# Seig SC4 Bearing Replacement / headstock rebuild



## GreatOldOne (Jul 28, 2021)

I‘m in the process of replacing all the headstock bearings in my Seig SC4. I’ve gotten the head stripped down fine:
















The old bearings did not seem to be particularly well lubricated - the taper bearing from the front of the spindle just seemed to be running in a thin grey goop - the residue Im guessing of whatever was used at the factory.






I’ve ordered all new SKF bearings - better quality than stock no doubt, but I’d like to keep them that way. The front bearing is as I said a taper roller. The rear is a double shield deep ball bearing. Then there’s two smaller deep ball bearings with dual shields that run a small counter shaft that transmits power from the motor up to the spindle via two spur gears.

The headstock is open at the bottom, so there’s no oil bath. And there isn’t any provision to get oil to the bearing once everything is in place. The chuck mounting flange covers the front seal and bearing and the rear bearing is covered by a seal and the preload nuts. The two smaller bearings are somewhat accessible… but the shields sort of prevent getting any real quantity of oil into them, especially as most will just dribble out the front.

so, question is - has anyone else done this? What did you do for lubrication? I was thinking high quality grease for the taper, but then I read all sorts of posts about how it’s not the best, and oil is your friend. Which is great, if you can get it to the bearing.

Any advice on this would be great. I mean, look at the official lubrication chart. Not that helpful, eh?


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## Alcap (Jul 28, 2021)

No knowledge of headstock bearings but very surprised that the bottom is opened ! Does the tapered bearing use a seal on the chuck side to keep dirt out ?


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## GreatOldOne (Jul 28, 2021)

Alcap said:


> No knowledge of headstock bearings but very surprised that the bottom is opened ! Does the tapered bearing use a seal on the chuck side to keep dirt out ?


Yes. Its a seal - bearing - seal arrangement:






Parts 146, 172 & 173. Both ’seals’ are steel press-fit disks, which have no rubber lip seals.

I’ve ordered some proper oil seals of the correct size, thinking that’s what they where - until I found out differently when I disassembled the spindle.


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## sdelivery (Jul 28, 2021)

The Grey group was one of a couple different lubricants.
White lithium turns Grey with metal dust.
There are some very high priced special lbearing lubricants but if it was mine I would plan to remove, clean and repack at an interval based on usage.


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## sdelivery (Jul 28, 2021)

Looking at the drawing this is sure a light duty arrangement with little spindle bearing preload.
Curious how it acts with a chuck on it and a cut away from the chuck.....


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## Richard King 2 (Jul 28, 2021)

Do you have the  part description page ?  172 looks like the spindle bearing.  173 and 146 look like seals.  New SKF bearings should help and I would use Mobil #  28 or 32 red grease in a 1 pound can and only fill the bearing 1/3 full.   Ask what class bearing your buying.  On a Timken tapered roller bearing class zero or double zero precision.  Precision bearings  have mounting marks that are the TIR or where the maximum run-out of the bearing is when mounted and it is 180 degree's from the run-out of the spindle.  On a lathe of that precision (or lack of) this may not be as important then a surface grinder spindle.  If you want to check, set the spindle in a V block and turn it aand measure with a tenths (.0001") indicator.


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## Alcap (Jul 28, 2021)

Will you be able to use the seals you bought ?


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## GreatOldOne (Jul 28, 2021)

Yes Richard, 172 is the tapered roller bearing. 146 & 173 are the seals. I’ve gone for this as the replacement:





						SKF
					






					www.skf.com


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## GreatOldOne (Jul 28, 2021)

Alcap said:


> Will you be able to use the seals you bought ?


We shall see when they arrive. They’re sized correctly, but may be a tad too thick.

