Custom bushings

[asid61]

What are some good materials for a large custom bushing?
I was experimenting with some interesting turret ideas, however, a few of them require large custom bronze bushings (~2.625" OD, 2" ID) in order to be geometrically correct.
The turret only weighs around 30lbs, so would aluminum bronze be an okay bushing material? Do machining sponsors hate working with bronze enough to refuse or is it different from copper in that respect?
What are some other bushing materials?

Also, this is assuming that we don't just buy bushings. This is pretty theoretical right now, so I wanted some opinions on fabrication and materials of custom bushings.

[RoboChair]

Bronze and brass are fairly easy to machine but unless your bit is nice and sharp it can leave a terrible finish. So just use some sharp bits and take your time and you will get a nice part.

[Adrian Clark]

Could you elaborate on what your building exactly? And what sort of load would the bushing be under? Axial? radial? both? I ask because you're talking about using a massive bushing for a very small load, and I think your design could be improved. And given that this is theoretical, I think that your time would be much better spent figuring out how to design your turret so that it doesn't require an expensive custom bushing.

My first thought is to suggest delrin. I say this hesitantly because I don't exactly know what this bushing is doing, but I think a delrin bushing would be able to handle 30lbs load with ease. Not to mention it would cost about a third as much.

If your heart is set on using a bronze bushing picking out the alloy should actually be pretty easy. From what I understand this is a low load (for the size of the bushing) and low speed mechanism, which means you don't need to use any of the harder more expensive bronze alloys. I suggest you look for a cheap bearing grade bronze with good machinability. Something along the lines of 932 multipurpose bearing grade bronze or machinable 936 bearing grade bronze. Both are available from mcmaster, onlinemetals also has a nice selection of 932 bronze tube. Your sponsor shouldn't have any problems working with either of these alloys. Bronze doesn't get hard to machine until you get into the harder high strength alloys, and even those aren't too hard to machine.

-Adrian

[Brandon_L]

What about a 'lazy susan' type bearing?

[DonRotolo]

Many plastics make good bushings if not compressively loaded much. Sintered bronze is the classic material, plain bronze and brass are OK. Aluminum is not that good as it tends to gall under load. Steel isn't as bad as you might think, but must have lubrication.

For the 3" range ball bearings are not a bad choice (and not as expensive as you think), and if there are axial loads a tapered roller bearing would be good. Just look for low-speed versions if price is an issue.

You could cast some Babbitt, but that's way old school.

[colin340]

Originally Posted by DonRotolo

You could cast some Babbitt, but that's way old school.

props to don for going Hit and Miss style on CD old engines are cool.

What about junk yard parts or an ATV spindle.

[highlander]

Originally Posted by Adrian Clark

Could you elaborate on what your building exactly? And what sort of load would the bushing be under? Axial? radial? both? I ask because you're talking about using a massive bushing for a very small load, and I think your design could be improved. And given that this is theoretical, I think that your time would be much better spent figuring out how to design your turret so that it doesn't require an expensive custom bushing.

My first thought is to suggest delrin. I say this hesitantly because I don't exactly know what this bushing is doing, but I think a delrin bushing would be able to handle 30lbs load with ease. Not to mention it would cost about a third as much.

If your heart is set on using a bronze bushing picking out the alloy should actually be pretty easy. From what I understand this is a low load (for the size of the bushing) and low speed mechanism, which means you don't need to use any of the harder more expensive bronze alloys. I suggest you look for a cheap bearing grade bronze with good machinability. Something along the lines of 932 multipurpose bearing grade bronze or machinable 936 bearing grade bronze. Both are available from mcmaster, onlinemetals also has a nice selection of 932 bronze tube. Your sponsor shouldn't have any problems working with either of these alloys. Bronze doesn't get hard to machine until you get into the harder high strength alloys, and even those aren't too hard to machine.

-Adrian

+1. We need to know what stresses you have.

[asid61]

It's a turret for a t-shirt cannon. Basically, the actual barrel rotates on something like what the arms this year had (stright piece up + angled claw) to be able to aim and shoot better. It's also practice for future years.
It doesn't weigh that much but due to the design which incorporates bevel gears, there is a large bushing on the bottom coaxial with a shaft going to a bevel gear to rotate the barrel up and down independent of the module's rotation. So the turret experices very slow radial loads in the 100rpm range but around 30lbs axial.
The load is on the flange of said bushing.

I looked into ball bearings in the 3" range, but they all cost more than $100. I also cannot design for this bearing to be smaller due to some interesting design issues that have to deal with a cim mounted to the bottom of this turret.

[Michael Hill]

Could you modify the design to use this? http://www.andymark.com/product-p/am-2714.htm

[Tyler2517]

You could try using a set up like 1640 uses for their swerve drive. It can support huge amounts of weight and take a good hit. Its also pretty compact. Just mount it upside down? It uses a thrust bearing to handle the axial loads and a very large bearing to handle radial loads.

[Bruce Newendorp]

The igus slewing rings would work for this. They are just so intriguing - someday I'm sure we'll find the perfect use for the one we have.

They have been available from FIRST Choice some years.

[asid61]

Originally Posted by Tyler2517

You could try using a set up like 1640 uses for their swerve drive. It can support huge amounts of weight and take a good hit. Its also pretty compact. Just mount it upside down? It uses a thrust bearing to handle the axial loads and a very large bearing to handle radial loads.

Sounds interesting. As I said though, because this is pretty low-budget (we have other stuff to work on too) I wanted to avoid ball bearings.

Slewing rings sounds interesting, but they are a little big.

[Gdeaver]

I've used 2 tapered roller bearing for turntables before. You could probably go down to 3/4" shaft size. Weight I assume is not an issue.

[David Guzman]

A great material for bushings is UHMW (Ultra High Molecular Weight Polyethylene).

We used this extensively, not only on the robot but at work for many bearing applications. It is very easy to machine, has a very low coefficient of friction and can withstand significant loads for a plastic.

You can get rods from McMaster fairly cheap.

[jman4747]

Originally Posted by David Guzman

A great material for bushings is UHMW (Ultra High Molecular Weight Polyethylene).

We used this extensively, not only on the robot but at work for many bearing applications. It is very easy to machine, has a very low coefficient of friction and can withstand significant loads for a plastic.

You can get rods from McMaster fairly cheap.

I would say +1 to UHMW, Delrin (Acetal Resin), or Nylon 6. All inexpensive all great bearing surfaces.

Another thing to consider if you can wait I would research different suppliers, Mc Master Carr is the fastest and arguably the best but not always the cheapest.

PS "All inexpensive" is a relative statement.