bushing material choice

I am involved in a repair on a toyota forklift and the rear axle pivot bearings are shot as well as the stub shafts. We are welding on new machined stub shafts made from 4140. The original
bushings are phenolic plastic. I did the scratch and sniff routine. Since they are 125 dollars apiece, I suggested a good bearing bronze. I am now wondering why anyone would design a heavily loaded pivot with such plastic bearings. Am I making a mistake going to bronze?? I am shooting for .002 clearance on a diameter of 2.5 inches . Is that about right? Randy
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I'm not sure why but something about your post caused a slight nagging feeling. I can't qualify why but I have had bronze fail where I didn't think it would. High loads and slow speeds seem to be common denominators. I have some high load slow speed shafts running in "Lignum Vitae" wood bearings that outlasted bronze by more than 50 to 1. Other bearing materials I have had good luck with are Nyloil, an oil impregnated nylon and graphite impregnated nylon. But the Lignum Vitae wood is KING! So, if the bronze fails -"I told you so" if it works out great, in a year's time you will have forgotten the bearings and my stupid post.

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Our first choice actually was some sort of nylon based bushing material much as you describe. We had difficulty getting the size we needed for machining so we went for Bronze. We figure the load is around four to five thousand pounds per bushing since they sit under the counterweight.. If the bronze fails then we will only have half a job to do since likely we will have serviceable stub shafts .... I hope. This is a pivot load so you could be right ... Don't sell your opinion short. Interesting wear pattern on the shaft though. The grease groove was almost 1/4 wide and that area is not worn on the shaft. Such a wide grease groove seems like a bad choice since it significantly reduces supporting area. The last time I saw a piece of Lignum Vitae was over forty years ago. I have heard of it being used for underwater bearings. Does it work in a grease situation? Randy

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Lignum Vitae is still available, I think they implegmate it with oil or such for bearings. For blonze bushings on my presses, I cut grease groves every 3/8" or so with a boring bar and then join them with 2 straight cuts with a die grinder and a burr. What ins the plastic used for lead screw nuts? It's very expensive but lasts forever.

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On Sat, 06 Mar 2004 01:00:06 GMT, "Randy Zimmerman"

It can be amazing what plastic can take and out last bronze. I rebuild a lot of bearings for pump jacks which are about that size and are pretty heavily loaded (though I'm not sure they are as heavily loaded as your application). A Nylatron (Moly impregnated Nylon 66) bearing will outlast a bronze several times over in a pump jack bearing. In fact it'll outlast the steel shaft!
I do know that a bronze bearing won't last worth spit in a extreme load situation like on a track hoe track idler wheel. In those cases if they're not hardened steel on hardened steel then I believe that aluminum bronze is the material of choice.
Wayne Cook Shamrock, TX
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That is the stuff that we first considered " Nylatron" I recognize the name mentioned. We had difficulty obtaining the size we needed. The bronze... I think is aluminum bronze from the colour and the wave pattern on the outside of the bushing stock. Hey I am a fabricator and I just asked for some sort of bearing bronze. It's yellow ! :'))) The old phenolic bushings were grooved with a cross pattern much like I have seen on old babbit bearings. I am thinking about putting a smaller grease groove in the center of the bushing say 1/8th and not bother with any cross patterns. Any ideas about what makes a good lubrication groove? Randy

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A dual start thread type shape would be most effective over a wide bushing such as this. keep the grooves 1/4-3/8 from the edges of the bushing and let them criss-cross
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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I think the metal you'd need, if you decide to use metal, is aluminum_nickel_bronze. I made a bushing out of it for a friend at work for a tractor. He'd gotten it from the landing gear shop at work and it was used for that application in some pretty heavily loaded pivots. Was some tough stuff to cut on a Shoptask, but I don't think the Clausing I've got now would have any trouble. Or any real lathe, I reckon.
Garrett Fulton
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On Sat, 06 Mar 2004 05:15:06 GMT, "Randy Zimmerman"

I've probably got Nylatron stock in that size depending on how long it needs to be. I am a little low at the moment but plan on waiting for the next bearing to come in before I order some more. In fact come to think of it there may be some old phenolic out there about that size.
I'm betting you've just got plain old bearing bronze instead of aluminum bronze. I've never had any aluminum bronze but I've seen some bushings I suspected was made out of it and they didn't have much of a yellow color to them.
With nylatron I don't worry as much about grooves as I do with bronze. Since it's got moly already it's somewhat self lubricating. The way I do most bearings is I put a groove in the middle (usually about 3/8" wide) and then either six or eight small grooves through the bearing to spread the grease. But keep in mind that most pump jack bearings are about 5-6" wide. I have in the past just put one very course thread thread through the bearing with a center groove to meet the grease hole. But you need a lathe capable of 2tpi for this to be considered. When using the threading method I usually use a very narrow tool on the order of 1/8" wide or so. For the straight through method I use the lathe as a shaper and run about a 3/16 or slightly narrower grooves with it.
In pump jack bearings there's nearly always a seal outboard of the bearing so I don't worry about the grooves coming out the end. But if I am worried about it then I cut a groove at each end and run the tool from groove to groove without breaking the ends.
In your case I'd say that a carefully placed center groove about 1/8"-3/16" wide (by carefully I mean it needs to be positioned right at the grease hole) and 6 small grooves through the bearing stopping at grooves on each end if there's not a seal. The reduction of bearing surface would be minimal but it would be sufficient to spread grease to the whole thing.
Wayne Cook Shamrock, TX
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Thanks for info Wayne. I will go with that center groove and a few cross patterns short of the edges. I wouldn't chance a screw cut on this old beast. The markings on the quick change are long gone and it takes a twenty inch diameter fourjaw with lots of room. We should know in a year from now if our repair holds up. At the cost of a forklift mechanic coming in and doing the job we can do the job twice and still save. Althought the machine has a regular six month inspection and service those grease nipple didn't see much grease. Sometimes it is better to do things yourself. Randy
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On Sat, 06 Mar 2004 23:37:39 GMT, "Randy Zimmerman"

If it's that big then it's definitely a candidate for the screw method. Most that size will do 2tpi or even courser.

I know the feeling.

Yep. :-)
Wayne Cook Shamrock, TX
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Randy Zimmerman writes:

Phenolic stock isn't that expensive or hard to find, if you're making your own.
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