Author Topic: Mini lathe chatter on facing cuts  (Read 650 times)

Offline Fergal

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Mini lathe chatter on facing cuts
« on: September 25, 2017, 05:22:19 AM »
Hi all

I recently got a used 7x14 mini-lathe (Amadeal CJ18). I've not touched a lathe for 35 years since school days, so I'm probably doing it all wrong, however I have adjusted all the gibs so everything is tight and that has improved the finish on turning cuts. Facing cuts on harder materials (stainless & mild steel) suffer from bad chatter though. I don't think it's the tools as I have tried HSS and carbide on HDPE with good results.

if I pull on the cross slide there is some slight movement across the main axis of the lathe which I can't seem to get rid of without making it so tight that I can't move it anymore. I've tried adjusting the leadscrew nut and the gibs to minimise this movement. Are there any other adjustments or modifications I can make to improve the quality of my facing cuts?

Thanks

Offline Stilldrillin

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Re: Mini lathe chatter on facing cuts
« Reply #1 on: September 25, 2017, 06:10:22 AM »
Hold a piece of bar, in the chuck. Preferably, with a dti on the chuck.

Push/ pull etc, to detect any movement, in the bearings......

Adjust, with the two locknuts at the other end of the headstock.
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline Fergal

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Re: Mini lathe chatter on facing cuts
« Reply #2 on: September 25, 2017, 06:41:48 AM »
So you think my problem is due to the headstock bearings? The previous owner changed them to the tapered ones and I've measured the runout on the spindle plate and it's about 0.01mm. I'll check them later.

Surely the movement in the cross slide can't be good? I think maybe I need to shim it as mentioned here:

http://www.mini-lathe.com/Mini_lathe/Tuning/tuning.htm#xbacklash

Offline Ben

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« Last Edit: September 25, 2017, 07:14:06 AM by Ben »

Offline bpud

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Re: Mini lathe chatter on facing cuts
« Reply #4 on: September 25, 2017, 10:51:53 PM »
I have a Sieg C3 ("mini lathe", 7" x 14"), which I think is similar to the machine in question.  Have a look at the carriage/saddle gibs, the standard ones are pretty tacky and hard to adjust adequately.  I changed mine to tapered gibs and the difference is surprising, much, much better.  I used Bogstandards method, which may still be available here.  There are lots of other guides though.  Well worth the effort.
cheers
Bill

Offline SwarfnStuff

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Re: Mini lathe chatter on facing cuts
« Reply #5 on: September 26, 2017, 02:41:49 AM »
Hi Fergal,
You said, "if I pull on the cross slide there is some slight movement across the main axis of the lathe ".   
    This to me sounds like you are describing backlash in the cross slide. Of course I have been wrong more often than not in the past.  But if it is backlash there should be a method of adjusting the cross screw nut.
  Something to ponder?

John B
Converting good metal into swarf sometimes ending up with something useful. ;-)

Online PekkaNF

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Re: Mini lathe chatter on facing cuts
« Reply #6 on: September 26, 2017, 04:03:32 AM »
One thing I would try to make sure that the tool tip is between guides (shears). If the tool tip is hanging out, it will tilt the cross slide and these lathes are light/weak and stability on tiltting is abysmally bad.

Pekka

Offline Fergal

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Re: Mini lathe chatter on facing cuts
« Reply #7 on: September 26, 2017, 06:14:26 AM »
On further inspection it seems like my lathe has all the problems mentioned above, that is ill-fitting gibs, backlash and slop on the cross slide screw.

I'll look into addressing all these issues in turn.

Thanks for the info.

Offline RotarySMP

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Re: Mini lathe chatter on facing cuts
« Reply #8 on: September 30, 2017, 06:49:29 AM »
You don't state what diameter steel and stainless you are trying to face.these are tiny machines with little mass. They can do a lot but can't suspend physics.
Mark