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Models for grinding HSS Lathe Tools
- Thread starter mikey
- Start date
Im prob going to end up buying the Derbyshire flip up rest at some point. I made to cut off blades. One in a 1/4 but i think came out kinda terrible and 3/16 .040 blade that is a little longer to reach in. They are not honed yet. On the parting off side should i put a bit of a relief from the cutting edge as well so there is not rubbing?
So i got to do some cutting on aluminum. The aluminum tool cut nice.
I am not use to having to move the tool post around between facing and turning for cutter clearance. After i tried out the generic cutter and i admit that i liked it alot better then the Aluminum tool.
It seemed to cut much nicer and a better finish. Now for my problem that i had.
The parting tool chattered like crazy as i cut. I ended up stalling the spindle once. (Did not smell good). Bc of the chatter the headstock would come loose a little also. So im guessing the cutting pressure is way to high? I decided to try cutting with some Cool Tool 2 cutting oil and the chatter was a little better. As i got to the center that chatter got even better so i am also curious if i was going to fast at first?
this is the finished parting tool. I did hone it, this is after i was done cutting. I have a 1 or 2 degree at the tip hoping to make the parted off part not have a tit. Well it did have a tit so i am curious if i should just go to a square nose? It also tapered the part alot as i cut the part off. I am assuming it was due to the chatter as well. What can i do to help this parting tool perform better and so i am not chattering so much?
I am not use to having to move the tool post around between facing and turning for cutter clearance. After i tried out the generic cutter and i admit that i liked it alot better then the Aluminum tool.
It seemed to cut much nicer and a better finish. Now for my problem that i had.
The parting tool chattered like crazy as i cut. I ended up stalling the spindle once. (Did not smell good). Bc of the chatter the headstock would come loose a little also. So im guessing the cutting pressure is way to high? I decided to try cutting with some Cool Tool 2 cutting oil and the chatter was a little better. As i got to the center that chatter got even better so i am also curious if i was going to fast at first?
this is the finished parting tool. I did hone it, this is after i was done cutting. I have a 1 or 2 degree at the tip hoping to make the parted off part not have a tit. Well it did have a tit so i am curious if i should just go to a square nose? It also tapered the part alot as i cut the part off. I am assuming it was due to the chatter as well. What can i do to help this parting tool perform better and so i am not chattering so much?
- Joined
- Dec 20, 2012
- Messages
- 9,422
Brento, grinding the tool at an angle will tend to steer the tool in the cut when the body of the tool is thin like yours is. This results in a concave or convex cut. You will find that grinding the tip straight across will work better for you.
As to why you're chattering, that has so many causes it's hard to list them all. However, one thing that is for sure contributing is the grind on your tool. Here is a close up of the tip:
See how the front profile is curved when it should be straight? The top of the tool is also reflecting a lot of light, which suggests the top of the tool is not flat or sharp.
One reason the chatter got better as you got closer to the center is because the surface speed drops as you approach center. This happens at about the inner 1/3 of the way in. The response to chatter is the same when parting or turning; reduce you speed and/or increase your feed. But first, try correcting the geometry of your tool.
As to why you're chattering, that has so many causes it's hard to list them all. However, one thing that is for sure contributing is the grind on your tool. Here is a close up of the tip:
See how the front profile is curved when it should be straight? The top of the tool is also reflecting a lot of light, which suggests the top of the tool is not flat or sharp.
One reason the chatter got better as you got closer to the center is because the surface speed drops as you approach center. This happens at about the inner 1/3 of the way in. The response to chatter is the same when parting or turning; reduce you speed and/or increase your feed. But first, try correcting the geometry of your tool.
Thanks mikey. I did have it honed before i used it. That picture is after i used it. I will touch it up today on the grinder as i make another cut off tool today but on the other side of the bit so i can get closer to the chuck. I will also obviously hone it again. Wondering if i should add more of a side cut relief or maybe a side rake? It seemed like it had some high cutting forces. I could be wrong. I guess i will do one at a time.
