Cracked a recess - Now what?

[Mark Burge]

Hello y'all:

Yesterday, I was roughing out a pretty large bowl (for me and my Jet mini). Because it was large and I had never tried a recess instead of a tenon, I thought I would try the recess method on my nova chuck. So I put on the expanding bowl jaws, cut the recess, and tightened it in. Everything was going fine until I got a small catch and CRACK, the bowl came loose. I stopped the lathe and examined the bowl. There was a crack in the side of the base.

So my question is, what now? I don't really want to shorten the bowl depth because I like the curve I've got going. I can still remount between centers, so I could clean things up a bit. My first thought is to flatten the bottom and glue a waste block on then mount on a faceplate. What do y'all think?

Thanks,

[Ken Fitzgerald]

Mark,

You could do as you say or turn a cylinder and fill the recess and use the cylinder as a tenon.

[Mike Minto]

when this has happened to me, i have kept the recess crack open with the chuck, then used some CA to fill the crack; when i remove the pressure, the crack will close, and then have been able to, carefully, use the recess again after the glue dries. mike

[Mark Burge]

Thanks for the suggestions Ken and Mike. I was thinking of trying the CA Mike but when I tried to pry the crack open, it split right off. I guess I the walls were too thin to begin with. Ken, I like your idea because that allows me to keep most of what I have already done. As I said, this is a rough out and I don't want to loose much of the wood yet.

[Mark Patoka]

Yep, turn a cylinder to act as your glue block/tenon. I can't imagine being able to glue the crack and have it still hold the expansion chuck without breaking again. You can clean up the glued on tenon when you finish turn the bowl bottom.

[Bernie Weishapl]

Mark I have did exactly what Ken said. I turned a cylinder to just fit snugly inside the recess. Used some CA glue to glue the cylinder to the bowl. When I turned the bowl around to finish the bottom with my donut chuck I turned a concave on the bottom which turned out all of the cylinder. Make sure you leave enough wood on the bottom so you don't end of with a beautiful funnel.:mad: I use all tenons now.

[Mark Burge]

Thanks all. I agree a cylinder into a tenon is the way to go. I was trying the recess because someone recently said something about how they have more mechanical advantage than a tenon. I didn't quite understand how, but I thought it was worth a try. Oh, well back to tenons.

[Leo Van Der Loo]

Mark a picture would maybe help to see why the recess broke ??
Yes a recess has a mechanical advantage over a tenon, but if you don't make it right all bets are off, and by the way, if you make a tenon and it splits off, which happens easily with certain woods and grain direction, what are you going to say then ??
Anyway glad you didn't get hurt, just be safe :)

[Mark Burge]

Thanks Leo. I agree that it was probably my inexperience at making the recess that ultimately caused the problem. I was really stating that I would go back to what I know better. Tenons have to be constructed correctly too and I try to avoid them if the wood is not solid or the grain direction and wood makes it probable that it will fail.

[Reed Gray]

I have glued a number of recesses back together. I prefer yellow glue (CA isn't good for shear type forces), apply glue, clamp it in place with a board over the top, and usually on a table corner, so I can clamp to the table rather than the bowl rim, helps keep it flat. Let it set up over night. The piece will never go back in perfectly, so you will have to true up the outside of the bowl again, and usually you will need to turn off the recess because the crack will show.

For a properly fitted recess, you need the recess to be as close to the size of your chuck jaws when closed as possible. So if your chuck closed measures 2 inches, you want a recess 2 1/16 to 2 1/8 inch wide. I have dedicated calipers/dividers for my chucks. You want to match the dove tail angle precisely too. I use a specialized dove tailed scraper for this. You also need a good shoulder outside the recess. On a 10 inch bowl, I would recomend minimum 1/2 inch. Depth wise, you have to get a feel for it. Most of the time I am at about 1/8 inch to maybe 3/16 for big bowls (16 inch or so). You can get away with less, but I like to be safe, and not have to worry about it. I used to go 1/4 inch, but you really don't need that much. You can bet a better grip by using bigger jaws. Also, when tightening, don't do the white knucle tightening method. With shallower recesses, or with small shoulders, you can blow the recess apart before you start to turn. You can get it tight enough so that you don't break it, but tight enough so that any tiny amount of extra stress like a catch can cause it to fail at the point of most stress. Get it snug with your key on one side of the chuck, then rotate and use the other side. On bigger pieces, I will go around a couple of times. Snug, not tight.

robo hippy

[Leo Van Der Loo]

/snip/snip/snip/

For a properly fitted recess, you need the recess to be as close to the size of your chuck jaws when closed as possible. So if your chuck closed measures 2 inches, you want a recess 2 1/16 to 2 1/8 inch wide. I have dedicated calipers/dividers for my chucks. You want to match the dove tail angle precisely too.

robo hippy

I certainly agree with what you say Reed, but want to qualify this, as it applies to dovetail jaws only.

