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/simple-hollowing-system-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.354239354240354241

[daryl moses]

I used wood.354239354240354241
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.

[Tom Giacomo]

I used one inch square steel for my homemade unit.

[Adam Petersen]

I used one inch square steel for my homemade unit.

Tom, how is it attached to your tailstock? That's what I want to do with mine.

Adam

[Robert Willing]

Ed your entire system is very unique "love it.":)

[Dane Riley]

Victor sells Morse taper to bolt thread adapters for cheap. Tap a block of metal and thread it in. A chain around your tailstock will lock it in.

6061 T6 aluminum is almost as hard and stiff and scratch resistant as steel.

354287

PM me with an email adress for a writeup.

[Tom Giacomo]

Adam here are two pictures of the clip I made. The clip consists of a 1 1/4 inch square tube 1/8 inch thick 2 1/2 inch long with one side cut off. Then a piece of metal as you can see in the picture was fabricated and welded to go from the tube to the tailstock depth locking handle. The things you cannot see in the pictures is a 3/8 inch bolt going through the center of the clip all the way through the tailstock barrel and you can see in the second picture it is connected with a turn locking handle. Also just behind the clip are three 2 inch washers with 1 1/4 inch center holes to take up the space left by the barrel not retracting all the way into the tailstock. I have been using this setup for about 4 years now with no problem. There are several advantages to this setup. 1. It is relatively inexpensive to make but requires one weld joint 2. It leaves the hollowing arm dead center no need for a lot of adjustments 3. You can move your tailstock with it attached 4. And the best of all I can install my hollowing arm in less the 30 seconds.

[Adam Petersen]

Okay, plans are set. Here's what I have. I'm going to take a bit of several people's designs and not reinvent the wheel here. I've attached a drawn out plan and pics of a wooden prototype I threw together to make sure everything articulated well, lined up, etc. This should be fun.

The arms will be 1" sq cold roll. It willl be attached to the tailstock with an MT2 that I ordered that will be welded to the 3" block at the tailstock. That MT2 has a 1/4-20 drawbore that will secure it in place to the tailstock with a handknob. The joints will be 1/2" grade 8 bolts with locknuts. There will be bronze washers between the arms at the joints. I will attach the laser to a 3/8" vertical bar that will have a square union of some aluminum I have laying around. It will be locked with set screws. The horizontal arm will also be 3/8" round and it will travel through the block and also have set screws so I can adjust it in and out and swing it left and right. The laser has been ordered from digikey (thank you Dane Riley for the email with the part numbers). The end bore will be 3/4" with set screws. I've ordered a John Jordan 3/4" straight hollower and also the bushing reducers to 5/8 and 1/2". That straight hollower, coupled with my Sorby bent arm, Harrison Simple Hollower and Crown multi-tip should give me a good array of tools to use. I can also work on making some of my own as needed.

I have one last question. I've read all types of info on bearings, bronze Oil-lite, etc. Do I really need anything other than a well drilled 1/2" hole and the Grade 8 bolts? I figured I'd Teflon coat them and put them in place and I can't imagine the wear would be too significant as to create slop in the joint. Any thoughts on this?

Again, thanks for everyone's input and I'll post the final product when I'm done. I'm going to have my dad use his auto-painting skills and make it red to match the lathe. Hopefully I'll have a sharp final product to show you.

Adam354402354401354400

[Richard Casey]

Adam, it will work as you described, but it will work much freer with brass or bronze sleeves. If you want it perfect you can also add toroidal end thrust bearings between each part as well.
Rgds,
Richard

[John K Jordan]

I have one last question. I've read all types of info on bearings, bronze Oil-lite, etc. Do I really need anything other than a well drilled 1/2" hole and the Grade 8 bolts? I figured I'd Teflon coat them and put them in place and I can't imagine the wear would be too significant as to create slop in the joint. Any thoughts on this?


I've never used one of these hollowing arms so all my experience with pivots is on other things. Seems like a large hollowing arm could be subject to significant twisting force.

With four pivots on the arm I would certainly want zero play in each joint. In my experience bolts make sloppy bushings but of course that would depend on the precision of the hole and length of the contact area. Note that teflon is pretty soft and might distort and make a sloppy joint, but again, a longer contact would help. Looking at things intended to pivot without play I usually see two bearings/bushings on each joint.

BTW, precision holes can be machined by drilling undersized and reaming on a milling machine or metal lathe.

At my local fab shop I found cold rolled rod and heavy wall tubing that fit well together made smooth and strong pivots. The rod, about 1/2" if I remember, fit the tubing very well. I made the pivot about 1.5" long since the longer the contact the less inherent play. I welded all of these in place but the rod could be threaded or grooves cut for retaining rings. With a little dry lube

JKJ

[Dane Riley]

The needle thrust beatings reduce the static friction. This gives a much better feel for the inside surface, which is all you have. And they are not very expensive.

