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Feed rod worm bushings - some musings

bll230

Hot Rolled
Joined
Jun 14, 2007
Location
Las Vegas
I am reassembling my apron, and I noticed when I was fitting the new thrust bearings next to the worm that the holes in iron feed rod bushings were worn .025 oversize.

This thread

http://www.practicalmachinist.com/vb/monarch-lathes/10ee-apron-removal-246730/

discussed boring the bushings out and pressing 3/4 bronze bushings in to repair the bearing surface, which was my 30 second solution as well.

However, after pondering overnight I am a bit puzzled by the Monarch design here. All the South Bend aprons have the worm supported in bushings that are mounted in the apron casting so that the feed rod/leadscrew only turns the worm and does not have to react to loads imposed by the worm, as the worm loads are transferred to the apron. Obviously since the feed rod bushings are wearing the worm gear is pushing on the worm and the loads are passed to the feed rod causing wear of the bushings.

I think that the ideal solution would be to support the worm in angular contact bearings in the apron, but the oil cup design doesn't have enough room. The next idea is to machine a large id deep recess into the bushings and have the thrust bearings in the recess captured by a bronze bushing that supports the worm. With this arrangement both the radial and axial loads are transferred to the apron and the only load on the feed rod is torsional. The original bushings might not be thick enough, might have to make new bushings out of 12L14.

Any thoughts? Is there any reason that Monarch may not have wanted the worm supported in the apron?
 








 
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