Centec 2A

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Centec 2A

This topic has 9 replies, 5 voices, and was last updated 7 September 2023 at 17:51 by Matt Smith.

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7 September 2023 at 00:20 #14898
Matt Smith
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@mattsmith88420
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7 September 2023 at 00:20 #659428
Matt Smith
Participant
@mattsmith88420
Hello there,

I’m in the process of cleaning/renovating a Centec 2A miller for my brother, apart from my rubbish paint job it’s been going OK. The one issue I do have is the y axis bronze lead screw nut, should this nut be rigidly fixed or “floating” to allow some self alignment of the screw?

Any help would be much appreciated.

Matt.
7 September 2023 at 07:03 #659433
David George 1
Participant
@davidgeorge1
On most machinery of this age there is play in the holes in the mounting plate where it bolts to the casting so you wind the screw in so it is near to the front which supports the nut to leadscrew and then tighten the plate bolts which eliminates the sag in the play of the set up.

David
7 September 2023 at 07:07 #659434
DC31k
Participant
@dc31k
Forwards/backwards, play will contribute to backlash so in that direction it is undesirable.

Left/right play will have no effect as the Y-axis is constrained by the ways.

Up/down play (float) would be good as it allows for manufacturing tolerances on the relative height of knee ways, saddle ways and screw centreline.
7 September 2023 at 09:05 #659439
Matt Smith
Participant
@mattsmith88420
Thank you both for such quick responses, the offending nut is a very tight fit in the knee casting, intentional or just years of crud I don’t know, I have, maybe unfortunately, twisted the nut left and right so now lead screw alignment is an issue! What to do! Do I trial and error it by removing the table and twisting the nut slightly until a satisfactory result or remove the nut clean and replace and expect a “smooth “ fit that will allow self alignment?

Thanks again,

m

Matt
7 September 2023 at 10:15 #659449
DC31k
Participant
@dc31k
Loose enough to self-align but not so tight as to restrain the leadscrew in any way other than the correct one.

If you do end up removing it, mark which side is currently facing the column and reinstall in the same way.
7 September 2023 at 11:36 #659460
Matt Smith
Participant
@mattsmith88420
Many thanks DC31K you have been a great help.

Matt.
7 September 2023 at 11:48 #659465
not done it yet
Participant
@notdoneityet
If it is fixed in position, it is important. If it ‘floats’ there is not much you can do about it. I can’t remember which it is (on my 2B).
7 September 2023 at 11:54 #659467
Dave Halford
Participant
@davehalford22513
Remove lead screw from table, screw into nut, twist nut with flat spanner till screw is parallel.

Old mineral oil from the 60's can set like loctite, the fix is the is the same – heat

Removal of the nut will give you the added issue of how deep in the knee does the nut go.

There was no need to disturb the nut, just clean it.

If you are tempted to take out the gearbox please be aware it is not like a car, there are no shoulders to tap a bearing up to and if you over do the taper bearing preload you have to dismantle again to tap the bearing outer ring the other way.

Drain the oil and if it doesn't glitter put fresh in and leave it.
7 September 2023 at 17:51 #659506
Matt Smith
Participant
@mattsmith88420
Thanks for all the replies, well I took the plunge and removed the nut, thoroughly cleaned and reassembled as a “snug” fit, all is well, no detectable increase in backlash so one happy Matt and an equally happy brother. Dave Halford— gearbox internals were very good, just gave it a good clean and flush and only removed horizontal spindle and bearings for inspection. Mill refurb now 95% done, just motor and associated electrics left. Got to admit the Centec has been great to work on, I really don’t know a lot about mills but for a small machine it is certainly well made and functions beautifully.

Thanks again,

Matt
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