Why grip a spigot?

[Bruce White]

I turn mostly bowls and platters.In perusing these pages it is evident to me that the majority of experienced turners favour gripping a spigot in the chuck to the expansion method. Why?

I have a large Vicmark chuck and decided early that it was safer and wasted less wood if I mounted the blank on a face plate, cut a rebate, shaped and finished the outside and then reversed it and gripped in the expansion mode. My logic tells me that the direction of the spin makes the chuck want to open, requiring regular tightening in the grip mode. Found that out the hard way. The spin assists the expansion method.

What is the advantage of using the grip mode?

[Bruce White]

Just found the thread started by rsser 23/3/10. The contributors describe the method I use perfectly. I too, cut the rebate with the skew (my favourite tool) at an angle and about 5mm deep. The only failure I have had with this method was when I made the collar too narrow on a fairly soft piece and it broke on tightening.

[orraloon]

Bruce,
A good question and I would also be interested in others views. I mostly use the expansion mode as it saves waste timber and I have found it easier to to line up again if it gets rechucked later. I have had the odd split grain happen due to the expansion mode but I am aware of the risk now so leave enough wood around the base to hold things secure. These days for bowls and platters I mostly use the chuck that came with my Leady lathe and it only expands anyway.
Regards
John

[Poloris]

I always expand into a recess when turning green wood.
Green wood spigots are very weak and break off easily.
When using a recess if I have a problem it can be re-chucked.

[kcam]

I often use a Forstner style bit to drill a recess and find it is normally pretty consistent when re-chucking, also if timber is scarce for a spigot I glue on a pre-turned one centreing it up with the tail stock and tooling it to ensure true alignment....just a few tips that I find works for me.:)

[hughie]

well I'll be the exception. I use spigots exclusively on bowls and always in contraction never expansion and this includes green and dry blanks. I have a face plate of which rarely if ever use.

I prefer to use a screw chuck to get me started along with the tailstock, turn the out side to finish with a foot and a spigot. Reverse the bowl and do the inside, finally removing the spigot on a Longworth chuck or donut chuck.

[Avery]

The few times that I have tried using expansion mode grip I have ended up with pieces of part turned bowl all over the shop, including one time where it smashed two fluro tubes.

Maybe it is just me...

[ticklingmedusa]

The grip that a 4 jaw chuck provides in the contraction mode is stronger than
expansion. For large pieces and off balance work I prefer to use a spigot.
Use of the the recess / expansion method can create a nice stable base for some vessels.
I had a spigot break off once and after I did the wash :D I went to a recess because the piece was already rough turned and there wasn't enough stock left at the bottom to make another spigot.
It's good to have options .

[WOODbTURNER]

Hughie,
I agree with the contraction way too, but I try and use my face plates if possible. This guarantees that they very rarely come off.

[Pat]

I use chucks in contraction mode mainly. Sometimes for small >100mm blanks I'll put in a recess and use in expanding mode. The spigot only needs to be between 3 - 10mm in depth, depending on the blank size and composition . . .

I do use screw chucks (Woodfast and a bespoke 25mm version) and faceplates from 82mm to 200mm. It all depends on the type of wood, it's condition and the phase of the moon . . . whether I feel brave or it's kevlar body armour time from some punky Redgum burl action:U

[issatree]

Hi All,
I agree with Hughie & Ticklemedusa, that I also have only ever used the Spigot, in the Contraction Mode, I mainly use the 35mm. S/Jaws, but have 45 & Pinocchio Jaws as well. Have just purchased another Black Nova Chuck, & it had 100mm. Jaws .
I also use my 3 Jacobs Chucks & if I get the right size of Wood, I Insert it in The Heads #2 Morse Taper, with the Tail Stock, but most of the work I do, I don't use the T / Stock. I mostly use 3000RPM.
Then again, I don't turn Bowls. Haven't used a Faceplate for at least 7 yrs.

[Bruce White]

Sounds like there is not much difference really, other than personal opinion/habit. I guess I will just keep doing what I have been to date.

Turned a tiger myrtle bowl today - love that coloured/patterned Tassie wood!

[jchappo]

I prefer a recess when turning face grain and a spigot with long grain.
A spigot on face grain can crush and tear the spigot away and, conversely, a recess in long grain can spread the grain apart.

[Skew ChiDAMN!!]

Hmmm... I tend to use a mix of both styles. :think:

If the blank has enough material I'll almost invariably mount with a spigot. If only because it's inherently a much safer method.

It's only when there's insufficient material for a spigot that I'll use expansion mode... and even then it depends a lot on the timber blank.

Any checking, resin lines or even if the species is just known for weak grain, and I'll glue on a waste block for either spigot or faceplate.

