Shopsmith Forums

I'm out of the sintered bearings for the 10ER speed changer. The correct size isn't available anymore so I have to machine them to fit.

When I called my bearing supplier today to order more they didn't have them in stock. 6 to 8 weeks to get them. He tried to talk me into buying graphite bearings. He said their better.

He said since their dry it's better for this dusty application. Where the sintered bearing can hold dust due to the "wet" oil. He also said sintered bearings are old school where graphite are modern and better quality.

What are your thoughts?

Thanks, Tom

I'm not a mechanical engineer, but I've worked with a couple when they were doing sleeve-bearing selection calculations. It's not trivial. (By coincidence, I have a professional tribologist consulting with me on a new project at work, on the design of a high-speed electrical slip ring.)

Without having the engineering data for the particular bearing material, it's impossible to say for sure if it could be substituted. But based on what I could find online about carbon-graphite bearings, I'm very doubtful that they would be appropriate for this application.

This Wikipedia article gives a good overview of bearing materials and performance calculations. If you want to dig into the engineering calculations, this paper and this paper have good information for sintered metal bearings and plastic (including carbon-graphite) bearings, respectively.

From the Wikipedia article, you can see that the pressure, velocity, and PV limits for Graphalloy are much lower than for bronze bushings.
The load on the speed-changer idler shaft is not trivial to calculate, but the speed is pretty easy. Assuming a motor speed of 1800 RPM, spindle speed of 6000 RPM, and equal drive ratios on both belts, the idler-shaft speed is about 3300 RPM. I don't recall the shaft size, but assuming 1/2", the surface speed would be (Pi * 1/2)/12 * 3300 = 432 FPM. At that speed, just any grade of bronze isn't even good enough. From the table above, you need the SAE 841 or the SAE 660. The Graphalloy isn't even in the ballpark.

I did find specs on another couple of other brands of graphite bearings online, and they were both similar to the Graphalloy. So unless your supplier has a very different type of graphite material, and can supply you with the engineering data for it, I wouldn't consider changing. If he does have the specs and the speed rating looks OK, you'd still need to do the pressure and PV calculations. And ideally, some life testing as well.

You might look at these, halfway down on the page.

http://mkctools.com/10erparts.htm

rcplaneguy wrote:You might look at these, halfway down on the page.

http://mkctools.com/10erparts.htm

Also Tom Houser lists them on eBay regularly although they are not there now. You can email him at hogwinslow@gmail.com.

I have used both tom's and Skip's and they work just fine.

jsburger wrote:

rcplaneguy wrote:You might look at these, halfway down on the page.

http://mkctools.com/10erparts.htm

Also Tom Houser lists them on eBay regularly although they are not there now. You can email him at hogwinslow@gmail.com.

I have used both tom's and Skip's and they work just fine.

Um, John, you might want to check out this thread regarding the OP's identity.

BuckeyeDennis wrote:

jsburger wrote:

rcplaneguy wrote:You might look at these, halfway down on the page.

http://mkctools.com/10erparts.htm

Also Tom Houser lists them on eBay regularly although they are not there now. You can email him at hogwinslow@gmail.com.

I have used both tom's and Skip's and they work just fine.

Um, John, you might want to check out this thread regarding the OP's identity.

OK, I didn't know.