[Brice Rogers]

Hot roll might be less expensive.
For your bolts, I'd suggest getting the kind that have a section (like 1" long) that is not threaded. That'll keep the threads from chewing into the bar or the bar from reforming the threads and getting sloppy.
The thrust bearings seem like a good idea but is something that you can add later.
I considered using Teflon washers between the sliding surfaces - - like a low-tech thrust bearing. But I ended up using HDPE (poly from the bottom of a bucket) and they are low friction.
Many drills will drill oversize. Some worse than others. It has to do with unequal sized cutting surfaces.. John's idea of drilling undersize and then reaming is good. Another alternative is to drill undersize (by perhaps 1/32nd) and then drill the final hole. Drill a test hole and then check it for slop or measure it.
Good luck. Keep us posted.

[Marvin Hasenak]

I used nylon lock nuts, so that I could tighten them and still have movement and they will not come off. For bearings, I drilled my holes larger then the bolts I used, 1/2" bolt and drilled 7/8" holes. Then back plugged the holes with sleeves I made from 7/8" diameter Delrin with 1/2" holes center drilled. The 1/2" bolts are a little less than 1/2" in diameter, so I had smooth movement.

[Tom Giacomo]

You have some good advise here may I also add as to fitting bolts I used 3/8" bolts with smooth shaft on them not have threads in the bore I used a letter drill for the hole making a tight fit, I agree with the nylon locking nuts. If you try to use bearings you'll find a need to drill a very large hole in a 1" square bar to fit a bearing or brass sleeve.

[Dane Riley]

Needle thrust bearings do not require drilling, although you certainly could. Nylon lock nuts are a must.

Why weld the Morse taper? http://www.victornet.com/detail/DCA-2M-1220.html and a tap set has to be cheaper and more likely to be straight.

[Adam Petersen]

Pfft. Because.....


I actually don't have a good answer other than I wanted one with a drawbore on the end to secure it in place. I couldn't find one with the threaded end with a drawbore on the other end. But of course looking at your link to victornet I see they have one and for about $6 CHEAPER than the one I ordered from littlemachineshop.com. Hmm.....maybe I'll ordered one of those and send the other one back. I'll look at it when it comes and decide. Thanks for that link!



Needle thrust bearings do not require drilling, although you certainly could. Nylon lock nuts are a must.

Why weld the Morse taper? http://www.victornet.com/detail/DCA-2M-1220.html and a tap set has to be cheaper and more likely to be straight.

[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.

Here's some crude pictures:
354645354646

[Clint Bach]

Ummmm.... Just how do you adjust the vertical height for different cutters? Not all cutters need the same height....

c.

[Mark Greenbaum]

Ummmm.... Just how do you adjust the vertical height for different cutters? Not all cutters need the same height....

c.

My system allows for vertical adjustments by moving the 2 set collars on the post. I looked at the post last night, and I am going to cut off about 6" from the top, and make a new tool rest.

[Russell Neyman]

Haven't made one but pondering it. Is this design secured well enough to the tailstock. Are there other options, i.e. an "entrapped/clamped" arrangement? Is a Morse taper enough?

[Mark Greenbaum]

Russell: My system is pretty much like the one I used at JC Campbell, by ELBO, with a mast. I'll be using my toolrest banjo (spare) and resting the end effector (hand) on the actual toolrest. I am trung to use all free materials where possible, and I am shaping a harden steel dowel pin to be my first cutter. Think of it like the post is the shoulder joint of your arm, first pivot is your elbow, 2nd pivot is the wrist, and the hand is the last tube with the tool mounted to it.

[Peter Blair]

Mark a drill bit makes a good cutter. It's already shaped, I just grind a little longer taper. It is the first cutter I used in my first hollowing system the ELBO.

[Adam Petersen]

I finished the art. arm hollower. Thank you everyone for help along the way. I tried it out briefly and it seems to work very well. It is definitely easier to get too aggressive with this tool than by hand. I'll have to practice and get used to the different feed back. I've got John Jordan's 3/4" straight hollower, a Sorby 3/4" slicer tool, their 3/4" multi-tool, a 1/2 Crown multi-tip tool and an Harrison straight hollower which is 5/8" I think. I got Jordan's adapters for the 3/4" bore hole. I think that should give me a good setup for hollowing. NOW I just need to get to work and make some turnings!

Things I learned along the way:

-I wouldn't paint it again, I'd just leave it as is.
-I had a machine shop bore the 3/4" nose hole and I'm glad I did, big bits are expensive and I think it was worth the $$.
-Digi-Key rocks for getting laser parts from. The laser is awesome!
-Buy more washers than you think you need to save trips.
-I'd go one less link than I have. It's pretty long and heavy. Heavy is good though.
-Glad I went STEEL and not ALUMINUM!
-Tapping threads in mild steel is much easier than I thought. I'm excited to use taps more now.
-Metal working is pretty fun. It's not woodturning, but fun in its own right. I enjoy drilling steel much more than wood.

Anyways, pics are below. Thanks again, - Adam355538355539355540355541355542355543

[daryl moses]

Looks very nice. Great build, I think it will work great.

[Dane Riley]

Ummmm.... Just how do you adjust the vertical height for different cutters? Not all cutters need the same height....

c.
I adjust the tool rest height. Only get a few tenth's of an inch, but that doubles or triples at the cutter.