Help with Proper Grinds

[John Kananis]

I have three questions really.

1) what is a good grind to undercut the inside lip/edge of a bowl so one can 'grab' it better? I've been using a 40/40 grind mostly and I can't get under the rim right, even if I remove the heel.

2) when would one use a conventional scraper over a negative rake scraper? Maybe I'm too novice to understand but it seems the nrs makes the other obsolete. Is it safe to re-grind my scrapers to nrs or bad move?

3) can I use my skew as a nrs? If not, can you explain the difference/reason?

Thanks everyone, I'm alone on this journey so your help, a couple of classes I've purchased and yt is all I have.

Edit: I have a tormek and a slow speed grinder available to me, both with cbn wheels. If that makes a difference.

[Don Stephan]

Do you wish to undercut the rim so that a chuck in expansion mode can "grab" the rim?

It can be helpful to have bowl gouge with different bevel angles. Using bar diameters, my most used are 1/2" and 3/4" with 40 deg grinds, a 1/2" with 50 degrees, and a 3/4" 70 degree for the transition zone and bottom.

[John Kananis]

Not exactly, Don. I'm trying to kind of create a recess of sorts right under the inside of the rim, the kind that your fingers grab onto when pulling the bowl out of the cupboard, etc.

Edit: thank you for the info though

[Mel Fulks]

Inside rim is usually on plastic bowls, not wood bowls .

[Russell Nugent]

I'm no expert but....
I use a 45 degree swept back bowl gouge on the inside wall when I'm doing a light undercut. I like the look of a slightly larger rim with an undercut, than the rest of the bowls wall, not that I do all my bowls that way.
I use a conventional scraper for material removal and shear scraping and a negative rake scraper sometimes for finishing(doesn't work really well on softer woods)
You can certainly use your skew as a negative rake scraper on the outside of a bowl, obviously not the inside, but even on a flat surface I don't like to sure the skew because the points contact and make it hard to level the surface.
I buy the cheap set of 2 bowl scrapers (PSI)on Amazon to turn into negative rake scrapers, as well as cheap skews that I reshape to a rounded profile.

[John Kananis]

Russell, the undercut on the inside of the rim is exactly what I'm trying to achieve. So just go 5° past where I normally grind and take the wings off? I have a 3/8 gouge I was going to dedicate to this purpose so I'll grind away and let you know.

As far as scrapers, I have a 1 inch and 1/2 inch round and a 1 inch square. I don't use them for material removal and not crazy about the surface they leave so they just sit in the tool rack. I guess I can just add a top bevel and see how they perform. Just wondering if the conventional grind is good for much outside of removing material? Also, as far as using a skew as a scraper, I'm trying to be frugal here but don't want to sacrifice anything outside of a little extra sharpening for that sake.

I'm no expert but....
I use a 45 degree swept back bowl gouge on the inside wall when I'm doing a light undercut. I like the look of a slightly larger rim with an undercut, than the rest of the bowls wall, not that I do all my bowls that way.
I use a conventional scraper for material removal and shear scraping and a negative rake scraper sometimes for finishing(doesn't work really well on softer woods)
You can certainly use your skew as a negative rake scraper on the outside of a bowl, obviously not the inside, but even on a flat surface I don't like to sure the skew because the points contact and make it hard to level the surface.
I buy the cheap set of 2 bowl scrapers (PSI)on Amazon to turn into negative rake scrapers, as well as cheap skews that I reshape to a rounded profile.

[Dave Fritz]

Scrapers work well as an undercut tool. You can shape it to fit into the space needed. Regular scrapers work fine, just use a light touch. They will remove more material than a negative rake scraper. I finish with a negative rake scraper to remove tool marks. I like an undercut rim for ease of handling as you mentioned. My scraper is an original D-Way that I got from Dave, before the negative rake scraper was so popular. It's ground with a 70 degree bevel and cuts like a dream. You can also turn the scraper to a 45 degree angle on the tool rest and scrape with that, it's a much lighter and cleaner cut than when flat on the tool rest.

[Reed Gray]

I really need to do some more videos..... To under cut the rim, which I think is what you are talking about, you need to point your gouge more towards the outside of the bowl. To make that entry cut, I start inside the bowl rim a little bit. Pivot your handle towards the middle of the lathe until it just starts to cut. Then to make the entry cut, pivot a little bit more, only a degree or two or three. If you pivot too much, you go through the wall of your bowl. I always use the 40/40 for this.

As for scrapers, and NRSs, both are still scrapers. Check out my video Scary Scrapers. One I need to do is NRSs. Both are still scraping. The NRS is good for sweeping across the bottom of a bowl to smooth your ripples out. A standard scraper can do this as well. The reason is because you are going across the grain rather than down through it. As for sweeping through the transition and up the walls, the NRS is still a scraper, and will tend to pull the fibers more than cutting. This remains true even for the super light cuts they can do. As always, your results can vary to huge degrees depending on the wood. In general, harder woods will have a better surface from the NRS than softer woods. With pacific madrone or pear, you can get pretty much glass smooth surfaces. With big leaf maple, not so.

As for what to use for a NRS. I never liked the ones that are basically a skew chisel. The problem with them is that they lose the burr almost instantly. My theory on that, which comes from years of using scrapers, is that you need a certain amount of metal under the burr to support it for any real cutting. I have settled on a 60/30 grind, which may actually be closer to 55/25. I do prefer a burnished burr most of the time. Generally, I will use the burr from the grinder, and then burnish it down and back up once or twice before going back to the grinder. I can get a couple of minutes out of one good burr rather than seconds, which is common for the skew chisel style NRSs.

My favorite finish cut is a shear scrape, and I did another video just on that. I find it leaves a better finish than the NRS, especially on the softer or more tear out prone woods. It was Jimmy Clewes who started me on using this cut. It also is great for removing tool marks and the small ripples you can get from the gouge. It also removes the burnished surface that rubbing the bevel will produce. This does seem to be more of a problem with dry wood rather than green wood. When you start to sand out any bowl, first thing you need to do is cut through the burnished surface. With a shear scrape, there is no burnished surface.

A NRS can leave surfaces on end grain pieces like boxes that do not need to be sanded, unless you are starting at 600 grit.

robo hippy

[John Kananis]

I think I have a better understanding now (I hope). I'll try both the techniques and grinds recommended. Also, I think I'll turn the small round and the square scrapers into nrs and leave the larger one, then do a Reed said

And Reed, please do make more videos, I've seen all you have out there many times.

[Kevin Jenness]

Ideally you would be making the undercut from the largest diameter out to the rim. A Hunter swan neck carbide tool wood be good for this.

A skew makes a good nrs, but the small included angle makes it even more fragile. A regular scraper is better for removing a lot of material or shear scraping.

[Edward Weber]

As you can tell from all the suggestions, it's not really the grind that's at issue. Many times it's the right tool and/or technique.
There are numerous ways to achieve the inside rim undercut, you'll have to find what tool is most comfortable for you.
I would use a bowl gouge to get the basic overall shape, then refine the undercut with a scraper, but that just me.

[John Kananis]

I really appreciate all the replies and I'm sure this is more issue with technique than anything else - I'll practice some more.

[Neil Strong]

1) what is a good grind to undercut the inside lip/edge of a bowl s

This the grind I use and this is how I do it with a bowl gouge...

Dedicated scrapers will do the same job.

[John Kananis]

Fantastic, thank you Neil!!