First posted on rec.woodworking - thanks, George - should have guessed that there was a dedicated bunch of computerised turners.
Anyway: I've had an axminster clubman chuck for a year or so and have only used it with the type C jaws. er, this is my first expanding chuck in case you can't guess from the rest of the post.
These have a dovetail on the outside and a lipped internal grip on the inside.
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After one or two disasters with the expanding dovetail on bowls where i had left insufficient wood around the outside of the recess to withstand the forces - and that the internal recess can be left on the bottom of a bowl but its not a great feature {George posted a link to one of his which is giving me second thoughts on this though}- i have tended to use the internal lipped recess for most stuff and then take off the stub after finishing. originally i would turn a stepped spigot to fit the lip - but i had one or two of those fly across the room with the "stepping" bit splitting. So i took to just doing a straight spigot.
But it tends to slip occasionally.
Two questions then - what does everyone else use - the inside stepped or the outside dovetail. If you use the inside stepped do you turn a stepped spigot or a straight one.
And would a different internal shape be better for bowls such as the serrated one on the type H Medium gripper or the dovetailed ones on the Type A ? (eg the kids don't know what to get me for xmas...)
Oh if it makes any difference - not just bowls of course - I'm still working on perfecting the ideal eggcup; have had an enjoyable bash or two at goblets and everybody seems to be getting boxes this xmas.
Couple of red flags showing here Ken. "stepped dovetail" is impossible. That ridge under the dovetail is the limit of depth, otherwise you lose the wedge, and start to try to drive a round peg in a round hole, which makes a split. You have to bottom the jaws in the recess, that's what takes the strain. Your wedge action helps draw it snug. You're not gripping, which is why you don't crank on the tension, you just snug the face of the jaws against the bottom of the mortise. Make sure it's free of dust and chips, and the bottom is perpendicular to the axis of rotation so it will seat without wobbling.
Same principle in gripping outside. What really counts is getting the shoulder you cut perpendicular to the axis of rotation flat up against the jaws of the chuck. You can use the dovetail, if your jaws have them, to wedge, but you don't want any part below the limit of the dovetail to steal the wedge from you by grabbing the wood.
If you use the serrated type for grip, you will have to snug the piece flat up against the jaws by using your tailstock or some other type of pressure, because there's no wedging action to draw for you. You might even end up pushing the piece out of register if you overtighten the jaws, because the serrations are really bi-directional wedges, and they'll push up and break through the fibers if you're not careful.
That's why I like the smooth jaws. When you make the tenon or mortise as close an approximation of the circle formed by the jaws as possible, you spread the load over a large surface. Means you won't exceed the elastic limit of the wood when you snug up.
As you saw in the picture I referenced, you can sneak your hold into a background of decoration pretty easily. The picture is actually of a mortise which was used initially, and the outside ridges were held as if a tenon afterward. Neither made a significant dent, and the piece was about
10" in diameter, yet held for hollowing and sanding just fine.
Think fox-wedged dovetails, or the wedge that holds your hammer head in place.
Thanks again - this is getting clearer - sorry to be so thick - look i'm an expert on coffee if I can do the "help desk" bit on that in return :-)
I hadn't appreciated the importance of a squared off shoulder- nor had the cleanliness occured to me
The jaws I have have a dovetail on the outside edge. They are easy to cut a hole for but have had the odd split out when i have taken the outside edge of the turning too close to the recess leaving insufficient wood to hold the work. So i could get a set of jaws which did smaller external dovetails, i suppose.
The alternative is the inside holding edge which is not a dovetail but is parallel and stepped - see
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and then click on the "jaw profiles " bit. Now - what shape spigot do i make for that? If i understand you i just cut a straight parallel spigot SHORTER than the total depth of the jaws so it relies on the shoulder of the wood to be faced flat and not the end of the wooden spigot - nor do i cut a stepped spigot which i had assumed was the ultimate profile.
and would i be better with one of the jaws which has a dovetail on the inside and out eg
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or
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(i am off the gripper type jaws after realising the sense of your "chews up" comments)st.
That profile grips outside with a squared shoulder, short enough depth (length) of spigot as not to bottom against the inside of the jaws, and a mild undercut of the point where the spigot meets the shoulder ( /spigot\ ) That way the ridge will find the path of least resistance to be snug up against the shoulder. Help it when tightening with your tailstock.
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> > or
I like the A&B type. Just got the similar pattern for my Teknatool NOVA chuck. They call them 75mm, though the minimum seems to be 82 for a recess, where they work just fine. Joy is in the broad faces on the jaws, which allows good wide shouldering of relatively small diameter tenons. Did some green wood goblets with them, and I'm hooked. The spigot jaws are now in their own box, like the extra sets of 50mm I acquired along with extra chuck bodies rather than in their compartment in the drawer. I'll be using them even less than I did before, which was hardly ever.
As to the grip types, there are those out there who swear by them rather than at them as I do. More suitable to dry wood than green, and they do grip square stock well. Mine were out of the box for a few ornaments a month ago for that reason. The O'Donnell type are nice for people who do wine stoppers, tops and such in a production environment, but my choice would be
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for that type of spigot use and as pin jaws for roughing out. Most useful type of jaw for general work I own.
What George said is about the same way I use my Nova 2 jaws.
Been using them for about a year now and this chuck and jaws are worth every penny.
On small light bowls and vessels I counterbore the first end of my bowl, chuck it with the outside dovetail of the jaws. Turn the bottom and outside. With that same mount I turn a shallow hole on the bottom (foot) of my bowl and give the wall of the hole slight dovetail angle.
Then dismount, turn the bowl around, and mount the bowl in the dovetail hole I made in the foot, and finish my bowl on this second mount.
On larger heavier bowls and vessels, I turn a spigot that is near the maximum opening size of my powergrip jaws. I also turn a step at the end of the spigot, so the ends of the jaws has something square to butt up against when I mount on the spigot.
One good tip.
Once you have your work mounted on the jaws, and it is turning perfectly round, mark the bowl right next to a mark on your jaw. This will give you a reference so that if you have to dismount your bowl you can remount it at the same spot you had it before reducing the chance of mounting it out of round the next time.
On spigots, this is far easier because the spigot will be a waste piece. On spigots I use a sharpie pen and mark the wood on the spigot where it shows in between the jaws. Spigot jaws will leave impressions on the wood as well, so you will want to "feel" your block back into the same spot when remounting.
cad hanturnedbowls.biz
Ken Wils> First posted on rec.woodworking - thanks, George - should have guessed that
Oddly,the chief advantage to the smooth jaws is they _must_ mount true. They have no other choice if you keep the mating surfaces clean and undamaged. Any place around the inside of the mortise or the outside of the tenon is equal to any other. If the first attempt on a reverse or remount doesn't rotate true, I consider it a clue that I have a shaving or something captured, and re-check. Not all that unusual that I use the recess or groove that that forms the bottom to re-mount a bowl whose finish I'm not satisfied with for shaving off the old finish to try again. Some get pretty thin, but by not eliminating my mount, I still have the capability. That's where I use the power-grip jaws the most, in scribed and perhaps burned rings which form the reveal at the bottom of a bowl. By turning them a close match, I get a second chance. Do hate having to work around the tailstock for the back, but it's doable.
Do your jaws meet flush on the front? That and using your tailstock as a bumper/clamp on the inside of an already turned bowl.
I've got one of the NOVA live centers which allows me to screw on tapered disks to wedge and center where I can't extend the quill all the way to the bottom.
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