- Joined
- Jan 2, 2014
- Messages
- 9,042
@Brento,
For me the thing I see as the most likely problem is tool flex.
Both of the below contribute to tool flex.
1) tool profile
My regular-use lathe bits are 3/8", but I believe you stated earlier (or in another thread) that due to your small lathe and tool-post it was easier to use smaller tool bits. That means that by the time you grind that thin cut-off tool profile, there's really not much "beam strength" in that tool. The cross-section of the tool will only be 3/16" tall by the width of the tool you ground 0.040".
2) tool length
If you are trying to part off a work-piece that is 1" diameter then obviously you need a tool with a minimum cutting length of 0.5". From here it looks like your parting tool is probably over an inch long, but you don't really need all that length for the current operation. I understand that you'd like to have one parting tool that you can use for most diameters of work-piece that you need to cut, however it may be worth having multiple tools with different parting lengths. Start with the shortest, and then move up as the cut progresses. Of course this means a bunch of hassle changing bits mid-operation and having to very carefully align them to the existing cut.
Both of the above would be helped immediately by using an adjustable parting tool and holder.
1) Compare the cross-section of what I believe your tool looks like compared to an "off the shelf" parting tool.
The blade on the left is based on the drawing from the first amazon hit on "P1-N or P1 blade" that @mikey recommended earlier:
https://www.amazon.com/HHIP-Parallel-Cut-Off-Blades-Various/dp/B01IAT7VXG
Neither drawing shows the taper or side relief, but they give the point.....
2) With an adjustable parting tool you can have only the small amount of stick-out you need for the current operation....in fact you can start the cut-off operation with minimal stick-out and then adjust the tool out further as you cut deeper.
Personally I have found parting tool strength to be a major factor in chatter. I originally thought that having a thinner parting blade would reduce chatter by reducing cutting forces, but what I found is that a wider blade tends to chatter less. To me it implies that the tool flex is a bigger factor than reduced cutting forces of the thinner blade.
-brino
For me the thing I see as the most likely problem is tool flex.
Both of the below contribute to tool flex.
1) tool profile
My regular-use lathe bits are 3/8", but I believe you stated earlier (or in another thread) that due to your small lathe and tool-post it was easier to use smaller tool bits. That means that by the time you grind that thin cut-off tool profile, there's really not much "beam strength" in that tool. The cross-section of the tool will only be 3/16" tall by the width of the tool you ground 0.040".
2) tool length
If you are trying to part off a work-piece that is 1" diameter then obviously you need a tool with a minimum cutting length of 0.5". From here it looks like your parting tool is probably over an inch long, but you don't really need all that length for the current operation. I understand that you'd like to have one parting tool that you can use for most diameters of work-piece that you need to cut, however it may be worth having multiple tools with different parting lengths. Start with the shortest, and then move up as the cut progresses. Of course this means a bunch of hassle changing bits mid-operation and having to very carefully align them to the existing cut.
Both of the above would be helped immediately by using an adjustable parting tool and holder.
1) Compare the cross-section of what I believe your tool looks like compared to an "off the shelf" parting tool.
The blade on the left is based on the drawing from the first amazon hit on "P1-N or P1 blade" that @mikey recommended earlier:
https://www.amazon.com/HHIP-Parallel-Cut-Off-Blades-Various/dp/B01IAT7VXG
Neither drawing shows the taper or side relief, but they give the point.....
2) With an adjustable parting tool you can have only the small amount of stick-out you need for the current operation....in fact you can start the cut-off operation with minimal stick-out and then adjust the tool out further as you cut deeper.
Personally I have found parting tool strength to be a major factor in chatter. I originally thought that having a thinner parting blade would reduce chatter by reducing cutting forces, but what I found is that a wider blade tends to chatter less. To me it implies that the tool flex is a bigger factor than reduced cutting forces of the thinner blade.
-brino