Quill Bearings for my King PDM 30 Round Column Bench Mill (RF 31 style)

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Active User
H-M Supporter - Gold Member ($25)
Jan 1, 2014
I am posting this information as there is probably a huge number of this exact style bench mill in use out there being as they are sold under many different brand names. Because they appear to have the identical features, I am assuming (?) that many will have the same quill design.

I bought my bench mill used in 2008 and did a full rebuild. With respect to the quill I just took it apart, cleaned everything, regreased the tapered roller bearings, and reassembled it. Working on a number of different mods this past year I had reason to pull the quill out of the mill again. I noticed that the top bearing was pushing the grease out topside as these bearings are not sealed in any way. Removing the dust/chip cover from the bottom of the quill showed that the cover does a poor job of keeping out debris so that a lot of little metal chips can eventually migrate into the bearing. Manufacturers same kind replacement bearings are really expensive - $142 for the pair.

After getting careful measurements of both bearings I went to a local supplier and we came up with FAG 40 degree angular double sealed ball bearings for $85. This bearing gives almost equal load strength on each axis, was fully sealed, and would be plenty strong enough for anything encountered in my operations. The lower bearing was a little narrower than the original but that is not an issue. A double row bearing would have been too wide and have hauled the spindle down so that the top locking nut would not grab the thread. Installation preload is a little more sensitive than the roller type. I ran the mill at 3000 RPM for 15 minutes and got a bit of heat buildup so had to relax the adjustment nuts a bit, but everything has been okay since. The dust cover still keeps most of the debris out but whatever does get by will not get into the bearing anymore.

The pictures are self explanatory. Maybe someone out there will find this fix useful.


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Active User
H-M Supporter - Gold Member ($25)
Sep 26, 2013
Thanks for the posts on upgrading your King/RF mill. I, like many others as you pointed out, have the same mill and find your information very helpful. :thumbzup:

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