Chuck in Expansion Mode -A Fresh Look

[Ned Ladner]

I'm still at the semi-beginners stage of turning and I've made a number of small bowls (8" diameter and less). I've primarily turned the bottom using a faceplate or worm-screw, then turned the inside using my Vicmarc dovetail jaws in a recess. During my learning curve, I have had a couple break the rim and roll off of the lathe but fortunately I've been turning at relatively low speeds (<1000 RPM).

I attended our monthly woodturning group yesterday and received quite a bit of advice from a very respected and accomplished seasoned turner. Part of that advice was to only use bottom recess on platters. He said for safety, I should use glue blocks, vacuum chucking, etc. and use the tailstock whenever possible for bowls.

Additionally, he said that when someone examines your piece, they should wonder how you held it on the lathe and that a shallow dovetailed recess was a "dead giveaway".

I've watched a number of Lyle Jamison videos and he seems to indicate that scrolling chucks are inherently poor and unsafe at holding wood.

I researched these topics on this forums past threads and really did not find a consensus. Please help. Experienced advice is greatly appreciated. I guess I'll research vacuum systems?

[Reed Gray]

Well, I knew it was Lyle before you said so. He is an excellent turner, and does things his way. I prefer a recess, both for mounting the blank to turn the bottom, and for reversing and turning the inside. As for the remaining recess being a dead give away as to how the piece was mounted, that only seems to matter to turners, and not to the people who have purchased my bowls over the years. The only problem with finding a consensus on this is that we all differ. When I get asked at demonstrations as to which holds better, I answer YES! As long as they are properly made and sized to fit the bowl you are making, both work equally well.

https://www.youtube.com/watch?v=5KHkkws9lWA

robo hippy

[Brice Rogers]

Robo Hippy gave you good advice.

I have found that if I get a big enough catch that it is likely to leave the lathe no matter if it was held by a recess, a tenon or whatever. But as you get more and more proficient, the frequency and severity of your catches will keep going down. So, it will become less important whether you are using a recess, a tenon, a glue block, a scroll chuck, etc.

Lately I have been preferring to use a recess rather than a tenon. I just think that it looks a little nicer and typically gives the piece a wider bottom on which to sit. When I do use a tenon (for structural considerations) I often remove most of it, for looks, just before I finish. BTW, it makes sense to use a live center whenever you can as it adds a lot of safety/security. But in order to turn the foot off, or soften the recess dovetail, you'll need to figure out how to hold the piece. In most cases, when you are doing this last step, you really DO NOT want a catch. So take your time, use sharp tools, take very light cuts, work towards the center, etc. Whether the piece is held by a vacuum chuck. hot-glue, stretch wrap/tape, donut chuck, jamb chuck, it will likely be a bit less secure than it was when it was being held by the scroll chuck. Another approach is to use the live center to hold the bowl as you are finishing the foot and then remove more and more of the wood under the live center until it is held by a little cone of wood. At that point, I'd probably turn off the lathe and use a spindle gouge as a sharp chisel to remove the last amount of wood as I am slowly rotating the piece by hand. Of course you could just snap it off, but it'll likely tear a little. When you cut it off, it'll probably leave a little "nib" but that can easily be sanded off by hand.

So, I guess that there are lots of ways to approach this. They all work. There is probably no "best way". The best way is whatever works for you and which you are equipped to handle.

[John K Jordan]

I agree with Brice, catches become rare with practice. I can't remember when I last had something come out of a lathe. With either recess or tenon I support the work with the tailstock as long as possible - after initial shaping heavy, risky cuts are never needed.

I almost always use recesses, occasionally glue blocks (used as tenons, to save wood) and less frequently, tenons. As for looks, if you put JUST a recess in a bottom, yes, it will stand out. But if you add other detail it can disguise the recess. Here are some examples:


holding_platterA.jpg bottom_IMG_4687.jpg holding_platterB.jpg

The recess can be less time and work because it often needs NO reversing and touchup of the base.

When I use a tenon it always requires reversing and holding somehow to clean up and detail the base.

