Size 12, Schedule 80, seamless Aluminum pipe? 3

[erosnicolau]

Hi, there,

My question is simple: do I stand any chance of finding some retail (short length) Size 12, Schedule 80, seamless Aluminum pipe anywhere on this planet?

I need it to machine 2 races for a contraption of a large diameter (~300mm), extremely thin bearing-type application, for a slow speed, rarely used gimbal.

Cutting these two rings/races from a solid block is an incredible waste of material and money. Casting is excluded because I need strong aluminum, not the porous disaster yielded by casting. Rolling some flat bar and welding it is the next best thing. Ideally, I could source this kind of pipe, out of which I could machine both races.

Since it's not for an industrial-size project, going to ring-rolling plants is excluded (I guess nobody knows a ring-rolling facility working on retail scale...)

Please, help me out here!
Thank you,
Eros

 

[racookpe1978]

Might be a waste of material, but consider the low machining cost of a block of short soft aluminum, compared to the shipping and locating time of finding such a piece of 12 inch "pipe" ...

Also, Al recycles easy.

 

[erosnicolau]

Yep, you're right for the short-term plan. For long-term, this pipe should make economic sense.

About recycling: it may be so, but we're talking about 90% of it or more being scraped for recycling at a low cost - it's still a hefty loss.

 

[boo1]

But you only need 2, water jet them from plate

 

[racookpe1978]

Machine/waterblast from a single piece of plate?

Depends on the length needed.

 

[erosnicolau]

Again, basting a 50mm high, 8mm thick, 310mm diameter ring out of a solid block, is wasting more than 90% of that block...

 

[metengr]

http://www.vitaneedle.com/aluminum-pipe.htm

 

[EdStainless]

But if you water jet them the bulk of the waste is a solid piece of material, which has a lot more value than chips.
It is the only practical way to get there.
You will not find that size of pipe.

And don't rule out casting, after all they do Al engine blocks and suspension components that are plenty strong.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[erosnicolau]

@metengr: Thanks, mate. I had already contacted them, and they were among the very few gracious enough to decline in a very kind and polite way

@EdStainless: I was only talking about backyard pouring Of course controlled environment, professional pourings are another question altogether. For now, I found some local guys willing to experiment with me and to go along with my "roll, weld, lathe" plan of action. Can't wait to see what comes out of that!

As a side-note: even finding lathes with 330 action here, in Romania, is proving to be a challenge, unfortunately. Luckily, these guys are well equipped.

 

[erosnicolau]

Hi again, folks,

Some updates:

1. The guys previously mentioned (willing to roll, weld, then lathe) the rings, proved to be an utter waste of time: after a month and a half, they were still leading me on with "tomorrow, maybe", so I bitterly ditched them explaining that this is not a normal business practice

2. I reduced the width of the bearing from 50mm to 25mm and, on EdStainless' advice, I water-jet cut the 3 rings out of 2 plates. Another local guy promised he could then lathe the rings to 0.01mm, "no problem". Not only did he prove to have his mouth bigger than his lathe, but it took me another 3 weeks to find a lathe worker willing to take on my challenge (they all said the chuck would deform the rings, and none would actually think of fixing the rings on an adapter plate...)

3. In the end, I found a local guy willing to take my adapter plate idea and help me out - which he eventually did, with only one of the 3 rings, and after another 2 weeks (of which, one and a half week of delay)

I machined the other 2 rings on our CNC milling machine and, with the 3 rings finally complete, I first tried out a version of the bearing with a plastic-made balls cage. The ball-cage-wire frictions were however way too much:

https://www.youtube.com/watch?v=Ubv3Z9XCYvc

So I gave up the idea of a ball cage altogether and filled the bearing up with balls leaving a free space corresponding to only 2-3 balls, and re-assembled it. Here it is, final, with its internal and external attachment brackets mounted on:

https://www.youtube.com/watch?v=6zM2_Yc8O8I

My conclusions:

1. EdStainless, thank you for the waterjet idea. Yes, It yielded spare plates to be used somewhere else, and I do have the working bearing prototype now. It was a great idea for the prototype
2. However, for plans for future larger run production, some fitting pipe to machine the rings out of still remains the best solution. I just have to find the stock...

