finish turning a dried bowl

[Daddy3x]

Ok, so it shouldn't get any more basic than this, and I recognize that there a MANY answers. I have some bowl that have air dried for 3 months with just a bit of paste wax on the end grain. I have also tried the DNA bath this weekend, and am anxiously awaiting to see how they dry out in the next few weeks.

So, when I go and rechuck a dried piece, what is the best order of attack? I have done two bowls by very carefully trying to re-true the outside of of a warped piece with just a 3/8 gouge, then work the inside over, smooth the rim with a scraper, sand, and finish with a wax/polish.
Next I turn the piece and jam chuck it and re-true the bottom and work the tenon to a nub. Remove bowl and use a VERY sharp chisel to pare off the remaining tenon. Is one of those jumbo jaw setups worth the cost, it also seems to be fairly time consuming to reconfigure the jaws, unless I let a whole stack of bowls back up waiting their turn.

[OGYT]

D3x, I've been turning a few dried bowls this week. I jamb the inside of the roughout against the jaws of my chuck, and 'sort of' retrue the spigot... just close... and then put it into the chuck. I then turned the outside to final shape with my 5/8 bowl gouge. Then I true the rim and turn the inside, and sand & finish the inside and out.
For finishing the bottom:
I don't think you can beat Leslie Longworth's invention... the Longworth Chuck... for finishing the bottoms of bowls. I made one with a hardwood Spigot piece on the bottom that mounts in my Nova Chuck's 47mm jaws. I just remove the bowl from the chuck, mount the Longworth, mount the bowl in the Longworth, and finish the bottom.
Then I remove the Longworth and start the whole process over. I don't have to keep removing and replacing the chuck.

[orraloon]

I am with Al on the Longworth chuck. Most people make it themselves. Quite a few threads on here with the how to so have a trawl.

Regards
John

[joe greiner]

What they said. But the method you're presently using is probably best for natural edge bowls, where the rim isn't a constant height from the bottom. Neither Cole jaws nor Longworth works very well there.

While you're pondering whether or not to build a Longworth, you can get by with a plywood disk attached to a faceplate, with a groove turned to mate with the rim. The rim can be re-worked for different sizes, and replaced when it can no longer be re-worked. Set the rim in the groove for centering, and wrap around to the back of the faceplate with duct tape or filament tape. This doesn't work very well, however, if the bowl has warped out-of-round. For those, Longworth is still best I think, as long as it has enough buttons to seize the rim. And I still use the tape for insurance.

Joe

[Daddy3x]

Thanks. I am fairly sure I know what you've got set up, would you mind sending some pics?

Thanks

[OGYT]

Here's the small Longworth that I made for the Oneway. This one is about 15.5" (390+ mm) diameter.
You can see in the pic with the bowl (which I just stuck in there for the pic), that the eight buttons will hold pieces that have warped.
Most of the time I don't use the tailstock for support, and I've never used tape... never thought of that.
You just cut the slots in two disks of ply (or whatever material you want to use) and flip one of them over. When you spin the disks opposite directions, the buttons move.

[Daddy3x]

Thanks. A picture really helps immensely. Other than a freshly sharpened gouge, any advice on making those first passes on a dried blank less...I don't want to say intimidating, but something less than that. I have had several catches that tore (cracked) cracked a chunk out. I appreciate everyones help, reading through these forums has taught me a lot, thanks.

[Skew ChiDAMN!!]

You could try using a freshly sharpened scraper instead.

Still a bit on the intimidating side and it doesn't generally give as good a finish off the tool as a gouge/skew, but if you present the scraper properly (ie. handle up, tip down) then you'll avoid serious catches.

Once you've brought the shape back to something less cam-shaped, then switch to the gouge and clean up the finish.

[Hardenfast]

You just cut the slots in two disks of ply (or whatever material you want to use) and flip one of them over. When you spin the disks opposite directions, the buttons move.

I've looked at these Longworth things with much interest for a while now Al, and have decided to have a go at making one. Your pics will be a great help, as will previous posts here.

Everything was fairly clear to me until your last instructons. I'm a bit lost with the "two disks" and spin in opposite directions etc. What am I missing here? Also, how do you go about centering the bowl when mounting on the Longworth. Is this why Joe adds the groove to face plate?

Good luck BTW daddy.

Wayne

[joe greiner]

Summarised here, Daddy3x (links & links to links): http://www.woodworkforums.ubeaut.com.au/showthread.php?t=72276&page=2 (post #25).

Wayne, the slots are cut in the two disks sandwiched together. That makes the slots identical. When the outer/front disk is flipped, the pattern of slots is symmetric, and rotating them with respect to one another places all the slot intersections at the same radius, so that the bowl is automatically centred. Pretty slick, eh? The crossing angle varies throughout the said rotation; the flatter the angle, the more precise and stronger the purchase of the buttons on the bowl. The classical Longworth design has the slot arcs tangent at the inner diameter, where more precision is valuable.

As for still using the tape on the Longworth, I once had a bowl with almost vertical sides. The buttons' purchase was less secure, and the bowl went into orbit (without damage, thank goodness). I've been using the tape ever since.

