Pin bushing - brass, bronze?
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  1. #1
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    Default Pin bushing - brass, bronze?

    Hey all - first post here great forum you have!

    I picked up a mini lathe and have been enjoying making some parts.

    I am going to be pressing out a plastic bushing that wears rapidly and replacing it with a pressed in metal bushing.

    Here is the component with the pin I made (304L SS pin):


    Lathed Pin by Jon Kensy, on Flickr

    That's just a rough finish yet, going to bring it to a smoother finish. The part is goes into has a plastic liner/bushing that wears especially with the hard stainless through it. Would I want to use brass or bronze for a replacement bushing and what alloy/type?

    Thanks all!

    (this is for a transmission gear selector rod that I am trying to tighten up and improve upon the factory design).

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    Bushing should be bronze, but you have made a very poor choice of material for the pin. Stainless is actually not very hard and not as strong as a good steel alloy like 4140 or 4340. Further, stainless is a gummy material and a poor conductor of heat, both of which mean it is very likely to gall. In your transmission shifter application it may not make any difference, but in a piece of machinery where a shaft is running in a bushing, try to use 4140 or 4340 for shafting. Same for bronze instead of brass. Brass is a little cheaper, but it will gall if used in a bearing application.

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    Quote Originally Posted by Mike C. View Post
    Bushing should be bronze, but you have made a very poor choice of material for the pin. Stainless is actually not very hard and not as strong as a good steel alloy like 4140 or 4340. Further, stainless is a gummy material and a poor conductor of heat, both of which mean it is very likely to gall. In your transmission shifter application it may not make any difference, but in a piece of machinery where a shaft is running in a bushing, try to use 4140 or 4340 for shafting. Same for bronze instead of brass. Brass is a little cheaper, but it will gall if used in a bearing application.
    I figured SS wasn't the best bet but for this application I can't imagine it being an issue at all. The factory uses some cad plated crappy sheetmetal rolled.

    Is there a specific type of bronze I should use?

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    Is there a specific type of bronze I should use?
    CDA93200 or C932 is a general purpose bearing bronze

  5. Likes Mike C., Clodhopper liked this post
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    On the Topic of Bushings:

    I am shure that beginning at a certain size, load and amount of neglect/lack of lubrication Bronze will display its superiority.
    But especially in the model engineering and fine mechnic etc. world there are hundreds and thousand of shafts, pins and guides rotating, pivoting and sliding in brass bushings. Never seen one galled.

    The one thing that should never be done is making both surfaces from the same material, with the notable exception of cast iron, hardened steel and probably some fancy things i dont remember, teflon on teflon should work too.

    The worst is soft steel on soft steel. I had to replace 7 pins of this Design this year. Actually it is amazing how long those lasted.

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    Far better option is to look up Igus bearings. Bronze wears badly if not frequently oiled. A igus on a good shaft - pin will have a very long life even in a dry hot dusty environment. The pin weather chromed or stainless needs a finish that's akin to near ground. You pin will eat anything, by the time its smooth enough it will be lose again, best start over and try a finer feed + better tool, also retract the frigging thing before pulling it away.

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    Here is a fairly good finish for reference, done on a 65 year old plain bearing grinder

    http://img.photobucket.com/albums/v3...Dcp_1147sm.jpg

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    Quote Originally Posted by adama View Post
    Far better option is to look up Igus bearings. Bronze wears badly if not frequently oiled. A igus on a good shaft - pin will have a very long life even in a dry hot dusty environment. The pin weather chromed or stainless needs a finish that's akin to near ground. You pin will eat anything, by the time its smooth enough it will be lose again, best start over and try a finer feed + better tool, also retract the frigging thing before pulling it away.
    I looked at the IGUS site. Sounds interesting. Not so sure about sources for the material itself though. Is there a generic name for this stuff? Where do you buy it? I have a grinder bushing project coming up that might be well served with IGUS or similar.

    Denis

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    " Bronze wears badly if not frequently oiled. "

    Yeah, the bronze bushings on my 1918 lathe will probably have to be replaced within the next 1000yrs. Any material improperly applied or neglected will wear out. As Denis says, this Igus stuff... where do you get it? how much does it cost? I can have a stick of bronze from .250 to 30" diam in my hand in about ten minutes by running to the supplier down the road.

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    You just buy the finished bearings from igus, or you can buy it in rod form again from them. Next day delivery is std here in the uk, don't know about over there. I highly recommend it for things that don't get oiled - or can't be and especially in dusty - gritty environments. Like most polymer bearings there not good at high speeds, but slow they hold up just fine. It holds up brilliantly in applications were lubrication can be a issue. Bronze bushings on lathes tend to get oiled. A lot - most car - truck gearbox linkages don't get oiled all the regularly!

    Please don't confuse genuine igus with oil filled nylon. The Igus stuff used to there specs really will deliver the goods. Oil filled nylon really is no comparison. IGUS is more a sintered like material but dense. its a blend of a range of diffrent things to give it the needed properties. Its not simply just one type of polymer. Its really solved some issues for one of my customers. They can get 2-3 times the life of anything else they tried. What is more when its worn it does not take the shaft out like a polymer coated metal sleeve bearings did (shame, made a killing welding and re machining those shafts :-) I think it was a 3/4" diamiter 5/8" long bush was sub £2.50 each for a sub 20 of qty. I have no connection other than being a happy customer. I am more than happy to recommend them too, they hold up really well in environments like linkages were a lot of other bearings struggle. I have also had them out perform roller element bearings in limited motion applications too. Roller or ball bearings fail very rapidly if only moved a few degrees of rotation back and forwards (like sub 2 million cycles, less than a hundred thousand complete revolutions!) Igus have cleared 8 million on the same application and last i checked at that customer there was still life left in them!


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