? on roughing hollow vessels

Re: ? on roughing hollow vessels

Brad Vietje

>Mike --

In my experience, yes and no. How's that or an exact answer ?!?

If side grain, then generally yes, but you will find that the closer the shape is to a sphere, (and the smaller the opening), the less mass you need to leave, as the wood seems to warp less as compared to an open bowl. Also, in my experience, the thinner you turn it, the lower the forces, and the better the enclosed shape seems to resist the warping effects.

If end grain (spindle orientation) then usually not so thick as a bowl; if centered on the pith, you can go almost to final thickness, leaving just a little extra (and then get rid of mass in the foot to avoid radial splits outward from the pith). If an end-grain hollow form away from the pith, you'll still get distortion as the wood dries, but not as much as an open bowl.

However, if the wood contains voids or bark inclusions, there will be more warping in select areas where the wood is weakest. Spalted areas will also warp more, as the wood is weaker, and sapwood will usually warp more than heartwood. Knots and crotches warp differently, too, so if you finish turn and wet sand to completion, you can use this differential warping to get some pretty cool effects, otherwise, leave a vessel with these features a little thicker if you intend to season it before finish turning.

I hope Wally chimes in here, too -- I'd like to hear what guidelines he uses.

Safe Spinning,

Brad Vietje

Thetford, VT

Re: ? on roughing hollow vessels

Wally Dickerman at Green Valley, Az.

>Brad has covered it pretty well. How thick should you leave the sidewalls? Depends on what kind of wood it is, and how wet it is, is it end grain, and will it be a closed form. If it's end grain, and especially if you plan on a fairly small opening, you can turn it fairly thin. However, I like the term "turn against heavy wood". If you rough turn it too thin in the lower portion of the vessel you'll find it difficult to hollow in the upper portion when finishing the vessel. Don't just wax the end grain. Do the whole thing. I don't wax the inside of a hollow form.

You'll want to think about buying or making a steady rest. I have a shop made 3 wheeler that works great. Oneway has recently come out with a 2 wheeler that has received some good reviews.

Wally

Re: ? on roughing hollow vessels

Mike Schwing from Md.

>Thanks men. I suppose for now I'll be experimenting with side grain pieces, mostly cherry, ash, and cherry, but I have waxed quite a few blanks that are end grain with future end grain turning in mind. I should have asked about mounting in the first post - I have the Supernova "Power Grip jaws". Should I use them or a face plate?

Re: ? on roughing hollow vessels

Brad Vietje

>Hey Mike,

Glad to know Wally generally agrees with me -- wherever we differ, take his advice over mine !

I use a SuperNova with the 100mm dovetail jaws for most hollow form turning, so the powergrip jaws should work fine for most work, and probably better on wet end grain rough outs. One problem that arises with serated jaws with little grippy teeth, is that it can be nigh on impossible to re-chuck something with accuracy once removed from the larhe. You might consider turning a new foot between centers before re-mounting after seasoning, which I do for every twice-turned piece.

For heavier, taller pieces, especially end grain, I think the jury will always come back with a faceplate as a more secure hold -- depends on the size of the piece, and how much wood you have to work with. You can always turn a wide, short tenon on the piece, then glue this into a turned recess in a piece of scrap to make a rugged glue block for a face plate.

I work between centers until I'm satisfied with the outside profile, so the piece is pretty well balanced by the time I start hollowing, so in most cases the chuck suffices. For end-grain hollow forms, the "back hollowing" method that Raffan shows on his box video is a real quick way to rough hollow a piece if you aren't going through a really tiny opening. I use this method whenever the hole is 5/16" or larger, but I can't reach very far over the rest with a 1/4" gouge, so in practice it works better for 1/2" or larger openings, so you can get a bigger tool in there. Its a great technique to master, and has all sorts of applications in end grain hollowing for boxes, goblets and end grain bowls & vases.

Safe Spinning,

Brad Vietje

Thetford, VT

Re: ? on roughing hollow vessels

Keith Tompkins

>Hey Mike, if you start now, you'll have one of Dominic's steady-rests finished before your new lathe arrives! where can you find yellow wheels? lol

Hey thanks Brad

Mike Schwing from Maryland

>And Wally..

I decided to have a go at it this evening. I mounted the blank on a face plate, turned the bottom for the power grip jaws, then turned it over and started on the top. The hollowing is not a fast paced event like roughing with my Ellsworth tool, thats for sure. My bad shoulder doesn't like the torsion of that Sorby multi tip scraper I used. If I'm going to do this again I'll need at least a stationary lever on the toolrest for a fulcrum. The back hollowing method, I've done that a time or two on a bowl, didn't even think of it.

Anyway - here's what I wound up with, a rather large piece of half dry crabapple. I took it down to about 5/8" thick all the way around. Looks like that bark inclusion on the side will give way to a hole on the second turning. I coated the entire outside with anchorseal to let it dry. Thanks again for your help. I'd really like to watch one of you guys hollow something out.

Was fun, but slow going.

Re: Hey thanks Brad

David Galloway

>Mike, this thread has been very helpful to me. Thanks to Brad and Wally for your insight. I am really enjoying hollowing and your tips are so useful. And Mike....great vessel! Looks great. My concern is the cracking.

David

Re: Hey thanks Brad

Mike Schwing from Md.

>Thanks - if it cracks no big deal, thats part of the learning process. Its all free wood that would have gone to a chipper otherwise. I think it might stay together though - that blank had been drying for about 8 months. The shavings were only slightly moist, but I did notice some hairline checking had occured by the time I took the form off of the lathe.

Re: Excellent !!

Brad Vietje

>Great start, Mike!

I sometimes glue in the bark inclusions, sometimes I let them decide if they're going to stay, and sometime I intentionally pick the bark out (but not usually). Not much rhyme or reason, just what I'm feeling inspired to create that day. Since the bark on a certain percentage comes loose despite my best efforts, I usually try to keep it in there, figuring I'll get plenty of voids from those that don't behave as expected.

In some vessels the bark, sapwood, and heartwood shrink so differently that gluing them does more harm than good, not allowing the bark to shrink with the wood. If they're turned thin while green, the differential shrinking will usually be converted to differential warping, but they usually stay together.

You can see David Ellsworth turn a hollow form in his videos -- they are worth borrowing from your club video collection if you have such a thing.

That's a fine start in hollow turning.

Safe Spinning,

Brad Vietje

Thetford, VT