Articulating arm hollowing system

[Paul Lajoie]

I am interested in building a Articulating arm assembly, I've notice most if not all are made with1" square steel bars. I have 3/4"X1" aluminum bars that were used in the medical field as a articulating arm tool tray of sorts. Would these be strong enough to use? These are solid bars not tubes.


Paul

 

[Bill Boehme]

Welcome to the AAW forum, Paul.

The answer to your question is very dependent upon your intended use. Will this be for a mini lathe or a medium size or a really large lathe? What size hollowforms are you intending to make? The depth and diameter of a hollow form make a huge difference. There are also other considerations that can't be easily quantified such as the hardness of the wood, the cutter being used, how you use the tool, and how much vibration is tolerable for what you are turning.

On one hand, you could spend the time and energy to apply classical beam theory to different materials or build something that is over-designed, cross your fingers, and hope for the best. The modulus of elasticity of aluminum is about 30% of the modulus for steel which in very simplified terms says that for equal stiffness, the aluminum bar would need to have about three times the cross section for equal stiffness. Perhaps much more important would be angular deflection in the knuckle joints. Overall. I think that the main issue is minimizing vibration, but if there will be a considerable overhung load on the boring bar then total deflection would be important. I assume that the boring bar itself will be steel just to keep the diameter reasonable.

The main advantage of an articulated arm hollowing system would be the situation where you have a short bed lathe and don't have the space to mount a gate to trap vertical movement of the boring bar. If that isn't your situation then something along the lines of Lyle Jamieson's hollowing rig is far simpler and less costly.

My assessment is that you are creating an unnecessary design challenge just because you have access to some (I assume, free) aluminum.

 

[Bill Boehme]

If you haven't looked at the recent thread by Raul McCai on his articulated arm assembly, you might want to take a look HERE.

 

[Paul Lajoie]

Welcome to the AAW forum, Paul.

The answer to your question is very dependent upon your intended use. Will this be for a mini lathe or a medium size or a really large lathe? What size hollowforms are you intending to make? The depth and diameter of a hollow form make a huge difference. There are also other considerations that can't be easily quantified such as the hardness of the wood, the cutter being used, how you use the tool, and how much vibration is tolerable for what you are turning.

On one hand, you could spend the time and energy to apply classical beam theory to different materials or build something that is over-designed, cross your fingers, and hope for the best. The modulus of elasticity of aluminum is about 30% of the modulus for steel which in very simplified terms says that for equal stiffness, the aluminum bar would need to have about three times the cross section for equal stiffness. Perhaps much more important would be angular deflection in the knuckle joints. Overall. I think that the main issue is minimizing vibration, but if there will be a considerable overhung load on the boring bar then total deflection would be important. I assume that the boring bar itself will be steel just to keep the diameter reasonable.

The main advantage of an articulated arm hollowing system would be the situation where you have a short bed lathe and don't have the space to mount a gate to trap vertical movement of the boring bar. If that isn't your situation then something along the lines of Lyle Jamieson's hollowing rig is far simpler and less costly.

My assessment is that you are creating an unnecessary design challenge just because you have access to some (I assume, free) aluminum.

Thanks for the info Bill. My lathe is a mini jet 10". With the bed extension. So the pieces won't be huge more on the small to almost medium. Don't have the $ to buy a rig so will use my Easy hollower, and keep looking for other supplies. Again thanks.



Paul

 

[Bill Boehme]

I've turned a few hollow forms on my Jet mini using various handheld tools and for what that lathe is able to handle, there really isn't any advantage in going to a captured bar or articulating arm. I also think that handheld hollowing helps develop a better intuitive feel for how the wood is being cut.

 

[Richard Coers]

The aluminum seems pretty small in section, but you are using it on a mini lathe. Some aluminum alloys are soft, so some sort of bearings might be needed for a smooth swivel. I made mine with steel on steel, with a bit of lithium grease on the 3/4" pins.

 

[Richard Coers]

I've turned a few hollow forms on my Jet mini using various handheld tools and for what that lathe is able to handle, there really isn't any advantage in going to a captured bar or articulating arm. I also think that handheld hollowing helps develop a better intuitive feel for how the wood is being cut.

Kinda depends on age and physical condition Bill. An articulated or captured system will ease the forces for someone with weaker or arthritic conditions. I'm just about to turn 63, I don't like to hollow by hand any longer.

