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Hollow forming question

Alan Carter

Alan Carter

Joined
Mar 23, 2009
Messages
37
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4
Location
Lisle, IL
Website
www.alancarterstudio.com
You all have been very helpful with my sanding questions so here's one about hollow form turning. How do I hollow a tall narrow vessel with a small opening in the top, say a vessel 6-8" tall, 2 1/2" diameter, with a 3/8" opening? Is that asking too much of the hollowing tools or is there something made to do this kind of work. I can get my mini-hollower (Sorby with the bent shaft) into the opening but as I go deeper than a couple of inches it chatters like crazy. I tried using a small spindle gouge but that felt dangerous and it also chattered a lot because of its small mass. (I assume)
Even if I make the opening bigger what do I use to get to the bottom of the vessel?
Thanks.
 
Unless you have an extremely delicate touch and the patience of Mother Teresa, isn't going to happen. You can't stress thin sections of metal that way without making them flex.

The way you get deep with narrow openings is to hollow from the bottom and conceal the plug or hollow from the top through a larger opening and install a collar. Pottery people can close their containers, we can only open ours.
 
Alan Carter said:
You all have been very helpful with my sanding questions so here's one about hollow form turning. How do I hollow a tall narrow vessel with a small opening in the top, say a vessel 6-8" tall, 2 1/2" diameter, with a 3/8" opening? Is that asking too much of the hollowing tools or is there something made to do this kind of work. I can get my mini-hollower (Sorby with the bent shaft) into the opening but as I go deeper than a couple of inches it chatters like crazy. I tried using a small spindle gouge but that felt dangerous and it also chattered a lot because of its small mass. (I assume)
Even if I make the opening bigger what do I use to get to the bottom of the vessel?
Thanks.
Click to expand...
Keltons small set of hollowing tools with a 1/2" shank are the smallest I'm aware of that would do a vessel that size.
 
The impossible takes longer. And you become frustrated that it detracts from other objectives. BTDT.

Drink from a glass that's half empty.😀

Joe
 
Alan

Each tool (and turner) have a maximum distance of effectiveness off the tool rest.

Many of the large forms with small openings are hollowed through the bottom.
A plug is cut out, the form hollowed, the plug glued back in, and the glue join hidden in a groove.

The 1/2 Bosch tools (straight and hook) will go 6" off the tool rest easily.
The design has nothing in the way so they work through the small opening
The cutter on the Bosch tool is about 3/16" so it isn't too grabby when off the tool rest.
At 8" off the tool rest You are pushing the limit of a 1/2 tool.
You have to work slower and take nibbles instead of bites.

put a scrap block in your chuck put the tool rest 2" away cut across the surface with your hollowing tool 3-4 passes
move the tool rest back in 2" increments and repeat. You'll see what happens and find your limit. With practice you can learn to extend it.

The deeper off the tool rest the tool needs to be sharper and the turner must take lighter cuts.
I find I can work comfortably with using a 3/4 inch bar to 10"-12 off the tool rest and with a 1 1/4 inch bar to 18 off the tool rest.

All that said there are folks who can use the 1/2 Ellsworth tools to hollow really big forms 12" deep an larger.

Hollowing is similar to using 1/4 gouge 4 to 5 inches off the tool rest. Working off the tool rest requires lighter cuts and reduced bevel drag. the pressure of cutting sets up vibration which increase until no cutting is taking place.
Happy turning
Al
 
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Along the same vein as Michael, I've made them boxes, then before parting off, CA the top to the bottom. To conceal the joint, I cut a shallow, 1/8" wide groove centered over the joint, then fill the joint with either brass, copper, coffee grounds, etc. using either epoxy or thick CA with accelerator after. I have also hidden the joint by rolling several beads in the area where the joint was, and that also hides it.
If you cut the top and bottom with a bandsaw, you can minimize the wood lose, and if you're really good, you don't have to hide the joint.

A light touch with a standard grind bowl gouge to remove the build up and then more light sanding.
The light touch for finishing cuts helps reduce sanding (by being able to start at higher grits.) Depending on the surface, I start sanding anywhere between 180 and and 280.

For any final cuts, I try to follow the advise I heard (sorry, but I can't remember who said it,) "Always ride the bevel, but the wood shouldn't know it."
 
Impossible, no, but definitely an advanced procedure.

Figure that the opening is the maximum diameter (bar) tool you could use without creating an opening somewhere else.

The more unsupported tool length off the toolbar, the more diameter, dexterity and or experience you would need. Work up to it using a larger bar to start with and then smaller and smaller bars. Think of it as a challenge.
 
Is there a picture or two somewhere of the plug and/or cut method?

Being a rank beginner, it is difficult to visualize the plug method. How would the plug be cut? Wouldn't the kerf be fairly substantial?

I hope it's not a "magician secret" that can't be given away! 😀
 
I hollow those type of vessels from the bottom. I try to part off a piece of wood near the bottom and then save this piece in a plastic bag. I turn the plastic bag inside out every day to slow the drying for a few days and then put it in a paper sack. I hollow the vessel and then let it dry. When dry I put it back on the lathe and true up the hole in the bottom (or sometimes I just drill it with a forestner style bit). Then I take the piece of wood from the bottom and turn it to fit the hole, align the grain and it's almost invisible.
I learned this from John Jordan. You can also just fill the hole with another piece of wood you have laying around the shop.
 
The plug is like a cork and is usually cut off the bottom

with the bottom toward the tailstock make a tenon, maybe 5/8 long
I put a slight taper on mine.
put a pencil mark on the plug and bottom so you can match the grain when you glue the plug in.
Cut the plug off with a thin parting tool and you will have 1/2" long plug.

Size the opening to fit the plug hollow and line up the pencil mark an glue in the plug.
you may need to have a tenon on the bottom so you can flip the piece to finish the top. then flip it again to finish the bottom.

John Jordan has great video on making a plug at the top. He finishes the plug to make it look like one piece.

happy turning,
Al
 
The Kelton minis (5/16" dia) may work for you for about the first 4 inches and around the shoulder area. It is sturdier than the Sorbys but you are still not talking about a whole lot of steel. Not really knowing what your form looks like it's hard to say about the rest of it. Going through the bottom or doing a two part form with some sort of texture or accent to hide the joint may be your only option. I have made some small hollowers out of 1/4" key stock drilled for a 1/8" HSS bit at an angle to use on minis. But again, the deeper the vessel the more steel you need to avoid impossible vibration.
 
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Alan,
I bet if you contacted John - he would sell you a copy of the video. John has a couple of videos out and all are worth the cost. John is a good instructor. You might also try your club library.
Hugh
 
Alan,you can hollow through the bottom and make you hole as large as the piece will allow. Turn your piece with a tenon on both ends. Then cut the one that is on the bottom off. First making a referance mark so you know where to line up the grain. Then turn the piece end for end and hollow through the bottom. After you are finished put the base in your chuck and turn the bottom so it is a thight fit. Glue it in and let the glue dry. Then turn the top of your piece. Now you can make the opening in the top as small as you want.
 
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