The part nobody talks about…

[John D Smith]

I have my bowl mostly turned, but I need help with the part nobody talks about. I have a sacrificial block on the bottom and I left a ‘tenon’ around the tailstock for stability but now I want to get rid of the tenon and finish smoothing the bottom and get rid of the sacrificial block. How do I do this and keep it centered?





How do I keep it centered? I don’t have steady rest and I don’t think my Longworth chuck will span a bowl so big. I need to get a chuck with jumbo jaws now that I have an 18” lathe, but I’m still paying for the lathe!

Help! How would you do this?

 

[Russell Nugent]

Lots of options for this. Drive block, jam chuck, cole/button jaws, donut chuck. I use a drive block mainly, what some will call a jam chuck, basically chuck up or mount a chunk of wood on a spare faceplate, get it round, make the face slightly concave. I put some shelf liner foam or even some paper towel between the bowl and block, hold it in place with the tailstock, reduce the tenon to a nub and then use a small pull saw to cut the nub short, then sand the remainder.

If you do a YouTube search for " finish the bottom of a turned bowl", you'll find some good helpful videos.

 

[Russell Nugent]

Also regarding your tenon, it's fairly small for the size of bowl you appear to be turning, and it seems to have maxed out the jaw set. The jaws will grip best when they are closest to being a perfect circle.
The tenon is also bottoming out in the bottom of the jaws so the bowl isn't held against the face of the jaws. This can make it easy for it to lever out of the jaws while turning. You want a gap between the tenon and the bottom of jaws so the bowl sits against the jaws.

 

[John D Smith]

Lots of options for this. Drive block, jam chuck, cole/button jaws, donut chuck. I use a drive block mainly, what some will call a jam chuck, basically chuck up or mount a chunk of wood on a spare faceplate, get it round, make the face slightly concave. I put some shelf liner foam or even some paper towel between the bowl and block, hold it in place with the tailstock, reduce the tenon to a nub and then use a small pull saw to cut the nub short, then sand the remainder.

If you do a YouTube search for " finish the bottom of a turned bowl", you'll find some good helpful videos.

I do have a jam chuck- came with my Longworth chuck- but I’ve never used it. I’ll try. Thanks.

 

[Bill Alston]

Also regarding your tenon, it's fairly small for the size of bowl you appear to be turning, and it seems to have maxed out the jaw set. The jaws will grip best when they are closest to being a perfect circle.
The tenon is also bottoming out in the bottom of the jaws so the bowl isn't held against the face of the jaws. This can make it easy for it to lever out of the jaws while turning. You want a gap between the tenon and the bottom of jaws so the bowl sits against the jaws.

Agreed. I also noticed a chuck adapter is being used. Ok for small jobs but not ideal for such a large project. Thats a lot of weight hanging a long way from the lathe bearings.

 

[John K Jordan]

I do have a jam chuck- came with my Longworth chuck- but I’ve never used it. I’ll try. Thanks.

Might be best to make a jam chuck by turning a piece of scrap wood or plywood for an exact fit. Can hold the wood with screws on a faceplate, or put it between centers and turn a tenon, reverse and hold with the chuck, then flatten the face and turn a bit to shape to fit nicely, snug, but not enough to damage the bowl. (The jam chuck can be another bowl blank that can be reused.

When mounting the piece in the jam chuck, it’s common to hold the tenon you want to remove with a live center in the tailstock. This will keep the work centered and more secure. Clean up the foot at the same time. Turn the tenon down until only a small central piece remains for support, then remove the bowl and cut off the support with a small saw or bench chisel, and sand smooth or better, use a hand scraper to smooth inside the foot.

If supporting by the tailstock and the workpiece is not too large or the rim might be fragile, instead of turning something to jam inside the bowl, sometimes I’ll turn a groove in the face of plywood sized to fit the rim of the bowl. The pressure from the tailstock will keep the piece secure. As always, don’t turn the speed up too fast!

If you end up doing a lot of these, there are other options. Search the forum, the internet, youtube, etc. I like books: two I like are “A Guide to Work-Holding on the Lathe” by Fred Holder, and Doc Green’s book “Fixtures and Chucks for Woodturning”, both available from Amazon - full of ideas!

If you are a member of a woodturning club, you can probably get ideas and even mentoring from experienced club members. Turning clubs are full of helpful people!