I use the Oneway jaws that do NOT need the exact size, nor the exact dovetail angle.

The patented Oneway jaws use a straight recess or tenon to hold the wood, have a look, and you will see a double edge on the outside of the jaws, they do grab the wood right closest to the bowl were the bowl should also sit up against the jaws, I prefer these jaws over the smooth dovetail jaws they have also.
And yes there's no need to be hardhanded when tightening the jaws, I make it a point to always use just one hand on the chuck key while holding and turning the piece around to tighten the jaws from side to side, it will give the ridges "bite" and wont split or crack the wood :D

[Reed Gray]

Leo,
I have never used a Oneway chuck. I don't think they were out when I got my first Vicmark, and I never felt the need to change. As to the 2 ridges on the jaws, well, they may help to hold better than straight smooth jaws and they may hold as well as a dove tail. I prefer the dove tail. I feel that there is a mechanical advantage as the angle will make it more secure, and wedge the bowl bottom into place. My recessed bottom is my finished bottom as well, so I wouldn't want ridges in them. Some of my warped bowls move so much that I couldn't return the bottom flat if I wanted to. Looking at the profile of the Oneway jaws, they are more rounded on the top edge, and to me, the shaper they are, the better they grip, as in more steel on the wood = better grip, and my recesses are shallow.

As to the closeness of the fit, I think with tenons as well as recesses, the closer the fit, the more steel there is on the wood, and you will get a firmer grip. The ridges on the inside of the Oneway will definatly hold better than smooth jaws, and so you have more range of sizes that will hold very well. With smooth jaws, closeness is very important. I think a very close fit is more important on a recess than it is on a tenon. Mostly because a tenon is a bigger diameter than most recesses, so there is a longer lever in action there. I wouldn't think of turning a 12 inch bowl with a 2 inch tenon, but have no problem with turning one with a 2 inch recess.

robo hippy

[Mark Burge]

Leo and Robo: Thank you guys for continuing this discussion. It has made me realize where I went wrong on my recess cutting. I tried to do it between centers and the tailstock was getting in the way. That left a very unfinished and not close fitting recess. This could have contributed to the break because the chuck was not seated well in the recess and I had to crank harder to get it firmly in the recess. I guess the next time (yes, Leo I'll try again) I should mount the bowl on a faceplate and cut the recess without the tailstock in the way - Yes? Since I don't have a dovetail gouge, I'll just have to eyeball it.

[Leo Van Der Loo]

Mark, Robo and I have been discussing turning for quite a few years already, it used to be the rec.crafts.woodturning site, but a lot of providers have been trying to get rid of those sites, as they cannot place advertising on them so they have dropped them, and the posts have dwindled to only a few, the other problem was that we could not place pictures as we can on these forums we now use, though I still go and visit the old site.
Reed I don't exactly know how long ago the Oneway chucks did come out, but I'm really pleased with them, I've used them for more than 10 years and never had a problem with them
Anyway, yes the chucks jaws should fit good to get the best hold, but it also helps when you know how to cut the wood with the least amount of leverage on the chuck and the wood, I use very narrow recesses and even tenons if required, but unlike reed I do return my bowls most often and always refinish the foot, I can afford that, as I turn for fun and not to try make a living, mind you I make more pieces than I can keep around, so they do get sold and used as presents also.
Here a couple of pictures that show the recess and the jaw marks after rough turning the bowl, the wood is fairly soft black walnut sapwood, also the bottom of the recess is slightly lower than the rest of the bowl for more strength and stiffness when chucking up the bowl.

129476
The tool I use is a professional body file, quite different from a normal file, and not hard and brittle, just for your information
129477
These are the marks from rough turning the inside of the bowl, while the wood was still green and wet.
129478

[Reed Gray]

Mark,
I never use a face plate any more unless it is a big (20 or so inch) bowl. I drill a recess into the top center of the bowl blank, and expand the chuck into that. Works pretty well, and after coring, the core is already centered. You can make a recess with a square scraper, and put the dove tail in with a skew used as a scraper, or a small spindle gouge which is more pointy and will let you get a good clean cut.

Leo,
I would consider your recess to be about the smallest I would go for a bowl that size. Coring does put some extra stress on the grip, and I am pretty agressive when I turn. I would have to be more gentle with that bowl.

robo hippy