Hey guys,

I must sound like a broken record about this but a rear-mounted parting tool holder is the way to go on a smaller lathe in my opinion. I routinely part stuff from 0.124" to 1.25" in steel, delrin, aluminum and brass with a P1N (0.040" thick) parting tool at speeds about 2-3 times higher than normal turning speeds. I have parted 2" steel with a P1 (1/16" thick) tool at about 1200 rpm and sliced it clean. My tool holder automatically aligns the blade perpendicular to the work and the blade can extend enough to part a 2-3" piece and remain on the centerline. I agree that parting close to the chuck is best but sometimes you just need to part somewhere that is not close to the chuck. In those cases I use a live center to support the work until shortly before completing the cut, then I remove the center support, slow down a bit and catch the part as it comes off.No problem.

I won't go into all the reasons why a rear mounted tool is better but if you haven't tried parting off from the rear you might consider it - it will make all your parting issues go away.

Mikey

Hi Elizme. In order to give more useful advice you need to give us a bit of information, such as:

• What material are you working with?
• What kind of lathe are you using?
• Dimensions of the workpiece and your required thickness you are trying to part off.
• How rigid is your parting tool setup? Is it a rear-mounted cutter?

In general, parting off most materials is a routine procedure but it can get tricky when parting thin parts on large diameters. I have found that rigidity of both the workpiece and the cutter is important, as is the right speed and a positive feed. Aluminum can be parted fairly thin, on the order of 0.025" thick, but to get that without any distortion requires careful work. Thin work also requires a freshly sharpened cutter, preferably HSS. If your workpiece is 3/4"OD or less then a 0.04" thick cutter should work well. If greater than this then you need to go with a thicker parting tool. Again, this is related to rigidity in your setup. You will find that a rear mounted parting tool (cutter mounted upside down) is more rigid than a front mounted cutter and is the way I prefer to part off. Be sure you lock your carriage before starting your cut. Finally, you need a lot of coolant when parting most metals, including aluminum. I find A-9 to be the best for critical cuts, while WD-40 actually works quite well for most cuts in aluminum.You don't have to flood it but do not let the cut go dry.

You may also want to try some trial cuts before commiting to cuts on a piece with a lot of work in it so you can nail down your speed and feed. As I said above, a positive feed is very important; you are looking for a continuous ribbon of material coming off throughout the cut.

Finally, as the cut progresses the SFM is dropping and you may need to increase speed a little or decrease your feed to avoid taking too deep a cut. Watch your chip, listen and feel the machine; it will tell you how the cut is progressing.

Hope this helps,

Mikey