how to correct gouge with concave wings

[blackhawk]

Hello All - I am having trouble getting the wings straight on my D-Way bowl gouge as you can see in the picture.  It is 3/4" diameter with a deep U-shape.  I am using my SVD-186 with hole A, P=65mm, and JS=2.  To correct this, I tried to grind the wings straight on my 1750 rpm grinder, then re-shaped them with the SVD-186 and the BGM-100.  Once I got close to sharp, I finished up on the Tormek SG-250 wheel.  That concave wing came right back.  After looking at it, I don't think it is possible to get the wings straight with the 65mm protrusion.  I can't rotate the gouge far enough before it hits the support bar.  With this large diameter gouge with such a deep flute, I believe that I need to move to a 75mm protrusion.  I set it up this way just to eyeball the situation and it seems like this will allow me to take more steel off at the end of the wings to get me back straight.

Does this sound like the problem?  Anything that I maybe missing?  Thanks

[Twisted Trees]

You need to take a bit more off the nose of this one. it helps to sharpen in 3 parts i.e. each wing, then the tip with a final blend of a full sweep pass at the end.

[blackhawk]

I really wanted to avoid taking more off the nose.  This flute is so deep, that even now, there is not much of a bevel to ride against the wood.  When doing a push cut on the outside of a bowl there is very little margin of error to keep the tool from vibrating.  I think a longer wing would also be nice for when I use it for scraping.

[Twisted Trees]

The bevel will remain the same after bringing the nose back far enough to remove the concave wings, concave is bad will cause catches and be hopeless at curves or scraping, straight or slightly convex is the target. at the moment the nose is the right shape but 3mm or so too far from the handle!

[RichColvin]

I agree with Twisted Trees. 

[blackhawk]

What Twisted Trees said makes sense to me now.  Since I wanted to try a 40° angle on my bevel, I changed my protrusion to 75mm and ended up having to take more off the nose and wing to get it straight.  I spent 1-1/2 hours on it, mainly because I went really slowly with my 1750 rpm grinder to prevent over heating the steel.  What helped me the most was flattening the gouge with the side of the stone.  Then I could see where to take off more metal by the width of the flat spots until I got all the flat spots back to sharp.  I got it pretty straight, there maybe only .005-.008" of concavity left in there. I'll work on that as I use it and re-sharpen.  This particular gouge is really tough to keep straight, not sure if it is the deepness of the flute or the U-shape.  I have a Sorby 5/8" diameter gouge with the parabolic flute and I have no trouble keeping it straight.  Hopefully, practice will make it easier.

How do others set their rake angle?  I set this by eyeball as I ground the cutting edge straight on the side of the stone.  Can you set the rake angle to anything you desire just by controlling your rotation of the SVD-186?  Or is there more of a limited rake angle range based on the SVD-186 settings that are being used?  My rake angle ended up being about 60°.

[RichColvin]

BlackHawk,

I've cataloged quite a bit of information about bowl gouges, including rake angles.  It may be helpful for you.

        https://www.sharpeninghandbook.info/WW-BowlGouge.html

Kind regards,
Rich