|andy mulholland||05/02/2019 16:16:36|
36 forum posts
ive just rebuilt my lathe and all seemed well.. but ive discovered that if I load the headstock axially say with a drill in the tailstock the mandrel stalls..
it appears it causes the front taper bearing bush to bind..
I did think I had set the running clearance as per instructions, so im wondering if I have not preloaded the two angular contact ball bearings that support the rear of the mandrel correctly.. could anyone tell me if that's the likely cause..
I thought I had followed the instructions and they do warn about overloading the ball races, but im getting something wrong as it behaved fine before the strip down..
as usual any and all advice much appreciated.
|3554 forum posts|
Preloading the angular contact bearings as per instructions, the preloading is determined by how tight you move the left hand end of mandrel adjuster. Clearance on the front taper bearing is determined by moving the pair of clamping rings form the point where rotation is just not possible to the specified position which gives the required running clearance. So it is prelaoding first, followed by the front bearing clearance, all by following the Myford written text.
|andy mulholland||05/02/2019 17:22:34|
36 forum posts
thanks for the reply.... thats pretty much what ive done... followed the instructions in the my ford manual..
set the preload on the rear angular contact bearings with the front taper bearing loose , then adjusted the running clearance on the taper bearing using the adjustable rings which lock the bearing outer races..
but as soon as you load the mandrel it is sticking , so im thinking I may not have the preload right.. ie a bit loose allowing a bit movement of the mandrel..
|Nick Taylor 2||05/02/2019 18:59:24|
|102 forum posts|
Did you remember the spacer between the two bearings?
Are the bearings the correct way around?
Did you remember to give the left hand collar a sharp tap with a small hammer?
|Chris Trice||05/02/2019 19:55:35|
1375 forum posts
As Kwil says, you have to think of the adjustment in two stages. The first stage is to set the preload with everything else loose. If all is well, the rear bearings will not let the spindle move to the left (or right) under pressure. Once stage 1 is complete, stage 2 is to move the combined preloaded and locked rear bearings as a unit to the left taking the spindle with them until the right clearance is obtained in the bronze bearing. If applying pressure from the tailstock locks the spindle in the bronze bearing then there is movement going on in the rear bearings. Note however that it take very little movement of the spindle (maybe only a thou or less) to take from the ideal position to a locked position so it only takes a gnat's adjustment somewhere in the assembly to make all the difference. Something I found before I converted the angular contact bearings to taper roller bearings was that in the search for the minimal clearance at the bronze bearing, get it free turning yet slightly too close and with neglected oil lubrication, you can find the lathe start to labour and tighten up if you work it hard as the nose end starts to heat up. Getting that sweet spot just right is a bit trial and error but if you're confident that your preload is correctly set, shifting the spindle just forward of the point where it might bind for any reason, is the sweet spot.
|Kiwi Bloke||05/02/2019 21:00:38|
|666 forum posts|
I had exactly the same experience with my Super 7, when it was nearly new. I was trying to use a rather brutish 'carbide'-tipped tool - a negative-rake metal-shifter. The only way chatter could be (mostly) eliminated was to tighten up the front bearing clearance. The bearing continued to run cool at high speed, so I thought the spindle may have been not optimally adjusted previously. Then I needed to drill from the tailstock, and the lathe stalled at the slightest provocation. Unfortunately, this behaviour is a 'feature' of this lathe - others have experienced the same.
The problem may be because of a lack of stiffness in the thrust bearings themselves - perhaps the taper roller mod helps. However, IIRC, with a sensitive indicator, I satisfied myself that the part of the headstock casting which carried the thrust bearings wasn't very stiff, when the spindle was loaded axially - a few 'tenths' movement could be induced wrt the bed. I don't recall being able to detect movement between spindle and the rear of the headstock. Incidentally, my Emco Maximat Super 11 coped with the tooling perfectly.
As you've discovered (and it sounds like you fully understand what you're doing), setting the position of the spindle is either a compromise, or you adjust it for the job in hand. It's a very sensitive adjustment. I guess most users settle for a compromise setting, which is where the lathe doesn't slow down with the heaviest anticipated axial load applied. But then look at the axial movement of the nose of the spindle, when loaded radially, and don't be surprised to see a couple of 'tenths' of movement. Remember, it's a light lathe, designed more for versatility than heavy loads. Despite its worship from its die-hard fan base, it's a dated design with many flaws: better* lathes are out there...
* Of course, it rather depends on what you mean by 'better'.
|andy mulholland||05/02/2019 21:41:21|
36 forum posts
thanks for all your comments and advice..
as I said the lathe has run perfectly in the past and coped with what I would call substantial axial loads for a small lathe , so I was a bit surprised when it stalled after the rebuild.. the bearings had not been removed at this stage so no question of incorrect installation , just the possibility of incorrect adjustment after removing the spindle to replace the drive belt.. ill keep working on the preload of the angular contact ball races to see if I can't find the right setting..
|3554 forum posts|
|510 forum posts|
I've had this note about S7 bearing adjustment (I can't remember where I found it) and you may care to read and follow:
Sounds like out of adjustment bearings. The pressure from the live centre is reducing the front bearing clearance to zero. Carry out the following as per Myford (Nottingham) practice:
ADJUSTING HEADSTOCK BEARINGS
This is what Myford Ltd used to do:
1. Power Down
2. Remove all belt tension.
3. Remove Chuck
4. Rotate RH collar one complete turn. (top towards you).
5. Rotate LH collar one complete turn. (top towards you).
Spindle should be completely free of front bush.
