Deep hollowing tool????

[Norm Smith]

I love turning large hollow forms but when I get past a 10 inched depth or width my frustration mounts. I have Don Pencils system and love it, The Elbo system, whick is OK for smaller stuff and a version of the Jamison system. None of these systems can get me to where I want to go with reasonable ease. I do not have access to a turning club, nor have I ever attended a Symposium. My access to turning information is through turning forms, magazines and videos, so I find it frustrating when trying to find the right tool for the job at hand. Obviously, I have purchased some tools that I dont need.
My question is, What is the best system for deep hollowing of large hollow forms with small openings?

Thanks,
Norm

 

[MartyL]

Deep Hollowing

Hi most of the usual hollowing tools are not sufficent for going beyond 10" depth, I have a deep hollowing system made up in a local shop from 1 1/2" solid steel with a 3/4 hole in the end to accept most hollowing tools as well as a few custom shapes I have made up. It is designed after the Frank Sudol "trap" system the depth is on the order of 25" with a total length of 5' for the entire bar, it weighs about 25#. I'll try to post a picture later today!

Marty

 

[john lucas]

I agree with Marty. I go to 12" using my homemade Jameison style boring bar with 3/4" bars but to go deeper takes a lot of patience. I have the steel but haven't had time to build the bigger system. I'm going with 1 1/2". I used one like that when I took a workshop once and it was so sweet. almost took 2 men and a boy to set it up on the tool rest but you could easily hollow 14" with one hand.

 

[Joe Greiner]

How deep? How small the opening? How much undercut? And what species of wood? And final wall thickness too, I guess.

Some combinations will be utterly impossible, generally due to chatter at the cutter because of a small cross-section strength/stiffness of the shank at the toolrest, as well as tool handle control. With a 1/2" shank holding a 45-degree offset Oland tool (1/8" HSS cutter), I've gone to about 9" deep before the effort falls out of bed. A larger shank would be the most effective remedy, but it could increase the required opening size. IMHO, the only way to establish the "best" is by accumulated and tabulated experimental results.

And so it goes.

Joe

 

[Norm Smith]

Thanks guys.

Marty, I look forward to seeing some pictures.

Norm

 

[Ken Grunke]

I wonder if a tube filled with lead shot would give increased hollowing depth over a solid steel shaft of the same size. I have a gut feeling that it would, but could be wrong. Somewhere in the back of my mind, I remember reading about lead-filled boring bars for use on a metal lathe.

 

[john lucas]

Ken I thought I read somewhere once that a hollow tube of the appropriate thickness was stiffer than a solid bar. I could be wrong since the ole brain doesn't work like it use to. I have a hollow bar and had thought about putting a solid bar that is shorter inside. I could extend this par as much as necessary.
I think maybe it was Frank Sudol who was going to experiment with an extendable tool rest kind of like the Bestwoodtools box hollowing tool rest but you could make it deeper. This would help reduce the size if bar needed but of course the entry hole would have to be larger.

 

[KEW]

Ken I thought I read somewhere once that a hollow tube of the appropriate thickness was stiffer than a solid bar.

The engineering theory states that a hollowed shape gives a higher strength to weight ratio than a solid piece of the same dimensions. Adding material to the inside will increase strength, but not very much compared to adding it to the outside!

 

[Charlie Knighton]

deep hollowing

Norm,

when i was at richmond i attended a rotation "the Critique Process", deep hollowing was not discussed but size was, Jim Christiansen had a hf piece of tigre maple that was deep, i am not sure if it was more than one piece, but i can tell you it was light as a feather, surprizing so for as tall as it was. maybe Jim will tell us what he hollows with, for he definity has the craftmanship.

"It is important to remember that size is a design element that should be purposely chosen to support a design element."

this is quoted from the handout.

the rotation was chaired by Jim Christiansen and Stephen Hatcher

 

[Mark Mandell]

Size Matters

Normal rule for boring bars is that the usable depth will be 15 times the bar's diameter to control vibration in the cut. You can exceed that ratio, of course, but the quality and degree of control of the cut falls off pretty quickly. There is also a factor for distance from the center line (further out = more force and flex, closer = less) but I can't find the info.

I use up to a 1" bar on my self-made trap rig and it does well up to about 16" off the tool rest with a sharp cutter. Pix of the rig are floating around here somewhere. If you want to look, search my posts with pix.

m

 

[Ken Grunke]

I did a search on rec.crafts.metalworking for "leadshot-filled boring bar" and the 'xperts seem to agree it's worthwhile to do.
John, a hollow tube is not stiffer than a solid bar, but you probably don't LOSE much stiffness by makiing it hollow. Depends on the wall thickness, of course. I don't have any engineering facts to back up my assumption but try looking at it this way: if you remove from the center of a round bar the equivalent of 50% of it's total mass, does that resulting tube become half as stiff? Probably not, it's easy to deduce. The thin-walled tubing in bicycles is a prime example. The surface area makes up a good amount of the strength.

In the pic below, is a gas strut I cut apart a while back, which might make a good lead-filled hollowing bar. Pretty thin-walled, however. To digress a bit, the shaft is hardened and earmarked for a toolrest edge to be epoxied to an angle-iron toolrest.

 

[John Jordan]

A couple of things help. As Mark pointed out, sharp tips are imperative. The tip should not be larger than 3/16" and can even be reduced to 1/8". If you are using rear rest such as Lyle's etc, the surface contact must be minimal and the tool easy to move. Use paraffin, beeswax etc. generously on the rests.

You should be able to do 12 inches with 3/4 inch tools. Sharp tools and a light touch and experience are good for another couple of inches.🙂

John

 

[MartyL]

Deep Hollowing

Hi couldn't load all the pictures I wanted to so follow this link to my blog where I've posted many pictures

http://woodbowls.blogspot.com

I'll be happy to provide measurments

Marty😀

 

[Norm Smith]

Hi Marty, I sure appreciate the great pictures. That looks like a heavy duty rig. I would appreciate some more info.

The length and width of the bar and the size of pipe used?

Is the bar made of hollow pipe with a solid piece of stock drilled to accept cutters and welded on the end?

What is the width of the trap and is the middle pipe a roller?

Do you have various cutters with different angles.

Any other necessary measurements.

Thanks,

Norm

I just reread your first post which answers some of the questions

 

[john lucas]

That is the same sort of rig I built to use a captured bar on my mini lathe except I built my stand out of wood.

 

[MartyL]

Deep hollowing

Hi Norm: Here are the stats the bar is 52 length 22 trap section 30" reach of 1 3/4 DOM with a solid plug on the holder end, drilled to fit custom tool holders as well as many of the popular tools (Jordan, Stewart etc).
Trap is 36 wide with a 2" roller on the bottom and fixed upper bar. It has an 8" adjustment to accomodate many different lathe heights.

Cutter holder, I have made a 90, 60, 45 and straight all will hold many differnt shapes of cutters that are on the market!

Marty:cool2:

 

[Norm Smith]

Marty,

Thank you soooo much. I sincerely appreciate you taking the time to advise me.
This system should solve my problem.

Regards,
Norm