CNC - Lathe Question

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gbtbtbt

Joined Mar 18, 2020
64
Explain why a face-grooving (trepanning) cutting tool must have a slightly different geometry than a tool meant to groove the side of the workpiece?
 

WBahn

Joined Mar 31, 2012
26,398
And this is electronics-related homework... how?

Regardless, we do not just answer your homework questions for you. YOU need to show your best attempt to answer YOUR homework questions. There are enough people with machining experience that there's a fair change that someone can help guide you toward a better answer.
 

jpanhalt

Joined Jan 18, 2008
10,917
In face grooving, the tool's cutting edges must have sufficient relief to clear the cut edge. Does this sketch help:

1606736874612.png

Look at how the cut edge interacts with a hypothetical rectangular cutter differently on the inner and outer radiuses. That geometry doesn't apply to plain surface turning; although, the tools will have some relief. But in boring a hole, it must also be considered.

Edit: Flipped image so lathe is turning CCW looking at the face, which is the usual direction.
 
Last edited:

shortbus

Joined Sep 30, 2009
8,169
Edit: Flipped image so lathe is turning CCW looking at the face, which is the usual direction.
It is in a conventional late, the CCW direction, but not too sure about in a/all CNC lathes. Even in a conventional/manual lathe you can usually take a heavier cut by flipping both the tool and spindle direction.

And you are correct about the trepan tool side clearance.
 

jpanhalt

Joined Jan 18, 2008
10,917
It is in a conventional late, the CCW direction, but not too sure about in a/all CNC lathes. Even in a conventional/manual lathe you can usually take a heavier cut by flipping both the tool and spindle direction.

And you are correct about the trepan tool side clearance.
Yep, I've flipped like that. Also have turned the cutter upside down, reversed the lathe, and machined from the front. My current lathes don't have a lot of clearance for the toolpost on the back side. I did modify by Prazi SD300 to give me a little extra room.
 

shortbus

Joined Sep 30, 2009
8,169
Yep, I've flipped like that. Also have turned the cutter upside down, reversed the lathe, and machined from the front
That's what I was getting at, machining from the front. The newer ball bearing spindle lathes aren't as bad as the old babbitt bearing spindles, heavy cuts were a chattering nightmare in them.
 

Picbuster

Joined Dec 2, 2013
1,025
That's what I was getting at, machining from the front. The newer ball bearing spindle lathes aren't as bad as the old babbitt bearing spindles, heavy cuts were a chattering nightmare in them.
Explain why a face-grooving (trepanning) cutting tool must have a slightly different geometry than a tool meant to groove the side of the workpiece?
Keep the following in mind;
an ax has a different cutting angle than a table knife.
The cutting angle is directly related to the material to work.
secondly the dept of the cut and material strength defines the speed,power and heat.
To fast tool will burn.
dept to high the tool will burn.
To slow and dept to big tool will break and this will make the machine jump.
example use 60 rpm stainless steel and take 20mm with 20mm feed look at your machine. ( don't do this !!!)
but @ 600rpm 2mm and 0,5mm feed no problem.
correct depth and speed all goes well.

Up to you to declare this true or false.

Picbuster
 

shortbus

Joined Sep 30, 2009
8,169
Keep the following in mind;
an ax has a different cutting angle than a table knife.
The cutting angle is directly related to the material to work.
secondly the dept of the cut and material strength defines the speed,power and heat.
To fast tool will burn.
dept to high the tool will burn.
To slow and dept to big tool will break and this will make the machine jump.
example use 60 rpm stainless steel and take 20mm with 20mm feed look at your machine. ( don't do this !!!)
but @ 600rpm 2mm and 0,5mm feed no problem.
correct depth and speed all goes well.

Up to you to declare this true or false.

Picbuster
What does that have to do with the original question? And I know how to manage my feeds and speeds, I have done machine work as a living since I was 18 years old, and at 72 am still doing it.

Jpanhalt answered the original question, on how the tool clearance is done, in his first answer even showed a picture of how and why.
 
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