Need help identifying culprit of bad swarf from parting off on lathe (pics inside)

I thank I am going to have to steal this idea on scribing a line on a tool height gauge ! I don’t know why I didn’t think of that, it’s such easy thing to do
BaronJ said:
I must confess that all I use to set tool hight is a scrap of "L" shaped alloy with a line scribed across it from a hard center placed in the lathe
spindle. I just sit it on the crosslide and adjust the tool to suit.

I've just checked the parting off blade and it is very fractionally below center, about the thickness of the scribe line. Remember I'm parting off from the rear of the top slide.
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Hi 9t8z28, You're very welcome, steal away :encourage:

Blacken the alloy surface first, then pop a hard center in the lathe spindle and use the point to scribe a line across the alloy face. I just put mine on the top of the cross slide, which is where I put it to scribe it.

I also use a "Norman" patent tool holder, which uses a single screw to adjust the hight. It makes getting the tool to the correct hight very easy.
 
I just use the teat left from facing a part to set the parting tool height, it does not have to be perfect within thousandths or the width of a scribe line to part off successfully.
 
9t8z28 said:
... I have heard that is better to be slightly above center than below.
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They're both bad. If you're slightly below center, as the top goes in the rake decreases and the clearance increases, until it eventually stops cutting and pushes under the work. If you're above center, the rake increases and the clearance decreases, until the cutting edge is no longer in contact with the work and the end of the tool crashes into the workpiece.



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Update: Issues with parting have been solved. The rear tapered roller spindle bearing was loose. I tightened it up while running the lathe at medium to high speeds while monitoring the temp and testing the deflection with a DTI. I put the parting tool on without even adjusting or checking the height and made a cut. It started cutting without any issues and I got that sweet hissing sound while nearing the center. Thanks to all who offered their help.
 
It happens unfortunately. About a year ago I upgraded The tapered roller bearing closest to the headstock and I also upgraded the rear deep groove ball bearing to a tapered roller. I initially set preload but I don’t think I had it quite right as the cup was what moved towards the headstck when I retorqued it. It’s all of these variables that come into play and when all else fails start looking elsewhere
markba633csi said:
Facepalm! LOL
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