Bowl gouge geometry

[Prashun Patel]

I'm making a bowl gouge sharpening jig similar to the vari-grind. Does anyone know a good reference (or can you explain) how to set the base length and how to set the pivot angle of the gouge arm?

[David Woodruff]

Hello Prashun, My opinion only. One can fabricate a grinding jig but I believe one is well advised to purchase grinding jigs on the market and follow the manufacturer's instructions. I have a Wolverine Vari-Grind and am very pleased with the sharpening results and reproduceability. Good chisel metal is expensive and anything one can do achieve a consistently sharp edge with minimum removal of metal is saving $$. Good Luck

[Prashun Patel]

Thanks, David. I'm permanently astraddle the line between smart and dumb frugality.

On this, though, I've made up my mind to attempt this first.

Anyone? Buehler?

[Sean Hughto]

http://www.thompsonlathetools.com/sharpening.asp

[Allen Neighbors]

Prashun, I made mine with a 30 degree slant on the leg, and use 2 3/4" tool tip extension. That makes my bevels almost exact with Doug Thompson's tools when I got them.
I adjust the pivot point to the proper length for the nose bevel.
Works every time. Consistent grinds.

[Jim Underwood]

Prashun,
There are quite a few tutorials on making your own grinding jigs. King Heiple, and Jean Michel are the fellows that come to mind. There are also tutorials on making the David Ellsworth type jig... (most of these you can find over on woodturningonline).

Somewhere, though, someone oughta have a tutorial on what to set your jigs at for the proper geometry.

I recently browsed Craft Supplies website for their Raptor gauge setup. I think they were suggesting to put the leg angle at 23°, and the tip of the gouge protruding 2" from the varigrind jig. Don't quote me on that, but go check it out in their video.

One of these turners has a book in which he goes into great detail about how to get an accurate grind... I'll have to look in my library to remember who it is... I think it's Springett, but I'm not sure... I'll try to remmber to post the title for you here tonight.

In my opinion, it appears that the Raptor gauge setup with a Wolverine jig (or similar) comes about as close to the good masters handgrind as you can get with a jig.

[Jim Underwood]

Nope. Not Springett, although he's pretty cool..

The one I'm thinking of is Mike Darlow's book, Woodturning Techniques.
You can get a copy on Amazon for as little as $1.09 right now, plus shipping. Worth the effort I think...

Anyway, he covers the technical aspects of getting your angles right in the book. It might be over the top, but the ideas are there. You may have to exptrapolate a little for your homemade jigs.

He's also got a video out on sharpening, but I don't know anything about it.

You can also get a good idea what proper geometry is on several YouTube videos...

[Jake Helmboldt]

Prashun, I'm right there with you on the frugality. Personally I think a lot of the claims are hype. Mahoney and Raffan and many others (I think Reed Gray, aka Robo Hippy here on the creek) all advocate freehanding it.

The jig simply allows repeatability, but you still need to know where to start and what to repeat, which isn't always clear from the instructions out there. I made mine out of wood and scaled the dimensions close to the Wolverine (based upon the sharpening suggestions from Thompson). I also set and keep my leg at the angle Doug Thompson suggests, though I didn't at first, because I didn't understand all of the details.

The biggest thing to realize is this: the leg angle does NOT set the bevel angle. It controls the sweep of the wings. Set the leg parallel (all the way against the tool handle) and you get a traditional, small bevel much like rolling the gouge on the rest.

The distance the support bar/cradle extends largely controls the nose bevel. Wolverine says you must have the support at a certain height below the wheel. Yet David Ellsworth uses a shorter height (4"), but his jig has what looks to be a longer leg in a fixed position. All of the jigs have a combination of settings that ultimately dictate the shape you get, and there will be some slight variation in replicating an exact grind (i.e. the Wolverine can't exactly duplicate the Ellsworth grind apparently).

Understanding the mechanics of grinding with/without a jig and being able to repeat it is much more important than the exact configuration of the setup.

[Reed Gray]

I do free hand sharpen, but I have a 2 by 4 inch table that I can preset angles on, and the gouges, scrapers, and skews all rest on the table when I sharpen. The problem with other tables is that you have to fiddle with it get the angle. Mike Mahoney has a You Tube video on sharpening, and he shows how to do it. It is surprisingly simple, and it doesn't have to be perfect. Also, it is a lot faster when you have as many gouges as I do.

robo hippy

[Jim Underwood]

I saw a Cindy Drozda video on youtube that demonstrates how to freehand sharpen a gouge.

http://www.youtube.com/watch?v=4_KDSIDAtGc

It's pretty much the way Mahoney and Batty do it.

