Hollow Form Technique

[Tom Winship]

I bought an elbow tool some time back including a swan neck attachment as well as a straight bar. This is made by a fellow in our local woodturners club.

I am anxious to try making a hollow form and was wondeirng about the sequence.
Please correct me where I'm wrong.
1. Are hollow forms cross grain like bowls or long grain like logs?
2. Turn between centers and turn tenon on tailstock end (Do you form the outside at this point or wait until you reverse ends into a chuck as in making a bowl?)
3. Turn OD form after chucking.
4. Drill hole in ID.
5. Start hollowing.
6. Finish OD and remove tenon.

All comments are appreciated.

[Dennis Ford]

I don't see anything wrong with the sequence you posted. I prefer to do hollow forms across the grain mainly because that allows me to avoid the pith. I form much of the outside while between centers and just true it up after chucking (or mounting on faceplate).
When you start hollowing; use the straight tool as much as possible (it is stiffer so it does not vibrate as easily and is less likely to get caught up in shavings inside the form). Stop and empty the shavings often (very often if you are getting curls). Measure the wall thickness each time you stop to empty the shavings.

[Rick Markham]

I think you largely have the sequence down and we all probably do it a bit different. Grain orientation is dependent on your choices mainly. I personally have the outiside of the form finish turned, and at least partially sanded before I tackle the inside. My outsides are finish sanded after the tenon is removed (and blended with the rest of the outside) The most important consideration in hollowing IMHO is the sequence that occurs inside of the vessel.

This is how I do the inside: First the hole is drilled, then that hole is opened up to a larger diameter to allow ample room for movement of the cutter head. Once that's done I will open up a section at the top inside of the vessel (the extent of which is dependent on the form's shape, size etc) I will then work my way carefully from the lip of the opening down to the shoulder (Opening space, or removing the "ridge" that's created by removing material, Once I have a couple inches nearly to final thickness, I will take my finishing cuts. I will then make my way down the form, removing material as needed for the cutter head, and blending each finish cut to the previous area above it. It's important to remember that like a bowl you are working from the lip down, once the lip is finished, it's important not to go back to it. Just take your time, and the best suggestion ever is... always sharpen your cutter before taking your finishing cuts on a section, as it dulls you can use it to "hog out" material ahead of you, resharpen, and finish cut. Don't let curlies build up, either vacuum them out or blow them out frequently. Wet wood especially will compact and either affect your cut, or break a thin walled vessel.

Also something that isn't often suggested but it helps me to "feel" around for the ridges I am creating during this process with the cutting tool itself (with the lathe off) I can then practice my movements required for a finishing cut several times to help generate muscle memory. The lathe is then started and the finishing cut made. I never have to go into a tricky cut blind if I use this technique. As you progress that becomes less and less necisarry (it's still very helpful though.) Another good trick is to use a flashlight and shine it directly at the bottom of the vessel, this will generate shadows caused by any ripple or ridge. It's a great trick to be able to see the areas that you need to work on. I check all my finished areas after I blend it with the previous one.

REMEMBER if you travel too far down the form before you spot something that you want to "fix" (higher up) it's probably too late. A catch on the inside of a thin walled vessel usually results in a broken vessel. At best the form will flex, and you will get chatter marks (that's if you are lucky)

[Dwight McNutt]

Don't mean to hijack this thread, but I have a question. In forming the outside of a hollow form, do you use a roughing gouge to round the blank and form it or do you something else to form the outside after rounding?

[Faust M. Ruggiero]

Tom,
To answer your original question, you can choose how to orient your grain depending on the look you want and the wood available. Cross grain hollow forms shrink unevenly and get oblong. If you are making a tall form, you may want to turn into the end grain. No need to include the pith for this style. Just find a log wide enough to take your blank along side the pith. If a wood warps too much or if I want a perfectly symmetrical final form, I turn twice, leaving the form walls thick and the opening smaller than I want my final opening.
I would advise you do your first forms on a face plate as versus a chuck. Others may disagree but a face plate will be the most secure hold and eliminate a lot of vibration. If you do get a catch, you will be really happy you have a good hold on the blank.

Dwight, I suppose a spindle gouge can be used for a blank being turned with the grain orientation following the ways but definitely not on a cross grain form. Truthfully, I use a bowl gouge on both.
faust

[Tim Rinehart]

To answer your question Dwight, stay away from roughing gouge for anything but spindle work. Not enough strength in the tang of most spindle roughing gouges to take a catch.
All forming of the outside of a HF is typically done with a bowl gouge, or heavy scraper as a few do. The most common I think is the swept back grind bowl gouge.

As to original thread, Rick provided a typical sequence that I also follow. I'll add this as a suggestion, especially if you've got green wood and are taking a while to finish. The areas that you've hollowed out are the ones that will start drying the fastest, and will heat up the most from any sanding or even the hollowing process. It doesn't hurt to keep misting the outside of your opening and any hollowed areas on the outside to keep from drying too quickly. If you have to stop work of hollowing overnight or for several hours, wrap the piece with plastic. I sometimes will coat the outside with shellac too.

If you don't want the piece to distort at final shape, rough turning the hollow form means you leave 10-15 percent of diameter (depends on how distortion prone wood is) of diameter in thickness to allow drying and come back to finish several months later. For example, if you have a 5" diameter vessel, you'd leave it between 1/2" or 3/4" thick, and then come back and final turn to perhaps 1/8-1/4". Be sure not to leave too much extra thickness at foot of vessel, the differential rates of drying thick pieces vs thin will often lead to cracking...DAMHIKT! I still goof this up occasionally for one reason or another.

[Scott Hackler]

Tom, you have the basics down in your list. Here is my process:

1) blank is mounted however the end result will look better (end grain or side grain or diagonal), blank between centers, rounded and tenon cut on tailstock side
2) mounted in chuck, tailstock for support, re-round and outside shaping done
(note, through finally "getting it" I started leaving a long "tail" on the bottom side so I can power sand up close on the bottom of the sides)
3) turned and sanded outside shape EXCEPT for the last 1" or so of the bottom. I leave it a bit thicker until the hollowing is done, for strength. Doing end grain hollowing I will sometimes take the bottom down to final shape but NEVER on side grain.
4) drill hole from tailstock to close to depth
5) either mount steady rest for the larger pieces or start hollowing.
6) hollow to desired thickness, starting at hole/shoulder and working way to bottom.
7) finish light cuts in inside, concentrating on finger depth inside hole. (everyone sticks their finger inside, so that area should be as smooth as you can get it)
8) sanding of inside (sometime I do, sometimes I don't) Most of the time I don't just because I dont have a great way of doing it AND the hole is generally 3/4" or smaller.
9) remove steady rest
10) turn bottom of sides IF needed and sand to final
11) part the bottom down while holding piece and finally cut off with a saw
12) using a small sanding drum on a die grinder, I sand the remaining unwanted stock off the bottom .
13) apply finish as desired.


Whew! That took longer than hollowing for real!

Look for Joe Landon's youtube videos. He does a fantastic job turning hollowforms and the videos are well made.

[Bernie Weishapl]

Ditto what Scott said. I pretty much follow his list. Joe's video is excellent.

Dwight I would not use a roughing gouge on a hollow form. I use a heavy bowl gouge for roughing bowls and hollow forms. Not enough strength in the tang especially on some mighty rough wood.