JKJ

 

[Alan Weinberg]

The jaws will grip best when they are closest to being a perfect circle.

I’ve considered that gospel and always tried to follow that dictum but recently in a 2 day class with Mike Jackofsky, he feels strongly that there is better grip at max jaw opening when instead the 8 corners dig into the piece. It’s also easier then to measure the bottom thickness while piece is still on the chuck. That really threw me for a loop.

 

[hockenbery]

and I left a ‘tenon’ around the tailstock for stability but now I want to get rid of the tenon and finish smoothing the bottom

How you remove the center tenon depends on your tools and your skill level
I can show you how I do it.
I often have a tenon in the center when turning NE bowls.
I use an Ellsworth ground gouge with the heel ground off.

I cut this tenon as a slight cone. First cuts without the tailstock gives a point to the cone


Once there is a point I start the cuts with the tip of the cone inside the flute and pull the tip a tiny bit left the the tool cuts straight down the top of the cone as the gouge gets bogged down shift the tool to cut the side of the cone



When the cone is about a 1/4” high I switch’s to cutting towards the center


The final finish cut is tiny tiny shavings

 

[hockenbery]

jaws will grip best when they are closest to being a perfect circle.

there is better grip at max jaw opening when instead the 8 corners dig into the piece.

My thought is the jaws do have max grip at perfect circle

Jaws have much more grip than is needed at wider openings up to max

 

[John K Jordan]

I’ve considered that gospel and always tried to follow that dictum but recently in a 2 day class with Mike Jackofsky, he feels strongly that there is better grip at max jaw opening when instead the 8 corners dig into the piece. It’s also easier then to measure the bottom thickness while piece is still on the chuck. That really threw me for a loop.

I do it both ways. The four corners do grip, but perhaps not as securely IF one has soft or punky wood AND is prone to get big catches!!

Can’t remember who, but years ago someone I knew recommended making a tenon or recess just enough bigger than the close diameter for the reason you mentioned - to fit calipers in the gaps between the jaws to check thickness.

BTW, I think the 8-corner grip is occasionally useful for another reason - if the piece is removed from the chuck, if necessary there is a better chance of remounting it with reasonable registration if the corners can be fit into the same jaw marks. (For this reason I always mark the wood with a red dot between jaws 1 and 4. Remounting doesn’t always align perfectly, but it does sometimes.)

JKJ

 

[Kevin Jenness]

A vacuum chuck will allow turning away the tenon without using the tailstock, assuming your bowl is not too leaky. I imagine that hockenberry is using a vacuum chuck in his pictures above but perhaps he has some other magic.

 

[Bill Alston]

The four corners do grip, but perhaps not as securely IF one has soft or punky wood AND is prone to get big catches!!


JKJ

I agree with you John. A separate issue is of course that (if it matters) a proper grip sized to the Jaws won’t mark the wood so badly.

 

[robo hippy]

I do agree that the tenon is a bit small. For me, I would reduce the stub in the center of the bowl a lot more, tapering it down to 1/8 inch max, then cut it off or snap it off, or even remove the tailstock and just finish turn it off at a very slow speed, like not more then 500 rpm, and take very tiny cuts. Also, NO CATCHES! If you can cut the stub off with a flush cut saw, then 80 grit will take care of it pretty efficiently.

robo hippy

 

[hockenbery]

vacuum chuck will allow turning away the tenon without using the tailstock, assuming your bowl is not too leaky. I imagine that hockenberry is using a vacuum chuck in his pictures above but perhaps he has some other magic.

I like using vacuum or a friction drive to turn away the chuck tenon.

In my post the bowl is still in the chuck.
The op asked about removing the center tailstock support tenon inside the bowl.

I use tailstock for hollowing NE bowls. And have center cone or tenon like the op showed in this picture.

 

[John D Smith]

Agreed. I also noticed a chuck adapter is being used. Ok for small jobs but not ideal for such a large project. Thats a lot of weight hanging a long way from the lathe bearings.