 

[john lucas]

Lyle Jamieson has plans on his site for building a captured bar hollowing rig. No moving parts so it's very solid. I do like the articulated systems. They take up less space and are easy to store. However Lyle's system is so simple and solid. I use mine all the time. I also find any of the captured bar systems easier on the body. Not quite as flexible or quick as hand held hollowers but for those of us who don't do a lot of hollowing it just takes the white knuckle out of it.

 

[Dwight R Rutherford]

Another vote for Lyle's captured bar system. I built mine from the plans on his website for less than $90.00 including the laser. I have been using mine for 7+ years doing hollow forms almost exclusively. Have tried articulated hollowing rigs and still prefer my copy.

 

[Richard Coers]

I prefer the articulated if you are working in small hole hollow forms, or large diameter squat forms. You can snake in the cutter, and not have to relocate the support structure of the capture system.

 

[Hu Lowery]

just a guess . . .

I am interested in building a Articulating arm assembly, I've notice most if not all are made with1" square steel bars. I have 3/4"X1" aluminum bars that were used in the medical field as a articulating arm tool tray of sorts. Would these be strong enough to use? These are solid bars not tubes.


Paul

Paul,

Considering the size of the lathe and the fact most stuff in the medical field is over engineered, I'd say take a shot at building a toy if you want to. I have some large blocks of 6061t6 that I have considered making an articulated hollower out of many a time. If I still had the machine capabilities I once had it would be a done deal. Aluminum alloys run such a wide range that it is impossible to make blanket statements about it. Too if the aluminum bars are paired up the distance between them matters. I have the Simple brand articulated hollower built from aluminum, so far no issues although I haven't used it a great deal. I hope to hollow a pretty deep piece of oak over the next day or two playing with the laser and a new camera set-up, should put the Simple system t a pretty good test too.

If you have to spend much money to try it I'd say consider how inexpensive some of the complete units are. If you are only spending time that you have available and using mostly stuff already on hand, give it a try. Pictures of the current design the aluminum is used for might give a better idea of the strength or lack of same of the unit.

Hu

 

[robo hippy]

I have limited hollowing experience. I do have one of the early Monster articulated arm set ups. They are fine for small hollow forms. They claim to be able to hollow up to 10 inches deep, or there about. I consider them to be fine for finish cuts, but not so good for roughing cuts. Mostly they do vibrate a bit when doing heavier cuts, and reaching out farther off the tool rest. There is always some flex in the arms. The only way to know for sure is to try it out. Having the proper bearings is as important as the diameter of metal arms you are using. Forms up to 6 inched deep, probably no problem. Deeper than that, well, more experience helps.

robo hippy

 

[Paul Lajoie]

Paul,

Considering the size of the lathe and the fact most stuff in the medical field is over engineered, I'd say take a shot at building a toy if you want to. I have some large blocks of 6061t6 that I have considered making an articulated hollower out of many a time. If I still had the machine capabilities I once had it would be a done deal. Aluminum alloys run such a wide range that it is impossible to make blanket statements about it. Too if the aluminum bars are paired up the distance between them matters. I have the Simple brand articulated hollower built from aluminum, so far no issues although I haven't used it a great deal. I hope to hollow a pretty deep piece of oak over the next day or two playing with the laser and a new camera set-up, should put the Simple system t a pretty good test too.

If you have to spend much money to try it I'd say consider how inexpensive some of the complete units are. If you are only spending time that you have available and using mostly stuff already on hand, give it a try. Pictures of the current design the aluminum is used for might give a better idea of the strength or lack of same of the unit.

Hu

Hu, you asked for pictures of the aluminum in its original state. The first is the support which would be attached to a wall or table, the second shows whole setup with a arm which is adjustable for height and the last piece is the arm which I would use to build the tool. That arm is 15" long and I have 2 of them. One thing of note the original setup uses bronze bushings for the pivot point. Some of the articulated arms I've seen use these and some use bearings, would bronze bushings be ok?

Paul

 

[Raul McCai]

Hu, you asked for pictures of the aluminum in its original state.

They made that with Solid Aluminum bar stock? Not square Tube?

, would bronze bushings be ok?

Bronze would work fine.
A little lube and you'd be golden.