40 : 40 freehand grind

[Haggy]

I have changed from using the fingernail grind back to the traditional 40:40 grind mainly because I don't want to be bothered fiddling with a jig.  I have found several advantages in favour of this grind but there is one drawback. I am having difficulty with the profile of the side angle. The sides should sweep back at 40 degrees in a straight line, but mine has a concave edge due to the C- profile of the flute.  This makes it unsuitable for shear scrapping. Is it simply a case of buying a gouge with a U- shaped flute or do turners modify the profile using the grinding wheel? 
   Haggy

[bodrighywood]

I grind off the sharp corner type bit at the end of the flute if that makes sense. Shear scraping I find that top be the main problem. I haven't a clue as to the angle I have but most are long grinds which I sort of arrived at before I found out about all the fancy ones and so am used to them.

Pete

[Paul Hannaby]

You will generally find that because there is more metal at the bottom of the flute, it takes a little more grinding to get rid of it. Just grind a little more in the centre to even up the profile.

[Bryan Milham]

As Pete says, lose the point, round it off.

The cutting area (except shear scraping) is just back from the most forward (I'll not use the term tip) part of the gouge. The point will make it a little unstable to control.

[Haggy]

Thanks Pete, Paul and Brian- I'll try rounding the cutting tip more as this appears to give better tool control.  Do I take it this type of grind isn't best suited to shear scraping as the contact area is small and possibly not convex (as in the finger- nail type grind)? 
         Thank you for your advice.
                  Haggy

[Bryan Milham]

Haggy,

the pictures are not quite clear enough to say for sure but it looks like the edge is fairly flat. That means the whole edge is touching the timber is your scraping (curve of the bowl notwithstanding), it does need a slight curve so you limit the touching area but this also gives you more control of where to scrape along the edge.

(does that make sense?)

[Paul Hannaby]

For sheer/shear (depending who you talk to!) cutting, the edge would be better either straight or convex. A concave edge would make it more difficult to control which part of the edge was in contact with the wood.

Taking this a stage further, I prefer the gouge edge to be at less of an angle. I go for a "standard" bowl gouge with a 48° bevel (around 50 is close enough!) and around half that angle for the sweep back on the edge so around 20-25°. However, I don't generally use that for sheer cutting on the outside of a bowl, just for push cuts (which if done properly leave a clean enough surface to not need any sheer cutting) and mainly for cutting the inside of the bowl.

[Haggy]

Thanks for your feedback Brian and Paul.  It does make sense what you say Brian, I've consciously rounded the gouge nose a little more and this certainly has NOT had a detrimental effect.  I can't quite get that convex edge right, the C profile doesn't help in this respect.  As you say Paul, when I get the push cut right it doesn't need any additional work, but at present I am still not able to get that beautiful flowing curve just how I want and scraping seems to get things back on track.  I am  enjoying the freedom of not  using a jig and appreciate the advice on grinding angles.
       Thank you    Haggy