[HSS]

I drill a hole with a forstner bit, expand hte chuck in that, turn the back (including a spigot), then grip in compression to do the inside. Having recently bought bowl jaws, I've started turning out the jaw marks on the spigot to leave a neat foot. I reckon I've had more bowls slip on the spigot than in a recess.

[Scott]

A mixture of both depending on the grain. Generally though, a spigot in contraction.

Seems as though, given these responses, there is no right or wrong way.

-Scott

[Bruce White]

How is it safer Skew Chi Damn? I found that I had to keep tightening the chuck when I tried using a spigot - lost a piece off the lathe - scary! That is when I worked out that the centrifugal force works against the spigot and for the recess. I do check the chuck periodically in the recess mode but have never found that it needed tightening.

[Skew ChiDAMN!!]

G'day Bruce.

In compression mode you can tighten your jaws until they start crushing wood fibres. (Not that you should but you can. :U) In expansion mode, such forces would most likely cause the blank to split.

Also, if the blank has a slight flaw, compression mode can hold the blank together. There have been times when I've discovered a hairline fracture, decided to keep on turning and then, when finally dismounting, had the piece fall in two as soon as I released the chuck.

That's not really a good thing, but in expansion mode I'd have probably worn those pieces much, much earlier. :;


With your problems with the spigot, it sounds like your compression technique needs some work; there are certain rules that need to be followed for a secure grip.

Eg. the end of the spigot should not"bottom out" in the the jaws. The spigot shoulders should be sitting hard against the ends of the jaws, with no spigot visible between them and the rest of the blank. Otherwise it will work loose!

Also, for any set of jaws there's a "best holding diameter." With nothing in the jaws, close them fully and then slowly open them up until the inside diameter forms a perfect circle. Measure that diameter... and that''s the diameter the spigot should be for those particular jaws. :)

Hopefully it is just poor technique and not a mechanical problem with your chuck! ;:

[rsser]

Hate to rehearse old debates ... but:

With dry timber there's no reason not to go expansion, provided you match the recess wall angle to your dovetail jaws. It's a dovetail joint. That means it's a locking joint by its nature and you don't need much pressure outwards on the chuck. I just take up the slack and then add a bit. And test if need be by locking the spindle, grabbing the workpiece and trying to wiggle it.

Note: I'm only talking about jaws that have a dovetail. Not the stuff that one maker calls spigot jaws. And that same maker produces some beaut 3" heavy duty bowl jaws with a generally dovetailed x-section but the outside jaw face is rounded over so you loose some critical depth that's needed for the keying.

[Skew ChiDAMN!!]

Hate to rehearse old debates ... but:

With dry timber there's no reason not to go expansion, provided you match the recess wall angle to your dovetail jaws. It's a dovetail joint.

Yes. And the same dovetail should be used in compression mode too! Although it seems not many people bother...

[Bruce White]

I think you are right Skew ChiDAMN!!!. I can see that there are, as you describe, situations where a spigot is preferable. And yes, it is was, from your description, certainly my technique when it failed previously. Will give it another bash but still favour the expansion mode.
Thanks to all for your opinions/advice.

[rsser]

Agree Skew, if you don't want to return the foot. Get the diam and angle right and you're scott free.

There are other variables too Bruce.

With an expansion joint and a foot, your chuck may give some some design probs. You need say 3/8" of foot width, and on the rule of thumb that a foot should be about 1/3 the diam of the bowl, on smaller bowls you won't get there.

Another variable is how hard you go in with your gouges.

I see some guys with 3/4" gouges and go in like their life depended on it.

Raffan's an exponent of expansion mounting and not coincidentally every time I've seen him demo he's said 'let the wood come to the tool'.

[NeilS]

The only times I use contraction mode on a spigot is when I'm coring large green bowls, sometimes when I'm green turning 20"+ bowls (and going in hard with the 3/4" or 1" bowl gouge...:rolleyes:), and on end grain blanks. In those cases there is a lot of extra weight and leverage on the style of foot ring that I use, which can break off if held in expansion mode.

___/ /___________\ \__


If you use a recess without a foot ring there is not the same risk, but then you have to come back and return the foot if you like a proud foot ring, as I do.

/____________\

Otherwise I use expansion mode in all other cases.
.

[sjm]

Yes. And the same dovetail should be used in compression mode too! Although it seems not many people bother...

The Supernova II manual specifically states this should not be done (page 13). It says the spigot should be parallel, and the lip should not be recessed.

[rsser]

OK, I'll wear the charge of imprecision.

Gen. principle: the tool should match technique, wood and application.

By way of illustration, pic depicts my first solo deep hollowing effort.