My full parts list that’s arriving some time this week is:
1 x 6206-2RS1 SKF Sealed Ball Bearing 30mm x 62mm x 16mm (rear spindle)
1 x OS30x62x7 R23 Metric Oil Seal (rear seal)
2 x OS35x62x7 R23 Metric Oil Seal (front seals, fore & aft)
1 x 32007 X/Q SKF Metric Taper Roller Bearing 35 x 62 x 18mm (front bearing)
2 x 61903-2RS1 SKF Sealed Thin Section Ball Bearing 17mm x 30mm x 7mm (counters shaft bearing)

Bear in mind that this is a small lathe -  not as small as the ‘mini’ 7x14 lathes, but it’s not some big lump of old iron:








						Axminster Engineer Series SC4 Bench Lathe
					

This compact lathe of very modern design has many convenient facilities ideal for the enthusiastic model engineer, small component manufacturer or in a teaching environment. A very rigid induction hardened cast iron bed with ground slideways gives a...




					www.axminstertools.com
				











						HiTorque 8.5x20 Bench Lathe 7500
					

Lathes 7500 Inch dials, inch and metric threading; 1000 Watt (1.34 HP) brushless DC drive with spindle speed readout; Power longitudinal feed and powe...




					littlemachineshop.com


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## sdelivery (Jul 28, 2021)

You would probably not notice any difference with a more precise fit of bearing on this machine. 
Save your money.
Richard is on the money with not over packing these bearings.


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## Richard King 2 (Jul 28, 2021)

Be sure to file or stone the leading edge of the spndle bearing mounts as many I have seen are sharp and will cut the oil seal.   I would micrometer (mike) the new and old bearing OD and ID before installation.  How did it come apart?  It may go in hard, so don't hammer it in.  You may want to use a threaded rod to pull it in.  It looks as if you have some skill and nice tools.  Hope I'm not insulting your intelligence (lol)  I also never use a hard punch to tighter the spanner nuts.  I use a hook spanner,  If you need a punch, use some leaded cold roll  As far as the thrust setting.  I would use and .0001" indicator and push the spindle laterally with the tails stock to push in and release to check the lost motion and then rig up a chaine and wood board to push it toward the Tail Stock, push and release - measure the lost motion and you leave it loose and tighten it so you haave no lost motion and then tighten the spanner nut one more notch on the spanner lock washer.   The after you get it running do a wear in of the spindle bearings.  Start out slow RPM for 10 minutes check for heat, then higher every 10 min, etc. .  The temp should not be over 140 F and 120 F is good.


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## GreatOldOne (Jul 28, 2021)

I’ve a bearing install kit with different cups and rods (from when I did my kit car) which I used to get the old bearings out of the casting, and the others where pressed off. Thanks for the advice - its nice to get it from such an esteemed member of the community. 

I’m having a hard time finding Mobil 32 over here. 28 no probs. I’m assuming the only real difference between the two is the heat resistance / ant-melting properties of the 32?


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## DAT510 (Jul 28, 2021)

Are Eurotrade has a nice guide for the disassembling the SC3 lathe.  Though not specifically for your SC4 lathe may be helpful.  The first page talks about lubrication.



			https://www.arceurotrade.co.uk/machineguides/SC3-Mini-Lathe-Dismantling-and-Reassembly-Guide.pdf


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## Richard King 2 (Jul 28, 2021)

# 28 is fine.  I used it for years and 32 was a newer number for a similar formula.  I buy 1 pound cans.  Just don't overpack the n the bearing with grease.  Less is better with grease.  30% unless your using Kluber.  it's expensive and 25% is the number.  a simple way to calculate it is to count the rollers and use 30% of that number.   It appears the machine is made is Asia?   If it is the bearing made in China is far inferior to SKF in my opinion..


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## GreatOldOne (Jul 30, 2021)

So I’m still waiting on the grease. When it arrives, should I remove the rubber seals on the rear ball bearing, wash out whatever grease is there and replace with the #28? Or is what SKF put in there from the factory good enough?


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## GreatOldOne (Aug 2, 2021)

Well, the deed is done. I've swapped out all the bearings as per the list on page 1 of the thread. I've also done some other modifications as I went along.

