Lapping a bronze bushing for a ball joint

FRporscheman · Jun 9, 2018

Hi, I'm a new member and I hope I chose the correct forum for this question.

I have a pair of control arms with integrated ball joints. The joints are worn out and need rebuilding, so I pieced together a kit - new bronze bushings, new ball pins.

Now that I'm finally trying to use this kit and rebuild these ball joints, I have learned that the new bushings usually come with their own ball pins which have slightly smaller diameter balls. Thus my ball pins won't fit into the bushings.

I want to retain the ball pins that I have because they are special ones with longer pins (for geometry correction). I'm wondering if there is a way to machine the bushing so the larger ball fits into it? Can it simply be lapped? And is that something I could do myself? I have access to a small lathe.

thanks

Illinoyance · Jun 9, 2018

I think it could be done on Bridgeport with a rotary table and boring head. A little time with CAD will let you determine the tilt angle for the head so the cutter will sweep the entire surface of the bushing. The centerline of the mill spindle has to pass through the center of the spherical surface. Not an easy setup to figure out.

I did a spherical surface many years ago using this technique. I did the external surface of the sphere. For an internal spherical surface the same general principles apply.

FRporscheman · Jun 25, 2018

Just wondering if anyone else has advice on this. The vendor of the aftermarket ball joints told me that when he used to sell the longer pin version, he would lap the bronze bushings so they'd fit. I'm not going to just take his word.

Even if I wanted to proceed, I wouldn't know how. Some quick searches on youtube for lapping made me realize that I have to be careful choosing the right compound, and I'm sure there are other factors I haven't even considered yet.

billzweig · Jun 25, 2018

Lapping removes very little material and is usually used when fitting parts that are less than 0.001" off. For any bigger difference in dimensions I would machine to size first.

FRporscheman · Jun 26, 2018

On the pins that I have (long ones) the ball diameter is 26.975mm (measured with Mitutoyo digital caliper recently).

On the pins that normally come with the kit, the ball diameter is 26.93mm (measured with harbor freight digital caliper a few years ago on a set of ball pins that I had back then).

So the difference is 0.045mm, or 0.0018". What do you think, lap or machine?

billzweig · Jun 26, 2018

45 microns (though calipers are certainly not accurate enough for those measurements) is more than what I would like to lap, but maybe possible. One could try with a non embedding lapping compound (like the Timesaver Lapping Compound) starting with quite coarse. The action should be rotating and tilting, like in lens grinding.
To machine a spherical surface to this tolerance is not trivial.

magneticanomaly · Jul 20, 2018

I used to rebuild quite a few ball joints.

First question, is your ball still spherical? If it is worn, there will be unavoidable slop but I am not sure if it will be a problem, if the joint is always under a load.

Lapping usually removes material from, the harder surface. The abrasive grit embeds in the softer, and cuts the harder. So lapping a bronze shell around a steel ball does not sound good.

I would fit these by scraping. Make yourself a little spoon-like scraper with a cutting-edge radius around 1/2 to 2/3 the desired finished radius, blue, print, scrape, repeat. You want a large number of bearing points. The low spots (they will be much less than .001" low) will hold grease, and it should work very well.

Richard King · Jul 20, 2018

I have been using Timesavers Yellow Lapping compound on Bronze bushings and punch press ball joints over 40 years. I learned of it from Bliss Press company when I helped one of there service engineers at a GE plant in Minneapolis.

Timesavers was used by the USA Navy on fitting propeller shaft bearings on ships. After I had lapped the pockets or bushings I hand scraped them oil pockets afterward like Magnet says. Timesavers is not Clover that would charge into the soft material. It's not the same. Also timesavers is what it says, you run the machine to do the lapping.

http://www.newmantools.com/lapping/timesaver_booklet.pdf

Timesaver Lapping Compound Yellow Label and Green Label Compounds, non imbedding lapping compound, manufactured by Micro Surface

rogertoolmaker · Sep 8, 2018

Lapping

FRporscheman said:
Hi, I'm a new member and I hope I chose the correct forum for this question.

I have a pair of control arms with integrated ball joints. The joints are worn out and need rebuilding, so I pieced together a kit - new bronze bushings, new ball pins.

Now that I'm finally trying to use this kit and rebuild these ball joints, I have learned that the new bushings usually come with their own ball pins which have slightly smaller diameter balls. Thus my ball pins won't fit into the bushings.

I want to retain the ball pins that I have because they are special ones with longer pins (for geometry correction). I'm wondering if there is a way to machine the bushing so the larger ball fits into it? Can it simply be lapped? And is that something I could do myself? I have access to a small lathe.

thanks

When lapping remember that the softer material is the one that becomes charged with the lapping materials. If I understand you, your wanting to lap the bronze bushing. Since the bronze will charged your going to cut the ball and not the bushing. Lapping won't work the way you would like and doesn't sound like your best route.

Roger

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Lapping a bronze bushing for a ball joint

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