The Ultimate Trick: Cutting off with the Mini Lathe

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Pcdoctor

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I have a Weiss 180 7x12 lathe, and had had a lot of problems cutting of, probably because of lack of rigidity. Then I fall over the above video on YouTube, and my problems were over.
I don't know if will work for everybody, but it works for me, and as I know a lot of people have problems with cut off, I hope it will help you too.
https://www.youtube.com/watch?v=-RZRq0olsxM

Happy New Year

from Denmark

Pcdoctor
 
thank you Doctor!!!
from another(imaginary on my part)Doctor...:jester:
 
Thank you for the tip!

I too own a 7x12 mini and admit that parting off with the little guy has always been a bit troublesome for me...:banghead:. I'm definitely going to give this a try!

Happy New Year!!!
 
I have difficulties to understand why the reverse cut in general is less prone to jam than a normal cut. The explanation that the tool is pushed away in reverse and sucked into the workpiece in normal turning sounds OK. But this would also happen or not for normal turning if the tool is above or under the centerline. The angle of the tool will also have a great effect.

So, it is easy to understand that the cutter location vs. centerline and it's tilt angle will have a great effect on releasing or jamming the cutter. The cutting force will however be reduced the lower the tool tip is and the more it is tilted down during normal turning. So it seems to be a balance of these parameters independent of the turning direction.

I don't buy the explanation that chips falling down by gravity will be a significant factor, unless the lathe is very weak like a mini lathe.

Someone who understands the fundamental reason(s) for reverse cutting better than me is very welcome to explain. I need a big cup of coffee now to reset the brain :))
 
I have a rigid lathe, so I've thought flipping the cutter over was BS. But I have seen the sickening "crunch" when a light lathe binds on cutoff. His simulation explains why that would be far less likely cutting upside down.

BTW, the insert he shows works WAY better on any lathe rigid enough to use it.

FWIW, my personal experience on the 7" asian lathes: cutoff with a hacksaw, then face your part.

Karl
 
The simulation would have showed the same difference for normal turning if the cutter would have been over alternatively under the centerline. It is not a matter of turning rotation. Well maybe it is, but I don't get it very well :thinking:

The coffee I've just drunk didn't help at all...
 
Think of it like a tire and a wood shim. Place the wood shim behind the tire. In one direction the wood has to travel under the tire (sucked in) and thrown out the other. In the other direction it simply gets pushed off the tire.


I sure whould not run a threaded chuck at speeds like that in reverse. When it unscrews it's gonna do it super fast
 
chuckorlando said:
I sure whould not run a threaded chuck at speeds like that in reverse. When it unscrews it's gonna do it super fast
Click to expand...

Yes! If you have a threaded chuck much better to build a rear tool post for the cross slide. Parting tool still goes in upside down but you keep the lathe rotating in the 'right' direction.

Would hate to contemplate the possible damage as the chuck unscrews, pushing and snaps the parting tool, then drops onto the bed ways.

PLEASE DONT TRY THIS WITH A THREADED CHUCK
 
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That is very true but I'm not sure it applies for the turning cut. It would be like pushing the tool upwards and having the cutter on the lowest part of the workpiece and this is not the case. It works great for cutting cheese slides though. The phenomena seems to be related to the better rigidity for tangential cutters, but in a opposite way.

I do also avoid reverse turning by the reason you say. A rotating chuck that come loose is very dangerous, especially if it is a heavy beast and there are not many threads to hold it so it can happen within a fraction of a second.
 
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