Author Topic: How tight is tight  (Read 16479 times)

Online steamer

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Re: How tight is tight
« Reply #15 on: January 12, 2014, 05:08:35 PM »
As a brief aside, the South Bend procedure is not that far off from what we've discussed.  Hurray for Pragmatism!

 :lolb:

Dave
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Offline Jo

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Re: How tight is tight
« Reply #16 on: January 12, 2014, 05:09:03 PM »
Yes I am glad its not a Colchester lathe with Gamet bearings @£4500 each

 :o I will look after mine then. Also be glad it is not a Schaublin Mill that Eric has just discovered that the knackered spindle bearings are also well into four digits  :(.

Jo

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Re: How tight is tight
« Reply #17 on: January 12, 2014, 05:11:55 PM »
That would be the source of the love/hate relationship I have with the Swiss stuff....sorry Florian...

Dave
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Re: How tight is tight
« Reply #18 on: January 12, 2014, 05:15:35 PM »
Something to be said for pragmatism....

http://www.lathes.co.uk/southbend9-inch/index.html

Dave
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Offline Hugh Currin

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Re: How tight is tight
« Reply #19 on: January 12, 2014, 08:05:42 PM »
The thinking with the shims are to space the inner race the same as the outer? If the same thickness then a matched pair of bearings should be set.

Would it work to cut shims from shim stock for both the inner and outer? I'd think that would better assure the same thickness?

I've thought about doing something similar with non-matched bearings. Mount them back to back, maybe just ball bearings, and clamp together. If this would create a heavy pre-load then shim so they are slightly loose. Then carefully measure the end play and make a shim this thickness. Put the shim in place and re-assemble with pre-load holding inner and outer races solidly. Do you all think this is feasible?

Thanks for the input.

Hugh
Hugh

Offline BaronJ

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Re: How tight is tight
« Reply #20 on: January 12, 2014, 08:51:29 PM »
Hi Guys,

I don't know if it helps,  on my Myford S7  the bearings when taken out and the shim removed have a perceptible gap between the outer bearing cages.  Also on mine, when cold, the spindle is quite tight in the bronze taper at the chuck end, however it rapidly loosens after running for a few minutes.  I find it very difficult to adjust but it has always been tight from new.
Best Regards:  Baron.

I don’t regret the things I’ve done, I regret the things I didn’t do when I had the chance.

Offline Graham Meek

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Re: How tight is tight
« Reply #21 on: January 12, 2014, 10:05:42 PM »
New angular contact bearings, especially a matched pair will have no perceivable gap between the outer tracks, any degree of pre-load built into the bearing by the manufacturer will be on the inner races, which you cannot see.

Tightness of the Myford spindle is down to the adjustment of the front bearing, it is adjusted by moving the whole angular bearing pack forwards towards the front bearing via the locking rings. This adjustment is not to be confused with what Stuart has originally asked.

To adjust the front bearing the whole bearing pack is adjusted towards the change wheels until the spindle just starts to lock up in the front taper bush, the inner most locking ring is then slackened by a 1/4" measured on the circumference of the locking ring. The rear locking ring is then tightened and the spindle should be correctly tightened.

Can I offer a tip when dismantling or adjusting things such as this, if you scribe lines on the locking rings and the headstock casting before you start, if you should get it hopelessly wrong you can always return things to where you started. I apologise to those who may be experienced in such matters for trying to tell them how to suck eggs, my advice is aimed at the person who may be afraid to make such adjustments and continues to struggle with his equipment when really there is no need.

My best regards
Gray,

Offline Graham Meek

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Re: How tight is tight
« Reply #22 on: January 12, 2014, 10:08:36 PM »
I had better add that these adjustments should always be carried out with a slack driving belt.

Gray,

Offline BaronJ

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Re: How tight is tight
« Reply #23 on: January 12, 2014, 10:52:12 PM »
Hi Gray,

Thank you for your explanation for the adjustment of the front bearing.  This is exactly the method described to me a long time ago.
Whilst I understand this procedure, what happens is, if I make the adjustment when the lathe is cold, there is perceptible play when warm.  If I make the adjustment when warm the spindle is tight to rotate when cold.  By comparison a friend who has the same lathe, the chuck can be turned more easily when cold than mine.  His suggestion is that my lathe hasn't done as much work as his even though my Myford is more than thirty years old.  The lathe was stripped and cleaned down about three years ago just before I retired.

You mentioned marking things before dismantling.  I put a paint marker spot on the adjustment rings to try to judge how much the spindle moved when adjusted.  You mentioned 1/4".  That amount is just about the difference between a loose spindle and being tight.

Your note about the belt is apt, though I make a habit of taking the tension off when not in use.

 
Best Regards:  Baron.

I don’t regret the things I’ve done, I regret the things I didn’t do when I had the chance.

Offline Stuart

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Re: How tight is tight
« Reply #24 on: January 13, 2014, 08:02:51 AM »
Gray

I have decideded as I have a matched pair which is marked up by SKF I will wait till the shims arrive measure the outer again and select the inner ones to match and install as solid unit with the manufactures pre load locked in so to speak.