Yes. I need a new, bigger chuck. Suggestions? 1 1/4 x8

 

[John D Smith]

First, let me say, this is why I’m here. I’m a new turner- learning by YouTube. Thank you all- your expertise is so greatly appreciated. I started on my Dad’s midi and I’ve recently upgraded to a Rikon 70-1824. I need a bigger chuck and It needs to have jaws that will accommodate a large bowl. Do I want a quick change chuck, or is the standard screw-on kind better? It needs to match the thread size, as pointed out, so that I’m not using the adapter. Also, yes, that is construction lumber with a layer of mahogany. It’s not great for turning, but it’s cheap and available and this is my first bowl bigger than 8” so if I wreck it…

I suppose I will have to consider a steady rest and/or a vacuum chuck. But first I need a good 1 1/4 chuck

 

[Russell Nugent]

First, let me say, this is why I’m here. I’m a new turner- learning by YouTube. Thank you all- your expertise is so greatly appreciated. I started on my Dad’s midi and I’ve recently upgraded to a Rikon 70-1824. I need a bigger chuck and It needs to have jaws that will accommodate a large bowl. Do I want a quick change chuck, or is the standard screw-on kind better? It needs to match the thread size, as pointed out, so that I’m not using the adapter. Also, yes, that is construction lumber with a layer of mahogany. It’s not great for turning, but it’s cheap and available and this is my first bowl bigger than 8” so if I wreck it…

I suppose I will have to consider a steady rest and/or a vacuum chuck. But first I need a good 1 1/4 chuck

Nova, oneway, vicmark, axminster, rikon and easy wood all make chucks that will all do the job pretty well. I'd encourage you to search a bit on here, we've just had a few threads about choosing a chuck and you'll find all kinds of different opinions. I have nova chucks because that's what was available to me and affordable when i started.
Apologies for the misunderstanding in your original post. I thought you meant the tenon held in the chuck. Hockenberry gave you the advice for turning down the nub in the bottom of the bowl.

 

[John D Smith]

Nova, oneway, vicmark, axminster, rikon and easy wood all make chucks that will all do the job pretty well. I'd encourage you to search a bit on here, we've just had a few threads about choosing a chuck and you'll find all kinds of different opinions. I have nova chucks because that's what was available to me and affordable when i started.
Apologies for the misunderstanding in your original post. I thought you meant the tenon held in the chuck. Hockenberry gave you the advice for turning down the nub in the bottom of the bowl.

No, actually you answered my question as well. That’s why I took a pic of inside and the bottom. I can follow his videos and remove the nub inside the bowl. My dilemma is how then to remove the one on the bottom and finish shaping the bottom of the bowl. It seems once I remove the nub inside, I don’t know how to keep the bowl centered when I turn it around and remove the block from the bottom.

I will follow your advice and not have my chuck jaws so spread out in the future, and also use a thinner block that doesn’t bottom-out in the chuck. I just really need a bigger chuck now that I have the bigger lathe. I have a donut/Longworth chuck but it isn’t big enough to accommodate a bowl that size, because it was for my midi lathe.

 

[hughie]

Other than the way I do mine as to having the tenon being the foot of the vessel. The other way you can do it is via a longworth chuck, I built my own out of polycarbonate several years ago to match my lathe. So technically it could swing 500mm and down to about 150mm or so, over all its 600mm dia

 

[Kevin Jenness]

My dilemma is how then to remove the one on the bottom and finish shaping the bottom of the bowl. It seems once I remove the nub inside, I don’t know how to keep the bowl centered when I turn it around and remove the block from the bottom.

I usually have a center point on the tenon bottom from the initial roughout- I always start between centers, and even if I used a screw chuck to start a bowl I would use the tailstock for stability, thus leaving a center mark. If you lack a center point you can estimate it by experimentation or striking a center on the tenon with a compass.

A jam or friction chuck registering on the inside of the bowl will tend to self-center. You can check for centering by setting your tool rest near the bowl rim and observing the runout as you turn the bowl by hand, and bump the bowl sideways to try to improve the setup. Once you get the bowl pinned between the friction drive and tailstock, reduce the wasteblock/tenon as hockenberry shows, saw off the nub and sand it out. I usually use a piece of leather to soften the friction drive and prevent marring.

I started out using a chuck with jumbo jaws, like a Longworth chuck, but found the friction chuck less cumbersome to set up. The Longworth setup does give you clear access for completely turning off the nub, though.

It's generally considered good practice to have the face of the chuck jaws bear on a shoulder outside the tenon, as that widens the contact area and improves the leverage situation.

