Turning Tool And Facing Tool Questions

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!
 
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Joe,
You made yourself a very nice looking tool!!! Now let's see how she cuts!!!


Regards-Carlo
 
Thanks Carlo, that is the next step.

I will include some pics when I do.

Joe
 
My apologies to all, for never getting back to this post with the results of the test that I promissed to do. I first thought that my "old man" health issues would only delay my report a week or so, but now, further tests on a completely unrelated issue have determined that I quickly start 9 weeks of radiation treatments, and by then, this post will be long forgotten. I was able to find enough time in the shop to grind a tool using mikey's angles, and have to say that it cut very well and left a very good finish. Mikey also posted a great response yesterday, to a thread by Pinresto "Lathe noob with some questions on first cuts". Reading that thread is what motivated me to make this post, as we are all lucky to have such giving members like Mikey and Jim Dawson, as well as many others. PLEASE NOTE; this post is intended to give mikey's tool grinding technique the credit it deserves, and to show why I didn't do as I promised. No sympathy posts are needed or wanted, as I will be back to making chips by October or sooner, and will still be on my favorite forum until then. Happy machining to all, JR49
 
JR, it looks like it is time to catch up on all those machining articles you been wanting to read.

Joe
 
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JR49 said:
My apologies to all, for never getting back to this post with the results of the test that I promissed to do. I first thought that my "old man" health issues would only delay my report a week or so, but now, further tests on a completely unrelated issue have determined that I quickly start 9 weeks of radiation treatments, and by then, this post will be long forgotten. I was able to find enough time in the shop to grind a tool using mikey's angles, and have to say that it cut very well and left a very good finish. Mikey also posted a great response yesterday, to a thread by Pinresto "Lathe noob with some questions on first cuts". Reading that thread is what motivated me to make this post, as we are all lucky to have such giving members like Mikey and Jim Dawson, as well as many others. PLEASE NOTE; this post is intended to give mikey's tool grinding technique the credit it deserves, and to show why I didn't do as I promised. No sympathy posts are needed or wanted, as I will be back to making chips by October or sooner, and will still be on my favorite forum until then. Happy machining to all, JR49
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JR, the most important thing in life is life itself. This forum, tool grinding posts or whatever else we do here have no importance when compared to what you're dealing with. You are in my thoughts and I will pray for your speedy recovery. Come back to us when you can - we'll be here.

Oh, and thanks for the kudos but I'm sure there are many others who would have posted the same stuff if I didn't get there first.
 
mikey said:
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.
Click to expand...

Mikey, any chance you have photos of your 3 bits, roughing, facing and finishing, that might be helpful. I for one would be interested in seeing them.

cheers
michael
 
Got the bits but the camera is on its way to China with a friend. Can I please ask for some time?
 
No problem Mikey, its great that you will be able to do that, should help a lot of folks. Even though I have been at this off and on for decades I still learn by seeing others tools and work.

cheers
michael
 
Joe Pitz said:
Hello All, I picked up a HF belt sander, normally $79.00, Item #69033, used a 20% discount coupon. Using mikey's articles
I have been practicing my tool grinding.

Here are some shots of my second attempt. A little more positive rake angle on the top and I should have it down.

I am using the general purpose grind in article 3 as a learning example.

I can say using the tool rest makes it much easier to repeat the compound angles.

I am really enjoying the learning experience.

Thanks

Joe
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Looks good Joe. The next thing to do is get a medium and a hard Arkansas stone (or medium and fine diamond hones) and hone that cutting edge. It'll make a world of difference. At the same time, you can stone a small radius onto that tip so that a) it leaves a smoother finish and b) it holds up longer.

Certainly looks better than my first attempt :)
 
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