Thompson 12V 1/2" bowl gouge versus 5/8' 40/40 grind gouge?

[Steve Mathews]

Since my start into woodturning I've been using a Thompson 12V, 1/2" bowl gouge that is ground with a 60 degree included angle. I've heard so much about the 40/40 grind that I wanted to give it a try. Luckily I have a 5/8" bowl gouge that is ground close to the 40 degree angle on the tip but not the wings. I reground it to a shape I believe is correct. What can I expect while using it? Are there any changes as far as technique that should be applied?

[Pat Scott]

I tried a 40 degree bevel and found it way too aggressive and self feeding for my taste. I've seen Stuart demo it several times but it's not for me. Believe it or not 45 degrees was much more controllable, and yeah I know we're only talking 5 degrees difference.

[Kyle Iwamoto]

I tried a 40 degree bevel and found it way too aggressive and self feeding for my taste. I've seen Stuart demo it several times but it's not for me. Believe it or not 45 degrees was much more controllable, and yeah I know we're only talking 5 degrees difference.

I agree. I have 5/8" Thompson V gouge that I did do the 40/40. It's way aggressive. BUT my V gouges are my roughers so no loss there.....

[Paul Heely]

Does the Thompson being a V instead of parabolic flute shape have any influence on the aggressiveness of the 40/40 grind? I just got through watching an Ashley Harwood video and she talks about preferring the parabolic flute over the V. She states it's because its a bit harder to sharpen the V shape and not get a little dip in the nose of the tool. I'm wondering though if the flute shape has any influence on the aggressiveness? May have to experiment.

Also, I think it was Stuart Batty who I heard say that he prefers a 5:1 ratio of handle length to tool overhang. Does a longer handle also reduce perceived aggressiveness? More leverage would seem to me to improve control and reduce the aggressive feel.

Of course, this is all conjecture on my part right now. I'm getting setup now to try the 40/40 grind and see how I like it.

[Pat Scott]

Does the Thompson being a V instead of parabolic flute shape have any influence on the aggressiveness?

I only use/own parabolic gouges. I tried the 40/40 on a 3/8" (1/2" shaft) Hamlet bowl gouge. When I went back to my regular 45 degree grind it was like night and day.

[Reed Gray]

I have a number of Thompson and D Way gouges, which are both pretty much a V flute, but more of an open V than like the old Glaser gouges which were a fairly steep V. Most of them are ground to a 40/40 grind, which to do properly, you have to do on a platform. For a long time I used the 40 degree setting on my robo rest and found that to be too pointy, and I ground my gouges on the 45 degree setting. Well, watching Nick Stagg demo for our club (he switched to Stuart's methods and grinds), I bought my 45/45 in to compare by eye, and mine was identical to his 40/40. No clue why the angle is off that far because, of course, the platform is a protractor, and it worked on paper..... Anyway, that 40/40 grind is my preferred tool for going down the outside of a bowl, and for going down the inside wall, but it doesn't work going through the transition and across the bottom of a bowl. It will work for a plate/platter, unless you have a sharp transition. It really does cut better than most other tools.

I do touch on this in my sharpening video, but that bird's beak as some call it happens from spending too much time in one spot when you are sharpening, and that can happen with both platforms and jigs. With some thing like a SRG (spindle roughing gouge) since the flute is a constant curve, you keep the same roll rate. With V flutes and even parabolic flutes, you spend more time on the wing and the nose, but it is a quick flip through the transition area. A slightly slower flip with a parabolic flute.

robo hippy

[John Keeton]

My thoughts on the various “magical” grinds .... I began woodworking in my teens, and over the decades I have done a variety of projects, many involving both hand tools and machines. It became clear that all woodworking required an intimate bond with the wood - I needed to “feel” the cut. When I got serious about turning (about 3 months after starting) I acquired several Thompson tools, including a 1/2” V. While relatively costly, it seemed prudent to find what grind felt right for me. I read about dozens of thoughts about “the perfect grind”, but many of them did not match the work I was doing. I finally settled on a 47* grind (35 for spindle gouges) using a Wolverine and varigrind jig. That number came about not by math, but by continually altering my grind ever so slightly until it worked for me. I still have a Thompson 1/2” V, my second, but I bought a D-Way gouge some years ago and prefer it to the Thompson. It does seem a bit less aggressive, but not significantly so. That said, my 3/8” Thompson V is my absolute favorite tool. I can make cuts with it that I cannot do with any other gouge.

So, my advice is to avoid chasing every “magical” grind that someone promotes and simply take a day, chuck a piece of wood, and sacrifice an inch of metal playing with minute changes in your grind until it works for you and the type of turning you do. What I do, or what Stuart does, only means it works for me or Stuart. It may work for you, but likely not.

[Louie Sherwin]

Hi Steve,

Its been a bit since you posted your question but I add my 2 cents. As a new turner I struggled to clear instruction for how to sharpen tools and proper and save techniques to turn bowls. I studied videos by Dave Schweitzer, Richard Raffan, Mike Mahoney and others. And while I was able to go out the workshop start turning some bowls I have to admit it was mostly a disaster. It was a circus of catches and bowl blanks flying off the lathe and occasionally a functional but crude bowl appeared. It was clear that I was missing something important and I wasn't seeing the solution.