For anyone who's also looking to do this on their SC4, some advise on order of assembly, and some pearls of wisdom:


Seat the tapered bearing race first. I had a bearing install / removal kit from when I built my kit car so I used this, which makes the job very easy.
Seat the front input shaft bearing next, and then put its bearing retaining cap on.
Install the rear input shaft bearing on the input shaft itself. I'm also lucky enough to have a press, so again this was no issue.
Slide the input shaft in to the headstock and prior to fully inserting it, slide the cir-clips and lower gear with its key on. (This lower gear is supposed to slide back and forth on the shaft, when moved by a selector fork. The SC4 has an optional milling attachment, and this allows the spindle to be stopped but still power the lead screw in a stock machine. My SC4 is never going to have a milling attachment installed, and the lead screw is completely separate now due to my ELS - so I have modified the gear to install a grub screw to stop it from moving, and deleted the whole selector knob and fork.)
Seat the input shaft and rear bearing into the headstock and install the rear bearing retaining plate.
Pack the new tapered roller bearing with appropriate grease - I went with Richard's suggestion of Mobil #28. Then press the bearing on to the spindle - NOT FORGETTING THE FRONT 'OIL SEAL' / CAP which needs to be on there in front of the bearing. I was about to press mine on the second time (more on that in a mo) when I realised I was missing it...
Tap in the rear 'Oil Seal' / Cap whilst you have access through the rear bearing seat. Don't bother getting replacement, real seals with lip seals and wipers etc. I did, and it was a waste of time. They will not fit properly due to be being too thick for the available space, and the front one will interfere with the proper location of the bearing. I tried but in the end I ended up stripping the spindle again to get rid of the new seal I'd Installed. Save yourself some grief and just clean up the old ones (which are actually turned steel components).
Pull in / Seat the rear bearing - this is pretty easy.
Pass the spindle into the headstock, and whilst the end is free inside, install the upper gear, cir-clips and the key. Be prepared to turn the air blue here as it's a pig trying to get them all on the spindle in the small amount of room you have - and the cir-clips in particular give a fight trying to get them in position.
Pass the tail end of the spindle through the rear bearing. Add the rear bearing cover and the first of the spindle nuts. The bearing cover seats on the inner race of the rear bearing, and the spindle nuts press on it to provide the pre-load to the front bearing.
Proceed to tighten the spindle nut, which will draw the spindle into the rear bearing. Keep going until the front bearing seats into the race, and then tighten it whilst checking for play and ensure it can still rotate.
Tap the front bearing cover into place by using a long punch through the chuck mounting holes on the front spindle flange.

I then ran the lathe for 10 mins at the lowest speed as advised, and then slowly ramped the speed up. All seemed well and it didn't get hot. So I gave the spindle nut another 1/8th turn and did the same, and it still barely got warm - rinse and repeat until at max speed (2000rpm) it was warm to the touch, but not hot. Whilst doing this I kept monitoring the runout - and by the time I called it 'good enough, don't bugger about anymore' it was about as close to zero as matters on a lathe like this. I slight tick on a 0.01mm indicator. I installed the second spindle nut and snugged it up to lock the two in place.




















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The other modifications I did was to delete that selector fork for good, but that left a hole in the head casting - so I printed a 'plug' for it to fit where the fork guide went through the front electrical box, to keep any crud from coming through:






And as there was no knob to turn anymore, and also because the front panel on my lathe was so grotty, I designed and printed a new front panel - one that had physical buttons instead of the silly membrane switches it used to have. I had to remove the original switches from the circuit board - I replaced them with some header pins and crimped some matching connectors to the switches so I could remove everything if needed.






















Did the bearing swap cure my issues? You bet. I can put cuts on I never dreamed of now - no chatter, no drama from the lathe. It's like night & day, and well worth the hassle.


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## Janderso (Aug 2, 2021)

I enjoyed the technical discussion and the final outcome.
You deserve a pat on the back for a job well done.


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## GreatOldOne (Aug 3, 2021)

Thanks Jeff. I do hope my trials help someone else - there’s not a lot of info out there about doing this to an SC4. Plenty for the SC3, but really next to nothing for its bigger brother. 

I really ought to do something about the paint job next. The flaky white paint is starting to bug me.


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