[Prashun Patel]

Thanks for all this useful info guys.

Long term I would like to be able sharpen all my tools freehand.

I can get a consistent grind across the bevel with the jig I've made. However, I'm not sure how deep to make the bevel and how long to make the wings. Irish, Texas Irish, Flat grind, where to start? What's the most versatile?

As I'm cutting the bowl, my instinct is that the angle is far less critical than it is with flat cutting tools, since you can alter your rotation and incidence angle to the bowl.

It also feels like the most important variable is the bevel angle. Assuming a fixed pivot arm length, you can adjust the v-arm base to set that bevel angle properly.

So, my instinct is the cut the pivot arm a little long (assuming an Ellsworth style jig). If the wings are too long, then just snip a little off the arm, and slide the base in a tad to match the bevel, and regrind.

Am I right?

Last, do you guys deburr the wire edge that develops on the inside flute of the gouge after grinding? I know that's important in plane blade sharpening.

[Reed Gray]

As far as bevel angles and sweep, a lot of it is personal taste.

One advantage of a long sweep back is that when you are roughing, you have a lot more cutting edge you can put into the wood. Another is that for doing shear cuts for finish work (handle dropped, and very light no bevel rubbing, take several passes to remove tool marks). My sweeps are much less dramatic, now, about half way between the Ellsworth, and standard 45/45 bowl gouge. The only time I hone the burr off the inside of the flutes is if I am going to be using the gouge for the finish cut. Since I prefer a scraper at a shear angle, this almost never happens.

To make the wings longer, you just roll the gouge more to the sides. If you want to change the bevel angle, you can do that by how much sticks out the end of your jig. Mine was set for 2 inches. If you have more sticking out, you get a shallower bevel, if you have less sticking out, you get a steeper bevel. You can also change the bevel angle by moving your pivot point.

As to angles, if you have only one gouge, then 45 degree with a 45 degree sweep is a good all purpose tool. This works fine for most shallower bowls and plates. Just about any gouge works on the outside of the bowl. The problem is that when turning the insides of deeper and bigger bowls, it is difficult to impossible to navigate the transition from the side of the bowl through the curve into the bottom of the bowl. Your gouge handle will hit the rim of the bowl, or the tool rest, and you can't ride the bevel. This is where having a gouge that has a 50 to 75 degree bevel comes in really handy. I think most of mine are now ground to about 50 degrees, and I have a couple of 'bottom of the bowl' gouges that have about a 75 degree angle, and almost no sweep. Perfect for going across the bottom of the bowl.

robo hippy

[Jim Underwood]

Thanks Reed, that was helpful...

I'm still getting set up for deep bowls. I've been using a scraper more often these days, now that I have a platform to get a good burr... If I had a burnisher, I'd have it made. But I just got a 1/2" (inside flute) P&N bowl gouge handled the other day, and now I'm nearly ready to tackle sharpening it for bowl bottoms..

And I have a Thompson 3/8" V bowl gouge coming in the mail soon, so I should be set...

[Mike Wenman]

I have a wolverine, but even with that have been having some problems lately getting a good grind and sharp tools. I have have been looking at youtube videos and there is a wealth of information on there ranging from how to build your own wolverine type system using wood scraps, to the Ellsworth sharpening guide and even as mentioned Cindy Drozda freehand.

And since we're on sharpening. I do have 100 and 120 grit wheels on my grinder, but lately it seems as even the lightest touch on either of these will put a groove / indentation in the center of the wheels. Bad wheels perhaps? Seems as when I first got them, I could get a few touch ups out of them before using a dressing stone, but now..each and every time.

[Don Orr]

Go to the Oneway site and look for the videos on sharpening. They show quite clearly how to set up a jig. I'm reasonably sure it applies to most any adjustable jig. Hope it helps.

[Prashun Patel]

Thanks for all the help. For now, my jig appears to work. For now, I'm just working with a 45 degree bevel. It appears to be fine for my basic attempts at turning for now!

[Reed Gray]

You can pick up a burnisher for a cabinet scraper at most hardware stores. I prefer the triangle ones for my scrapers. Maybe $10, can't remember though, been a while. A couple of strokes and you have a burr. Keep the burnisher at 90 degrees to the top of the gouge. I have heard that a drill bit will work, and so will the strut from an auto shock absorber.

robo hippy