Making a Live Center

1514168370552.pngI found this is another site.
1514168430741.png
 
ddickey said:
I found this is another site.
Click to expand...
That's a little fuzzy, but I can kinda make out dimensions.
Looks like 5203 bearing size-it's about 1.574" O.D. . That's
the dual-row angular contact bearing series. My concern is that a simple bearing will
take load by tilting downward, and that rotation is only constrained by the two rows
of balls which are rather close together. 0.001" radial movement (deflection), with row spacing about
8.7 mm = 0.342", would allow tilt of 0.33 degrees.
If you stack TWO 5203 bearings, the same 0.001" applies to four rows of balls, the farthest
being 26.2mm= 1.031" apart, tilt would be 0.11 degrees.

Two 5203 bearings would fill a socket 35mm deep = 1.378", and I'm thinking
that's what the BB complement of that design is intended to be. Each can take over 9000 N
lateral force (that's 2000 lbs).
 
I've done a bunch of reading and think I've decided on a design. I'm going to try and copy the Royal in that they have a shorter more rigid shaft. Three duplex angular contact bearings back to back with a needle bearing supporting the rear of the shaft. 1144 stressproof for the housing and O1 for the shaft. Wish I had the bearings as I have a week off starting thursday. May have to go up to the cities and find a bearing distributor.
 
I've done some quick searches on Amazon and am surprised at the cost of the bearings.
 
ddickey said:
I've done some quick searches on Amazon and am surprised at the cost of the bearings.
Click to expand...
A good way to find relatively inexpensive high grade bearings for our projects is to try to find some that are made in large production runs for use in common consumer goods, like automobiles. It pays (literally) to start your search in that way. Another way is to look at surplus sources, if you can buy spares at the same time or don't think you will ever need a replacement. Sometimes there are real deals on stuff that will fit obsolete high grade military stuff. Just do not plan on ever finding them again.
 
ddickey said:
Take a look at this design. It is the cheap Royal center. Anyone have an idea of the bearings used? Interesting in that the entire body turns.
http://www.royalproducts.com/content/files/products/Value_Turn_LC.pdf
Click to expand...
The body-turns feature means you can finish-grind the point while driving the body with a rubber
tire.
It seems to rely on the thrust bearing having cutaway races, so the point-side race bears only
against the OD of the point-side BB, and the shank-side race bears only against the ID of
the shaft-side BB. Either grinding on the races, or making some spacer elements to add to the
design, will be required. A 'full-size' race could bear on both the shaft and body, and that's galling.

For a small center, the common-as-dirt 6001 ball bearing, and 51201 thrust bearing (from vxb.com catalog)
would work. 12mm I.D. and 28mm O.D. for both --VXB's catalog allows easy search on dimensions so
you could explore for other matches.

The odd way the thrust bearing is stressed seems worrisome to me; the races could become
dished, or even break. A pair of angular-contact bearings (7001 type), and two spacers,
would be my preference. Spacing instead of stacking gives more moment against rotating
the point down under loads.
 
On this book (The Amateur's Lathe by L.H. Sparey) there a good plan for a live center. And there a good idea anyone can use:
He put a threaded hole on body(between two bearings). After everything ready and mounted, he screwed a bolt in this hole locking the rotating tip. This way is possible to do a finish cut with everything in place and center mounted on MT spindle taper.
 
Wouldn't you need the tip rotating in the body to get an accurate cut/grind?
 
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