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uute
11-18-2012, 06:42 PM
Am I the only one who prefers LH end mills for milling in the lathe?

uute

Bob Fisher
11-18-2012, 10:32 PM
If you have a threaded spindle, it seems a bad idea. Also, wouldn't it tend to raise the carriage?
My thoughts on the matter. Bob.

uute
11-19-2012, 01:43 AM
Yes, a threaded spindle could be bad, but hopefully you have those mills in a collet of some kind.

If you're milling on center (slotting) a LH cutter will tend to raise will carraige (and I'd use a RH here), but if you're making a less than full dia cut, cutter direction isn't the determining factor is it?

If cutter is below work, cutting forces will be down w/ RH or LH mill, won't they?

If end mill is above work, cutting forces are then up (lifting) w/ RH as well as LH mill. NO?

Kinda makes me wonder why I seem to prefer LH cutters. lol

My last project, the work was mounted on a threaded spindle, a LH mill seemed prudent so as not to unscrew the setup.

uute

oldtiffie
11-19-2012, 05:02 AM
Left-handed end milling cutters are ideal for machining the edge/s of "thinner" (sheet"?) material as it will tend to force the edges down rather than up which is the case with the common right-handed cutters.

vpt
11-19-2012, 09:22 AM
I use whatever is cheap and in the tool box. I have a threaded spindle and my collet system is threaded on just like the chuck.

Since I don't have a mill yet I do all my milling in the lathe and quite a bit of it I think.

Paul Alciatore
11-19-2012, 01:23 PM
I have done some milling in my lathe and do not see any reason for LH vs. RH milling cutters. All of my work was done with standard and shop made RH cutters. I do use a collet for end mills but have a fly cutter that mounts directly on the spindle threads. The forces on the carriage are significant and must be considered for any milling cut in the lathe. But, they can be reversed by just starting the cut from behind instead of in front of the spindle axis (or vice-versa). For many cuts you are cutting a channel and the forces are the same both ways.

rohart
11-19-2012, 01:36 PM
Tiff, for that application you just want a reverse spiral. It doesn't matter whether it's a RH or LH cutter.

rustamd
11-19-2012, 01:53 PM
Tiff, for that application you just want a reverse spiral. It doesn't matter whether it's a RH or LH cutter.

aka downcut end mill

RussZHC
11-19-2012, 06:34 PM
The forces on the carriage are significant and must be considered for any milling cut in the lathe. But, they can be reversed by just starting the cut from behind instead of in front of the spindle axis (or vice-versa)

Paul: you partially (or entirely?) answered what I was wondering...my lathe does not have power cross feed which perhaps adds to the fun of milling on the lathe, am I better off, given the choice, of moving the workpiece away from the operator or towards the operator?
Is my thinking correct in relating the forces to whether the cut off tool is in front or rear mounted? And the those advantages gained...?

Paul Alciatore
11-20-2012, 01:19 AM
Paul: you partially (or entirely?) answered what I was wondering...my lathe does not have power cross feed which perhaps adds to the fun of milling on the lathe, am I better off, given the choice, of moving the workpiece away from the operator or towards the operator?
Is my thinking correct in relating the forces to whether the cut off tool is in front or rear mounted? And the those advantages gained...?

My thinking, which has been somewhat proven in practice, is that with a normal, RH end mill, it is probably best to start with the work in front and move it to the rear for the cut. This places the force of the cut in a downward direction which seats the carriage and cross slide tight on the ways. If you started such a cut from the rear, it would tend to lift the work and you would get more chatter.

This is not comparable to a rear mounted cutoff tool because a cutoff tool cuts continously so there is a constant upwards force. This constant upwards force forces the cross slide up and the dovetails keep it in a fixed position. The carriage is also restrained from lifting too much by a fixed clamp under it or some other means. Milling cutters have 2, 3, 4, or even more cutting edges. These cutting edges each must enter the work, cut through it, and exit. This gives you a constantly changing upward force and the work will tend to jump up and down; the downward force coming from gravity.

Most of your milling work in a lathe will be best if done in this manner so try it first. But DO USE LIGHT CUTS. You simply can not hog out metal like you can on a mill. It is a matter of mass and rigidity in the machine, not HP. A lathe simply was not designed for this kind of cut. On the other side, some cuts that are more difficult on a mill can be easily done on a lathe. Consider how you would mill a rectangular hole in the end of a long shaft (say a 10 foot long shaft) even if a radius at the corners is allowed.

Now, some cuts may not work well with a RH cutter and working from front to back. If you are having trouble, try back to front. See which way is best.

uute
11-20-2012, 03:10 AM
My thinking, which has been somewhat proven in practice, is that with a normal, RH end mill, it is probably best to start with the work in front and move it to the rear for the cut.

Exactly right Paul, assuming the cutter is below work. I think this is why I got to liking LH mills, then you run the work up from the back so it is easy to see whats happening.

Remember too, that reversing work travel puts you in a climb milling situatiion which is prolly best avoided. (RH cutter low & work from back to front = climb milling, same LH cutter & work front to back.)

If the cutter is above the work, the relative directions will be reversed for same reasons.

uute