Machining T-nut

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geraldsd

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First thank you to everyone that helped me to get started machining a new t-nut for a wedge type tool post for mu South Bend 9A. I have the piece set up in the 4-Jaw chuck and have started to cut the surface. I am getting a concave cut. It is deepest in the middle. What is up?
 
Most lathes were set up to cut a concave cut across the face of the chuck or faceplate.

The "why" of this escapes me but I'm sure some one on here can enlighten us.

Ron
 
ozzie46 said:
Most lathes were set up to cut a concave cut across the face of the chuck or faceplate.

The "why" of this escapes me but I'm sure some one on here can enlighten us.

Ron
Click to expand...


That is new to me Every lathe I have run cut flat across the face. :dunno:

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Try locking your carriage down and snug up the gibbs on the cross slide.
 
This is my first lathe what would you check to determine the cause?

kd4gij said:
That is new to me Every lathe I have run cut flat across the face. :dunno:

- - - Updated - - -

Try locking your carriage down and snug up the gibbs on the cross slide.
Click to expand...
 
Is the cross slide square to the ways? You can mark one jaw of the chuck ,mount an indicator on the compound/tool post and indicate the jaw at 0. turn the jaw 180 degrees and run the cross slide in and check the marked jaw for the same reading. If the cross slide runs slightly towards the chuck as you run it in it will cut concave. Something to check anyway.
 
I have never seen. heard of, or operated a lathe set up to cut concave across a face. That's just not right. Do some checking for your cross slide being square as in the previous post.
 
I would suspect tool geometry/hieght or loose compound or a combination of both......somethings not right.

Chuck
 
I saw that happening when I was cutting my T-nut on the lathe. What I figured out was happening was as the cutter moved further away from the center (I started "in" and worked "out") the continual pounding of the interrupted cuts was hammering the carriage away from the headstock.

My solution was to lock the carriage and take lighter cuts.

-Ron
 
geraldsd are you using the crossslide handle to move the cutter across the part or are you using the upper compound handle to move cutter? using the upper handle to try and move your cutter can work only if it is exactly 90 degrees to the face of chuck. once you tighten your tool post and line the cutter bit to the exact center of your piece, then rotate your compound to the angle you want and lock it down with the two nuts on each side. then using the cross slide handle your bit will go straight across--only go to the middle of the piece each cut--if your bit is on the center height ok it will not leave a nub in the center. hope this helps---Dave
 
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