Joe

[TTIT]

............Everything was fairly clear to me until your last instructons. I'm a bit lost with the "two disks" and spin in opposite directions etc. What am I missing here? Also, how do you go about centering the bowl when mounting on the Longworth. Is this why Joe adds the groove to face plate?
Maybe a pic of a see-through one will help clear it up Wayne. Both sides of this were stuck together with double-sided tape while the slots were routed and the finger holes drilled. Then one side is flipped over so that the slots then run in opposite directions or angles if you like as you can see in the pic. This way when the 2 sides are rotated in different directions, the bolts move in or out the same distance as each other to clamp the work in place. Hope that helps :U

[OGYT]

D3x, when I mount a warped roughout on the chuck, I usually turn it fairly fast, and then take light cuts with the gouge, while I'm making it re-round. I'm talking fairly fast... around 1200 to 1400 rpm. If you use a freshly sharpened Vee-flute gouge, and then use right close to the point, it takes a nice shaving out of the wood.

[Little Festo]

When I rough the bowl out I mark the centre of the tenon, just use the tailstock. This makes centring the the piece easier. Then I just use a rubber faced disk of plywood, must be rigid, and use pressure from the tail stock to hold it in place. As long as you don't have the revs up too high it's no problem and it's the same old story once it's in "better round" you can take the revs up a bit higher, bear in mind that the inside will be a bit out of round too so even if the outside is trued up it may not in balance. You would need to get a pretty serious catch to pull the piece off the setup described.

I've had some very warped pieces that would difficult to secure on cole jaws.

Peter

[OGYT]

Sometimes, for a jamb-chuck, I'll use a rubber Dek-tite over the chuck. Dek-tite is a brand name of the rubber boot that is made to go around a vent pipe sticking through the roof of your house. I just cut the flange off of it. Also, it's not got a hole in the center... you cut it out to fit the size of the pipe... so I leave it intact, to give a 'springy' rubber bumper to help spin the piece, and protect the inside of a finished natural edged piece.

[Daddy3x]

Maybe a pic of a see-through one will help clear it up Wayne. Both sides of this were stuck together with double-sided tape while the slots were routed and the finger holes drilled. Then one side is flipped over so that the slots then run in opposite directions or angles if you like as you can see in the pic. This way when the 2 sides are rotated in different directions, the bolts move in or out the same distance as each other to clamp the work in place. Hope that helps :U


Sometimes by "not seeing something" we can then see it. About a thousand light bulbs went. That is a very nice piece of work with the plexiglass. Very nicely built. I need to put one together now.

[Hardenfast]

I love it when a plan comes together!!

Much appreciated explanation Joe. A very slick invention indeed! You guys (and Mr Longworth) are way too cool for school!!

Yes, a picture paints a thousand words Vern. Many thanks. Is this your own fabrication? I can see myself hauling out the router and creating a few elipse templates in the near future. I actually like the idea of the plexiglass discs. Makes it look very professional - like a bought one.

It's all making sense now Al. For some reason I've looked at these things over the last few months without even realising they were comprised of 2 separate discs. And I like your idea with the Dek Tite - I've got a few of those laying around here somewhere. It's great when you don't even have to buy something to keep up with the latest and greatest!

See Daddy? Ask and you shall receive!

Wayne

[rsser]

Just to backtrack ...

To rechuck a rough-turned bowl at the green stage you can either cut a groove inside for your chuck to expand into, or leave a tenon inside to clamp on to, for when you come back to true it up.

So it's now dry and you mount it as per above. If it's a deep or wide bowl you will have checked to see if your setup will cope. If not, some comments below. So you now true the outside and foot. If you want to avoid faffing around with Longworths you can either cut a recess in the foot to re-rechuck (and keep the width and depth in mind from the beginning to safely do this) or dimension the foot to take a clamping chuck with or without jaw end marks.

Then you reverse the piece and finish hollowing the inside.

If you've clamped on the foot and left jaw marks, then you need Cole jaws or a Longworth to clean them up. But if you've dimensioned the foot so that the jaw ends haven't marked it, then you're done.

Another option to clean up a foot is to turn a mushroom with either a shank to fit your chuck or a MT taper to go straight into the spindle. Place some router mat over the mushroom and use it as a friction drive. (Useful for nat edge bowls). Important here is to plan it and leave a mark in the foot centre. You support the piece by bringing up the tailstock and locating the live centre point on your mark and off you go.

Leaves you the mark to clean up (off the lathe) so an alt. here is not to bother with the foot centre mark at all and do trial and error to centre it, and use something non-marking on the live centre (I use a hose tap fitting; 3/4" BSP at one end and click-fitting at the other; the wide end goes over the centre and the other is broad enough to support the piece without marking it.)

Minor error in centring can be turned/sanded out as you clean up and refine the foot. You can't tell by looking, usually.

An alt to a friction drive with a nat edge bowl is a vacuum chuck with an appropriate size diam tube.

[Daddy3x]

I cut out a 15" diameter disk on the bandsaw, glued and coverd it with a a tacky shelving material, and bored a hole centered for the chuck to expand into to. The trued the tenon. Took off the disk, finished the bowl, then used the disk and tailstock to very carefully remove as much tenon as possible, removed last 1/4 inch with a very sharp chisel. Not the most pure way to do this, but until I get the router out and try a plexiglass setup, this will be great. Thanks.

[rsser]

Good thinking Daddy.

Another variant on a friction drive.