Unequal bevel on Sorby Bowl gouge

[Kerrowman]

I have just acquired a tool sharpening jig to allow me to produce repeateable sharpening on my tools and have noted something surprising.

When I presented the 1/2” Sorby bowl gouge to the wheel using the jig I found the bevel angle on one of the wings very different from the tip and the other wing - see pics.

I find it surprising given the supposed quality of these tools and wondered if anyone else has encountered similar?

Thanks

 

[Lazurus]

I twould appear you are not swinging or rolling each side equally

 

[Kerrowman]

It’s not possible to get the left wing flat on the wheel if I keep the jig in the V slot where it’s supposed to be. The other side is fine. The bevel is a different angle on that side.

I will take some more pics if needed.

 

[Kerrowman]

I guess I will need to regrind that side so it lies flat on the wheel when the other side and the tip are doing the same.

 

[Kerrowman]

These pics should make it clearer:

As far as I’m aware it should be a consistent bevel all round independent of how far I’m rolling it over.

 

[Paul Hannaby]

If the base of the jig is exactly alighned on the centre of the wheel then it should produce the same angle each side but bear in mind, the jig just puts the tool at the correct angle, how much you grind away is down to you, not the jig. If the bevels on each side of the gouge differ, keep grinding until they are the same. The initial differences may be due to how the gouge was sharpened before the jig was used.

As can be seen from your photos, you have ground too much away at the wings and not enough in the centre so the tool has developed a pronounced "beak". That needs to be removed by grinding away at the centre. When you look at the tool from the side, the profile should be a convex curve or at worst, a straight line - never a concave curve.

 

[Kerrowman]

I haven’t ground the tool at all - it’s brand new! If there’s a problem with the angles and tip shape then that’s a Sorby issue. Hence my query if others have met similar. How should I reshape the tool if it’s wrong to start with?

 

[Kerrowman]

Here’s a top view of the tip.

 

[Kerrowman]

As regards the side view, surely the curvature of the grinding wheel will tend to produce a concave side profile? Even if that’s not what one wants.

 

[scooby]

If you are talking about the profile of the wing cutting surface, you can make it convex/straight on a grinder wheel. You need to concentrate on the high points.

I'd advise fitting a finer grit wheel if possible. It'll cut slower and allow you to refine the shape easier. End result should be sharper too.

 

[Kerrowman]

Apparently there’s too much beak and it’s not rounded enough at the tip as well as the bevel being too concave - and unequal on each side. I’m using a 120 grit ‘fine’ wheel and I can’t see how to avoid a slightly concave bevel at the tip when that’s the natural curvature of the wheel.

 

[scooby]

Here’s a top view of the tip.
View attachment 108021

This has me a bit puzzled. Jig fingernail grinds on bowl gouges usually produce this shape (image copied from popular woodwork with arrow added by me). Not sure why the 'arrowed' area isn't visible on your grind.
It'd be interesting to know.

 

[scooby]

Apparently there’s too much beak and it’s not rounded enough at the tip as well as the bevel being too concave - and unequal on each side. I’m using a 120 grit ‘fine’ wheel and I can’t see how to avoid a slightly concave bevel at the tip when that’s the natural curvature of the wheel.

Ah sorry, didn't realise you were using a 120 grit.

 

[Kerrowman]

This has me a bit puzzled. Jig fingernail grinds on bowl gouges usually produce this shape (image copied from popular woodwork with arrow added by me). Not sure why the 'arrowed' area isn't visible on your grind.
It'd be interesting to know.

Well it hasn’t yet had a jig grind from me and the tip shape I show in my later pic is how I received it. I’m writing to ask the supplier for comment. I will have a go with a jig grind in the hope of balancing it up and getting the sort of shape you show in your pic.

I’m still curious how to avoid a slightly concave bevel at the tip due to the inherent curvature of the grinding wheel? To avoid that would surely require a slight rocking toward and backward to offset the wheels curvature.

 

[scooby]

The bevel will always be hollow (concave) on a wheel.

I was referring (and Paul Hannaby) to the cutting edge of the wing. That needs to be straight or convex (yours is heavily concave).
I think the easiest way to explain how to remedy that is by equating it to grinding a bench or plane iron. You spend more time grinding the high points away and don't touch the low points.

Another point is jig moves in an elliptical motion, so the wing bevel angles won't be the same as the nose/tip bevel.

 

[Kerrowman]

Ok I see better now re why the bevel changes as one goes around the profile. However the overall shape of the gouge is certainly not standard (too pointy) and whatever bevel angle the wings have is not equal on both sides as per my original photos. I’m hoping my Sorby is not a poor copy or somehow adjusted by the seller.

 

[scooby]

Ah right, you received it like that. I, and I think everyone else, presumed you'd ground it like it. Apologies.
I don't own any Sorbies, but I seriously doubt it'd have left the factory with that grind.

Was it purchased as new or used? Where from?

 

[Kerrowman]

This is why I’ve sent a message and pics to where I got it. I suppose it’s all right to say I got it new from ‘Turners-Retreat.co.uk

 

[scooby]

I'm sure they'll do the right thing. I've bought from them quite a few times, had a problem with one order and they sorted it out pretty quickly.

 

[Kerrowman]

Good to hear