Tool Height On A Lathe

Franko

Franko

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My PM1228-VFLB lathe had to be modified to accommodate an AXA Quick Change Tool Post.

I had to mill some off the bottom of the turntable seat to allow a tool to cut in the center of the spindle line.
Milling off .050 allowed the tool to set a few thousandths below center.

It started me wondering if there is ever a time when I would want to use a tool below the center
line and if so, how far?
 
Other than half a knurling tool, I can't think of any tool intentionally below center on a lathe.
 
Franko said:
Franko, It started me wondering if there is ever a time when I would want to use a tool below the center
line and if so, how far?
Click to expand...
Franko,
Should the need arise, can't you just use a 3/8" tool?
 
You may find that some cutoff tooling requires the tool holder to be lower than a typical 1/2" insert tool holder.

Jay
 
Thanks for the replies.
RJ, 3/8" tooling is definitely an option.

Tom, how much below center on a half knurling tool?
At present, the only knurling tool I have is a double wheel and it seems to work fine.

Jay, same question, how much below center on a cut-off tool?

When I saw how close I came with milling .050 off the turn table seat, I wondered if I should have taken an extra 10 or 20 thousandths. There is plenty of meat on that part, it wouldn't be a big deal, and it is a very simple operation.

On the other hand, with what I took off, the tools can be set perfectly on the center with just a little to spare, and they are cutting very well.
 
cut off tools must be dead on center, cutting tools its said that a thou above is good, but on center is good, never below, it causes dig and pulls the tool into the work, that's why you go a thou above
 
I had the same problem with my Emco Super 11. 1/2" HSS tools were just okay but inserted carbide tools would be tiny bit too high. I resorted to milling 0.100" off the bottom of the tool shanks but will buy 3/8" tools from now on. The 1/2" tools are much heftier though, and I like my milled down tools.

The first tool I made for my lathe was a tool center height gauge. I know all the ways to approximate center height but my little post-type gauge will get me on center without a nub or guessing the first time.

There is never a time when a parting tool is set below center height. Turning tools should be on center height as well. I have seen guys say that they set the tool above center with the assumption that the tool tip gets pushed down under load but I've never done it, nor have I needed to.

The 1/2 of a knurling tool was sort of tongue in cheek, I think. The wheels are equally spaced on either side of center.
 
One of the advantages of a dovetail toolpost is the easy height adjustment, are you saying that you cannot adjust the holder low enough?
Or am I missing something.
 
I don't know about Franko but for me, yup, won't go low enough before bottoming on the top of the top slide surface the post mounts to.
 
chevydyl said:
cut off tools must be dead on center, cutting tools its said that a thou above is good, but on center is good, never below, it causes dig and pulls the tool into the work, that's why you go a thou above
Click to expand...


I agree with you about cutoff tools, but I'm going to have to disagree with you on turning tool height. I have found that under some circumstances, going way below center works very well. I'm still not sure why it works and flys in the face of what we have been taught. Here is a good illustration of my experience cutting with the tool below center, starting with this post http://www.hobby-machinist.com/threads/building-a-high-speed-punch-press.32063/page-2#post-276397
 
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