Burnishing Bushings with Balls

[BRENT in 10-uh-C]

Has anyone ever used a precision ball bearing to size and burnish a bushing? I think I am going to experiment with it.

If you are unfamiliar with this process, I just came from two different shops that uses balls to size their bushings in driveline components instead of honing or reaming. These balls are expensive but are accurate in sizing a bushing to 10-millionth of an inch (0.000010"). In watching it done, the ball is pushed thru the bushing with a large arbor press in one slow but steady motion. The ball is warm when it comes out due to the friction, -but not too hot to hold. You cannot immediately reuse the same ball in the next bushing until it has cooled to room temperature as it grows in size after use from the friction. Below is a picture of the container the ball comes in. Notice the measured size of the ball.
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[dennis lumbert]

Very interesting

[Terry Burtz, Calif]

This is a process developed by the Aerospace industry to achieve accuracies needed for certain parts. Excessive heat from the friction is not desirable, so instead of one ball doing the sizing, several progressively larger balls are often used.

[BRENT in 10-uh-C]

Originally Posted by Terry Burtz, Calif

This is a process developed by the Aerospace industry to achieve accuracies needed for certain parts. Excessive heat from the friction is not desirable, so instead of one ball doing the sizing, several progressively larger balls are often used.

Great suggestion Terry, and thanks for the insight.

Most of the applications I was thinking about for a Model-A have multiple bushings (i.e.: Brake Actuator Shaft, Sector Shaft, Distributor Housing, Oil Pump, Spindle Bolts, etc.) where I think the alignment between the two bushing would not be on true plane if only sized with a ball, however I would like to use it on some other marques of vehicles.

[rotorwrench]

The use of expanders for piston pin bushings in connecting rods and possibly a few other applications have been used over the years. A lot depends on backing materials and construction of the bushing. Some have an interlinked split line, some are straight split line, and some have no seam at all. Various type of expanders have been used over the years including a driven ball type.

[GRutter]

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Interesting process. Where does the extra material go? Are you compressing the bushing? What keeps the bushings in place? Seems like the bushings would be pressed out of their bores.

[Synchro909]

The father of one of my friends told us about how they used to use balls of increasing size to take the dents out of mangled motorcycle exhausts after a crash. The balls were on a chain which was lowered through the pipe, the damaged area heated and the ball pulled through, then repeated with the next sized ball until the repair was effected. He used to do it in the 1920s.
The principal has been around for a long time but if Terry can make it work for him, good on him.

[airjam]

Very interesting topic. Crazy tolerances

[johnneilson]

Have used ceramic bearing balls in bronze guides.
I still prefer to use expanding hone mandrel.

J

[Synchro909]

Other than the academic interest in obtaining those accuracies, can anybody see a real world benefit for a Model A? IMO, one ten thousandth of an inch is plenty accurate. I doubt even in modern cars, they reliably work to greater accuracy other than in ball and roller bearings. Interesting, none the less.

[Dodge]

Brent,
We use precision balls to re size bronze valve guide inserts. They seem to work well.
They don't move much metal though so Terry's idea of the progressively larger balls maybe needed. I wonder if a quick ream to get close and a finish with the ball might
be the way to go. I leaves a real nice finish.

Dodge

[nkaminar]

Didn't Ford use steel balls to finish the cylinder bores on the Model T? If I remember correctly (questionable) it left a compressed finish to the cast iron that was more wear resistant.

[rotorwrench]

Ford used a steel roller head to burnish the cylinder walls in similar fashion to the way hydraulic cylinders are burnished. This link has an old photo.
http://www.mtfca.com/discus/messages...tml?1377361579

[GeneBob]

One caution: The ball follows the hole that it is pressed through, especially a hole that is many times the diameter in length and/or has a lubrication hole drilled through the side. You can end up with a hole that is extremely precise at each cross-section location but still not be able to put a pin all the way through. This is where a long reamer will have an advantage, at least to establish the straightness before final sizing with a ball.

[ronn]

synchro-
same process used on dented band instruments. small to large till dent is gone.