Rehabbing a bowl gouge

[rsser]

My memory's failing; we discussed this some time ago and I put up a link to a vid. I can't imagine the relevant search terms.

The prob is when you over-grind the wings and end up with a concave profile.

The solution is to put both wings to the grind wheel and and reshape the profile to convex seen side on, and then sharpen as per normal.

There's a pic of step one here

[badgaz]

Hi Ern

After almost 12 months of serious effort into this wood turning thing, I think I'm actually beginning to get the hang of the fundamentals. Good tools, basic yet reliable lathe and good habits have helped.

You post a topic relevant to the very question that came up on the weekend as I was putting an edge on one of my bowl gouges....the convex profile on gouges.

Yes, I turn Aussie hardwoods predominantly
Yes, I keep my gouges sharp
Yes, I use an AlOX grinding wheel and grinding jigs for all of my tools
Yes, I use a light touch when grinding
Yes, I turn anything from pens to bowls and spindle work and have the quality HSS tools now to do the job (always room for more though)
Yes, I get a consistent grind on all of my tools...BUT...

NO...I cannot achieve a convex profile....more like a convex edge with a concave section right at the nose of the tool "the Beak". I have attempted to re-establish the profile and re-grind a couple of bowl gouges, paying particular attention not to dwell too long on the sides of the gouge (or the nose for that matter)...Guess what...I get the Beak!
Not happy to waste any more chisel steel until I figure out what the problem is.
I read one clue in the Jerry Glaser article (right at the end).

"The distance of the pivot point from the face of the grinding wheel has a strong effect on the geometry of the bevel edge"

My question...What does this mean?

Is the optimal distance for each tool a case of trial and error, considering:
not all tools are the same width
not all bevels are the same angle
Will adjusting the distance of the pivot point really stop "the beak" from happening?
Do I set it further away, or closer? I acknowledge I can adjust the angle of the pivot arm to preserve the bevel angle either way.

If I had some cheap gouges to experiment on I would try a few things, but without such beasts lying around in my shed I'm averse to grinding away good steel without some margin for success.

Convex profile: How is it done?????


Regards

Gazza

[RETIRED]

Gazza I would hazard a guess and say you need to take a little more off the point of the tool to bring it back a little.

Remember that when you have nearly got it right to reset the tool protrusion to finish the grind.

It is dependent on the flute shape as to how you grind them sometimes.

[Jim Carroll]

[badgaz]

Okay Blokes

Let me see if I've got this right:

1. Set the gouge profile/angle on the jig as per normal
2. Grind
3. Loosen the gouge in the jig
4. Move the gouge forward a touch (in the old language)
5. Regrind the "beak" of the nose down to blend it in with the side profile
6. Bingo! Convex profile

Sometimes it has to be a two stage process....They never tell you this stuff in books and DVD's...do they?

I'm guessing this is an ongoing measure.... the more you sharpen the gouge - over time, the more the "beak" re- appears. When this happens repeat step 1 to 6.

Is that it???

I'll give it a go on the weekend and report back

Cheers

Gazza

[rsser]

OK, found the thread on a radical repair. Couple of vids.

https://www.woodworkforums.com/f8/help-sharpening-90889/

[RETIRED]

Okay Blokes

Let me see if I've got this right:

1. Set the gouge profile/angle on the jig as per normal Yes.
2. Grind Yes. Sharpen just the front until the beak disappears.
3. Loosen the gouge in the jig No. As you have shortened the tool by taking the beak out, reset the tool in the jig back to the correct protrusion.
4. Move the gouge forward a touch (in the old language) See above.
5. Regrind the "beak" of the nose down to blend it in with the side profile Yes.
6. Bingo! Convex profile Hopefully.

Sometimes it has to be a two stage process....They never tell you this stuff in books and DVD's...do they?

I'm guessing this is an ongoing measure.... the more you sharpen the gouge - over time, the more the "beak" re- appears. When this happens repeat step 1 to 6.

Is that it???

I'll give it a go on the weekend and report back

Cheers

Gazza

Once you have it right it becomes pretty easy to keep it right.

The reason that it happens is you try to get a long grind down the side and as said previously some flute shapes do not allow it unless you freehand sharpen.

[Calm]

My memory's failing; we discussed this some time ago and I put up a link to a vid. I can't imagine the relevant search terms.

The prob is when you over-grind the wings and end up with a concave profile.

The solution is to put both wings to the grind wheel and and reshape the profile to convex seen side on, and then sharpen as per normal.

There's a pic of step one here

OK, found the thread on a radical repair. Couple of vids.

https://www.woodworkforums.com/f8/help-sharpening-90889/

Not bad Ern 13 hours 56 minutes - you better go have a sleep now

I think most people get into trouble sharpening by grinding from one side to the other then back again.

Shaping or retaining the shape of a gouge is done by only grinding the section/bit that needs material removed, when you have the desired shape then one grind from side to side gives a continuous finish and the tool is sharp. Have a look at the length/depth of the section - the tip has more material to remove than the wings so obviously it takes longer/more effort.

As said - If it has a beak grind the beak off - reset the tool protrusion in the jig sharpen the whole tool then finished.

Cheers

[rsser]

Actually it was the sleep that helped David ;-}

Just grinding the tip off isn't enough with a hashed geometry in my book. You want both wings convex and the same curve. (For normal sharpening I start with a light pass or two or each wing and then blend the tip in.)

What Glaser's radical surgery does is reset the flute shape as the starting point for the bevel geometry.

And yes, some flutes (eg. some P&N gouges) are U shaped with a distinct transition from wall to bottom that can yield a clunky cutting edge shape. Changing the grind (more or less swept back wings) can often help improve it.

[NeilS]

It is dependent on the flute shape as to how you grind them

Yep.

.....

[rsser]

And the position of the flute in the rod.

[NeilS]

And the position of the flute in the rod.

Agreed, but to a lesser extent than flute profile... if I remember correctly. It's been quite a while since I had to sort this out. Some early P&Ns were the most recalcitrant, as you said.

....

[rsser]

Yes. I had a P&N Supa gouge, around 17mm, which had the distinct flute wall to bottom transition. Not a prob as a roughing gouge.

Have several small P&Ns with a U shaped flute. With care, they can be freehand ground to produce a modest ladyfinger shape and I've done a lot of work with them in this form. Am now migrating them to medium swept back; requires different presentation obviously but so far so good.

Still remain a fan of the Superflute a la Child in Henry Taylor form. Either ladyfinger or swept back.

Charlesworth says somewhere that some tools you make friends with. The Superflute and I are real close ;-}

[NeilS]

Still remain a fan of the Superflute a la Child in Henry Taylor form. Either ladyfinger or swept back.

Me, too.

.....

[jefferson]

My limited experience in sharpening bowl gouges leads me to the following:

Henry Taylor - needs lots of work on the front bevel, less on the sides
Hamlet - same as the HTs
P & N - more work on the side, less on the short front (a truly unkind flute shape IMO)
Sorby - midway between the above.

In all, the Sorby flute shape seems to suit me best. I can grind on the Tormek simply from side to side and take enough off the front to achieve an ideal convex shape. That is, the front gets two swipes against one for each side.

And yes, I do resort to the spark grinder to rectify beaking on the HTs and Hamlets - and to restore a decent profile on the P & Ns. In time, I will replace with Sorby tools as my favourite.