# TLC for Central Machinery compound action



## visenfile (Dec 20, 2021)

Model 33274 , apparent cousin of other asian lathes.  New to me!  (about time).... The compound slide action :  wobbly handle, and the two measurement  dials (metric-inch) would separate over 1/8" on dialing  (slop).  Finally got the handle off and then down to the bearings. The CM drawing items 11,13 call the bearings "8101," but they are marked "51101."  Nominal ? dimensions 26mm x 12mm x 9mm.  To unaided eye the bearings and races look good, but with a 10x loupe the races are heavily scored.  The balls seem ok @ 4.74 mm.  The "stack" height of two loose races and balls is 8.85 mm measured (there are 2 bearing assemblies). 

Finally made a .003 " shim with 12mm hole (shaft size) and placed it on the shaft flange where the outer bearing sits.  When assembled the slop seemed gone, but.. if 9mm stack is expected and I had 8.85mm measured , the .003" shim is more than required so...Maybe I just adjusted the assembly with the outer knurled nut (item 15) ?  ( I had this thing apart several times).  

There is an allen screw holding on the outer nut,  but this thing is ornery to get off. Looking into the threaded screw cavity there is a brass contact which may have taken a shallow thread from pressure. Makes getting the nut off tedious because of the need to hold the shaft with out damaging the big thread or journal areas.  I took a 1" long screw having the allen nut thread and used it  in that hole as a lever arm on the nut while using a  drill shank to hold the shaft end.  Once the nut is off a couple time it gets easier.

Ebay has the bearings ranging from $5 greater China to NSK $20 (times 2).   The "hover" photos of the ebay cheapies from China are humorous to me as they look worn and rusty in places.  Since my bearings only run at 1 rpm or less I have not decided whether to even replace them.  The wobbly handle seems to need a new hole and roll pin.


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## Mitch Alsup (Dec 20, 2021)

In general, it is NOT the bearings that eliminate slop in the compound, but the gib(s).

The bearings, the movement nut and the screw are used to move the compound, 
but the gib in the dovetail is what makes the compound move straight and have the required stiffness and still move like a knife though warm butter.


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## Larry$ (Dec 20, 2021)

visenfile said:


> if 9mm stack is expected and I had 8.85mm measured , the .003" shim is more than required


The thrust bearings you have are probably fine for what they need to do. Put some lube on them and call it good.  I think you may be giving more credit to the accuracy of manufacture than is due, worrying about a slight over size stack. Snug the gib to give a slight drag and don't worry about a bit of slop if you can't get it all out. Always feed in so the slop is taken up.


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## visenfile (Dec 21, 2021)

I managed to get the slop out .  I think the nut was loose.  The cross-piece handle fit was also loose so I managed to slip in 2 pieces of .001"  shim stock where the shaft enters , and then make an oversized pin to replace the 3 x 16 mm one.  The .131" pin seems to work. We'll see.  The details and final execution of the handle at the factory is a head shaker...precise brass bushings in the handle and then the shaft drilled off-center.  Thanks for comments.T


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