- Joined
- Dec 20, 2012
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- 9,408
This is going to sound really stupid but when I first started grinding tools I wondered how long each face of the tool "should" be. There isn't a formula for this but over the years I have settled on making the side cutting edge 1-1/2 to 2 times the height of the tool (so, for a 3/8" square tool bit the side cutting edge should be 9/16 to 3/4" long). The end cutting edge ends up whatever it is depending on tool shape. For the top rake, 1 to 1-1/2 times the size of the bit works well. This is the length from the tip of the tool to the end of the side rake angle.
When grinding a roughing tool, if you angle the tool so that you make the side cutting edge to the above length while also taking off about 40% of it's width at the end, the tool shape works well. For a facing tool take off 70% and for a finisher take off 80%. For a general purpose tool, take off about 60%. These are approximations but work well for me.
EDIT: I should make it clear that the reason for the amounts taken off as above is to provide the lead angle required by these different tools to work properly when the tool shank is perpendicular to the work. If you look at the books the lead angle is actually a bit less than I use but I have found these shapes to work better for me. I just want to be clear that this is MY practice; do what you think is best.
Here's one that never made sense to me. A rougher cuts primarily with the tip and side cutting edge, while a facer cuts mainly with the side cutting edge near the tip and a finisher cuts primarily with the nose radius of the tool. Each tool is meant to take the load in different areas to perform different functions. Why, then, do all the angles in the typical angle table remain the same for all of these tools for a given material? I don't know why but it makes sense to me that the angles should change to suit the purpose of the tool ... so I change 'em and it has made all the difference!
When grinding a roughing tool, if you angle the tool so that you make the side cutting edge to the above length while also taking off about 40% of it's width at the end, the tool shape works well. For a facing tool take off 70% and for a finisher take off 80%. For a general purpose tool, take off about 60%. These are approximations but work well for me.
EDIT: I should make it clear that the reason for the amounts taken off as above is to provide the lead angle required by these different tools to work properly when the tool shank is perpendicular to the work. If you look at the books the lead angle is actually a bit less than I use but I have found these shapes to work better for me. I just want to be clear that this is MY practice; do what you think is best.
Here's one that never made sense to me. A rougher cuts primarily with the tip and side cutting edge, while a facer cuts mainly with the side cutting edge near the tip and a finisher cuts primarily with the nose radius of the tool. Each tool is meant to take the load in different areas to perform different functions. Why, then, do all the angles in the typical angle table remain the same for all of these tools for a given material? I don't know why but it makes sense to me that the angles should change to suit the purpose of the tool ... so I change 'em and it has made all the difference!
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