Then while browsing the AAW video catalog I came across Stuart Batty's video collection on what he calls his 7 Fundamentals of Woodturning. In these tutorials he explains and demonstrates a complete framework for the practice of turning wood. The 40/40 bowl gouge is just one component of this framework. Trying to use a 40/40 gouge outside of the techniques of this framework is unlikely to produce results any better than you are currently experiencing. If fact it might even not work as well. As John stated there is not a "magical" grind that will solve all your problems.

However, I have found that by studying these videos carefully and taking what I learn out to my lathe and practicing, I can say that the results I am getting are "magical". It is pure joy to shape the outside of a bowl in one pass to a finished surface with minimal effort (i.e. no tear out and only minor tool marks). I am now confident in my basic techniques and I can now start putting my attention on the esthetics. I look forward to a turning session rather than being apprehensive.

This is not to say that there are come tricky techniques that need to be learned. There are and one of the key ones is being able to create an accurate 40/40 grind on your bowl gouges. Without that the rest kind of falls apart. It requires that you learn how to to this freehand. And it is one technique that is not covered in Stuart's 7 Fundamentals videos. However, Cindy Drozda has an excellent video tutorial Platform Sharpening of Woodturning Gouges that shows you exactly how to do this grind. It works equaly well with a traditional parabolic flute gouge or Thompsons V flute gouges. However, not at all with any "U" shaped flutes or any spindle gouges.

I found that practicing the spindle turning techniques shown in the 7 Fundamentals set was the best way to learn both the basic techniques that Stuart is describing and to refine my sharpening techniques. If the end grain cuts were not working it was usually because my sharpening was off in some way, i.e. that wing not straight, wing at the wrong angle, poor blending at the nose. etc.. Once I was able to dial in my grinding technique the rest started to fall in to quickly fall into place.

One telling operation is putting a dove tail tenon on the end of a spindle blank. If my 40/40 grind was dead on, forming the tenon for a dovetail jaws was dead simple. If my grind was even a little off it was difficult even impossible to form a clean, strong tenon. I had a lot of sharpening practice working on this technique.

The nice thing about practicing these techniques on spindle blanks is that they are easier to come by and easy to part off and start again. So you can get a lot of practice. And the the basic techniques are directly transferable to bowl turning even though the grain direction is completely different.

There are also two long videos that were made of demonstrations by Stuart at a couple of woodturning clubs. They show his complete process of turning a bowl including some things not in the 7 Fundamentals videos including how to make and use a jam-chuck. They are chock full of additional tips and techniques and some fun stories. I have watched them repeatedly and still learn something new each time.


Stuart Batty demonstrates bowl turning with his 40/40 grind at Mid-Maryland Woodturners

Stuart Batty - How Gouges Cut at Rocky Mountain Woodturners


-louie

[Chance Raser]

I have a 5/8 U gouge from D-way which used to be my go-to. Then i watched Stuart Batty demonstrates bowl turning with his 40/40 grind at Mid-Maryland Woodturners and felt compelled to get a 40/40 grind. I ended up getting the thompson 5/8 V with the 40/40. It very rapidily became my favorite. It is easily my most used gouge. And i have watched that video a few times as well, modelling my hand placement and my stance after Stuart's.

Platform sharpening has not been difficult, just a bit of practice, nothing to be scared of.

[Brice Rogers]

Paul Heely asked: " Does a longer handle also reduce perceived aggressiveness?"

I think that it does. I was turning something where I had more overhang than I like. IIRC, I was using a round nosed scraper with a fresh burr on it and was attempting to clean up some tool marks at the transition as a final step. It would periodically grab and be aggressive. So, I bought some black gas pipe, tapped it for some allen screws and added it to the wooden end my round nose scraper. I modified the larger scraper slightly so that it would fit inside of the pipe. But I took so little wood off that I don't notice it when using it without the extension.

I made two. One is long enough that I can tuck it under my arm or capture it between my arm and my body. Also, the added mass has some inertia so it is less likely to catch or bounce around. When I'm not using the pipe extension, it only takes 15 seconds to remove it.

[Brian Deakin]

Stuart has a number of videos on Vimeo

https://vimeo.com/woodturning

Including videos on handle length,overhang and diameter

and on the web site

http://www.dmwoodturners.com/?page_id=642

Stuart provides a range of useful information

eg see page 27 of the Advancing the art of Woodturning

http://www.dmwoodturners.com/wp-cont...G-AUG-2013.pdf

for advice on conventional scrapper angles

[Reed Gray]

Coming into the transition area with a scraper can be hazardous. I discuss this in my video 'Scary Scrapers'. What happens is that when sweeping across the bottom you are using mostly the nose, then when you hit the transition, you are using the nose and the side of the scraper, so you end up with much more cutting edge in the wood at one time. If you pivot as you come into the transition, no problem. Some do use longer handles, and while they work, they add more weight to the tool. I keep the tool rest close, and use smaller scrapers. Longer handles also mean you are tempted to hang out farther off of the tool rest than you would normally, which adds to that problem.

robo hippy