What I learned about cutting off on the lathe

kyler

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I did my first cut off last night. I've been ruining a good bar of aluminum and finally got around to trying to cut off a piece.

Lesson 1 - if you think the piece is to long to cut off unsupported, it is.

Lesson 2 - if you think your cutoff tool is absolutely perpendicular to the work, it isn't!

Got to use my steady rest for the first time last night...
 
Being very new to this I've not even attempted that operation yet but saw a good vid recently that showed a couple of ways to get the cutter square to the material and one was to bring the cutter to the face of the chuck and ensure its flat against it and lock it there. Easier to do with a quick change tool post as you can bring the holder to the face of the chuck and do the same.
 
Being very new to this I've not even attempted that operation yet but saw a good vid recently that showed a couple of ways to get the cutter square to the material and one was to bring the cutter to the face of the chuck and ensure its flat against it and lock it there. Easier to do with a quick change tool post as you can bring the holder to the face of the chuck and do the same.

Lately my cut-off experiences have improved. I use a small square to set the cutting tool perpendicular to the work, make sure the cutter is sharp- usually a light grind if I even think it could be sharper and make sure the top of the cuttig tool is at the center of the work and use oil when cutting.

My father made a gage to set the top of the cutting edge at the center height of the work, works real well.

Prior to doing these things consistantly my cut-off work was a disaster at best.
 
If it is a relatively large diameter you are parting, there is no need to have the partoff tool extended the full required distance. Start off with it choked up a bit to get a good straight start, then slide it out to finish the cut. It may take two stages, but it may result in more satisfactory results.
 
If it is a relatively large diameter you are parting, there is no need to have the partoff tool extended the full required distance. Start off with it choked up a bit to get a good straight start, then slide it out to finish the cut. It may take two stages, but it may result in more satisfactory results.

I did that. When I put a magnifying glass on the part after the cutoff, I then saw the incrdibly small gap/misalignment.

Dang but this is a sensative procedure!
 
Well, it can be. Especially is this so with a smaller machine. You can get by with less than ideal conditions on a larger machine, but you need everything as true and square as you can get it, and he tool ground properly to do it on a small, less rigid machine. Even with a heavier machine, to get a square face, I run an indicator down the lade and make sure it is parallel with the cross-slide. I use an inserted partoff tool from Iscar. And I used neutral inserts. Tool height I run on center to about 0.003 high, because it will flex down just a bit. Too low and the work will tend to ride up over the tool and you will get chatter.

Yep, it can be touchy, but attention to details can result in a successful job.
 
As has already been emphasized, alignment is critical. I actually run an indicator on the parting tool if I'm going to make a deep cut. The steady application of a good sulphur cutting oil helps as well. You can also get "T" shaped parting tools which are less apt to seize up in the groove. They work much better than the standard beveled parting tool.

Tom
 
If you only have the old fashioned lantern type tool post,take a block of steel and make a simple holder for a cut off blade. Just a groove milled into the side of the block,which holds the blade at the right height,with 3 socket head cap screws to hold the blade in the groove,will yield a great improvement over the lantern type tool post with the angled,off center old type cutoff tool. I use the "T" type HSS cutoff tool. I sharpen the cutting edge at a slight angle,so there is no teat left on the piece being cut off.

My first lathe was a 12" Atlas,with the old lantern toolpost. I made such a block for it,and the rigidity of the cut off tool was greatly improved. With cutting off,rigidity is a very important issue.

As soon as you can afford it,get an Aloris type tool post and holders. The wedge type is better than the piston type,but either is MUCH better than the lantern type.
 
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