Centec,again

This topic has 14 replies, 5 voices, and was last updated 23 March 2020 at 18:00 by Dave Halford.

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1 May 2019 at 17:31 #407365
Frank Gorse
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@frankgorse
Well,I’ve taken the excellent advice about my raising block question and will be ordering a block of aluminium. By using a fairly big flycutter it should be possible to do each surface at one setting,the dovetails are another matter.

In the meantime I set out to investigate a bit of looseness in the main (horizontal milling) spindle. I’ve tightened up the adjusting nuts on the back as the handbook says but there is still almost a sixteenth (1.5mm) of end float when the overarm is removed and some radial play depending on which way it is loaded. I’ve now taken off the locknuts,pulley,sleeve and the plates back and front which are retained by four screws. I’ve also drained the gearbox and removed the covers to get a better view but am at a loss as to how to remove the spindle and bearings for inspection. Can anyone out there help please?

Presumably having done all this it would be sensible to replace the bearings in any case,can anyone recommend a helpful supplier?
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1 May 2019 at 17:31 #13507
Frank Gorse
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@frankgorse
2 May 2019 at 10:04 #407457
RMA
Participant
@rma
I did this on my first Centec, but so long ago I can't remember the exact procedure, but it's fairly easy to replace the two bearings. Before you take it apart check that you are tightening them correctly. Taper roller bearings need to be rotated back and forth to seat the rollers at the thrust end of the bearing, otherwise you will get end play.

I replaced mine with standard Timken bearings, but they are not cheap.You'll find them at any bearing supplier. I served my apprenticeship with them many year's ago and getting bearings wasn't a problem then. Today however they are all made abroad and the UK factory site is sadly now a housing estate!
2 May 2019 at 10:36 #407460
Dave Halford
Participant
@davehalford22513
Frank,

If the oil was clean the taper bearings just need adjustment. The the fit is tight so the adjuster takes a lot more effort than you would expect expect.
2 May 2019 at 11:26 #407469
peak4
Participant
@peak4
Frank, I'd certainly be interested to hear about your experiences making one, as I'm after something similar myself.
Did you have to re-mortgage the house for the lump of alloy bar?

I don't think Tony is going to get any more commissioned unfortunately.

Bill
2 May 2019 at 19:59 #407536
Frank Gorse
Participant
@frankgorse
Thanks for that chaps. I changed the oil when I first bought the machine and was amazed by how clean it was- I doubt that the previous owner had ever changed it- and the bearings looked perfectly ok so far as I could see. So I tried a bit more force. I’d already made a clamping arrangement with 2 lengths of M10 studding and now added,dare I say it,a few sharp taps with a hammer. Lo and behold,barely perceptible end float and it turns as sweetly as can be.

As for the proposed raising block the cheapest supplier I’ve found so far is about £94 inc vat and delivery so I’ll probably order that fairly shortly. I have an old toolmaker friend who will be getting a call if-when-I get stuck. The sensible thing would be to ask him to do it anyway but I’m hardly likely to start doing the sensible thing after all these years.

Frank
2 May 2019 at 22:01 #407542
not done it yet
Participant
@notdoneityet
I would suggest that the bottom dovetail is the more important one. Any reasonably accurate top dovetail could be made separate (in steel, even?) and bolted/dowelled in position.

Is this for an extended riser like recently shown by Gary Wooding?

Only really needed for avoiding the inconvenience (and considerable physical effort) of removing the riser and vertical head when changing between milling modes – and no extra storage space required either. But certainly the extended version is my preferred option!
2 May 2019 at 22:50 #407548
Frank Gorse
Participant
@frankgorse
Yes,definitely the long version for all the reasons you say. I hadn’t really thought about the composite approach but I will consider it.If I can get the top and bottom surfaces parallel to one another I think I’ll be half way there,if I can’t it’s time to get professional help
2 May 2019 at 23:22 #407551
not done it yet
Participant
@notdoneityet
That is generally about all you need. I’ve never yet tilted the head on my machine – but one can never tell…. Apart from that the top dovetail alignment is not so important – unless you get it so far out that the drive belt is twisted!

Bottom dovetail is longer than the Centec bed travel, so would need some care in getting it straight, but the top needs only to be as long as the vertical head, so the top needs only to be parallel for that length?
3 May 2019 at 09:56 #407573
RMA
Participant
@rma
Posted by Frank Gorse on 02/05/2019 19:59:46:

Thanks for that chaps. I changed the oil when I first bought the machine and was amazed by how clean it was- I doubt that the previous owner had ever changed it- and the bearings looked perfectly ok so far as I could see. So I tried a bit more force. I’d already made a clamping arrangement with 2 lengths of M10 studding and now added,dare I say it,a few sharp taps with a hammer. Lo and behold,barely perceptible end float and it turns as sweetly as can be.

As for the proposed raising block the cheapest supplier I’ve found so far is about £94 inc vat and delivery so I’ll probably order that fairly shortly. I have an old toolmaker friend who will be getting a call if-when-I get stuck. The sensible thing would be to ask him to do it anyway but I’m hardly likely to start doing the sensible thing after all these years.

Frank

Not a good idea to hammer bearings in! If the cups have been seated square and correctly, the cones can then be fitted to give the correct end float or preload as required. This shaft should have a preload condition, and in this case they are oil lubricated, but if lubrication is with grease, pack the cone with grease before fitting, and leave it at that. Many taper roller bearings fail due to having too much grease.

I'm in the process of making a raising block for my 2A, but I've only just got round to buying the cutter. Hopefully I'll have it done by the summer!
3 May 2019 at 10:51 #407585
Frank Gorse
Participant
@frankgorse
I didn’t exactly say I’d hammered them in! I was trying to take out the huge amount of endfloat on the existing bearings. The adjusting nuts on the spindle had no effect so I made a clamping plate,a close fit on the spindle to press on the spacing sleeve. With that fully tightened and beginning to bow I applied a tap-soft hammer-to the other end of the spindle which had the desired effect of unsticking the inner race from the spindle-no impact to the actual bearing at all. I don’t know what preload means in this context but I’ve finished up with no end float and no tightness.

What are you making your raising block from and are you going to make it on the Centec?
3 May 2019 at 11:13 #407591
RMA
Participant
@rma
Sounds as if you've got the adjustment right, just keep an eye on it in case the rollers 'settle in' to the thrust end, you don't want any end float.

I already have a block 75 x 100 so I'm making it from that. It'll give me an extra 75mm to play with, but more importantly to me, I'll be keeping the vertical head in situ, too heavy these days to lift on and off. It will be possible to machine it on the Centec,……just, but I have a club member willing to do it. Just a matter of finding the time now and getting on with it. Good luck with yours.
3 May 2019 at 14:53 #407608
not done it yet
Participant
@notdoneityet
I would expect end-float to be as close to zero as possible with minimal pre-load, because the casing and gear shafts are being maintained at the same temperature throughout the normal operating range by the circulating lubricant. With the slight difference of linear coefficients of expansion, the pre-load will tend to increase (marginally, if measurable) as the temperature rises.
23 March 2020 at 11:51 #459078
Frank Gorse
Participant
@frankgorse
Bill,Bill,and Martin,PM’s sent. Frank
23 March 2020 at 18:00 #459162
Dave Halford
Participant
@davehalford22513
The dovetails are not a very tight fit and the factory tolerances for them seem quite generous, my 2 and 2A are different.

The non clamping dovetail should be parallel to each other.
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