(BTW, the platter with the multi-axis base was done with Frank Penta's method. You may notice the actually recess is only three small triangular pieces about 1/8" deep. This is all that was needed to hold the 18" platter. This was plenty secure for turning the inside of the platter. (light cuts, no catches)

Frank's instructions for platter bases:
http://www.frankpenta.com/index.php/...k-penta/detail
http://www.frankpenta.com/index.php/...penta/download

JKJ

[Jamie Straw]

I'm a novice, freshly returned from a 1-day workshop with Tom Wirsing (platters extraordinaire). That day was the first time I used a recess hold. We were all amazed how how small ("short") the recess was when he demo'd a fairly large platter. His instructions/tips were to (a) shape the edge of the recess to perfectly match the shape of the expanding jaw; (b) have the jaws very close to "closed" position; and (c) keep the blank under 1000 rpm when concerned about a launch.

[robert baccus]

All good dvice above except the negatives about scroll chucks. One big consoderation is the type of wood you are dealing with. With good strong dry wood they all work fine even on large pieces. With endgrain to grab CA glue works very well--even on green wet wood. Not a place for recesses without a tailstock backup. Tenons tend to slip on green wood as well and waste pretty wood. Glueblocks and recesses should be done with good craftsmanship and care. Screw chucks are top notch--not on soft green woods and the same for any endgrain pieces. I push the envelope probably but I mount very heavy green endgrain vases with a stout glueblock and a single screw mount to that. Thick CA glue only. Heavy, strong green wood is not the same as soft woods (green or dry) when using a single screw mount.

[Reed Gray]

I guess one more comment.... I would NEVER use expansion with an end grain piece. That would be like using a splitting wedge......

robo hippy

[Pat Scott]

Take a look at production bowl turners such as Mike Mahoney or Glenn Lucas and watch their videos. They only use a tenon when making bowls, and I do the same. I have different size Vicmarc jaws and can make the tenon whatever size it needs to be to match the size of bowl. Jamie's advice from Tom Wirsing (a member of our club and a friend of mine) also applies to creating tenons: shape the tenon to match the dovetail shape of the jaws, and size the tenon so the jaws are almost closed. Tom is well known for his platters, Glenn and Mike are known for their bowls. Lyle is not a production bowl turner and has his own way.

The only time I ever use a recess is when making plates or platters. A properly made recess (cut to match the jaws when almost closed) will hold well. My recesses are usually no more than 3/16" deep. But just like with a tenon, the size of the recess is matched to the size of plate/platter. Meaning I would never use 2.5" jaws to hold a 15" platter! I don't care how perfect you make the tenon/recess, that small with that large of turning and you will not have the stability needed and are asking for trouble. I have jaws up to 7", so I can make a large tenon or large recess to hold whatever I turn. On dinner plates, many times I leave the recess because it's so small, but on platters (that I charge more for), I will reverse the platter and turn the recess into a bead or remove the recess completely.

I do have a vacuum chuck to remove the tenon and shape the foot when I'm done. My tenons are usually no more than 1/4" thick, so the comment about wasting wood is not a concern. A vacuum chuck really opened things up for me.

There are several reasons why I don't use a recess on bowls. One of them is that it can interfere with the design and curve of the bowl. Everyone pretty much agrees that a foot should be 1/3 of the diameter. Do you make the recess 1/3 or do you make the overall size of the foot 1/3? The correct answer is the overall size of the foot. With a recess you have to be sure there is enough wood beyond the recess so you don't break or split the foot. In order to make sure there is enough wood, you may end up using a smaller recess than you should, which again can lead to stability issues. Or you end up with a wider foot which can affect the shape and design of the bowl. Depending on how deep you make the recess, so you don't cut through the bottom you end up with a thicker bottom and heavier bowl. With a tenon - knowing that I'll remove it at the end - I can shape the outside how I want, have consistent wall thickness to the bottom, and cut the bottom as thin as I want. Then I reverse the bowl on the vacuum chuck and completely remove the tenon and shape the foot however I want. Minutes later all traces of how the bowl was held are gone.

[Leo Van Der Loo]

I use a recess probably more than 90% of the time, I have used tenon’s and still have some on the early turned pieces (many years ago before I had my Oneway chucks) where I used screws to hold the piece on a faceplate and needed this extra wood for the screws and to be able to turn that away later.

