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Any idea why this lathe is chattering? Spindle bearings?

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loply:
Hi DavidA, absolutely positive. Had the whole thing apart no more than a few days ago, plus, I have a complete spare spindle + headstock sitting on my workbench :) Unfortunately it has no bearings so I can't compare or use it...

The 280 is a lot more complex and has more bearings (plus I think a taper spindle nose?). They're much better machines I think. The threaded spindle nose is a real weakspot.

These older lathes only have one bearing in the front and one in the rear. Originally there would have been a sleeve on the spindle but it purely carried some gears - it wasn't a bearing spacer - but it's gone anyway as I have a taperlock pulley on there now instead.

Here's a video - the more I think about it, this definitely doesn't seem normal? I'm pushing quite hard mind. I'd appreciate it if anybody else could make a similar check on their lathe.

DavidA:
Loply,

You are correct, they are very different.

Hope you get it sorted. i am still having teething problems with my 280.

Anyway, if all else fails, ask the company. They are still there and will probably be happy to advise you.

http://website.denford.ltd.uk

Dave.

PK:
Do both bearings have the same ID? If not, could there be a shoulder on the spindle the rear bearing is hitting before it loads up against the headstock. (yes this is a stupid question, my experience in these things is that my own mistakes are often illuminated by them).

Pete.:

--- Quote from: loply on January 02, 2016, 05:46:55 PM ---Hi guys,

Thanks for all the advice. I appreciate all the comments although some of them have missed some of my original points.

Regarding the spindle bearings, if I grab a long bar e.g. the 50mm x 150mm piece of steel in the video, I can deflect it's ends up or down about 0.03mm quite easily with just a bit of hand pressure. I've no idea whether that's normal or not as I've never tried it on another lathe before. Could somebody else confirm what they get on their lathe for a similar size bar?

If I put a really sensitive indicator on a ground MT3 test bar and spin it by hand, the needle does jump around randomly a bit. The indicator has increments of 0.002mm (ie about a tenth). It doesn't run out by a consistent amount. That might just be normal though as the indicator is so sensitive. With a normal 0.01mm indicator it looks pretty smooth.

I initially had no preload on the bearings, then gradually tightened them until I couldn't move the nuts any tighter with an 8 inch spanner. Strangely the bearing friction didn't increase noticeably. They don't seem to be getting hot when ran at full speed though I can only check by touching the casting.

I will double check the chuck-spindle connection carefully, that is a good point, thanks. I did have the chucks on and off quite a few times today mind and it was the same each time, maybe there is a ding in the thread which I didn't notice though.



To address some of the points which I don't think are relevant (though I could always be wrong!) -

The workpiece isn't the issue, the bar is a traditional size for a test bar, ie 50mm steel bar 150mm long, so it's only sticking out by 3x it's diameter, no need for tailstock support. Indeed that would defeat the entire point since it's meant for testing the headstock alignment. This is a fairly normal test you would do on any lathe of this size (albeit often with two 'collars' by relieving the middle somewhat). Besides which the chatter occurs even right next to the chuck so it's nothing to do with the length of the workpiece.

The tool is also irrelevant, it does the same with any type of tool. In the video it's a high back rake HSS tool - about 12 degrees on all sides but about 20 on the back rake, and razor sharp. Same thing happens on carbide inserts and brazed carbide. The exact same tools on my previous lathe cut perfectly. Definitely on center by the way - checked that several times and tried slightly above and below too just out of desperation. I get better performance with really high back rake (like 30+ degrees) but that shouldn't be necessary.

I tried two different chucks too by the way, a 4 jaw and the 3 jaw in the video. Cranked both of them really tight to be sure.

Cheers,
Rich

--- End quote ---

1 thou up and down on the spindle is miles too much. I think you have a problem with your spindle fitment, borne out by the fact that as above you should be able to bind the spindle with heavy adjustment.

Have you got a photo of the spindle assembly out of the headstock?

loply:
PK, I understand what you mean, but no, the spindle is one diameter where the rear bearing is, with no shoulder.

I've just been out and took the chuck off to eliminate the chuck:spindle connection. I can move the spindle up and down by about 0.01mm by pushing hard with my fingers on a 200mm long bar in the spindle taper. Again I don't know whether that's normal or not?

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