Eros

 

[tbuelna]

Watching the second video it looks like your gimbal ring still has quite a bit of internal friction. With this much internal friction your bearing assy may quickly overheat if the operating speed is even moderately high. Have you made some calculations of the contact stresses between the steel balls and aluminum race surfaces of your bearing under operating loads?

One question I would ask is how did you assemble the bearing with such a large compliment of balls? Did you use a filling slot?

Another question is what did you use for outer/inner race osculation dimensions? And what amount of internal operating clearance did you allow for, if any? Is the internal friction that seems to be present in the video possibly due to radial runout in the race surfaces?

With an aluminum race and steel balls most of the strain at the ball/race contact will be in the much lower modulus aluminum race. And the surface compressive fatigue life of an aluminum race will be extremely limited. In this regard it probably does not matter much whether the aluminum race material is cast or wrought.

 

[erosnicolau]

Hi, @tbuelna!

To answer your very pertinent questions one at a time:

1. This gimbal will very seldom move, if ever at all. It is meant for slight adjustments of the ROLL position of the camera. Even at full speed, in this particular application I made it for, it would only achieve 1-2RPM. At this speed, heat is a non-issue. Also, the balls don't touch the aluminum at all - I made it a wire race bearing, instead - very clever solution invented in the early 30's of the last century - see here. So the wearing contact surfaces will be steel on steel, not steel on soft aluminum. And speaking of aluminum, I chose to work with the toughest grade of aluminum I could get my hands on, for the casings - EN AW 7075.

2. The assembly, after some learning curve, went very smoothly with no filling slot at all. Seeing the 3 rings construction of a typical wire race bearing, you'll get the idea. The only trick was to get the wire races to be as perfectly round as possible, in order not to yank the balls out of whack at the kinks. For this, I designed and built a wire straightening gig, and a small, hand-held, wire rolling mechanism, which I fed the wires through until they came out perfect to 0.25mm radial tolerance - see
here, here, here, here and here.

3. No osculation calculation whatsoever. Because the amount of clearance is simply adjusted by finely tightening together the two rings that make up the outer race. This action finely adjusts the distance between the two outer wire races, which in term adjusts the total amount of internal preloading of the bearing. That's the sweetest part about a wire race bearing design - the possibility to adjust the preload at any time (that, and the fact that you get excellent radial and axial performance at big radii in a very lightweight package)

4. Since the iron-aluminum interface is a continuum contact between the fixed, smooth wires and the cages, rolling contact and fatigue life become a non-issue.

Hope this answers your questions. Mine (where do I get pipe fit to machine these rings out of) still remains unanswered, for now...

Cheers,
Eros

 

[tbuelna]

Eros-

Thanks for the reply. So just to clear, this is a ~300mm slew ring used in a camera mount to permit rotation of the camera about the roll (longitudinal) axis? Or do you mean the yaw (vertical) axis?

I'm familiar with wire-race rolling element bearings, although the wire-race bearings I've seen all use wire that has a profiled cross section. The main reason for using wire-races on large diameter bearings is to reduce weight by minimizing the steel content of the bearing assy. Both ball and cylindrical roller types use wire that has a profiled cross section. The round wire used in ball bearings has a concave surface section on one side that is conformal to the ball, similar to the race surface of a conventional ball bearing. Thus it requires a suitable osculation curvature. The round wire used in cylindrical roller bearings simply has a flat on one side. One significant advantage of using a wire-race in large diameter cylindrical roller slew rings is that the back side of the circular section wire sits in a conformal housing groove which allows it to twist in-plane locally when the housing distorts, and this allows the wire's flat race surface to maintain uniform contact with the cylindrical roller body rather than edge loading.

Here's a catalog of large diameter wire-race slew rings that provides some reference data on load capacities, internal friction torques, etc.

