Sharpening

[Bruce Golling]

I am trying to make sense out of the criteria for sharpening lathe tools. Particularly the Wolverine type jig.
Where do the rules for 7 inches away from the face of the wheel and 4 inches below the center of the wheel come from? Is it designed a set a particular angle for grinding? If so doesn’t that angle change depending on the size of the tool being sharpened.
It is easy for me to wrap my head around the sharpening of a plane blade. Because everything is precise and the angle is the angle each and every time its due to be sharpened.
Then I see experts like Eli Avisera who just freehand the grinding process.
In other words, I am able to put a very nice edge on bench chisels and plane blades because the rules are set in stone, so to speak, and I know where to start and finish. But what is the starting point for skew chisels for instance? I’m not even sure if I am making my point understandable, so try to bear with me, but if you do understand what I’m trying to say then please help set me straight. Thanks for reading.

[John Keeton]

Skews and scrapers are usually sharpened using the platform jig on the Wolverine - or a Robo rest. For gouges, once you have your grinder and Wolverine base set up, there are three variables.

The amount of tool extension from the Vari-grind jig must remain constant (I use 2", but somewhere between 1.75" - 2"), set it and leave it.

The angle setting of the Vari-grind must remain constant - see Doug Thompson's site for a diagram about this setting. The angles you set on these two will affect, to a degree, the angle/profile of the wings of gouges.

The third variable will determine the angle of your nose grind, and, of course, to a degree the wings. You will need to play with that setting to get the grind you desire on your gouges. I use 35* for spindle, 47* for bowl, and 70* for my bottom feeder bowl gouge. I have those marked on my V arm with a scratch line.

I use a CBN wheel, so the diameter of my wheel does not change. If you are using a stone wheel, then the angle of your grind will change over time as the wheel wears away.

[Thom Sturgill]

+1 on John Comments. The 4" is to make the Vari-grind work properly in the wolverine arm. For spindle roughing gouges and spindle and bowl gouges with a 'conventional grind' the butt of the tool is placed in the socket of the arm and the arm adjusted so that the tip of the tool meets the wheel evenly. As John points out the platform can also be used for this. This length will vary with each tool and even then change over time as the tool length changes. The Vari-grind is for fingernail or Irish grinds. David Ellsworth introduced Americans to this grind which is sometimes called an Ellsworth grind and sells a fixed jig to produce his grind. He specifies a different geometry for the arm, but the wolverine jig can be used.

[John King]

Check out Oneway info at http://www.oneway.ca/images/pdf/part%202480%20vari-grind%20dec%202010.pdf. - John

[Reed Gray]

Well, hand plane blades and bench chisels are easy to understand. The settings for the various jigs may seem confusing, but you are simply setting up pivot points for the jigs so you can sharpen a compound curve on round bar stock that has a flute or channel in it. There are a few standards, but every one does it differently, and there is also a lot of difference in preference of bevel angles. The biggest convenience is in being able to repeat your settings. This is why there are so many jigs. With the coming of the CBN wheels, spacers can be used for settings because the wheel size and geometry never change. I am a platform sharpener, and don't use jigs any more. Just preference. I have a couple of sharpening clips (and others) if you type in robo hippy on You Tube.

robo hippy

[Mike Peace]

For skews, a rule of thumb of making the bevel length about 1 1/2 the thickness of the skew is good. It will give you about a 43 deg angle as I recall. Somewhere between 40 and 45 is good. For a SRG I differ from some and prefer to use the platform as I believe it to be a bit safer than the arm. An angle of about 50 to 55 degrees is good.

[Michael Mills]

Maybe this short article will help explain the different angles, mainly on bowl gouges. The steeper angle would be like a "bottom feeder" grind.
http://www.woodturningdesign.com/askdale/14/14.shtml

No rules are set in stone but IMO most fall within a +- 5*to 7* of a norm. ie For a skew some may like a -5 from a norm or 40* and some may like a + 5 from a 40*.
These give an "about" angle. The jig allows you constant grinds in order to not waste steel; whether you like 42* or 49* is up to you but these give you a starting point.

http://www.woodturningvideosplus.com/bevel-angles.html
http://www.thompsonlathetools.com/images/extra/Sharpening.pdf