Homegrown articulated arm hollowers - Steel or Aluminum?

[Adam Petersen]

I'm early in the planning process for an art. arm hollower and was wondering if anyone has used aluminum square stock for the linkages, or if I should stick to steel. Thoughts are appreciated.

Thanks,

Adam

[Doug W Swanson]

I used steel on mine. Never really gave any thought to using aluminum but I would think it would work just fine....

[Clint Bach]

Aluminum... Softer, less mass, maybe more chatter. More expensive. May bend under hard use.

i would go with steel...

c

[Brice Rogers]

As Clint said, lower mass. I think that you want higher mass to dampen out any potential vibrations. Steel weighs 3x as much as aluminum per square inch.

I made mine out of 1" x 1" square steel. I bought it new at the steel yard and IIRC, I paid around $2 per foot.

I drilled the joints on a drill press and drilled some intermediate holes up to about 1/32 or 1/64th under the final hole. That way the final drilling operation is almost like a reaming and it is less likely to drill oversize. I wanted a close fit. Where the steel would rub against another piece of steel at a joint, I put in some HDPE "washers" and greased the holes to make the action really smooth. I also used shoulder bolts rather than have the threads working on the drilled hole. Additionally, I used Ni-loc nuts so that they don't self tighten our loosen.

[Peter Blair]

in my experience aluminum will nick and scrape and eventually make movement more difficult. Steel, especially hardened steel will I believe make for a more usable tool.

[Marvin Hasenak]

I went cheap and easy on my system. I used some 1018 steel that I had in the shop. I kind of followed the Monster Hollowing System, I actually followed the pics from the Rocky Roost Woodturning website. The same steel is available at most big box home stores. I made my first proto type out of maple with a steel rod for the cutter. The maple works almost as good as the steel version. I think the aluminum would be fine for the articulating part, but would use steel for the long arm.

[Robert Willing]

The Harrison hollower http://harrisonspecialties.com/simpl...em-with-laser/ is made from aluminum, but it has bushings at the joints for wear. I really like mine.

[Thom Sturgill]

I think it would depend on the depth you are trying to hollow. Typically articulated arms are used for shallower hollowing unless made from very heavy stock like the Cobra. For hollowing under 6" depth aluminum is fine. Go deeper and captured systems like the Jameison are probably better, and typically are steel.

[Mark Greenbaum]

I am completing one that I made from 1.5" square aluminum tubes (square corners inside and out), 1/8" wall, and used about $50 worth of Oilite Bronze bushings and shoulder bolts, and nylon lock nuts. All that I have remaining to do is make the actual cutting end. It should be fine because all of the rotational loads are going to be carried through the 1/2" diameter shoulder screws and bronze bearings. I'll take pictures and report on how it works after I get the end effector completed.

[Adam Petersen]

So the consensus is steel over aluminum. I had looked at a bunch of the commercial art. arms and I think the only one I saw that was aluminum was the Harrison. I know he advertises a 13" hollowing depth with his biggest cutter. I think the vibration argument will be what seals the idea of solid steel for me. It is not something I was thinking about in this planning and is obviously very important in this process. I know most of the vibration would be absorbed into the steel boring bar and the tool rest, but any dampening should be good in this application I would think, especially as you extend out further. I did some digging and found a local steel supplier that I'll swing by Monday and grab some 1 by 1 square.

Mark, I would really be interested in seeing yours too, if you get a chance to post some pics. I too was thinking bronze bushings from the multitude of posts I dug through. I'm curious as to the installation of those bushings. My dad has some metal working experience and I was talking with him about it. I can't remember the term he used but he said we'd freeze the bushing and heat the steel (or the other way around, I don't remember) to get a ________ fit. Does this sound right to anyone? Is that how you put in your bushings?

Thanks,

Adam

[Ed Morgano]

I used wood.DSC07317.JPGDSCF9225.JPGDSCF9233.JPG

[daryl moses]

I used wood.DSC07317.JPGDSCF9225.JPGDSCF9233.JPG

Now that is awesome!! Great looking set up Ed.

[Adam Petersen]

Yeah you do Ed! For everything! How does it hold up? Do the arms get wall'ered out at all? If wood works I've got to think there'd be no issues with alloo-minyiom. I guess it probably all comes down to how overbuilt you want to make it.

Just curious, what's the deepest you've gone with an articulated arm unit?

[Doug W Swanson]

What size lathe do you have? I built a hollowing system for a 12" lathe but have since upgraded to a PM 3520. I may sell the base part if you're interested. It would be a good starting point....

[Adam Petersen]

It's a Nova 16-24.