Also, just for giggles here's a listing from a Chinese manufacturer for a 300mm wire-race four point ball bearing with an aluminum housing, almost exactly like what you require. If you believe their advertisement, the price is only $500.00 each for a min. qty of 10 pcs.

Lastly, since this slew ring is for a camera mount you'll want to make sure your bearing rotates very smoothly with no vibration. It should have very minimal breakaway friction torque characteristics so that it doesn't produce a jerk when rotated from a stop. And it should have provisions for preloading the bearing to remove freeplay, which is something you appear to have considered based on your last post.

Sounds like a fun project. Best of luck to you.
Terry

 

[racookpe1978]

Irritating that you faced so many machining problems.

Symptomatic of today's world though: No "craftsmen" only "load-a-part-on-the-CAD/CAM" ...

 

[erosnicolau]

Hi, again, guys!

@tbuelna: Yep, roll (longitudinal). I'm inserting a link here so you can better see the context of that bearing. About the cross-section profile: since, for this prototype, I used relatively soft steel wire, after some grinding in, the wires automatically begin to form exactly the optimal cross shape (they deform slightly to form exactly that cross-section, more or less, based on the balls-wire contact). Again, this is for a very light load application, compared to the diameter of the ring - only about 5-10Kg of payload - so I'm just assuming that my current design is strong enough for this. Keeping my fingers crossed here. I'm no engineer, just a beginner.
I did contact both sources indicated by you: Franke gave me a ~1700EUR/unit price tag, while the Chinese guys left me somewhat hanging, after some pretty detailed discussion with them. Vibration will not be an issue, since this is for a time-lapse application (move-stop-shoot-move cycles - so the whole rig will stay still while actually shooting). What might be an issue - hopefully fixable - is the required start/move friction. Again, not for smoothness sake, but for the stepper motor to actually be able to rotate the inner ring as required.
Preload - as you noticed - is easily adjustable by tightening or loosening the 6 screws that squeeze together the 2 halves of the outer ring.
Just as a note: my expenses for this bearing were: 130$ for the aluminum (of which now I have plenty of scrap for other smaller parts), 140$ for water-jet cutting it out of the plates, 20$ for 300 4mm diameter SKF bearing balls, 110$ for machining the inner ring on a big diameter lathe, and 5-6 hours of me CNC-ing the outer rings and fiddling with the assembly. So 400$ + a couple of man hours on my part. And it includes the inner and outer brackets too, as you can see. Further optimizations for further units would include: only water-jetting the thick parts (cost reduction of about 20% for this), leaving the inner ring as a solid part before lathing (would reduce the lathe cost by up to 80-90%), less balls (I think 200/unit should do). With these in mind, I should be able to break even at ~275$/unit. Still too much, if you ask me, but we'll see.

@racookpe1978: Irritating is a mild word. Apparently in my country "high precision work" is never below 0.02mm. And lathe workers are rare and in between, and then when you find them they're too busy to take you seriously or to bother thinking about custom solutions.

 

[tbuelna]

Eros-

Thanks for the picture of your camera mount, that clears things up.

If it's any help, I did a quick search on eBay found an NIB 11"x11.625"x.3125" 4-point ball bearing (Kaydon KB110XPO) with mounting flange for $195. This is very close to the size you need, it is very thin section and lightweight, and it is a 4-point contact type which means it can handle combined axial/radial/moment loads with minimal freeplay. The only issue is that the bearing is open, so you will need to figure out some way to seal it. Here's a link to Kaydon's engineering data for this bearing, including starting torque on p.101.

Hope that helps.
Terry

 

[erosnicolau]

You welcome, man!
And thanks for the link. I had visited that link myself, too. The same unit is also for sale on a Japanese surplus store site - so at least you know where it's coming from.
Unfortunately, this is a one-off (a spare, sold at 1/10 of the real price) and my concern is to find a long-run solution. Both Kaydon and Franke ask around 1700eur/part for such beauties...
Eros