New and Simple DIY Jigs for Accurate Bevel Angles on the Wolverine Sharpening Jig

[Paul Ruud]

I just got into turning so I am unsure whether to post something here that I just posted on the AAW forums. It's a new and very simple way to set the platform or the Vari-Grind jig accurately for a desired angle. All you have to do is cut one accurate width. It works for grinding wheels with any radius, so it applies to composite wheels that shrink over time. It works for any Vari-Grind jig setting and any gouge protrusion. So, it is not as limited as the Raptor setup tools or any other method that fixes the setting on the Vari-Grind. That means you can use it for Ron Brown's approximation to Stuart Batty's 40/40 grind and for a grind with swept back wings.

Yes, it's all that. I'd be happy to explain here as well if that is appropriate.

[Randall Pitts]

please do, very interested

[Paul Ruud]

please do, very interested

Thanks for the encouragement! Consider two (transparent) jointed pieces of wood with the same dimensions except one is wider. Place each with one edge on the platform and then rotate the platform until the opposite parallel edge is tangent with the grinding wheel. The platform will have a lower angle for the wider piece.

Oneway Wolverine Sharpening Jig 1.jpgOneway Wolverine Sharpening Jig 2.jpg

The angle of the bevel ground into a bowl gouge placed on the platform also changes. The wider piece corresponds to a platform angle that produces a larger bevel angle.

There is a relatively simple mathematical relationship between the width of the piece of wood and the bevel angle. If r is the radius of the grinding wheel and A is the bevel angle then the width of the piece of wood is r (1 - cos A). So, we can make simple jigs that consist of a jointed piece of wood of various widths to obtain our desired bevel angles for bowl gouges. The jig becomes easier to use if we add a lip to the top edge so that the jig can rest on the wheel and establish the tangency. Still easier for some of us, clamp the jig to the platform so that you can just rotate the platform down until the lip rests on the grinding wheel, tighten the platform clamp, and you have your platform in place.

IMG_9566.jpg

Some notes:

This geometry can also be applied to the Vari-Grind jig. The basic difference is that the piece of wood rests on the top of the gouge in the Vari-Grind jig (instead of the platform) and the tangency to the wheel is created by an arm that extends from the top of the piece of wood parallel to the gouge to the top of the grinding wheel. The other point of contact is the nose of the gouge.

Angle Gauge Photo 1.jpg

This jig works for all settings of the Vari-Grind jig and any length for the protruding gouge. So, for example, you could use it for Ron Brown’s approximation of a 40/40 grind or for long swept-back wings.

Also,

1. The distance of the platform from the grinding wheel does not affect whether this jig works. The angle of the platform will change with the distance, but the resulting bevel angle will always be the same.
2. Place the jig so that one face is against the grinding wheel. This ensures the correct position of the jig on the platform.
3. Because you can account for the radius of your grinding wheel, this approach works for composite grinding wheels that get smaller over time. When the radius r gets smaller, the desired jig width does also. So, as your grinding wheel shrinks you can trim your jig to compensate.
4. If you are very particular about obtaining a specific bevel angle, then you will want to adjust the width of the jig slightly to account for the curvature of the grinding wheel.

More on this last note: The width formula, r (1 - cos A), produces the angle A at the heel of the ground bowl gouge. To get closer to the desired overall angle on the nose of the gouge, you want this angle at the middle of the bevel. So, increase the width of the jig by half the thickness of the gouge from the bottom of the flute to the bottom of the gouge. For my ½-inch bowl gouges this is 0.088 inches, or a little more than a sixteenth of an inch and a little less than 3/32 of an inch.

Also, if you are grinding the top of the gouge for the shape of the wings, you probably want to move the angle to the tip of the gouge so that you can then lift the gouge to produce a flat or convex profile and get the desired angle at the tip. That would mean adding the depth of the flute to the width of the jig.

For the Vari-Grind jig application, take into account the depth of the flute by subtracting it from the width.

Here’s a table of angles and widths for an 8-inch grinding wheel (r=4):

Angle (degrees)	Width (inches)
15	0.136
20	0.241
25	0.375
30	0.536
35	0.723
40	0.936
45	1.172
50	1.429
55	1.706
60	2.000
65	2.310
70	2.632
75	2.965
80	3.305
85	3.651

It’s not something everyone will want to do but it couldn’t be easier to try. I hope some of you do and find it helpful.

[Paul Ruud]

Here's a PDF file with an explanation of the formula. I hope the link works. The file is just a little too big for the forum.

[Paul Ruud]

Also, if there are questions please ask. I tried to keep my post brief. But it may be too brief to be clear. So, please let me know if I can clarify.

[Neil Strong]

Paul

I can see the benefit of your jig for those still using friable wheels that reduce in size with use. I guess some are still using those at times.

[Paul Ruud]

Paul

I can see the benefit of your jig for those still using friable wheels that reduce in size with use. I guess some are still using those at times.

Indeed, Rikon, Grizzly, and probably others still sell their slow speed grinders with those wheels.

[Neil Strong]

Indeed, Rikon, Grizzly, and probably others still sell their slow speed grinders with those wheels.

If you have the space and $s, having at least one coarse friable wheel on one of your bench grinders is a good thing to have for heavy re-profiling of your tools. A #40 grit friable wheel will get the job done much quicker and it also saves your finer grit and/or more expensive CBN wheels.

Coarse low grit friable wheels or belts are what toolmakers use to get the initial profile that your tools come with. Some of them may also then finish off the grind on a finer grit wheel.

Most of us started out with the sparky wheels because they came with our grinders and also because of their lower cost, and for some of us that is all that was available when we began turning, so methods to adjust jigs and rests to compensate for the reducing diameter of those are helpful.

But, if you get to do lots of turning eventually you get to the point where the diminishing length of your tools and replacing them becomes more of a cost than adding CBN wheels (or less aggressive wet grinders) to your sharpening setup, which eliminate the reducing diameter issue.

Replacing the friable wheels also had the advantage for me of eliminating the fine dust that comes off them from the constant dressing of them. There are enough other respiratory challenges in a woodturning workshop without adding fine silicon carbide or aluminium oxide fine dust exposure into the mix. But, if that is what you currently have/use, at least have some PPE to reduce that risk.