6.Loosen Allen screw on collar at end of spindle.
7. Using the Allen key tighten collar as tight at it will go by hand.
Inner tapered roller races are now locked together with correct pre-load.
8. Back off LH collar one complete turn + a bit (top away from you).
9. Rocking the spindle by holding the spindle nose tighten the RH collar by hand (top away from you).
10. When you feel resistance to movement stop.
11. Collar should be just tight enough that spindle can just be moved by hand holding the nose.
12. Do up the LH collar by hand (top towards you). You should still feel resistance when turning the spindle by the nose.
13. With the crescent wrench (adjustable spanner) on the LH collar tap the end smartly with a 12oz hammer.
The spindle should move forwards by a couple of tenths and be completely free running.
14. With the lathe running slowly (lowest direct speed) put the oil gun in the front oil cup and pump until oil issues from the front bearing. (It comes out of the back and is sprayed around by the bull wheel at least it did on mine).
15. All should be sweetness and light with great rejoicing in heaven and on the earth.
|Kiwi Bloke||06/02/2019 07:44:17|
|666 forum posts|
Andy - it may just be loose terminology, but now I'm worried that you seem to be still fiddling about with changing the preloading of the angular contact bearings (set by the split, threaded collar, at the end of the spindle). Essentially, once all the 'slack' is taken up, increasing the preload will achieve little, if anything, in terms of axial rigidity, but will cause the bearings to have a harder time - or fail. Do not over-tighten them. The relationship of the spindle to its tapered nose bearing is what needs careful fiddling. This is set by the two rings, using C-spanners, patience and suitable language. It's easy, but tedious. I think you know that...
The above instructions are correct, in principle (although be careful with the 12oz hammer...). Very small spanner angle adjustments are needed to get the best adjustment. In fact, you may find that you can change from a tightening spindle to a well-behaved one simply by bumping the spanner on the rear ring to make it a little tighter. I've always used the heel of my carefully-calibrated hand, not a hammer.
I suspect - but have no evidence - that the type of oil used in the front bearing may have a significant effect. Myford's recommendation may be rather old-fashioned. One day, I'll try something 'slipperier'. Any suggestions, anyone?
|Chris Trice||06/02/2019 10:33:53|
1375 forum posts
It is worth substantially tightening the adjusting ring on the end of the spindle to make sure that the inner part of the bearings are positioned hard up on the spindle, loosening it and then resetting the preload. Tapping the spindle with a hide or rubber mallet might help to ensure things are sitting where they should be, then set the bronze bearing clearance.
|Martin Kyte||06/02/2019 11:22:09|
2751 forum posts
Have you replaced the spindle during your rebuild? I have had this problem which ws caused by the spacer (Item31 on the exploded diagram link below) not seating right up to the shoulder on the spindle but jamming just short. This is firm enough to seem like all is well when you adjust the front bearing clearence but when a thrust load is applied from the tailstock the spacer moves and the front clearence is lost. The quick way to solve this is as Chris says above adust the collars to give a generous front bearing clearance. Then tighten the split collar as tight as you can get it to ensure the spacer is tight to the shoulder. Loosen off and set the preload as normal. Then you can set the front bearing clearance.
If you want to fully diagnose the issue. Take the spindle out and inpect the fit of the collar (item 31) on the spindle. There are some new spindles around where the collar gets tight just before it contacts the shoulder. I did stone my spindle off just to ease the fit so it's only a matter of a few tenths but enough to cause an issue.
|andy mulholland||06/02/2019 18:06:51|
36 forum posts
hi Kwil , its not intentional .. ill look into that and sort it out.. im not particularly savy when it comes to all this online and forum stuff but I will get there... my location is south tyneside.. specifically South Shields...
now I see I have further replies , and some quite lengthy so I must get them read and respond where necessary...
thanks for all the help.
|andy mulholland||06/02/2019 18:51:18|
36 forum posts
thanks for that comprehensive list of instructions Dave.. I've read and understood them with the exception of item 7 where it suggests tightening the collar with an Allen key... what do they mean ?? as that is the split solar and the Allen key is used simply to unlock the collar so that you can move the colar .. does it mean use the Allen key as a lever to assist in the hand tightening of the solar??
kiwi bloke... that is in fact what I have ended up doing.. ie tightening that split solar far more than I would normally have done... the instructions suggest it should be tightened just sufficiently to remove the end float on the spindle, but ive ended up giving it a bit more and have to say that things have improved regarding the axial loads lacing the spindle..
cheers Chris... that is more or less what ive done..ie applied a bit more preload.. could be that the inner races were sticking a bit and giving a false feel or setting..
Martin.. I haven't replaced anything other than the drive belts and a few oil nipples.. and re set the saddle shims.. and the spindle was removed so I know the collar you are referring to is an easy fit on the spindle..it sits tight against the shoulder on the spindle..
thanks again everyone for your time
|510 forum posts|
That's it, Andy. Use the Allen key as a lever.
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