The Shop > Tools
Any idea why this lathe is chattering? Spindle bearings?
RussellT:
I haven't watched the video but it might also be worth checking the fit of the chuck to the spindle nose - a bit of swarf could cause this sort of problem.
Is this the original or the spare headstock.
Russell
Arbalist:
--- Quote from: SteveT on January 02, 2016, 02:51:53 PM ---The tool looks like its about 10mm wide and flat to the cutting surface the tool should have a clearance rake so you are only cutting at the tip.
--- End quote ---
That's what I was thinking. I'm also unsure about the height of the tool as well.
DavidA:
Loply,
According to the manual for my 280 Synchro there should be no end float at all.
It instructs one to adjust the preload but not to allow excessive heat to be generated in the bearings.
it reads...
The machine should run at top speed and the bearings should not exceed 65 C.
that may be your problem; loose taper bearings.
Dave.
hermetic:
To sum up everyones comments! The bar is far too long and large to be not supported at the outer end., the tool angle is far too obtuse, I don't think the cutter is on centre height, and the machine speed is too fast, and also there is probably some flex in the QCTP. Watch doubleboosts early videos on youtube using a similar lathe. Then put a centre in the bar and support with the tailstock centre, re sharpen the tool, set on centre height. Slow down the lathe, and slow down the feed, and that should cure the problem :D
loply:
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
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