Munro, gen. 1, hand-held. Wood: described by the donor as some kind of pine; turned green. Looks like Cypress to me. Total 40 cm. Hollowing depth: 20 cm. Recess 75mm. Recess depth (with Vicmarc jaws): 5mm.

No chatter, no drama. Will say that deep hollowing hand-held is best learned with medium density woods, and with the pines of various kinds doing it semi-green seems to work best.

That's my two bob's worth for the day.

[rsser]

The Supernova II manual specifically states this should not be done (page 13). It says the spigot should be parallel, and the lip should not be recessed.

Nova Spigot jaws are not the same as dovetail jaws.

[sjm]

Nova Spigot jaws are not the same as dovetail jaws.

True. Just thought I'd mention it, because when I started out, people were telling me I needed to shape a dovetail on my spigot, and I had all sorts of trouble. Different jaws need different spigots.

[Skew ChiDAMN!!]

The Supernova II manual specifically states this should not be done (page 13). It says the spigot should be parallel, and the lip should not be recessed.

True. However, I also have the precursor to their Precision Midi chuck and in that manual it states that it should be done.

Similarly, I've had slips of paper included with jaw sets that show the specs for the spigot/mortise for that jaw set. They usually show a slight dovetail in the shoulder. (Shark jaws, Powergrips and Teknatool's big "Spigot jaws" being the notable exceptions.)

I think that what was happening was people were tapering the whole spigot rather than just the shoulder, so Teknatool covered their butts against being sued for misinformation by taking the simple path and saying "don't."

But you're quite right that different sets of jaws require different spigots!

[NeilS]

Different jaws need different spigots.

Yes, the jaw profiles vary.

Look at the profile of the jaw being used and match the recess/spigot to that jaw profile.
.

[powderpost]

You can overcome all the problems of matching dovetails, spigots, tenons or what ever. Screw a waste block to a smallish face plate, hollow it out and glue the job to the hollowed waste block. Turn to your hearts delight, inside and outside. Then cut the job off with a hand saw, through the waste block and clean the surplus of the foot with hand plane, sand paper. You can even rechuck in a longworth or jam chuck, to refine the foot. Very cheap and you can make the diameter of the foot as thick or thin or a diameter as you like, without being dictated to by a chuck manufacturer. Haven't lost a job yet, using this method.
Jim

[NCPaladin]

I use the expansion method most times based upon my chuck manufacturer recommendations and general mathematics (remember pi [RxR] ). I do try to leave one inch of wood surrounding the expansion, especially in green wood. For 50mm jaws a spigot has 3.14 square inch of wood, in expansion, with the center 3.14 deducted, you still have about 9 square inches left.

My initial opening is the same as the jaws closed, if they have a dovetail they will expand to proper diameter to even reach the wood. This would not be true for straight jaws.

[robo hippy]

Here we go again.

First, I have never understood the idea that a recess wastes or saves more wood than a tenon. A 3/16 tenon turned off is the same as a 3/16 recess turned off.

Second, every problem I have ever heard of with failures when using a recess or tenon are from doing some thing wrong, which can be corrected, not from inherent shortcomings of either method.

Over tightening is one problem. You want it snug, not as tight as you can get it. If you have a keyed chuck, tighten in one key, then rotate and tighten in the other. On big pieces, I will rotate it through a couple of times.

Not having enough shoulder on the outside of your recess is no different than using too small of a tenon. You can get away with small and dainty, but when you do, you need to turn very gently.

The wood will compress no matter which method you use, and it makes no difference if the chuck is pushing out or in. Chuck jaw alignment with wood grain does make a difference, especially in wet wood when mounting. You do not want 2 jaws on end grain, and 2 on side grain because side grain compresses more than end grain. Rotate your chuck/bowl about 45 degrees and that solves that problem.

I would never use an mortice when turning end grain. Might as well take an axe to it and split it that way. If there is a bark inclusion or crack of some sort in the middle, then a large tenon will offer some extra degree of support, but any piece that is not good solid wood needs extra care/attention to safety, when turning. Flooding any defect with super glue will give minimal support, but isn't any where near as strong as solid wood.

The closer the tenon or recess is to your jaw size and angles, the better your grip will be. You get more metal on the wood.

I always use a recess for turning bowls, green or dry. I use a forstner bit to drill a recess to mount for turning the bottom, turn a recess on the base and reverse. On big bowls (over 18 inches) I do use a face plate, as I can't get a forstner bit big enough for a proper sized recess on the top side, and my drill press won't reach out that far. This has worked fine for me for very aggressive turning and coring for thousands of bowls.

I have a dedicated dove tailed scraper for forming my angle. It appears to be angled at about 7 degrees which is what is most common in the flat world for dove tail joints.

robo hippy