bottle, depending on the vintage ). Thankfully my pallet is not refined enough and I would not appreciate a La fête
The Wicked edge system is the 5,000 dollar stereo.
1 user thanked author for this post.
A couple points/questions… Tom, So how would the math work if you had two positive numbers something like 1+ on the left and 6+ on the right? You would actually subtract them then, correct?
Yes, +1 and +6 would mean the faces are displaced by 5 degrees. The centerline is 2.5 degrees and the blade is leaning 3.5 degrees (2.5 + 1) to the right. The object of my method is to find the displacement between the two faces so that you know what the centerline is, so you can calculate the amount of cant/lean. In your video, you measured 3.3 degrees, with what you thought was a centerline of 1.65 degrees. The real centerline is 2.35 degrees (4.7 / 2). While your method ends up with the correct offset, for this clamping instance, you can’t use that centerline again when you remount the blade. For example, if the next time you mount the blade, you measure +1.30 degrees on the left and you subtract that from your old 1.65 centerline, you’ll deduct 0.35 degrees (1.65 – 1.30) from your left rod setting when you should deduct 1.05 degrees (2.35 – 1.30). Your bevels will be off by 0.70 degrees. So long as you use your complete procedure, you’ll be OK, but you’ll have an incorrect value for the primary grind angles, because your formula is convoluted. Perhaps this is a big deal for me, because my EDC Delica gets touched up about once a month, and I depend on knowing that the primary FFG angles are 3.75 degrees inclusive. I just read the left face of the blade and bingo – I’m done. Whereas you (Josh) don’t think in terms of the centerline angle – you just depend on the procedure getting you to the correct answer (which it does) and I think this is confusing to those who are trying to understand what and how you are doing this.
Thanks… Makes sense now.
Alan: This isn’t a math puzzler by any stretch of the imagination. Any child who’s had 5th grade arithmetic should be able to execute the simple math here.
- Measure the angle of each side of the blade.
- Add the two numbers; result is the included angle of the blade’s primary grind.
- Then divide this included angle by two; result is blade’s centerline.
- Subtract the smaller of the blade side angles from blade’s centerline; result is the lean angle (How the blade leans to that side)
- Subtract the lean angle from your intended sharpening angle; result is rod angle for that side.
- Add the lean angle to the intended sharpening angle for the opposite side; result is the rod angle for that side.
Easy peasy.
Tom, your instructions are amazingly clear and yes its “simple” but what I’ve found for myself and Im sure(?) many others is a diagram is worth 1000 words. Sadly computer drawing is not in my wheelhouse. I love the “Sweet Spot” diagram that was recently posted. Ive heard it described 100 different ways but there it is in a picture and my brain “gets it” instantly. More spacial/visual then verbal I guess…
1 user thanked author for this post.
- You must be logged in to reply to this topic.