deep hollowing system

[Albert Cwirko]

I need some advice on buying a large hollowing system, I have checked the carter XL and the jamieson custom made with 2" boaring bar. my goal is 25"deep are there any other systems out there that would work also.is there any advantage between a round bar and square bar for hollowing,solid or tube.I would appreciate any info

 

[Mark Jundanian]

I can make this comment, when/if the bar rubs on the opening as you're hollowing round does better than square.

 

[Brandon Sloan]

I can’t advise on any deep hollowing system but I did read this forum topic the other day that might help. http://www.aawforum.org/community/index.php?threads/deep-hollowing-question.15030/

Good luck!

 

[Richard Coers]

Please don't take this wrong, but hollowing comes up on the forum many times a month. It's repeats over and over and no new systems have entered the market lately. The search function should keep you busy for at least a day. Steve Sinner's is the only one I would consider at that depth.

 

[Mike Johnson]

When you get into large hollow turned pieces a large percentage of these pieces are turned from several pieces and then glued together and finished on the lathe. The deeper and larger diameter solid billet hollow forms require large tools with a solid support system to control the tool as it makes its way into the hollow form. If you have a choice turning several pieces and gluing them together will save you time and is much easier to finish the surface areas for the finished item.

 

[Doug Rasmussen]

I need some advice on buying a large hollowing system, I have checked the carter XL and the jamieson custom made with 2" boaring bar. my goal is 25"deep are there any other systems out there that would work also.is there any advantage between a round bar and square bar for hollowing,solid or tube.I would appreciate any info

Comparing a square bar to a round bar of the same size, like for instance a square to a round with the diameter same as a side of the square, my quicky calculations show the square is about 1-1/2 times stiffer. Stiffness has to do with the distribution of mass away from the central axis, obviously a square has more mass away from the center..

My experience is more related to deep boring in metals. When there's a problem with chatter switching to a solid carbide bar helps. There are also other bars labeled as "heavy metal" with some sort of internal vibration dampening inserts. Of course either one of these type bars in a 3/4" diameter by 12" length would be cost prohibitive, costing more than most complete hollowing systems.

One way to dampen chatter/vibration is to use a trick borrowed from auto mechanics when they turn brake drums. They wrap the outside of the drum with heavy rubber bands. When rpm's are high a hose clamp over the rubber will prevent is from expanding away.

Another trick is to use a very small tool tip radius with a positive cutting rake. But positive rake tools have a tendency to catch so that requires some precautions to prevent.

I have no experience with hollowing systems, links to several systems on this forum and seeing a few at the Portland symposium last year is all I know. Most seem to me to be a bit on the flimsy side, not enough mass to effectively dampen chatter. But, the makers may be working to a price point so mass means more dollars.

Mark Lindquist is a person I suggest you contact (he probably an AAW member). He works on large pieces with huge machines so I bet he's done deep hollowing.

 

[Mike Johnson]

If you can get your tool rest inside the hollow vessel where it can support the cutting tool that is half of the battle, however it seems most people these days are trying to turn a vessel with a small opening that does not allow enough room to insert the tool rest through the hollow vessel opening. You are then left with no option but supporting the cutting tool from outside the vessel opening which requires a heavy strong metal bar with enough mass to overcome the harmonic chatter that will be generated by the cutting tool and the length of the cutting bar extended into the hollow vessel past the tool rest system. As Doug mentioned above you have to overcome chatter and vibration of the system which leaves you with very few options. A ring or hook style cutter would create less chatter and vibration if you could have one made for a large deep hollowing system.

 

[RichColvin]

I have and use the Carter XL. It works quite well, but it is heavy. Just putting the captured D bar up on the roller takes quite a bit of heaving.

If you get one, get the Hunter carbide bit add-on. It is best to use for hogging out, and then the tear drop cutter is good for evening out the surface.

 

[Dennis J Gooding]

Comparing a square bar to a round bar of the same size, like for instance a square to a round with the diameter same as a side of the square, my quicky calculations show the square is about 1-1/2 times stiffer. Stiffness has to do with the distribution of mass away from the central axis, obviously a square has more mass away from the center......
.

A more precise value for this comparison is 1.7, However, if you compare round and square bars that will fit into a given size opening, then a round bar is stronger by a factor of 2.36

 

[Doug Rasmussen]

A more precise value for this comparison is 1.7, However, if you compare round and square bars that will fit into a given size opening, then a round bar is stronger by a factor of 2.36

Dennis, thanks for a more accurate number for the stiffness comparison. As to sticking a square bar in a round hole, I can't quite understand why anybody would do that. It'd make more sense to turn the end of the square to fit the round hole wouldn't it?

Anyway getting onto discussing hollowing systems..... As I said I have no hands-on experience with any of them, but from what I'm reading there may be a simpler method without need for laser beams and cameras, etc, etc. Over the years in my business we designed and built 3 custom turning machines for specialized applications. One would have been perfect for hollowing, it's use was pre-polish surface finishing the inside and outside of bronze bell casting. The tool was guided by a manually operated template tracing mechanism.

As far as I know none of the hollowing systems use a tool guided off a rigid template. Each piece would need a template taken off the outside contour of the turning which wouldn't be a big deal (probably no more trouble than fiddling with a laser).

The big advantage I see of guiding the tool off a template, aside from accuracy in wall thickness and ease of use, is being able to use free-cutting high positive cutters that can't be hand fed without risk of catches and gouging.

One of these days maybe I'll mock something up to prove the concept.