SC3 Headstock bearings

Hi all,

I am in the process of carrying out some mods' to my SC3, While I have it stripped down I am considering doing a bearing change on the headstock bearings to the taper type.

From what I have read, the taper type are a distinct advantage. But there appear to be two types. The Spindle Taper and the Angular Taper. First of all, is one any better than the other?

The reason for asking is that the 7206B Angular will fit in with no machining, whereas, for the Spindle Taper there is a need to have a 'spare' lathe to turn a spacer. Needless to say I do not have a 'spare' lathe.

However, if it came to it I'm sure that I could find someone to make one.

I've read all the info on the Arco site and I don't think that the job itself will present any serious problems. The only difference I can see is that the Spindle type can be adjusted to take account of wear, but as it looks as if the Angular type are a sealed unit and there may be no room for adjustment.

Could someone put me right on this and pass on any tips they may have, please.

Many thanks, and, although a bit late, Happy New Year

Colin.

Colin,

For clarification:

Standard deep groove ball bearings 6206-zz or 2RS fitted to SC3.

Angular Contact Bearings (Ball) 7206B-2RS dimensionally same as 6206. In your case, use these.

Taper Roller Bearings 30206 (Roller). This is where you may need another lathe for making spacer, as inner ring dimensions are different.

ACCURACY:

Taper Roller bearings (TRB) - Highest accuracy possible, with lowest max speed.

Angular Contact bearings - Little lower accuracy than TRB, but not so noticeable on a mini-lathe. Max speed higher than TRB, but lower than deep groove ball bearing.

Deep Grove ball bearing - General purpose accuracy, as not really designed for pre-load. Highest max speed.

Ketan at ARC.

I turned my spacer down with the new bearings fitted - the load required for reducing eth plastic spacer is so small there's not really any danger of things going wrong if you take it easy.

Neil

Thanks for that info Ketan, I will go for the 7206B just for the convenience, however I reserve the right to change them later.

Neil, doh! Never thought of doing that! By the way Neil, I bought your book on the mini lathe the other week, excellent!

I have also have the one by David Fenner. Also very good, but the photo's are not always clear. Not David's fault, but it does help if they are in colour. But there is some very good information and projects in there.

Always good to get the benefit of experienced folk. Many thanks.

Colin.

Colin,

I have replaced bearings on both mill and lathe in the Sieg "mini " series.

I opted for trb's.....this requires polishing of the bearing journals on the spindle to permit the inner race to slide, thus enabling the preload to be set correctly.

If you go the trb route, the plastic spacers need to be replaced with metal, the plastic ones will crush and a false preload setting will ensue....

Good luck with the modifications..

Thanks John,

I did wonder about the plastic spacers with wear and the pressure on them. It's something to bear in mind if and when I go down the TRB route!

Cheers, Colin.

Thanks Colin

@John, I haven't come across either of those issues with my machine and the taper rollers have been in their about eleven years now Looks like my rear journal was a less tight fit, according to what i wrote at the time I just oiled the mandrel and i was able to ease the race on with the nut and spacer.

Neil,

I recall doing the lathe, found the spindle journals quite a challenge when it came to fitting the new bearings...

I guess its all down to tolerances- bearings and spindle...who knows..?

I imagine there's been a fair bit of variation over the years - my machine has 1998 stamped on the chuck.

Neil

Hi all,

Well, here's the up-date.

It has been quite an eventful journey in changing the bearings. To start with all was going very well, until I put the first bearing on. Oh, it went on perfectly, the only trouble was I forgot to put the Nylon cover on next to the faceplate! Panic!

I must admit there were one or two mild (Yeah, right!) expletives. Okaaaay, remove bearing, put Nylon cover on, put bearing back. Hands up those of you who have never heard of 'Sods law'..... Mmmm, thought so! The bearing would not come off, to make matters worse the %&**&^ thing split into two separate parts. ( For those of you with delicate ears read %&**&^, as 'silly'!!). I did manage to re-assemble it and try it. It worked but was noisy, anyway, I bit the bullet and ordered another bearing. Guess what, I was unable to get the 'silly' thing off again. It had split in two again and I had to resort to very, very carefully grinding the housing down on opposite sides until it was thin enough to gently tap it off. I couldn't use the press as there was no clearance between what was left of the bearing and the shoulder of the spindle. The good news is that it is all back together and is working extremely well.

Lessons learned: 1. Check everything twice before you start a job.

2. That 'hindsight' is a wonderful ability to have! Looking back, what I should have done was to have cut the Nylon cover, slipped it over the spindle, then 'superglued' it and saved myself a lot of stress!!

3. Panic is NOT an ability!!

Cheers, Colin.

Does the plastic bearing cover have to be shimmed out to accommodate the extra width when fitting TRBs, if so by how much ?

Or do the covers need to have a recess cut out ?

Or can a rubber o-ring be fitted behind the cover to space it out and seal it ?

Also does anyone know the original width of the spindle spacers if there's no speed sensor wheel fitted ?

"Does the plastic bearing cover have to be shimmed out to accommodate the extra width when fitting TRBs, if so by how much ?"

7206B is 17.25 mm wide

6206 is 16 mm wide

Polish the spindle opposite the chuck under the bearing to a firm sliding fit to allow the preload to be set properly.

Eric

Thanks oldvelo, good tip on the polishing.

I know the TRBs stick out by 1.25 mm, this means the cover would be tightening up against the inner race outer face, so would it be best to recess the cover, shim it out or fit an o-ring.

I've found some info online on the spindle spacers but without stripping mine down (yet) I was wondering if anyone knew if the following are correct, I have the Warco super mini.

I have found widths to be 22.5 mm drive end, 45 mm hi/lo gear width and total 22.5 mm on the flange end, made up of 17.5 mm spacer, 1 mm thick speed sensor interrupter and another 4 mm spacer. My lathe has the speed sensor on the end of the spindle so I will probably have just another 22.5 mm spacer at the flange end.

So it appears a total length of 90 mm between the standard bearings. The inner TRB races stick out 1.25 mm so I would need two 23.75 mm spacers to convert if my calculations are correct.

Hi Eic,

Just a small correction:

7206B-2RS is angular contact bearing with 16mm width.

30206 is a taper roller bearing with assembled width of 17.5mm.

Keith: Why don't you just use 7206B-2RS's instead of TRBs.

Ketan at ARC.

I think I might do that Ketan, will they be a big improvement on the standard bearings and do they need any pre-loading ?

I'll save the TRBs I bought for a near future project. I'm thinking of replacing the High/Low setup with a spindle belt drive so getting rid of the gear and spacers. I already have a brushless motor on my Warco Super mini lathe (which looks like it has the SC3 motor pulley, if I buy your SC3 spindle pulley, the longer SC3 belt and modify the end spacer, would that work ?

Hi Keith,

ACB's reed pre-loading in the same way as TRBs. In either case, I would only change the standard ball-bearings if and when necessary. Yes ACB's and TRB's do make a big improvement. the difference in improvement between ACB's and TRB's in a mini-lathe environment are very marginal... in my opinion.

Regarding your conversion issue to belt-drive, I would say - don't do it, as explained with reasons in my response to you in your 'Brushless Motors' thread.

Ketan at ARC.

Thanks again for the advice Ketan.

I think I'll save my drive belt conversion for some time in the future, when I get bored with this lathe and hey ho, if I blow it up I can always buy one of your Sieg SC3s.

regards........Keith

Hey Keith,

The idea is to help you protect and progress with your current investment, and to avoid blowing things up and loosing interest in the hobby.

Good luck.

Ketan at ARC