Gouges - do you hollow grind or not?

[violins88]

Do you hollow grind your gouges?

 

thanks

john

[MikeC]

I just finished sharpening one flat on a stone.  If you hollow grind you have to use a wheel so you have to be careful not to lose the temper in the steel.  

 

[violins88]

1 hour ago, MikeC said:

I just finished sharpening one flat on a stone.  If you hollow grind you have to use a wheel so you have to be careful not to lose the temper in the steel.  

 

How do you ensure the bevel is “flat”? 
 

Also, if you use a Cbn wheel, it won’t burn the tool.

[MikeC]

I'll have to look up cbn wheel was not aware of that.   I hold the stone loosely in my hand so it can move freely.  Doing that will cause it to self level on the existing bevel.  It's not as perfect as some kind of jig or holding device but it works.  

I'd like to know a good way to hone the insde surface of the gouge.  Sharpening can cause a burr there.  I hone it off with a leather pad with green abrasive on it.  Works ok but a slip stone might be worth getting.   

 

[Dennis J]

I find hollow grinding just about a necessity when sharpening gouges and I'm careful to avoid overheating. But I do use a grinder with 8 inch aluminium oxide wheels running at 1725 r.p.m. so I don't have any trouble.

And that could be more of a problem using a grinder running at 3000 r.p.m.

But it should be manageable. The main thing to avoid is to keep away from the intended cutting edge a little and repeatedly cool the gouge in water.

Before regrinding a gouge bevel I use a fine diamond stone to square off the cutting edge and hollow grind as close as possible to it without breaking through. I then use a jig to hone the edge with a mainly side-to-side motion. I adjust the jig so that the gouge is making good contact at the cutting edge and just touching the back edge of the hollow grind.

As soon as I get a burr developing on the inside surface I switch to a 4000 grit water stone to finish honing, followed with a cotton buff charged with chrome oxide or rouge to remove the burr.

I would add that the hollow grind will disappear after a couple of honings so you will end up with a flat surface anyway and the back edge can be rounded over as well to assist the cutting action. Hollow grinding is just a way of keeping the honing surface to a minimum width and only needs doing occasionally.

 

Edited November 9, 2020 by Dennis J
addition

[nathan slobodkin]

I also find it a necessity to hollow grind all blades. I use a 6" wheel driven by a 1725 rpm motor with a 2:4 pulley set up to cut the speed in half. I made a tool rest which I can run my finger along to guide the grinding and slide the gouge or chisel in or out to get the wheel in contact with the center of the bevel of the tool. Rounding the wheel slightly helps to keep the angle constant as I turn the gouge. It is important not to let go of the gouge once you start so that you don't change the bevel. I want a single hollow surface right up to the edge all the way across the gouge. After the grinding is done a couple of swipes across a flat stone touches only the edge and the heel and as long as the hollow remains it is easy to lock in on to the correct angle for honing and then a few swipes with a fine slip stone removes the burr.

[Brad Dorsey]

5 hours ago, violins88 said:

Do you hollow grind your gouges?...

Yes.

[Davide Sora]

9 hours ago, nathan slobodkin said:

I also find it a necessity to hollow grind all blades. I use a 6" wheel driven by a 1725 rpm motor with a 2:4 pulley set up to cut the speed in half.

Hi Nathan, this is interesting.

Would it be possible to see an image to get an idea how you did it?

[Urban Luthier]

I hollow grind all my blades using a tormek grinder. I find it easier to sharpen and hone free hand with a hollow grind. 

[HoGo]

I have no real education in this and learned sharpening the "hard way" on my mistakes and I settled on "undergrinding" if there's such word (actually I don't have any grinder and do it all by hand) and just hone the final bevel near the edge to my favorite angle which is different for every blade I have. Different steels have shown me what they need over years of use. I never measure exact angle and just eyeball it...works for me.

[MikeC]

Do any of you have a preferred bevel angle?  I have one that doesn't cut very well and I think the angle on it is too steep.  

[violins88]

I think 27 degrees is good for maple. Lower for spruce.

The jig I show in the pic facilitates accurate sharpening angle. Now, instead of sand paper, I use diamond plates. I got thin ones very cheaply from China.

[MikeC]

8 minutes ago, violins88 said:

I think 27 degrees is good for maple. Lower for spruce.

The jig I show in the pic facilitates accurate sharpening angle. Now, instead of sand paper, I use diamond plates. I got thin ones very cheaply from China.

Looking at your picture.  How are you attaching the handle to the board?  Drill a hole in the end of the handle and that pin goes into the hole?  

[violins88]

51 minutes ago, MikeC said:

Looking at your picture.  How are you attaching the handle to the board?  Drill a hole in the end of the handle and that pin goes into the hole?  

Yes. More like a dimple.

[nathan slobodkin]

On 11/9/2020 at 7:22 PM, MikeC said:

Do any of you have a preferred bevel angle?  I have one that doesn't cut very well and I think the angle on it is too steep.  

The angle depends more on the steel of the tool than what is to be cut. I have some "Swiss made" gouges which  I like a lot but they  are very soft and need a fairly obtuse angle while some of my Grandfather's Addis tools can be sharpened much more acutely and seem to hold their edge forever. As long as the bevel is consistent and between 25 and 35 degrees they should work fine.

[Thomas Coleman]

I do hollow grind my chisels.  I use a Baldor slow speed grinder (1800rpm) with 6" Norton 3x wheels.  I prefer this to a Tormek.  I just feel it's a little more versatile as far as tool shaping goes. 

35 minutes ago, nathan slobodkin said:

The angle depends more on the steel of the tool than what is to be cut. I have some "Swiss made" gouges which  I like a lot but they  are very soft and need a fairly obtuse angle while some of my Grandfather's Addis tools can be sharpened much more acutely and seem to hold their edge forever. As long as the bevel is consistent and between 25 and 35 degrees they should work fine.

Agreed.