What I found a few times was that the tenon wood split, being thicker than the rest of the bowl/platter, I just finished a Mulberry bowl last week where the tenon had split, luckily it wasn’t right through, so I turned the tenon away, but by that time the bottom of the bowl was so thin it was flexing when pushed against it, it was about 1mm thick, so I used a piece of Mahogany to make a base/foot and glued that on, as soon as I have time to make a picture I will show the bowl.

With me using a recess and the Oneway chucks I use, I don’t need to make an exact tenon to fit the chuck’s jaws, and I don’t need to have all those different size jaws either.

A recess needs very little depth and certainly not as much as a tenon where the wood around it has to be turned away to make the tenon.

As I shape the bowl there is nothing to stop me from shaping to a design I want, as there is nothing sticking out and in the way while doing this, as I usually have a slight foot on my pieces I don’t have to give up any wood if that is ever a concern.

Then I reverse the piece and while green, I will leave the wood thick enough so I can return it when dry, at that time I don’t have a shrunk and warped tenon that now won’t fit the jaws perfectly anymore and have to return that, I just round the recess, held in my Oneway Jumbo or Mega Jumbo jaws or with my vacuum chuck (hardly ever as it is now a warped bowl).

I very often can hold the bowl with the oval recess without first rounding it, as the jaws will hold it securely enough to flatten the rim, and then return the whole outside of the bowl held in the Oneway Jumbo jaws, then do the inside, reverse one more time if I, as I usually do, pretty up the foot/bottom/recess.

Here is a picture of an American Beech bowl, Can you tell if it was held with either a tenon or a recess

American Beech.jpg

[Tom Albrecht]

Lots of good points in these posts and more proof that there's often more than one way to get the same result until you learn what works for you.

Leo, why did you leave out the price on #579? It's a handsome piece.

[John K Jordan]

I stopped in for a visit with Frank Penta yesterday and mentioned this. He said it almost always uses recesses for his face turning. From his gallery, his face turning is mostly platters, some huge.

BTW, Frank will be demoing at the TAW this year - laminated turnings, off axis, more.

JKJ

[Mike Goetzke]

Recently Stuart Batty gave a demo at the wood turning club I just joined (Bob Bergstrom is a senior member). I was so new to turning I sucked up lots of info like a sponge, but, since I was a newbie it was a porous sponge so hope I remember it right. For a bowl:

• Mount between spur drive and tail stock
  
  • flatten the face
  • cut a recess - close to the max. your chuck can open (he wants large footprint)
  
  
• Mount blank with chuck in recess and bring up tail stock
  
  • push cut to round blank and bring in balance
  • smooth face
  • cut off corner of cylinder/blank with couple cuts
  • shape bowl
  • form tenon
    
    • put chamfer on tenon (Batty does this so in case you get a catch it releases the bowl w/o fracturing the tenon. This way you don't loose the bowl)
  
  
• Mount blank on tenon
  
  • core the bowl

Of course there are many more steps but just outlined one production turner/instructor method of mounting the blank. I've used this method on three bowl blanks, plus what Bob B. has taught me, and like the results so much that think I will keep my lathe.


Mike

[robert baccus]

I find this to be quick and foolproof. If the piece is flat just drill and mount with a single screw to shape & turn the expansion ring on the bottom. If a irregular, natural piece is to be mounted use a small faceplate and 2&1/2" screws on the curve side and shape the bottom and recess. This only requires one reversal. Use different length screws to attach the faceplate.

[Justin Stephen]

Some random comments on the topic, FWIW.

1. Most of my recent work have been platters, for which I use a recess, but mostly because I am starting from 8/4" lumber and want to save that extra wood depth in case I need it later. For (non-segmented) bowls, I almost always use a tenon. I don't have a great reason for this, just preference. I cannot honestly remember the last time I have had a piece come out of the jaws, to be honest. All of my (non-segmented) pieces start on an appropriately-sized faceplate.

2. Using the correct jaw size is pretty critical to safety. I fear that a lot of newer turners do what I did for awhile when I was still new to the craft, which is buy a chuck with #2 jaws and use it for everything, regardless of size. For larger pieces, this can start to get a bit unsafe and reduce the quality of the finished product.

3. As far as looking at a dovetail on a finished piece, this is a non-issue. I have never not finish-turned (or turned away entirely) a tenon or a recess. High quality work demands this on the vast majority of pieces, IMHO.