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- Dec 20, 2012
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I am moving this discussion on rear mounting a parting tool to this thread rather than continue to hijack another one.
In this thread, I noticed that @NC Rick had t-slots running the length of his cross slide and suggested to him that he consider making a rear mounted parting tool. For those of us with small lathes, I feel that rear mounting a parting tool is one of the best mods you can make if you have a t-slotted cross slide or can otherwise find a way to mount one.
To answer Rick's question about how the tool is mounted, yes, it is mounted upside down and the lathe is turning in the normal direction.
Here is an article I wrote about my original parting tool post made for my Sherline lathe. It shows the original prototype that frankly never got improved because it worked so well that I never bothered to make a prettier one for myself. The great benefit to mounting a parting tool this way is that it significantly improves the rigidity of the tool, so much so that even a light lathe like a Sherline can part stuff at high speeds without a hint of chatter. As for materials, if the lathe can turn it, this tool will part it off without any issues.
In addition to the benefits of rear mounting parting tools in the article, my continued experience with this tool has taught me that:
If you have a cross slide that allows for rear mounting your parting tool, please consider making one. It is far, far better than a hacksaw or bandsaw and I assure you that you will not regret it.
And for you Sherline owners, keep in mind that the spindle centerline height on every lathe is different. It has been my experience that the tip of your parting tool must be on the exact centerline of your lathe so buying one from Sherline might work, might not. Production tolerances being what they are, I would suggest you measure your center height and make your own parting tool post to suit your lathe. Of all the mods a Sherline owner can do, this is one of the most important.
In this thread, I noticed that @NC Rick had t-slots running the length of his cross slide and suggested to him that he consider making a rear mounted parting tool. For those of us with small lathes, I feel that rear mounting a parting tool is one of the best mods you can make if you have a t-slotted cross slide or can otherwise find a way to mount one.
To answer Rick's question about how the tool is mounted, yes, it is mounted upside down and the lathe is turning in the normal direction.
Here is an article I wrote about my original parting tool post made for my Sherline lathe. It shows the original prototype that frankly never got improved because it worked so well that I never bothered to make a prettier one for myself. The great benefit to mounting a parting tool this way is that it significantly improves the rigidity of the tool, so much so that even a light lathe like a Sherline can part stuff at high speeds without a hint of chatter. As for materials, if the lathe can turn it, this tool will part it off without any issues.
In addition to the benefits of rear mounting parting tools in the article, my continued experience with this tool has taught me that:
- The overhang or extension of the parting blade is NOT critical when it is rear mounted. No kidding; I just slap the tool into the tool post and go.
- Higher speeds make feeding easier to do by feel, thus avoiding chatter caused by improper feeds. To be honest, I don't even pay much attention to the speeds I am parting at; I just feed to suit whatever speed the lathe happens to be set at and the part comes off without a hitch. I often part up to 2-3 times normal turning speeds because the faster I go, the lower the feed forces are and this makes it much easier to feed smoothly. I honestly cannot remember the last time this tool chattered.
- A thinner parting blade is better than a thicker one because it is a form tool and a thinner form tool creates much lower cutting forces. A thinner tool that cuts with lower forces is also more accurate; my HSS P1-N blade (0.040" wide) will part off a washer in the 0.010" thick range. I've also found that a P1-N blade that is normally only used on part diameters up to 3/4" OD can part double that or more when mounted upside down in the rear, and it will part more accurately than wider blades.
- Parting tools stay sharp longer, at least for me. My parting tool gets honed maybe once or twice a year and I use it often. I might regrind the tool every five years or so. I believe this is because the tool cuts; it does not rub so wear is kept to a minimum. My current blade is about 25 years old and has maybe been reground 3-4 times, I forget.
If you have a cross slide that allows for rear mounting your parting tool, please consider making one. It is far, far better than a hacksaw or bandsaw and I assure you that you will not regret it.
And for you Sherline owners, keep in mind that the spindle centerline height on every lathe is different. It has been my experience that the tip of your parting tool must be on the exact centerline of your lathe so buying one from Sherline might work, might not. Production tolerances being what they are, I would suggest you measure your center height and make your own parting tool post to suit your lathe. Of all the mods a Sherline owner can do, this is one of the most important.
