Replacing Sherline Spindle Bearings
Some time ago I buy a used (indeed abused) Sherline manual lathe planning convert it to cnc (a in-course project). The headstock spindle of this lathe had a worn feeling so new bearings were needed. Replacing bearings was easier than expected (no strong hits were required), and here is what work for me.
- Electric stove (something like this)
- Leather gloves
- 1 1/4″ soft metal rod
- A small part to protect spindle from damage when hammer is used.
- Oviously a pair of new 6004ZZ bearings. Mine were Japan made.
- Remove front cover and back nut.
- Set stove to medium level an heat headstock for a few minutes. Don’t now exact temperature, but you should not be able to touch without gloves. Too hot it’s not good of course.
- Wearing the gloves hit the spindle back while holding headstock by hand. Be careful as spindle and front bearing may jump away.
- Use the rod to hit rear bearing from inside.
- Place back front bearing in spindle housing, but in reverse position, an hit spindle back again.
- Wait headstock to cold (20 min or more).
At this point some cleaning and checking is required.
- Clean bearing housings and spindle, using sand paper and oil if required (I use 600 grit aluminum oxide paper). I found some nasty brown coating in the rear bearing, may be some kind of glue.
- Search for nicks in bearing housing borders, and file if required (those may difficult bearing fit).
- Check front bearing fit on spindle; you should be able to move it by hand (a little force may be required).
- Coat spindle, bearings and housings with oil.
This is pretty much the inverse process.
- Heat headstock as before.
- Mount front bearing on the headstock and insert spindle. Hit spindle nose while holding by hand, until complete fit. No too much force should be required. Remove assembly from headstock.
- Mount rear bearing; careful alignment is required. (I should hit a bit as the border had a nick and filing was not perfect).
- Put back spindle, hitting should not be required.
- Ensure bearing fit are ok and wait to cold.
Once the headstock is cold you can mount in the lathe and put back the nut to adjust preload (Sherline instructions here). To me this was a bit hard as the nut was a bit tight, so adjustment was difficult. I adjust preload so there was very low friction added. Measurements were:
- Nose runout: 0.008 mm
- Nose play: 0.003 mm (may be a bit tight but I can’t get any greater)
- Face runout: 0.006 mm
After checking old bearings, I realized that front bearing was severely worn, while rear bearing doesn’t feel bad.
I would like to try 7004 angular contact bearings, but haven’t found a provider (there’s only a ceramic version on ebay, costing around $100).
Now I’m pretty sure the nasty brown coating was bearing retaining compound. I suppose this is required when there’s some play between the assembled parts. Maybe I should have use this for spindle-bearing assembly.
I forgot to say it seems original and new bearings where normal class (or ABEC1). I guess that normal bearings will do the work, but with ABEC3 bearings costing US10 on ebay (as Andy points out), there’s no reason to spare.
What grade of bearing did you use? ABEC 1, ABEC 3, etc…
Good question. New bearings only said “6004Z KOYO”, so I assume they are normal grade or ABEC 1.
Original bearings said “6004ZZ ZXT” (very unknown manufacturer). Nothing special.
Thanks for the reply. I ordered some 6004ZZ ABEC 3 C3 bearings made by RBI from ebay. About $10 including shipping for two. Removing the old bearings was as easy as you said. I heated the headstock in a small toaster oven set to 200F for about 30 minutes. A couple taps and the bearings came right out. I didn’t find any nasty brown stuff around either of my bearings like you did.
Fantastic I changed my bearings too, that brown stuff you mentioned on the spindle may be lubricating grease that leaked from inside the sealed bearing
My lathe started of as a model 4000A with a brass bed built in 1987 I brought it secondhand September 1998 from penny farthing tools in the UK, Ive had it a long time now and after changing the main bearings I decided to upgrade my Lathe with model 4400A 17 x 3.5 parts enabling me to do longer jobs.
Despite being quite old my lathe still has a spindle run-out close to factory specifications, between 0.0002 0.0004 and 0.005 run-out with the knackered self centering chuck that I still use.
I think thats pretty good and certainly accurate enough for me.
Nice to hear that. Just a bit curious about such old lathe… there’s noticable wear on the saddle? (in the bed contact surfaces)
I haven’t measured the saddle as I had replaced all the gibs when I upgraded the lathe, There are no noticeable scratch marks from excessive wear and its not so slack that I notice by hand.
I found this page when trying to disassemble my Sherline spindle assembly. The heating in the oven was a great tip. 200 degrees for 30 minutes got most of the assembly apart except for the lower bearing off the spindle itself. 30 more minutes at 250 degrees and a trip to the vice with a hammer got the bearing off. I didn’t have to hit it too hard but it definitely wouldn’t come off by hand. I ordered ABEC3 replacement bearings off of eBay.
My new bearings came and they are now installed. I’d like to share my assembly experience as it differs from the authors’.
I tried installing both bearings in the housing first, then installing the spindle. This resulted in the spindling only going in halfway before the interference fit between the spindle and the bearings couldn’t be overcome.
First, make 2 drifts, one that fits the bearing inner race and one that fits the outer race. This is important as you won’t be able to go assemble these parts by hand.
I heated the bottom bearing at 250 F for 30 minutes (in a toaster oven) and froze the spindle (fridge freezer). I dropped the bearing on the spindle and it only required very light tapping with the drift to fully seat down by the collet-end of the spindle.
I heated (at the same time as above) the aluminum housing and froze the upper bearing. These two parts went together much easier. Make sure you pay attention to which side you put the bearing into because the housing definitely has an ‘up’ side and this is where the bearing needs to go at this point.
Next, I heated the Housing and Bearing Assembly and froze the Spindle and Bearing Assembly, for the same time/temp: 250 F / 30 minutes.
I had a friend hold the spindle vertical on a piece of wood (to prevent damage) as I lowered the heated housing down over the spindle. I had to use the Inner Race Drift to get the upper bearing over the spindle’s bearing journal, but it went easily with light taps. After making sure everything was seated fully, I let it cool in a vertical position so gravity was keeping everything assembled (just in case).
Afterward the parts cooled, spindling the spindle is silky smooth. This is totally worth doing if your spindle bearings are a little chunky and clunky.