From what Dave has said it look like the design was to for fill two things
1 to get oil in
2 to enable them to buy single bearings

Hence a cost saving

I will post when it's back together ,with the method used

Many thanks to all who have taken the time to contribute, as usual I have learn a lot as to why it was done and the design limitations , and the reason why


Stuart
My aim is for a accurate part with a good finish

Offline Graham Meek

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Re: How tight is tight
« Reply #25 on: January 13, 2014, 11:29:46 AM »
Hi Baron,

No bearing arrangement, unless it is specifically designed to accommodate temperature variation is going to be able to accommodate large fluctuations in temperature as is usually the case in the Home Workshop. My own Maximat Super 11 will tell me it is a cold morning with a pronounced difference in the whine of the geared headstock, and this is in a worksop that is thermally insulated, double glazed and with a 5 degree C background heat.

If your friends lathe has done more work than yours, then yes, the bearing wear on the front bearing as well as wear on the angular contacts are all going to add to the clearance in the system, especially if the machine has never had the bearings adjusted from day one. If your friends machine was adjusted and had an identical temperature environment then I would expect similar results, but you cannot compare one machine with another without these considerations.

When I had my Super 7 I encountered this problem early on and in order to keep some stability in the temperature I used 2 X 40 watt light bulbs wired in series, these were placed under the lathe bed. The lathe cover was then draped over the lathe followed by an old curtain. It is surprising what heat these two bulbs deliver, bearing adjustment was carried out one morning after using this set up for a few nights and I never ever had a tight spindle from then on, nor was it too loose during a workshop session. The bulbs were dispensed with during the summer months.

As regards marking I use the end of my rule and a scriber, the marks are dead in line and it is not possible to return anything other than dead in-line.

My best regards
Gray,

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Re: How tight is tight
« Reply #26 on: January 13, 2014, 01:58:10 PM »
That all seems quite reasonable Gray.  Thanks.    Take a look at all that Stuart and I am sure we can progress.

Dave
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Offline BaronJ

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Re: How tight is tight
« Reply #27 on: January 13, 2014, 11:05:29 PM »
Hi Baron,

When I had my Super 7 I encountered this problem early on and in order to keep some stability in the temperature I used 2 X 40 watt light bulbs wired in series, these were placed under the lathe bed. The lathe cover was then draped over the lathe followed by an old curtain. It is surprising what heat these two bulbs deliver, bearing adjustment was carried out one morning after using this set up for a few nights and I never ever had a tight spindle from then on, nor was it too loose during a workshop session. The bulbs were dispensed with during the summer months.

As regards marking I use the end of my rule and a scriber, the marks are dead in line and it is not possible to return anything other than dead in-line.

My best regards
Gray,

Thank you for your notes:  The workshop has a frost heater and rarely gets below 48F.  Though I can soon rig up something to provide additional heat.  I too have the original Myford thick vinyl lathe cover which is getting a little tired now.  Since you mention that you had similar behaviour with your S7 I'm not going to worry too much.  At least everything else seems to be fine.

Based on your final comment I have now scribed a line through the paint spots, though for the time being I am not going to play around adjusting anything.

Your wisdom is much appreciated.

 
Best Regards:  Baron.

I don’t regret the things I’ve done, I regret the things I didn’t do when I had the chance.

Offline Stuart

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Re: How tight is tight
« Reply #28 on: January 14, 2014, 02:18:43 PM »
Well Guys and Gals

the jobs a good un just barley a whisper at speeds above 2K the motor makes more noise  :cartwheel: :cartwheel:

the plan went oolong the line as commented on by Gray i ordered up some shim washers from a different place http://www.springfasteners.co.uk  who are Caleb Components   i had to order a pack but they have no min order and the P&P was £3.25
 the total with the Vodka And Tonic came to £9.84   ordered on line Sunday arrived today Tues so good service for a small order.

As Gray stated they are rarely on size the pack of 30 varied between 0.176 mm to 0.197 mm so a sort and match was done and the stack gave me a pre load locked up solid of 0.05mm

anyway I can see why Myford use the method they do because its was a pain in the butt to get the new shims in without trapping them off centre, I had to put the main shaft in backwards form the left hand end to locate the shim bearing stack whilst I pushed in the inboard race  yes I know it seem backwards but in practice it was easier to do it that way , i did offer it up the other way but it was no good

whole rebuild took about 1 hour inc sorting out the shims and as some of you know the tumbler reverser has to come off along with the first two transfer gears ( banjo can remain set ) the back gear lever has to come off  as well to allow the lower closer to drop down to allow the pulley back gear cluster to come out , a point to note flip up the back gear locking lever on the spindle to allow the two to separate , use your c spanner to push the out board bearing pack to the left ( note you have released the lock nut and removed the gear from the out board end else you will not be able to move it ) this give just enough room to wriggle out the pulley assembly

Please note these are my findings with a Myford connoisseur poly belt drive yours may vary as they were not all made equal

Again I must than all who gave me the information that I needed to get this done

BTW Gray I mentioned the tumbler reverse but as you know mine is fitted with one of your dog clutches , But i mentioned it for those that do not have the dog clutch fitted ( shame on them  :lolb:)

Stuart

My aim is for a accurate part with a good finish

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Re: How tight is tight
« Reply #29 on: January 14, 2014, 02:59:33 PM »
Glad it worked out Stuart!.....Thanks for the help Graham! :praise2:

Dave
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Damned ijjit!

 

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