How do you finish a shaft to a mirror finish to run through a bearing?

[jbmauser]

I have an old SB9 C lathe and I have yet to end up with even a smooth finish. Do you need to mount a grinder to get a smooth finish? I guess the same issue is a concern on the id of a piece of brass cut as a bearing.

 

[benmychree]

Fine tool finish, file, and emery cloth ID finish needs finish cut with a tool with a radius on the point or finish fit with an adjustable reamer.

 

[middle.road]

Have a look at Clickspring's videos on YouTube.

 

[mmcmdl]

You'll never get a mirror finish off a lathe . Cylindrical / centerless grinders will get you in the ballpark of possibly a 2-4 rms with polishing . Send a reamer or bore thru the brass followed by polishing or lapping .

This is dependent on what you really need though . Mirror , or smooth .

If it's standard size , go with Thompson rod .

 

[OTmachine]

20 RMS is about the best possible finish on a lathe with the proper tool nose radius, feeds, and speeds. Then you could polish to about a 10 RMS finish repeatedly using fine emery paper and then gray or red 3M (Scotchbrite) pads. I used to do this all day long when I worked at NAS Pensacola. My .02

 

[machPete99]

You can do pretty good with a toolpost grinder setup on a lathe. The spindle and grinder bearings need to be in good shape.

Otherwise, do as good as you can with a sharp HSS cutter, leave about .001 oversize and hand file it down from there, finish with emory. Do lots of checking with a good mic and you can get things within a couple of tenths.

 

[RJSakowski]

I use successively finer grit wet or dry sand paper finishing with 2000 grit and then used .5 micron diamond paste for the final mirror finish. This works well on stainless steel.

For aluminum ,I take advantage of the rapid oxidation of aluminum, essentially forming aluminum oxide particles. I used to make parabolic mirrors for long distance optical sensors. I would cut the mirror on the lathe and begin the polishing process with 400 grit wet or dry and WD40 as a lubricant. When all tooling marks were removed, I switched to a drill mounted buffing pad charged with an self cleaning car wax. The aluminum particles wbeng removed contributed to the polishing process and as the polishing went on, the particles got smaller and smaller and the finish got finer. As a final step, I polished by hand using a random motion.

 

[mmcmdl]

Here's a quick way to check . If you have ever ground or lapped to rms specs . The difference between an 8 and a 4 is tremendous . The profilomitor (sp) tells all .

 

[FOMOGO]

As to your original ?. You don't really want a polished, slip fit finish, on a bearing shaft. The inner race should be a relatively firm fit so the bearing is doing it's job, and the inner race is not just turning on a polished shaft. As to turning a smooth finish, that is mostly about a function of tool grind, and setup. As outlined above, using various forms of grinding, sanding, and polishing, truly beautiful finishes can be achieved when required, and don't get me wrong, I loves me some shinny stuff. Mike

 

[pontiac428]

Tool post grinders are great for finishing, but they don't work at all on brass. If you're working to a critical dimension, I think lapping with a shop-made arbor is the way to go.