 

[Darryl Fective]

After the inside is done, you can put a piece of scrap in the chuck and make a disk with a rounded edge that fits against the bottom of the bowl. You can sort of pad it with a piece of leather, or a few layers of paper towel, then bring up your tailstock to push it against the block. It's just a friction drive setup. The center point on the tenon will center it and you can finish the bottom and turn away most of the tenon. (down to 1/2" diameter or so) Remove it from the lathe, then chisel and sand away the last bit of the tenon. (hope that makes sense)

The Quad City Woodturners meet in Rock Island, IL and have multiple meetings and events, mentoring, etc. One can learn on Youtube, but it's probably a lot more fun (and easier) with others.

 

[Kent Reisdorph]

The tenon is also bottoming out in the bottom of the jaws so the bowl isn't held against the face of the jaws. This can make it easy for it to lever out of the jaws while turning. You want a gap between the tenon and the bottom of jaws so the bowl sits against the jaws.

This cannot be overstated. The face of the jaws must seat up against the bottom of the bowl. Without that, you have significantly less holding power, and a catch will likely cause the tenon to shift in the jaws. Normally you will create a shoulder for the jaws to butt up against. That shoulder can later be used as the foot, or turned away altogether if you don't want a foot.

 

[Kent Reisdorph]

First, let me say, this is why I’m here. I’m a new turner- learning by YouTube.

You absolutely, positively, need to check out www.turnawoodbowl.com. This search provides a handful of articles on tenon (and to a lesser degree, mortise) technique: https://turnawoodbowl.com/?s=tenon

I also have the Rikon 1824 and am very happy with it.

 

[John K Jordan]

I agree with you John. A separate issue is of course that (if it matters) a proper grip sized to the Jaws won’t mark the wood so badly.

The same when working the other way, expanding jaws into a recess (which I do most of the time when turning dry wood) and I leave the recess in the bottom as a design element: - make the recess diameter just slightly larger than the outer jaw diameter, maybe less than 1/16" larger. No detectable marks inside the recess.
(The two platters are about 14" and 19" in diameter)


BTW, there is a also safety reason some pros point out for keeping the jaws as close to the closed diameter as possible on either tenons or recesses: opening the jaws a lot leaves wide gaps between them and presents four sharp jaw sides as hazards for careless knuckles or tools!

This cannot be overstated. The face of the jaws must seat up against the bottom of the bowl. Without that, you have significantly less holding power, and a catch will likely cause the tenon to shift in the jaws. Normally you will create a shoulder for the jaws to butt up against. That shoulder can later be used as the foot, or turned away altogether if you don't want a foot.

I strongly agree. I make sure the bottom of the piece has a precisely turned flat shoulder for the top of the chuck jaws to seat against, even if its not the actually bottom of the bowl. This provides a horizontal contact support component as in addition to the radial grip on the circumference of the tenon - it better locks the piece to the chuck and better resists it being pried from the chuck in the event of a bad catch! Contact with the shoulder is important for alignment too.

If you don't want the jaw faces to contact the bottom of the bowl, just make the top end of the tenon a bit larger just to form the shoulder.

@John D Smith, as well as our opinions, here are a couple of references from experts:

Doc Green states this well in his book "Fixtures and Chucks for Woodturning", the section on scroll chucks:
"A Secure Grip: A scroll chuck's jaws must but against the shoulder of a tenon and the tenon must NOT contact the bottom of the jaws."

Richard Raffan says this in his book "Turning Wood":
"The rim of the jaw must abut a shoulder on the blank for maximum support"

JKJ

 

[John D Smith]

After the inside is done, you can put a piece of scrap in the chuck and make a disk with a rounded edge that fits against the bottom of the bowl. You can sort of pad it with a piece of leather, or a few layers of paper towel, then bring up your tailstock to push it against the block. It's just a friction drive setup. The center point on the tenon will center it and you can finish the bottom and turn away most of the tenon. (down to 1/2" diameter or so) Remove it from the lathe, then chisel and sand away the last bit of the tenon. (hope that makes sense)

The Quad City Woodturners meet in Rock Island, IL and have multiple meetings and events, mentoring, etc. One can learn on Youtube, but it's probably a lot more fun (and easier) with others.

I’m in Dubuque. Sadly, not retired yet (maybe another year) so a trip to QC isn’t out of the question, but takes some planning. I’d also love to get in on classes at Iowa City Woodcraft. Maybe this summer.