Gripping a Hollow Form

[Brian Greb]

I am about to turn a HF that is 14" tall by 8" in diameter. What is the best size for the tenon and what jaws are best to use?

[John Keeton]

Brian, I have never done a form that deep, but it would seem to be well within the range of 50mm jaws. I would want the tenon to be just barely larger than the minimum capacity of the jaws so I could have maximum wood/metal contact. As far as length of the tenon, if you have dovetail jaws, going longer than the dovetail portion wouldn't be necessary and probably not a good idea.

But, the real question is - should you use a steady for the form? I would think to hollow something that deep it would be a definite advantage, if not a necessity.

[Brian Greb]

Brian, I have never done a form that deep, but it would seem to be well within the range of 50mm jaws. I would want the tenon to be just barely larger than the minimum capacity of the jaws so I could have maximum wood/metal contact. As far as length of the tenon, if you have dovetail jaws, going longer than the dovetail portion wouldn't be necessary and probably not a good idea.

But, the real question is - should you use a steady for the form? I would think to hollow something that deep it would be a definite advantage, if not a necessity.

Thanks John,
Would bowl jaws be a better choice due to they have a ribbed gripping surface?
Good point on the steady rest.
I should clarify that I'm going to "cheat" on this one, I'll turn the bottom 9" as a bowl. Then I'll cap the bowl, and hollow the cap.

[Allen Neighbors]

I would use my 100mm jaws if it wasn't end grain, and my 47mm jaws if it was end grain. I would also use a steady rest.

[John Hart]

I would use a faceplate and 2" Stainless lag screws.

...but then...that's what I do with most everything.

[Steve Schlumpf]

I agree with the use of a steady rest but the size jaws depends on how big you plan on leaving that portion of the hollow form. Example - it wouldn't make sense to use a #3 jaws if the finished foot of the HF is going to be 2" or less. Use whatever size jaws you have that comes close - but is still larger - than the finished foot. JMO.

[Bernie Weishapl]

I use the large jaws for the Vicmarc which is the 4" Dovetail jaws. They grip 3-3/8" to 4-1/4". They hold well.

[Mike Peace]

Not sure about other chucks but I think you need more than 2" jaws with a SN2.

The Teknatool manual says you should not exceed 6" long and 4" in diameter with a tenon using 50 mm jaws. Using the Powergrip jaws gripping a tenon 3.1" to 4" they saw you can safely grip a piece 12" long and 8" in diameter with a tenon.

[Brian Greb]

sounds like I need to go buy some new jaws and a stedy.

[Steve Mellott]

Brian:

I have a followup question to your comment:


I should clarify that I'm going to "cheat" on this one, I'll turn the bottom 9" as a bowl. Then I'll cap the bowl, and hollow the cap.
Why don't you hollow both the bottom and the top separately and then glue them together? I've seen this done as a demo and it turned out (no pun intended) very well.

Steve

[Brian Greb]

Brian:

I have a followup question to your comment:

I should clarify that I'm going to "cheat" on this one, I'll turn the bottom 9" as a bowl. Then I'll cap the bowl, and hollow the cap.
Why don't you hollow both the bottom and the top separately and then glue them together? I've seen this done as a demo and it turned out (no pun intended) very well.

Steve

I may do that I just want to make sure that the transition is nice and smooth.

[Dennis Ford]

+ 1 on the face-plate method, I have done a couple that were slightly larger using a face-plate and 1-1/2" lag bolts. (There were 12 1/4" x 1-1/2" lag bolts involved)

[Joe Meirhaeghe]

I use the standard 2 1/2" jaws on the Vicmarc 5 1/2" chuck or One Way Strong hold chuck on most pieces. ( I use both chucks)
I've used them to turn vessels from 3" tall X 2" dia. all the way up to 480 lb logs that are up to 24" dia. X 36" long.
I make most my dovetailed tenons about 2 1/2" to 2 3/4" dia. X about 3/8" long, even on the 400 plus lb. logs.
I good Steady rest is a MUST though to support the work piece.
The main purpose of the tenon is to drive the piece NOT to Support it. That's what the steady rest is for.