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How do I undo these leadscrew nuts?

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choochoo_baloo15/11/2019 11:22:54
252 forum posts
54 photos

Continuing my Tom Senior disassembly, I heeded the previous advice to leave the taper pin-ed end, and remove from the handle side of the X axis table screw.

Now I'm flummoxed by these double nut things. No grub screws or pins to remove. That's a ball bearing race immediately to the left.

  • Do they need a pin spanner type thing?
  • Are they double nuts?

Thanks in advance.


Brian Wood15/11/2019 11:35:41
2202 forum posts
37 photos

Yes, they are double nuts, one locks the other and they are used to set the pre-load on the bearing

You can release them with spanners shaped like hook wrenches, but with pins to fit the holes rather than squared off hooks. They are not difficult to make really. Test the pre-load on the bearing, one of which is a thrust bearing, before you release them so that you have a feel for how they were set beforehand.

Before I made such spanners, and you will be surprised at how often they are used on machinery, all in different sizes of course, I used a pair of water pump pliers when I had to move mine in a hurry. Being slim they are about the right size.

Regards Brian

Peter Simpson 115/11/2019 11:39:24
165 forum posts
8 photos

I just used two allen keys in both holes. came away very easy.

choochoo_baloo15/11/2019 14:05:23
252 forum posts
54 photos

Thanks both. Will use allen keys or round bar Peter.

Posted by Brian Wood on 15/11/2019 11:35:41:

Test the pre-load on the bearing, one of which is a thrust bearing, before you release them so that you have a feel for how they were set beforehand.

Brian; to check I understand what you mean.

I plan to mark their current alignment to each other, and count how many rev's to undo the outer nut. Is this all?

Brian Wood15/11/2019 15:50:40
2202 forum posts
37 photos

C--C-- Baloo,

No, not really. It is more a case of feeling the degree of resistance to motion that exists in the bearing when the nuts are clamping it, especially the thrust bearing, and reproducing that later when you reset them. Doing that by counting or marking won't be sensitive enough

Too much pressure on a thrust bearing can in time indent the race and the bearing begins to feel 'digital' I can't think of a better description. For that to take place it would have set been so tight as to be stiff to move and clearly unhappy Too far the other way and it is then too slack to take up end play. The happy medium is to achieve no detectable end play along with free rotation of the bearing.

It is all a question of judgement which was why I suggested you felt it's rotation characteristics by hand before you disturb the setting of the two nuts and return to that condition after you have done whatever you are doing.

I hope that helps.

Regards Brian

old mart15/11/2019 16:26:23
1824 forum posts
148 photos

I replaced the thrust bearings with metric ones, they were slightly greater od, so the housing bores had to be enlarged. The new bearings are heavier duty.

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