Mechanics and Construction > Mechanics and Construction

Rover suspension ideas needed

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jwatte:
Thanks to the advice in this thread, I will only steer on two wheels. I am also looking at a-frame or double wishbone suspensions. I want to build every part if I can,  but the a frame design simplifies steering decoupling and hub mounted motor.
Turns out, ball joints with quarter inch fittings are very cheap - less than $25 for ten!

Next question is one of axles and bearing fit.

I ordered some .125 steel rod and some 1/8" inner diameter flange ball bearings. However, the bearings don't fit on the rod. Measuring with calipers, I get the rod at .125 spot on but the bearings at .115" inner diameter. (Calipers are not great for this measurement, but this was as good as i could get)Is this an expected result?

How can I make sure to get bearings and an axle that will fit?

Th232:
Not sure where you bought the bearings, but I'd be sending an email back to the vendor.  Even if there's supposed to be an interference fit for the bearings, 0.115 vs 0.125 is way off.

One way to make sure things will fit is to turn the axle yourself, but that's dependent on access to a lathe.  You did say you wanted to build every part if you could, right? :P

jwatte:

--- Quote ---One way to make sure things will fit is to turn the axle yourself, but that's dependent on access to a lathe.  You did say you wanted to build every part if you could, right?
--- End quote ---

I could use a manual lathe at Tech Shop if I took their class on it... Maybe now's the time :-)

(Also, there's a fourth axis/lathe for the Tormach CNC that I already use there; there might be a turn/mill option for me, too)

Soeren:
Hi,


--- Quote from: jwatte on December 07, 2012, 10:56:38 PM ---I ordered some .125 steel rod and some 1/8" inner diameter flange ball bearings. However, the bearings don't fit on the rod. Measuring with calipers, I get the rod at .125 spot on but the bearings at .115" inner diameter. (Calipers are not great for this measurement, but this was as good as i could get)Is this an expected result?

--- End quote ---
You can check the inner diameter by grinding down a plastic axle/stick until it fits snuggly, then measure the axle
Put the axle in a drill and let it run, while pressing a piece of emery paper on a flat stick (very lightly) against the axle - check the size frequently.

If both axle and bearing is 1/8" AND they're both perfect down to molecule level, you'll still need to press fit the bearing onto the axle.
Given a little roughness, you may need to cool the axle a couple of hours in a freezer, while heating the bearinga bit - say to ~45C - don't go much higher, or you'll damage the lubricant.
To press it on, remember to use a method that only presses on the inner ring of the bearing (or you will hurt it).

jwatte:

--- Quote ---Given a little roughness, you may need to cool the axle a couple of hours in a freezer, while heating the bearinga bit - say to ~45C - don't go much higher, or you'll damage the lubricant.

--- End quote ---

I would never have thought of that! Thanks a lot for the practical advise!

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