View Full Version : Bearing loads
07-02-2007, 12:26 AM
I want to replace the bearings on my wood lathe. To reveal my ignorance, is the load on the bearings in a wood lathe radial or axial and could someone explain the different effects on bearings in general?
Thanks in advance,
07-02-2007, 12:32 AM
probably both, the load end-wise from the tailstock in the centers, and the load from the cutting, which is largely radial, but can be axial (bowls).
I would think in general rather light, compared to metal lathes, unless you work nasty woods.....
07-02-2007, 12:41 AM
I would think a bearing that goes on a car or truck wheel would be the right type and quality for a wood lathe. its takes both type of force.
A spindle is a spindle. I dont care what its in.
07-02-2007, 12:44 AM
I wish I could give you a simple answer, but the real answer is "both." Most of your cutting force is going to generate radial loads -- ones pushing towards (or away from) the center-line of the lathe's spindle. Your tailstock, however, is going to generate axial loads on the spindle bearings. (For what it's worth, certain cutting operations will also generate axial loads.)
Some bearings are designed to take only one of these forms of loading, while others can take a combination of both. A standard ball bearing can usually take heavy radial loads but can withstand only small axial loads. The design of such bearings offers little support for the balls under axial loading, so the bearings can easily pop apart. Thrust bearings, on the other hand, can take huge axial loads but are completely unable to take radial ones. Lathes usually use tapered roller bearings in their headstocks. These bearings can take relatively high loads in BOTH the axial and radial directions.
Adding one more comment on lathe headstocks: Lathes usually use two or more tapered roller bearings, installed in opposite directions, so that spindle pre-load can be applied. Such an implementation allows slop or play to be adjusted out of the spindle.
Hopefully I understood your question and provided a helpful answer.
Edit/addition: Tapered roller bearings are commonly used on car/truck wheels. tattoomike was right in his thinking.
07-02-2007, 04:45 AM
Chances are the bearings that are in your wood lathe aren't anything particularly special. Replacing them with the same size deep groove ball bearing type should be entirely satisfactory. Look up the axial and radial loading specs for bearings that meet your size requirements, and you'll probably agree that the ratings for both types of loading are well within what you would be applying under any normal use.
If you try to accommodate another type of bearing, you could be in for an exercise in frustration. I'm not saying don't do it, but it's likely that you wouldn't want to modify the spindle or the bearing seats, or make up spacers to adapt.
When I was using my wood lathe, a nice old beaver brand, I re-packed the bearings and it has been fine. If your bearings are truly shot, swap new ones in for sure, but I don't thing there's anything to gain by trying to get tapered rollers in there. If you can find a deal on some angular contact types that will fit, then why not, but then you'll definitely have to use pre-load, and that might become problematic. Wood lathe speeds are fairly high, and you could easily find that your bearings heat up quite much if adjusted for no play when cold, or if adjusted for cooler running they might be somewhat loose when cold.
Just my gut feeling, but I'd say stick with a standard deep groove ball bearing, unless you find that it does have special bearings.
Same as Darryl said. The bearings in the mini mill are deep groove ball bearings and are adequate if not the best. The loads are much higher than a wood lathe. Standard ball bearings can withstand both radial and axial loads with the amount depending on the proportion of each and RPM. The loads in a wood lathe are trivial compared to a metal lathe and the accuracy requirement far less.
In general, deep groove ball bearings (the standard type) can take about 1/2 the radial load rating as axial load at low rpms. Near maximum rpm this drops to about 10%. The axial load times 2 is subtracted from the allowable radial load to calculate the total allowable loads.